Author name code: chae
ADS astronomy entries on 2022-09-14
author:"Chae, Jong Chul" OR author:"Chae, Jongchul"
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Title: Propagating Alfvénic Waves Observed in the Chromosphere
around a Small Sunspot: Tales of 3-minute Waves and 10-minute Waves
Authors: Chae, Jongchul; Cho, Kyuhyoun; Lim, Eun-Kyung; Kang, Juhyung
Bibcode: 2022ApJ...933..108C
Altcode:
  Recent observations provided evidence that the solar chromosphere
  of sunspot regions is pervaded by Alfvénic waves-transverse
  magnetohydrodynamic (MHD) waves (Alfvén waves or kink waves). In order
  to systematically investigate the physical characteristics of Alfvénic
  waves over a wide range of periods, we analyzed the time series of
  line-of-sight velocity maps constructed from the Hα spectral data of
  a small sunspot region taken by the Fast Imaging Solar Spectrograph of
  the Goode Solar Telescope at Big Bear. We identified each Alfvénic
  wave packet by examining the cross-correlation of band-filtered
  velocity between two points that are located a little apart presumably
  on the same magnetic field line. As result, we detected a total of
  279 wave packets in the superpenumbral region around the sunspot and
  obtained their statistics of period, velocity amplitude, and propagation
  speed. An important finding of ours is that the detected Alfvénic waves
  are clearly separated into two groups: 3-minute period (&lt;7 minutes)
  waves and 10-minute period (&gt;7 minutes) waves. We propose two tales
  on the origin of Alfvénic waves in the chromosphere; the 3-minute
  Alfvénic waves are excited by the upward-propagating slow waves in
  the chromosphere through the slow-to-Alfvénic mode conversion, and
  the 10-minute Alfvénic waves represent the chromospheric manifestation
  of the kink waves driven by convective motions in the photosphere.

Title: Fast Spectral Inversion of the H And Ca II 8542 Line Spectra
    Based on a Deep Learning Model
Authors: Lee, Kyoung SUN; Chae, Jongchul; Park, Eunsu; Moon, Yong-Jae;
   Kwak, Hannah; Cho, Kyuhyoun
Bibcode: 2021AGUFMSH44A..01L
Altcode:
  Recently a multilayer spectral inversion (MLSI) model has been
  proposed to infer the physical parameters of plasmas in the solar
  chromosphere. The inversion solves a three-layer radiative transfer
  model using the H alpha and Ca II 8542 Å line profiles taken by
  the Fast Imaging Solar Spectrograph (FISS). The model successfully
  provides the physical plasma parameters, such as source functions,
  Doppler velocities, and Doppler widths in the layers of photosphere
  to chromosphere. However, it is quite expensive to apply the MLSI to
  a huge number of line profiles. For example, the calculating time is
  several hours for a scan raster. We apply deep-learning methods to
  the inversion code to reduce the cost of calculating the physical
  parameters. We train the models using pairs of absorption line
  profiles (H alpha and Ca II 8542 Å) from FISS and their 13 physical
  parameters (source functions, Doppler velocities, Doppler widths in
  the chromosphere, and the pre-determined parameters for photosphere)
  calculated from the spectral inversion code for 50 scan rasters
  (~2,000,000 dataset) including quiet and active regions. We use a fully
  connected dense layers for training the model. In addition, we utilize a
  skip connections to avoid a problem of vanishing gradients. We evaluate
  the model by comparing the pairs of absorption line profiles and their
  inverted physical parameters from other quiet and active regions. Our
  result shows that the deep learning model successfully reproduces
  physical parameter maps of a scan raster observation per second within
  15% of mean absolute percentage error and the mean squared errors of
  0.3 to 0.003 depending on the parameters. Taking this advantage of
  high-performance of the deep learning model, we plan to provide the
  physical parameter maps from the FISS observations to understand the
  chromospheric plasma conditions in various solar features.

Title: Investigation of the subsurface structure of a sunspot based
    on the spatial distribution of oscillation centers inferred from
    umbral flashes
Authors: Cho, Kyuhyoun; Chae, Jongchul; Madjarska, Maria S.
Bibcode: 2021A&A...656A..86C
Altcode: 2021arXiv210911185C
  The subsurface structure of a solar sunspot is important for the
  stability of the sunspot and the energy transport therein. Two
  subsurface structure models have been proposed, the monolithic
  and cluster models, but no clear observational evidence supporting
  a particular model has been found to date. To obtain clues about
  the subsurface structure of sunspots, we analyzed umbral flashes
  in merging sunspots registered by IRIS Mg II 2796 Å slit-jaw
  images. Umbral flashes are regarded as an observational manifestation
  of magnetohydrodynamic shock waves originating from convection cells
  below the photosphere. By tracking the motion of individual umbral
  flashes, we determined the position of the convection cells that
  are the oscillation centers located below the umbra. We found that
  the oscillation centers are preferentially located at dark nuclei
  in the umbral cores rather than in bright regions such as light
  bridges or umbral dots. Moreover, the oscillation centers tend to
  deviate from the convergent interface of the merging sunspots where
  vigorous convection is expected to occur. We also found that the
  inferred depths of the convection cells have no noticeable regional
  dependence. These results suggest that the subsurface of the umbra
  is an environment where convection can occur more easily than the
  convergent interface, and hence support the cluster model. For more
  concrete results, further studies based on umbral velocity oscillations
  in the lower atmosphere are required. <P />Movie is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141500/olm">https://www.aanda.org</A>

Title: Electric resistivity of partially ionized plasma in the lower
    solar atmosphere
Authors: Chae, Jongchul; Litvinenko, Yuri E.
Bibcode: 2021RAA....21..232C
Altcode:
  The lower solar atmosphere is a gravitationally stratified layer of
  partially ionized plasma. We calculate the electric resistivity in the
  solar photosphere and chromosphere, which is the key parameter that
  controls the rate of magnetic reconnection in a Sweet-Parker current
  sheet. The calculation takes into account the collisions between ions
  and hydrogen atoms as well as the electron-ion collisions and the
  electron-hydrogen atom collisions. We find that under the typical
  conditions of the quiet Sun, electric resistivity is determined
  mostly by the electron-hydrogen atom collisions in the photosphere,
  and mostly by the ion-hydrogen collisions, i.e. ambipolar diffusion, in
  the chromosphere. In magnetic reconnection events with strong magnetic
  fields, the ambipolar diffusion, however, may be insignificant because
  the heating by the reconnection itself may lead to the full ionization
  of hydrogen atoms. We conclude that ambipolar diffusion may be the most
  important source of electric resistivity responsible for the magnetic
  flux cancelation and energy release in chromospheric current sheets
  that can keep a significant fraction of neutral hydrogen atoms.

Title: Multilayer Spectral Inversion of Solar Hα and Ca II 8542
    Line Spectra with Height-varying Absorption Profiles
Authors: Chae, Jongchul; Cho, Kyuhyoun; Kang, Juhyung; Lee, Kyoung-Sun;
   Kwak, Hannah; Lim, Eun-Kyung
Bibcode: 2021JKAS...54..139C
Altcode:
  We present an updated version of the multilayer spectral inversion
  (MLSI) recently proposed as a technique to infer the physical parameters
  of plasmas in the solar chromosphere from a strong absorption line. In
  the original MLSI, the absorption profile was constant over each layer
  of the chromosphere, whereas the source function was allowed to vary
  with optical depth. In our updated MLSI, the absorption profile is
  allowed to vary with optical depth in each layer and kept continuous
  at the interface of two adjacent layers. We also propose a new set of
  physical requirements for the parameters useful in the constrained
  model fitting. We apply this updated MLSI to two sets of Hα and Ca
  II line spectral data taken by the Fast Imaging Solar Spectrograph
  (FISS) from a quiet region and an active region, respectively. We
  find that the new version of the MLSI satisfactorily fits most of
  the observed line profiles of various features, including a network
  feature, an internetwork feature, a mottle feature in a quiet region,
  and a plage feature, a superpenumbral fibril, an umbral feature, and
  a fast downflow feature in an active region. The MLSI can also yield
  physically reasonable estimates of hydrogen temperature and nonthermal
  speed as well as Doppler velocities at different atmospheric levels. We
  conclude that the MLSI is a very useful tool to analyze the Hα line and
  the Ca II 8542 line spectral data, and will promote the investigation of
  physical processes occurring in the solar photosphere and chromosphere.

Title: Ionization of Hydrogen in the Solar Atmosphere
Authors: Chae, Jongchul
Bibcode: 2021JASS...38...83C
Altcode:
  The ionization degree of hydrogen is crucial in the physics of the
  plasma in the solar chromosphere. It specifically limits the range of
  plasma temperatures that can be determined from the Hα line. Given
  that the chromosphere greatly deviates from the local thermodynamic
  equilibrium (LTE) condition, precise determinations of hydrogen
  ionization require the solving of the full set of non-LTE radiative
  transfer equations throughout the atmosphere, which is usually a
  formidable task. In many cases, it is still necessary to obtain a
  quick estimate of hydrogen ionization without having to solve for
  the non-LTE radiative transfer. Here, we present a simple method
  to meet this need. We adopt the assumption that the photoionizing
  radiation field changes little over time, even if physical conditions
  change locally. With this assumption, the photoionization rate can be
  obtained from a published atmosphere model and can be used to determine
  the degree of hydrogen ionization when the temperature and electron
  density are specified. The application of our method indicates that in
  the chromospheric environment, plasma features contain more than 10%
  neutral hydrogen at temperatures lower than 17,000 K but less than 1%
  neutral hydrogen at temperatures higher than 23,000 K, implying that
  the hydrogen temperature determined from the Hα line is physically
  plausible if it is lower than 20,000 K, but may not be real, if it
  is higher than 25,000 K. We conclude that our method can be readily
  exploited to obtain a quick estimate of hydrogen ionization in plasma
  features in the solar chromosphere.

Title: Spectroscopic Detection of Alfvénic Waves in the Chromosphere
    of Sunspot Regions
Authors: Chae, Jongchul; Cho, Kyuhyoun; Nakariakov, Valery M.; Cho,
   Kyung-Suk; Kwon, Ryun-Young
Bibcode: 2021ApJ...914L..16C
Altcode:
  Transverse magnetohydrodynamic waves often called Alfvénic (or
  kink) waves have been often theoretically put forward to solve the
  outstanding problems of the solar corona like coronal heating, solar
  wind acceleration, and chemical abundance enhancement. Here we report
  the first spectroscopic detection of Alfvénic waves around a sunspot at
  chromospheric heights. By analyzing the spectra of the Hα line and Ca
  II 854.2 nm line, we determined line-of-sight velocity and temperature
  as functions of position and time. As a result, we identified transverse
  magnetohydrodynamic waves pervading the superpenumbral fibrils. These
  waves are characterized by the periods of 2.5 to 4.5 minutes, and
  the propagation direction parallel to the fibrils, the supersonic
  propagation speeds of 45 to 145 km s<SUP>-1</SUP>, and the close
  association with umbral oscillations and running penumbral waves in
  sunspots. Our results support the notion that the chromosphere around
  sunspots abounds with Alfvénic waves excited by the mode conversion
  of the upward-propagating slow magnetoacoustic waves.

Title: The chromospheric component of coronal bright points. Coronal
    and chromospheric responses to magnetic-flux emergence
Authors: Madjarska, Maria S.; Chae, Jongchul; Moreno-Insertis,
   Fernando; Hou, Zhenyong; Nóbrega-Siverio, Daniel; Kwak, Hannah;
   Galsgaard, Klaus; Cho, Kyuhyoun
Bibcode: 2021A&A...646A.107M
Altcode: 2020arXiv201209426M
  Context. We investigate the chromospheric counterpart of small-scale
  coronal loops constituting a coronal bright point (CBP) and its
  response to a photospheric magnetic-flux increase accompanied by
  co-temporal CBP heating. <BR /> Aims: The aim of this study is
  to simultaneously investigate the chromospheric and coronal layers
  associated with a CBP, and in so doing, provide further understanding on
  the heating of plasmas confined in small-scale loops. <BR /> Methods:
  We used co-observations from the Atmospheric Imaging Assembly and
  Helioseismic Magnetic Imager on board the Solar Dynamics Observatory,
  together with data from the Fast Imaging Solar Spectrograph taken
  in the Hα and Ca II 8542.1 Å lines. We also employed both linear
  force-free and potential field extrapolation models to investigate
  the magnetic topology of the CBP loops and the overlying corona,
  respectively. We used a new multi-layer spectral inversion technique
  to derive the temporal variations of the temperature of the Hα loops
  (HLs). <BR /> Results: We find that the counterpart of the CBP, as
  seen at chromospheric temperatures, is composed of a bundle of dark
  elongated features named in this work Hα loops, which constitute an
  integral part of the CBP loop magnetic structure. An increase in the
  photospheric magnetic flux due to flux emergence is accompanied by
  a rise of the coronal emission of the CBP loops, that is a heating
  episode. We also observe enhanced chromospheric activity associated
  with the occurrence of new HLs and mottles. While the coronal emission
  and magnetic flux increases appear to be co-temporal, the response of
  the Hα counterpart of the CBP occurs with a small delay of less than
  3 min. A sharp temperature increase is found in one of the HLs and
  in one of the CBP footpoints estimated at 46% and 55% with respect
  to the pre-event values, also starting with a delay of less than 3
  min following the coronal heating episode. The low-lying CBP loop
  structure remains non-potential for the entire observing period. The
  magnetic topological analysis of the overlying corona reveals the
  presence of a coronal null point at the beginning and towards the end
  of the heating episode. <BR /> Conclusions: The delay in the response
  of the chromospheric counterpart of the CBP suggests that the heating
  may have occurred at coronal heights. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202039329/olm">https://www.aanda.org</A>

Title: Detection of Opposite Magnetic Polarity in a Light Bridge:
    Its Emergence and Cancellation in Association with LB Fan-shaped Jets
Authors: Lim, Eun-Kyung; Yang, Heesu; Yurchyshyn, Vasyl; Chae,
   Jongchul; Song, Donguk; Madjarska, Maria S.
Bibcode: 2020ApJ...904...84L
Altcode: 2020arXiv201010713L
  Light bridges (LBs) are relatively bright structures that divide
  sunspot umbrae into two or more parts. Chromospheric LBs are known to
  be associated with various activities including fan-shaped jet-like
  ejections and brightenings. Although magnetic reconnection is
  frequently suggested to be responsible for such activities, not many
  studies present firm evidence to support the scenario. We carry out
  magnetic field measurements and imaging spectroscopy of an LB where
  fan-shaped jet-like ejections occur with co-spatial brightenings
  at their footpoints. We study LB fine structure and magnetic field
  changes using TiO images, Near-InfraRed Imaging Spectropolarimeter,
  and Hα data taken by the 1.6 m Goode Solar Telescope. We detect
  magnetic flux emergence in the LB that is of opposite polarity to that
  of the sunspot. The new magnetic flux cancels with the pre-existing
  flux at a rate of 5.6 × 10<SUP>18</SUP> Mx hr<SUP>-1</SUP>. Both
  the recurrent jet-like ejections and their base brightenings are
  initiated at the vicinity of the magnetic flux cancellation, and show
  apparent horizontal extension along the LB at a projected speed of up
  to $18.4$ km s<SUP>-1</SUP> to form a fan-shaped appearance. Based on
  these observations, we suggest that the fan-shaped ejections may have
  resulted from slipping reconnection between the new flux emerging in
  the LB and the ambient sunspot field.

Title: Impulsive wave excitation by rapidly changing granules
Authors: Kwak, Hannah; Chae, Jongchul; Madjarska, Maria S.; Cho,
   Kyuhyoun; Song, Donguk
Bibcode: 2020A&A...642A.154K
Altcode: 2020arXiv200812779K
  It is not yet fully understood how magnetohydrodynamic waves in
  the interior and atmosphere of the Sun are excited. Traditionally,
  turbulent convection in the interior is considered to be the source of
  wave excitation in the quiet Sun. Over the last few decades, acoustic
  events observed in the intergranular lanes in the photosphere have
  emerged as a strong candidate for a wave excitation source. Here we
  report our observations of wave excitation by a new type of event:
  rapidly changing granules. Our observations were carried out with the
  Fast Imaging Solar Spectrograph in the Hα and Ca II 8542 Å lines
  and the TiO 7057 Å broadband filter imager of the 1.6 m Goode Solar
  Telescope at the Big Bear Solar Observatory. We identify granules in
  the internetwork region that undergo rapid dynamic changes such as
  collapse (event 1), fragmentation (event 2), or submergence (event
  3). In the photospheric images, these granules become significantly
  darker than neighboring granules. Following the granules' rapid
  changes, transient oscillations are detected in the photospheric and
  chromospheric layers. In the case of event 1, the dominant period of
  the oscillations is close to 4.2 min in the photosphere and 3.8 min
  in the chromosphere. Moreover, in the Ca II-0.5 Å raster image, we
  observe repetitive brightenings in the location of the rapidly changing
  granules that are considered the manifestation of shock waves. Based on
  our results, we suggest that dynamic changes of granules can generate
  upward-propagating acoustic waves in the quiet Sun that ultimately
  develop into shocks. <P />Movie attached to Fig. A.1 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202038288/olm">https://www.aanda.org</A>

Title: Inference of chromospheric plasma parameters on the
    Sun. Multilayer spectral inversion of strong absorption lines
Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho,
   Kyuhyoun
Bibcode: 2020A&A...640A..45C
Altcode:
  The solar chromosphere can be observed well through strong absorption
  lines. We infer the physical parameters of chromospheric plasmas
  from these lines using a multilayer spectral inversion. This is a
  new technique of spectral inversion. We assume that the atmosphere
  consists of a finite number of layers. In each layer the absorption
  profile is constant and the source function varies with optical depth
  with a constant gradient. Specifically, we consider a three-layer
  model of radiative transfer where the lowest layer is identified
  with the photosphere and the two upper layers are identified with
  the chromosphere. The absorption profile in the photosphere is
  described by a Voigt function, and the profile in the chromosphere
  by a Gaussian function. This three-layer model is fully specified
  by 13 parameters. Four parameters can be fixed to prescribed values,
  and one parameter can be determined from the analysis of a satellite
  photospheric line. The remaining 8 parameters are determined from a
  constrained least-squares fitting. We applied the multilayer spectral
  inversion to the spectral data of the Hα and the Ca II 854.21 nm
  lines taken in a quiet region by the Fast Imaging Solar Spectrograph
  (FISS) of the Goode Solar Telescope (GST). We find that our model
  successfully fits most of the observed profiles and produces regular
  maps of the model parameters. The combination of the inferred Doppler
  widths of the two lines yields reasonable estimates of temperature and
  nonthermal speed in the chromosphere. We conclude that our multilayer
  inversion is useful to infer chromospheric plasma parameters on the Sun.

Title: Inference of chromospheric plasma parameters on the Sun
Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho,
   Kyuhyoun
Bibcode: 2020arXiv200611981C
Altcode:
  The solar chromosphere can be observed well through strong absorption
  lines. We infer the physical parameters of chromospheric plasmas
  from these lines using a multilayer spectral inversion. This is a
  new technique of spectral inversion. We assume that the atmosphere
  consists of a finite number of layers. In each layer the absorption
  profile is constant and the source function varies with optical depth
  with a constant gradient. Specifically, we consider a three-layer
  model of radiative transfer where the lowest layer is identified
  with the photosphere and the two upper layers are identified with
  the chromosphere. The absorption profile in the photosphere is
  described by a Voigt function, and the profile in the chromosphere
  by a Gaussian function. This three-layer model is fully specified
  by 13 parameters. Four parameters can be fixed to prescribed values,
  and one parameter can be determined from the analysis of a satellite
  photospheric line. The remaining 8 parameters are determined from a
  constrained least-squares fitting. We applied the multilayer spectral
  inversion to the spectral data of the H$\alpha$ and the Ca II 854.21 nm
  lines taken in a quiet region by the Fast Imaging Solar Spectrograph
  (FISS) of the Goode Solar Telescope (GST). We find that our model
  successfully fits most of the observed profiles and produces regular
  maps of the model parameters. The combination of the inferred Doppler
  widths of the two lines yields reasonable estimates of temperature and
  nonthermal speed in the chromosphere. We conclude that our multilayer
  inversion is useful to infer chromospheric plasma parameters on the Sun.

Title: The Application of the Filtered Backprojection Algorithm to
    Solar Rotational Tomography
Authors: Cho, Kyuhyoun; Chae, Jongchul; Kwon, Ryun-Young; Bong,
   Su-Chan; Cho, Kyung-Suk
Bibcode: 2020ApJ...895...55C
Altcode: 2020arXiv200506388C
  Solar rotational tomography (SRT) is an important method to reconstruct
  the physical parameters of the three-dimensional solar corona. Here
  we propose an approach to apply the filtered backprojection (FBP)
  algorithm to the SRT. The FBP algorithm is generally not suitable
  for SRT due to the several issues with solar extreme ultraviolet
  (EUV) observations—in particular, a problem caused by missing data
  because of the unobserved back side of corona hidden behind the Sun. We
  developed a method to generate a modified sinogram that resolves the
  blocking problem. The modified sinogram is generated by combining
  the EUV data at two opposite sites observed by the Atmospheric
  Imaging Assembly on board the Solar Dynamics Observatory (SDO). We
  generated the modified sinogram for about one month in 2019 February
  and reconstructed the three-dimensional corona under the static state
  assumption. In order to obtain the physical parameters of the corona,
  we employed a differential emission measure inversion method. We
  tested the performance of the FBP algorithm with the modified sinogram
  by comparing the reconstructed data with the observed EUV image,
  electron density models, previous studies of electron temperature,
  and an observed coronagraph image. The results illustrate that the FBP
  algorithm reasonably reconstructs the bright regions and the coronal
  holes and can reproduce their physical parameters. The main advantage of
  the FBP algorithm is that it is easy to understand and computationally
  efficient. Thus, it enables us to easily probe the inhomogeneous coronal
  electron density and temperature distribution of the solar corona.

Title: Source Depth of Three-minute Umbral Oscillations
Authors: Cho, Kyuhyoun; Chae, Jongchul
Bibcode: 2020ApJ...892L..31C
Altcode: 2020arXiv200310542C
  We infer the depth of the internal sources giving rise to three-minute
  umbral oscillations. Recent observations of ripple-like velocity
  patterns of umbral oscillations supported the notion that there
  exist internal sources exciting the umbral oscillations. We adopt the
  hypothesis that the fast magnetohydrodynamic (MHD) waves generated at
  a source below the photospheric layer propagate along different paths,
  reach the surface at different times, and excited slow MHD waves by
  mode conversion. These slow MHD waves are observed as the ripples that
  apparently propagate horizontally. The propagation distance of the
  ripple given as a function of time is strongly related to the depth
  of the source. Using the spectral data of the Fe I 5435 Å line taken
  by the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at
  Big Bear Solar Observatory, we identified five ripples and determined
  the propagation distance as a function of time in each ripple. From
  the model fitting to these data, we obtained the depth between 1000
  and 2000 km. Our result will serve as an observational constraint to
  understanding the detailed processes of magnetoconvection and wave
  generation in sunspots.

Title: A Study of Small Flares Associated with Plasma Blobs Outflowing
    along Post-CME Rays
Authors: Kim, Yoo Jung; Kwon, Ryun-Young; Chae, Jongchul
Bibcode: 2020JKAS...53....1K
Altcode:
  The recent study of Chae et al. (2017) found a one-to-one correspondence
  between plasma blobs outflowing along a ray formed after a coronal
  mass ejection (CME) and small X-ray flares. In the present work, we
  have examined the spatial configuration and the eruption process of
  the flares that are associated with the blobs by analyzing EUV images
  and magnetograms taken by the SDO/AIA and HMI. We found that the main
  flare and the successive small flares took place in a quadrupolar
  magnetic configuration characterized by predominant magnetic fields of
  positive polarity, two minor magnetic fragments of negative polarity,
  and a curved polarity inversion line between them, which suggests that
  the formation process of the blobs may be similar to that of the parent
  CME. We also found that the successive flares resulted in a gradual
  change of the quadrupolar magnetic configuration, and the relevant
  migration of flaring kernels. The three-dimensional geometry and the
  property of the current sheet, that is often supposed to be embedded
  in an observed post-CME ray, seem to keep changing because of mutual
  feedback between the successive flares and the temporal change of the
  magnetic field configuration. Our results suggest that the observed
  post-CME rays may not reflect the characteristics of the current sheet
  responsible for the impulsive phase of the flare.

Title: Launch and early operation result of charged particle detector
    in the range of 20 keV to 400 keV with deflecting electrostatic
    field for in-situ measurement of suprathermal electrons, protons,
    and neutrals
Authors: Seo, H.; Kim, E.; Ryu, K.; Shin, G. H.; Chae, J. S.; Shin, Y.;
   Woo, J.; Seol, W.; Lee, C. H.; Lee, H.; Sohn, J. D.; Min, K.; Seon, J.
Bibcode: 2019AGUFMSH41E3306S
Altcode:
  Medium Energy Particle Detector (MEPD) is an instrument capable
  of measuring energy distribution of electrons, protons, and
  neutrals in the energy range of 20 ~ 400 keV with 6.25 keV linear
  or 2~24.32 keV pseudo-log energy resolution, 1~128 Hz cadence, and
  10<SUP>6</SUP>~10<SUP>8</SUP>/cm<SUP>2</SUP>•sr•sec•keV dynamic
  range of incident fluxes. The apparatus consists of two identical
  telescopes, each with a field of view of 15 º x 70 º and total
  geometric factor of about 0.01cm<SUP>2</SUP>·sr, with orthogonal
  placement for the detection of different pitch angles of 0 º and 90
  º. Each telescope utilizes an electrostatic field of 4,000 V / (3 ×
  10<SUP>-3</SUP> m) to deflect trajectories of incident particles and
  a silicon detector with 4 identical pixels relatively placed along
  the direction of the electric fields. MEPD produces spectral data
  by recording number of detected particles with respect to individual
  energy bins divided into 64. MEPD is a subset instrument of Instrument
  for the Study of Space Storm (ISSS) launched on a sun-synchronous orbit
  at an altitude of 575 km on December 4th, 2018. During the launch and
  early operation period, commissioning observations are performed with
  a measurement time of about 250 seconds in the sub-auroral, auroral,
  and low-latitude regions. Typical spectra observed in sub-auroral
  regions represent dominance of electrons with the pitch angle of 90 º
  implying trapped electrons of the outer radiation belt. The measurements
  in the auroral regions demonstrate downward suprathermal protons with
  the pitch angle of 0 º in response to the electrostatic field. The
  observations regarded as ENAs are found in both low-latitude and
  high-latitude regions by examining the distinct spectra not affected by
  the electrostatic field. The spectra acquired by pointing the telescope
  toward the magneto-tail bound in the low-latitude regions are correlated
  with D<SUB>st</SUB> index indicating ENAs from the ring current,
  whereas the spectra regarded as ENAs in the high-latitude regions are
  measured with the pitch angle of 90 º indicating polar wind neutrals.

Title: Linear Acoustic Waves in a Nonisothermal
    Atmosphere. II. Photospheric Resonator Model of Three-minute Umbral
    Oscillations
Authors: Chae, Jongchul; Kang, Juhyung; Litvinenko, Yuri E.
Bibcode: 2019ApJ...883...72C
Altcode:
  The velocity oscillations observed in the chromosphere of sunspot
  umbrae resemble a resonance in that their power spectra are sharply
  peaked around a period of about three minutes. In order to describe
  the resonance that leads to the observed 3-minute oscillations, we
  propose the photospheric resonator model of acoustic waves in the solar
  atmosphere. The acoustic waves are driven by the motion of a piston
  at the lower boundary, and propagate in a nonisothermal atmosphere
  that consists of the lower layer (photosphere), where temperature
  rapidly decreases with height, and the upper layer (chromosphere),
  where temperature slowly increases with height. We have obtained
  the following results: (1) The lower layer (photosphere) acts as
  a leaky resonator of acoustic waves. The bottom end is established
  by the piston, and the top end by the reflection at the interface
  between the two layers. (2) The temperature minimum region partially
  reflects and partially transmits acoustic waves of frequencies around
  the acoustic cutoff frequency at the temperature minimum. (3) The
  resonance occurs in the photospheric layer at one frequency around this
  cutoff frequency. (4) The waves escaping the photospheric layer appear
  as upward-propagating waves in the chromosphere. The power spectrum of
  the velocity oscillation observed in the chromosphere can be fairly well
  reproduced by this model. The photospheric resonator model was compared
  with the chromospheric resonator model and the propagating wave model.

Title: The Observational Evidence for the Internal Excitation of
    Sunspot Oscillations Inferred from the Fe I 5435 Å Line
Authors: Cho, Kyuhyoun; Chae, Jongchul; Lim, Eun-kyung; Yang, Heesu
Bibcode: 2019ApJ...879...67C
Altcode: 2019arXiv190601971C
  The umbral oscillations of velocity are commonly observed in the
  chromosphere of a sunspot. Their sources are considered to be
  either the external p-mode driving or the internal excitation by
  magnetoconvection. Even though the possibility of the p-mode driving
  has been often considered, the internal excitation has been rarely
  investigated. We report the identification of the oscillation patterns
  that may be closely related to the events of internal excitation
  from the observations of velocity oscillations in the temperature
  minimum region of two sunspots. The velocities were determined from the
  spectral data of the Fe I 5435 Å line, a magnetically insensitive line,
  taken with the Fast Imaging Solar Spectrograph of the 1.6 m Goode Solar
  Telescope at the Big Bear Solar Observatory. As a result, we identified
  four oscillation patterns of 2.0 × 10<SUP>3</SUP> km coherent size
  that were clearly identified for about 7.9 minutes with an oscillation
  amplitude of 9.3 × 10<SUP>-2</SUP> km s<SUP>-1</SUP>. The power of the
  oscillations in these centers was concentrated in the 3 minute band. All
  the oscillation centers were located above the umbral dots undergoing
  noticeable morphological and dynamical changes that may be regarded
  as an observable signature of small-scale magnetoconvection inside
  the umbrae. Our results support the notion that magnetoconvection
  associated with umbral dots inside sunspots can drive the 3 minute
  umbral oscillations.

Title: The Physical Nature of Spiral Wave Patterns in Sunspots
Authors: Kang, Juhyung; Chae, Jongchul; Nakariakov, Valery M.; Cho,
   Kyuhyoun; Kwak, Hannah; Lee, Kyeore
Bibcode: 2019ApJ...877L...9K
Altcode: 2019arXiv190508908K
  Recently, spiral wave patterns (SWPs) have been detected in 3 minute
  oscillations of sunspot umbrae, but the nature of this phenomenon has
  remained elusive. We present a theoretical model that interprets the
  observed SWPs as the superposition of two different azimuthal modes
  of slow magnetoacoustic waves driven below the surface in an untwisted
  and non-rotating magnetic cylinder. We apply this model to SWPs of the
  line-of-sight (LOS) velocity in a pore observed by the Fast Imaging
  Solar Spectrograph installed at the 1.6 m Goode Solar Telescope. One-
  and two-armed SWPs were identified in instantaneous amplitudes of
  LOS Doppler velocity maps of 3 minute oscillations. The associated
  oscillation periods are about 160 s, and the durations are about 5
  minutes. In our theoretical model, the observed spiral structures are
  explained by the superposition of non-zero azimuthal modes driven 1600
  km below the photosphere in the pore. The one-armed SWP is produced
  by the slow-body sausage (m = 0) and kink (m = 1) modes, and the
  two-armed SWP is formed by the slow-body sausage (m = 0) and fluting
  (m = 2) modes of the magnetic flux tube forming the pore.

Title: Depth of Ellerman Burst Derived from High-resolution Hα and
    Ca II 8542 Å Spectra
Authors: Seo, Minju; Quintero Noda, Carlos; Lee, Jeongwoo; Chae,
   Jongchul
Bibcode: 2019ApJ...871..125S
Altcode:
  High-resolution spectra of an Ellerman burst (EB) sampling the Hα
  and the Ca II 8542 Å lines obtained with the Fast Imaging Solar
  Spectrograph (FISS) installed on the 1.6 m Goode Solar Telescope
  at the Big Bear Solar Observatory are compared with synthetic line
  profiles constructed using the RH code for nonlocal thermodynamical
  equilibrium radiative transfer. The EB heating is modeled by a local
  temperature hump above the quiet-Sun temperature. Our first finding is
  that FISS Hα and Ca II 8542 Å intensity profiles cannot be reproduced
  simultaneously by a single hump model as far as the hump is thicker
  than ≥100 km. Simultaneous reproduction of both line profiles is
  possible when the EB temperature enhancement is confined to a layer
  as thin as ≤20 km in the photosphere where the Hα wing response is
  high and that of the Ca II 8542 Å is not. Moreover, when we examine
  the EB spectra at different times, we find that the EB at a time of
  weaker appearance is located at lower heights, ∼50 km, and moves
  upward to ∼120 km at the time of maximum intensity. Complementary
  calculations of the Na I D<SUB>1</SUB> and Mg I b<SUB>2</SUB> lines
  as well as that of UV continuum at 1600 and 1700 Å with the deduced
  EB atmosphere are also performed to test the result, which allows
  us to discuss the shortcomings of this plane-parallel static model
  atmosphere for understanding the physical properties of EBs.

Title: Development of the SNU Coelostat: Conceptual Design
Authors: Kang, Juhyung; Chae, Jongchul; Kwak, Hannah; Yang, Heesu
Bibcode: 2018JKAS...51..207K
Altcode:
  A coelostat is often used for solar observations, because it corrects
  the image rotation automatically by guiding sunlight into a fixed
  telescope with two plane mirrors. For the purposes of education and
  spectroscopic observation, the solar group at Seoul National University
  (SNU) plans to develop the SNU coelostat (SNUC) and install it in the
  SNU Astronomical Observatory (SAO). Requirements of the SNUC are &lt;1''
  positioning accuracy with 30 cm beam size on the entrance pupil in the
  compact dome. To allow for installation in the small dome, we design a
  compact slope type coelostat with a 45 cm primary plane mirror and a
  39 cm secondary plane mirror. The motion of the SNUC is minimized by
  fixing the position of the slope frame. Numerical simulations of the
  available observational time of the designed coelostat shows that the
  sun can be observed ay all times from June to early August and at least
  three hours in other months. Since the high accuracy driving motors
  installed in the SNUC can be affected by external environment factors
  such as humidity and temperature variations, we design a prototype to
  test the significance of these effects. The prototype consists of a
  20 cm primary plane mirror, a 1 m slope rail, a direct drive motor,
  a ballscrew, a linear motion guide, an AC servo motor, a reduction
  gear and a linear encoder. We plan to control and test the accuracy of
  the prototype with varying atmospheric conditions in early 2019. After
  testing the prototype, the SNUC will be manufactured and installed in
  SAO by 2020.

Title: Evolution of Photospheric Vector Magnetic Field Associated
    with Moving Flare Ribbons as Seen by GST
Authors: Liu, Chang; Cao, Wenda; Chae, Jongchul; Ahn, Kwangsu; Prasad
   Choudhary, Debi; Lee, Jeongwoo; Liu, Rui; Deng, Na; Wang, Jiasheng;
   Wang, Haimin
Bibcode: 2018ApJ...869...21L
Altcode: 2018arXiv181011733L
  The photospheric response to solar flares, also known as coronal
  back reaction, is often observed as sudden flare-induced changes in
  the vector magnetic field and sunspot motions. However, it remains
  obscure whether evolving flare ribbons, the flare signature closest to
  the photosphere, are accompanied by changes in vector magnetic field
  therein. Here we explore the relationship between the dynamics of
  flare ribbons in the chromosphere and variations of magnetic fields
  in the underlying photosphere, using high-resolution off-band Hα
  images and near-infrared vector magnetograms of the M6.5 flare on 2015
  June 22 observed with the 1.6 m Goode Solar Telescope. We find that
  changes of photospheric fields occur at the arrival of the flare ribbon
  front, thus propagating analogously to flare ribbons. In general, the
  horizontal field increases and the field lines become more inclined
  to the surface. When ribbons sweep through regions that undergo a
  rotational motion, the fields transiently become more vertical with
  decreased horizontal field and inclination angle, and then restore
  and/or become more horizontal than before the ribbon arrival. The
  ribbon propagation decelerates near the sunspot rotation center,
  where the vertical field becomes permanently enhanced. Similar magnetic
  field changes are discernible in magnetograms from the Helioseismic and
  Magnetic Imager (HMI), and an inward collapse of coronal magnetic fields
  is inferred from the time sequence of nonlinear force-free field models
  extrapolated from HMI magnetograms. We conclude that photospheric fields
  respond nearly instantaneously to magnetic reconnection in the corona.

Title: Linear Acoustic Waves in a Nonisothermal Atmosphere. I. Simple
    Nonisothermal Layer Solution and Acoustic Cutoff Frequency
Authors: Chae, Jongchul; Litvinenko, Yuri E.
Bibcode: 2018ApJ...869...36C
Altcode:
  We investigate the behavior of acoustic waves in a nonisothermal
  atmosphere based on the analytical solution of the wave
  equation. Specifically, we consider acoustic waves propagating upwardly
  in a simple nonisothermal layer where temperature either increases or
  decreases monotonically with height. We present the solutions for both
  velocity fluctuation and pressure fluctuation. In these solutions,
  either velocity or pressure is spatially oscillatory in one part of
  the layer and nonoscillatory in the other part, with the two parts
  being smoothly connected to one another. Since the two parts transmit
  the same amount of wave energy in each frequency, it is unreasonable to
  identify the oscillating solution with the propagating solution and the
  nonoscillating solution with the nonpropagating solution. The acoustic
  cutoff frequency is defined as the frequency that separates the solution
  that is spatially oscillatory for both velocity and pressure and the
  solution that is not oscillatory for either velocity or pressure. The
  cutoff frequency is found to be the same as the Lamb frequency at the
  bottom in the temperature-decreasing layer but higher than this in the
  temperature-increasing layer. Based on the transmission efficiency
  introduced to quantify the wave propagation, we suggest that the
  acoustic cutoff frequency should be understood as the center of the
  frequency band where the transition from low acoustic transmission to
  high transmission takes place, rather than as the frequency sharply
  separating the propagating solution and the nonpropagating solution.

Title: Observation of the Kelvin-Helmholtz Instability in a Solar
    Prominence
Authors: Yang, Heesu; Xu, Zhi; Lim, Eun-Kyung; Kim, Sujin; Cho,
   Kyung-Suk; Kim, Yeon-Han; Chae, Jongchul; Cho, Kyuhyoun; Ji, Kaifan
Bibcode: 2018ApJ...857..115Y
Altcode:
  Many solar prominences end their lives in eruptions or abrupt
  disappearances that are associated with dynamical or thermal
  instabilities. Such instabilities are important because they may be
  responsible for energy transport and conversion. We present a clear
  observation of a streaming kink-mode Kelvin-Helmholtz Instability (KHI)
  taking place in a solar prominence using the Hα Lyot filter installed
  at the New Vacuum Solar Telescope, Fuxian-lake Solar Observatory in
  Yunnan, China. On one side of the prominence, a series of plasma blobs
  floated up from the chromosphere and streamed parallel to the limb. The
  plasma stream was accelerated to about 20-60 km s<SUP>-</SUP>1 and
  then undulated. We found that 2″- and 5″-size vortices formed,
  floated along the stream, and then broke up. After the 5″-size
  vortex, a plasma ejection out of the stream was detected in the
  Solar Dynamics Observatory/Atmospheric Imaging Assembly images. Just
  before the formation of the 5″-size vortex, the stream displayed
  an oscillatory transverse motion with a period of 255 s with the
  amplitude growing at the rate of 0.001 s<SUP>-1</SUP>. We attribute
  this oscillation of the stream and the subsequent formation of the
  vortex to the KHI triggered by velocity shear between the stream,
  guided by the magnetic field and the surrounding media. The plasma
  ejection suggests the transport of prominence material into the upper
  layer by the KHI in its nonlinear stage.

Title: Nonlinear Effects in Three-minute Oscillations of the Solar
    Chromosphere. II. Measurement of Nonlinearity Parameters at Different
    Atmospheric Levels
Authors: Chae, Jongchul; Cho, Kyuhyoun; Song, Donguk; Litvinenko,
   Yuri E.
Bibcode: 2018ApJ...854..127C
Altcode:
  Recent theoretical studies suggest that the nonlinearity of three-minute
  velocity oscillations at each atmospheric level can be quantified
  by the two independent parameters—the steepening parameter and the
  velocity amplitude parameter. For the first time, we measured these
  two parameters at different atmospheric levels by analyzing a set of
  spectral lines formed at different heights of sunspots ranging from
  the temperature minimum to the transition region. The spectral data
  were taken by the Fast Imaging Solar Spectrograph of the Goode Solar
  Telescope, and by the Interface Region Imaging Spectrograph. As a
  result, from the wavelet power spectra of the velocity oscillations
  at different heights, we clearly identified the growth of the
  second harmonic oscillations associated with the steepening of the
  velocity oscillation, indicating that higher-frequency oscillations
  of periods of 1.2 to 1.5 minutes originate from the nonlinearity
  of the three-minute oscillations in the upper chromosphere. We also
  found that the variation of the measured nonlinearity parameters is
  consistent with the theoretical expectation that the nonlinearity of
  the three-minute oscillations increases with height, and shock waves
  form in the upper chromosphere. There are, however, discrepancies as
  well between theory and observations, suggesting the need to improve
  both theory and the measurement technique.

Title: Transient rotation of photospheric vector magnetic fields
    associated with a solar flare
Authors: Xu, Yan; Cao, Wenda; Ahn, Kwangsu; Jing, Ju; Liu, Chang;
   Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin
Bibcode: 2018NatCo...9...46X
Altcode: 2018arXiv180103171X
  As one of the most violent eruptions on the Sun, flares are believed to
  be powered by magnetic reconnection. The fundamental physics involving
  the release, transfer, and deposition of energy have been studied
  extensively. Taking advantage of the unprecedented resolution provided
  by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of
  vector magnetic fields, about 12-20° counterclockwise, associated
  with a flare. Unlike the permanent changes reported previously,
  the azimuth-angle change is transient and cospatial/temporal with
  Hα emission. The measured azimuth angle becomes closer to that in
  potential fields suggesting untwist of flare loops. The magnetograms
  were obtained in the near infrared at 1.56 μm, which is minimally
  affected by flare emission and no intensity profile change was
  detected. We believe that these transient changes are real and discuss
  the possible explanations in which the high-energy electron beams or
  Alfve'n waves play a crucial role.

Title: Observation of a Large-scale Quasi-circular Secondary Ribbon
    Associated with Successive Flares and a Halo CME
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Kumar, Pankaj; Cho,
   Kyuhyoun; Jiang, Chaowei; Kim, Sujin; Yang, Heesu; Chae, Jongchul;
   Cho, Kyung-Suk; Lee, Jeongwoo
Bibcode: 2017ApJ...850..167L
Altcode: 2017arXiv171100622L
  Solar flare ribbons provide an important clue to the magnetic
  reconnection process and associated magnetic field topology in the
  solar corona. We detected a large-scale secondary flare ribbon of
  a circular shape that developed in association with two successive
  M-class flares and one coronal mass ejection. The ribbon revealed
  interesting properties such as (1) a quasi-circular shape and enclosing
  the central active region (AR); (2) the size as large as 500″ by
  650″ (3) successive brightenings in the clockwise direction at a
  speed of 160 km s<SUP>-1</SUP> starting from the nearest position to
  the flaring sunspots; (4) radial contraction and expansion in the
  northern and the southern part, respectively, at speeds of ≤10
  km s<SUP>-1</SUP>. Using multi-wavelength data from Solar Dynamics
  Observatory, RHESSI, XRT, and Nobeyama, along with magnetic field
  extrapolations, we found that: (1) the secondary ribbon location is
  consistent with those of the field line footpoints of a fan-shaped
  magnetic structure that connects the flaring region and the ambient
  decaying field; (2) the second M2.6 flare occurred when the expanding
  coronal loops driven by the first M2.0 flare encountered the background
  decayed field; (3) immediately after the second flare, the secondary
  ribbon developed along with dimming regions. Based on our findings,
  we suggest that interaction between the expanding sigmoid field and
  the overlying fan-shaped field triggered the secondary reconnection
  that resulted in the field opening and formation of the quasi-circular
  secondary ribbon. We thus conclude that interaction between the AR and
  the ambient large-scale fields should be taken into account to fully
  understand the entire eruption process.

Title: Thermal and Nonthermal Emissions of a Composite Flare Derived
    from NoRH and SDO  Observations
Authors: Lee, Jeongwoo; White, Stephen M.; Jing, Ju; Liu, Chang;
   Masuda, Satoshi; Chae, Jongchul
Bibcode: 2017ApJ...850..124L
Altcode:
  Differential emission measure (DEM) derived from the extreme ultraviolet
  (EUV) lines of the Atmospheric Imaging Assembly (AIA) on board the Solar
  Dynamic Observatory is used in the analysis of a solar flare observed
  by the Nobeyama Radioheliograph (NoRH). The target was a composite event
  consisting of an impulsive flare, SOL2015-06-21T01:42 (GOES class M2.0),
  and a gradual flare, SOL2015-06-21T02:36 (M2.6), for which separation
  of thermal plasma heating from nonthermal particle acceleration was of
  major interest. We have calculated the thermal free-free intensity maps
  with the AIA-derived DEM and compared them against the observed NoRH
  maps to attribute the difference to the nonthermal component. In this
  way, we were able to locate three distinct sources: the major source
  with thermal and nonthermal components mixed, a nonthermal source
  devoid of thermal particles, and a thermal source lacking microwave
  emission. Both the first and the second nonthermal sources produced
  impulsively rising 17 GHz intensities and moved away from the local
  magnetic polarization inversion lines in correlation with the flare
  radiation. In contrast, the thermal sources stay in fixed locations
  and show temporal variations of the temperature and emission measure
  uncorrelated with the flare radiation. We interpret these distinct
  properties as indicating that nonthermal sources are powered by
  magnetic reconnection and thermal sources passively receive energy
  from the nonthermal donor. The finding of these distinct properties
  between thermal and nonthermal sources demonstrates the microwave and
  EUV emission measure combined diagnostics.

Title: Three-minute Sunspot Oscillations Driven by Magnetic
    Reconnection in a Light Bridge
Authors: Song, Donguk; Chae, Jongchul; Kwak, Hannah; Kano, Ryouhei;
   Yurchyshyn, Vasyl; Moon, Yong-Jae; Lim, Eun-Kyung; Lee, Jeongwoo
Bibcode: 2017ApJ...850L..33S
Altcode: 2017arXiv171106489S
  We report a different type of three-minute chromospheric oscillation
  above a sunspot in association with a small-scale impulsive event
  in a light bridge (LB). During our observations, we found a transient
  brightening in the LB. The brightening was composed of elementary bursts
  that may be a manifestation of fast repetitive magnetic reconnections
  in the LB. Interestingly, the oscillations in the nearby sunspot umbra
  were impulsively excited when the intensity of the brightening reached
  its peak. The initial period of the oscillations was about 2.3 minutes
  and then gradually increased to 3.0 minutes with time. In addition,
  we found that the amplitude of the excited oscillations was twice the
  amplitude of oscillations before the brightening. Based on our results,
  we propose that magnetic reconnection occurring in an LB can excite
  oscillations in the nearby sunspot umbra.

Title: Nonlinear Effects in Three-minute Oscillations of the Solar
    Chromosphere. I. An Analytical Nonlinear Solution and Detection of
    the Second Harmonic
Authors: Chae, Jongchul; Litvinenko, Yuri E.
Bibcode: 2017ApJ...844..129C
Altcode:
  The vertical propagation of nonlinear acoustic waves in an isothermal
  atmosphere is considered. A new analytical solution that describes a
  finite-amplitude wave of an arbitrary wavelength is obtained. Although
  the short- and long-wavelength limits were previously considered
  separately, the new solution describes both limiting cases within a
  common framework and provides a straightforward way of interpolating
  between the two limits. Physical features of the nonlinear waves
  in the chromosphere are described, including the dispersive nature
  of low-frequency waves, the steepening of the wave profile, and
  the influence of the gravitational field on wavefront breaking and
  shock formation. The analytical results suggest that observations of
  three-minute oscillations in the solar chromosphere may reveal the
  basic nonlinear effect of oscillations with combination frequencies,
  superposed on the normal oscillations of the system. Explicit
  expressions for a second-harmonic signal and the ratio of its amplitude
  to the fundamental harmonic amplitude are derived. Observational
  evidence of the second harmonic, obtained with the Fast Imaging Solar
  Spectrograph, installed at the 1.6 m New Solar Telescope of the Big
  Bear Observatory, is presented. The presented data are based on the
  time variations of velocity determined from the Na I D<SUB>2</SUB>
  and Hα lines.

Title: Magnetic vector rotation in response to the energetic electron
    beam during a flare
Authors: Xu, Yan; Cao, Wenda; Kwangsu, Ahn; Jing, Ju; Liu, Chang;
   Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E.; Wang, Haimin
Bibcode: 2017SPD....4810001X
Altcode:
  As one of the most violent forms of eruption on the Sun, flares are
  believed to be powered by magnetic reconnection, by which stored
  magnetic energy is released. The fundamental physical processes
  involving the release, transfer and deposition of energy in multiple
  layers of the solar atmosphere have been studied extensively with
  significant progress. Taking advantage of recent developments in
  observing facilities, new phenomena are continually revealed, bringing
  new understanding of solar flares. Here we report the discovery of
  a transient rotation of vector magnetic fields associated with a
  flare observed by the 1.6-m New Solar Telescope at Big Bear Solar
  Observatory. After ruling out the possibility that the rotation is
  caused by line profile changes due to flare heating, our observation
  shows that the transverse field rotateded by about 12-20 degrees
  counterclockwise, and returned quickly to previous values after the
  flare ribbons swept through. More importantly, as a consequence of
  the rotation, the flare loops untwisted and became more potential. The
  vector magnetograms were obtained in the near infrared at 1560 nm, which
  is minimally affected by flare emission and no intensity profile change
  was detected. Therefore, we believe that these transient changes are
  real, and conclude the high energy electron beams play an crucial role
  in the field changes. A straightforward and instructive explanation is
  that the induced magnetic field of the electron beam superimposed on
  the pre-flare field leads to a transient rotation of the overall field.

Title: Evidence for a Magnetic Reconnection Origin of Plasma Outflows
    along Post-CME Rays
Authors: Chae, Jongchul; Cho, Kyuhyoun; Kwon, Ryun-Young; Lim,
   Eun-Kyung
Bibcode: 2017ApJ...841...49C
Altcode:
  Bright rays are often observed after coronal mass ejections (CMEs)
  erupt. These rays are dynamical structures along which plasmas
  move outward. We investigated the outflows along the post-CME rays
  observed by the COR2 on board STEREO Behind on 2013 September 21
  and 22. We tracked two CMEs, two ray tips, and seven blobs using the
  NAVE optical flow technique. As a result, we found that the departure
  times of blobs and ray tips from the optimally chosen starting height
  of 0.5 {R}<SUB>⊙ </SUB> coincided with the occurrence times of the
  corresponding recurrent small flares within 10 minutes. These small
  flares took place many hours after the major flares. This result
  supports a magnetic reconnection origin of the outward flows along the
  post-CME ray and the importance of magnetic islands for understanding
  the process of magnetic reconnection. The total energy of magnetic
  reconnection maintaining the outflows for 40 hr is estimated at 1.4×
  {10}<SUP>30</SUP> erg. Further investigations of plasma outflows
  along post-CME rays will shed much light on the physical properties
  of magnetic reconnection occurring in the solar corona.

Title: Performance of the Autoregressive Method in Long-Term
    Prediction of Sunspot Number
Authors: Chae, Jongchul; Kim, Yeon Han
Bibcode: 2017JKAS...50...21C
Altcode:
  No abstract at ADS

Title: Analytical description of nonlinear acoustic waves in the
    solar chromosphere
Authors: Litvinenko, Yuri E.; Chae, Jongchul
Bibcode: 2017A&A...599A..15L
Altcode:
  <BR /> Aims: Vertical propagation of acoustic waves of finite
  amplitude in an isothermal, gravitationally stratified atmosphere is
  considered. <BR /> Methods: Methods of nonlinear acoustics are used to
  derive a dispersive solution, which is valid in a long-wavelength limit,
  and a non-dispersive solution, which is valid in a short-wavelength
  limit. The influence of the gravitational field on wave-front breaking
  and shock formation is described. The generation of a second harmonic
  at twice the driving wave frequency, previously detected in numerical
  simulations, is demonstrated analytically. <BR /> Results: Application
  of the results to three-minute chromospheric oscillations, driven
  by velocity perturbations at the base of the solar atmosphere, is
  discussed. Numerical estimates suggest that the second harmonic signal
  should be detectable in an upper chromosphere by an instrument such as
  the Fast Imaging Solar Spectrograph installed at the 1.6-m New Solar
  Telescope of the Big Bear Observatory.

Title: Photospheric Origin of Three-minute Oscillations in a Sunspot
Authors: Chae, Jongchul; Lee, Jeongwoo; Cho, Kyuhyoun; Song, Donguk;
   Cho, Kyungsuk; Yurchyshyn, Vasyl
Bibcode: 2017ApJ...836...18C
Altcode:
  The origin of the three-minute oscillations of intensity and velocity
  observed in the chromosphere of sunspot umbrae is still unclear. We
  investigated the spatio-spectral properties of the 3 minute oscillations
  of velocity in the photosphere of a sunspot umbra as well as those
  in the low chromosphere using the spectral data of the Ni I λ5436,
  Fe I λ5435, and Na I D<SUB>2</SUB> λ5890 lines taken by the Fast
  Imaging Solar Spectrograph of the 1.6 m New Solar Telescope at the Big
  Bear Solar Observatory. As a result, we found a local enhancement of
  the 3 minute oscillation power in the vicinities of a light bridge
  (LB) and numerous umbral dots (UDs) in the photosphere. These
  3 minute oscillations occurred independently of the 5 minute
  oscillations. Through wavelet analysis, we determined the amplitudes
  and phases of the 3 minute oscillations at the formation heights of the
  spectral lines, and they were found to be consistent with the upwardly
  propagating slow magnetoacoustic waves in the photosphere with energy
  flux large enough to explain the chromospheric oscillations. Our results
  suggest that the 3 minute chromospheric oscillations in this sunspot may
  have been generated by magnetoconvection occurring in the LB and UDs.

Title: Chromospheric Plasma Ejections in a Light Bridge of a Sunspot
Authors: Song, Donguk; Chae, Jongchul; Yurchyshyn, Vasyl; Lim,
   Eun-Kyung; Cho, Kyung-Suk; Yang, Heesu; Cho, Kyuhyoun; Kwak, Hannah
Bibcode: 2017ApJ...835..240S
Altcode: 2017arXiv170106808S
  It is well-known that light bridges (LBs) inside a sunspot produce
  small-scale plasma ejections and transient brightenings in the
  chromosphere, but the nature and origin of such phenomena are still
  unclear. Utilizing the high-spatial and high-temporal resolution
  spectral data taken with the Fast Imaging Solar Spectrograph
  and the TiO 7057 Å broadband filter images installed at the 1.6
  m New Solar Telescope of Big Bear Solar Observatory, we report
  arcsecond-scale chromospheric plasma ejections (1.″7) inside a
  LB. Interestingly, the ejections are found to be a manifestation of
  upwardly propagating shock waves as evidenced by the sawtooth patterns
  seen in the temporal-spectral plots of the Ca II 8542 Å and Hα
  intensities. We also found a fine-scale photospheric pattern (1″)
  diverging with a speed of about 2 km s<SUP>-1</SUP> two minutes before
  the plasma ejections, which seems to be a manifestation of magnetic
  flux emergence. As a response to the plasma ejections, the corona
  displayed small-scale transient brightenings. Based on our findings,
  we suggest that the shock waves can be excited by the local disturbance
  caused by magnetic reconnection between the emerging flux inside the
  LB and the adjacent umbral magnetic field. The disturbance generates
  slow-mode waves, which soon develop into shock waves, and manifest
  themselves as the arcsecond-scale plasma ejections. It also appears
  that the dissipation of mechanical energy in the shock waves can heat
  the local corona.

Title: Solar Eruption and Local Magnetic Parameters
Authors: Lee, Jeongwoo; Liu, Chang; Jing, Ju; Chae, Jongchul
Bibcode: 2016ApJ...831L..18L
Altcode: 2017arXiv170804055L
  It is now a common practice to use local magnetic parameters such as
  magnetic decay index for explaining solar eruptions from active regions,
  but there can be an alternative view that the global properties of the
  source region should be counted as a more important factor. We discuss
  this issue based on Solar Dynamics Observatory observations of the three
  successive eruptions within 1.5 hr from the NOAA active region 11444 and
  the magnetic parameters calculated using the nonlinear force-free field
  model. Two violent eruptions occurred in the regions with relatively
  high magnetic twist number (0.5-1.5) and high decay index (0.9-1.1)
  at the nominal height of the filament (12″) and otherwise a mild
  eruption occurred, which supports the local-parameter paradigm. Our
  main point is that the time sequence of the eruptions did not go with
  these parameters. It is argued that an additional factor, in the form
  of stabilizing force, should operate to determine the onset of the
  first eruption and temporal behaviors of subsequent eruptions. As
  supporting evidence, we report that the heating and fast plasma flow
  continuing for a timescale of an hour was the direct cause for the first
  eruption and that the unidirectional propagation of the disturbance
  determined the timing of subsequent eruptions. Both of these factors
  are associated with the overall magnetic structure rather than local
  magnetic properties of the active region.

Title: Strong Blue Asymmetry in Hα Line as a Preflare Activity
Authors: Cho, Kyuhyoun; Lee, Jeongwoo; Chae, Jongchul; Wang, Haimin;
   Ahn, Kwangsu; Yang, Heesu; Lim, Eun-kyung; Maurya, Ram Ajor
Bibcode: 2016SoPh..291.2391C
Altcode: 2016SoPh..tmp..131C; 2020arXiv200506404C
  Chromospheric activities before solar flares provide important clues
  to the mechanisms that initiate solar flares, but are as yet poorly
  understood. We report a significant and rapid Hα line broadening
  before the solar flare SOL2011-09-29T18:08 that was detected using
  the unprecedented high-resolution Hα imaging spectroscopy with the
  Fast Imaging Solar Spectrograph (FISS) installed on the 1.6 m New
  Solar Telescope (NST) at Big Bear Solar Observatory. The strong Hα
  broadening extends as a blue excursion up to −4.5 Å and as a red
  excursion up to 2.0 Å, which implies a mixture of velocities in the
  range of −130 kms−<SUP>1</SUP> to 38 km s<SUP>−1</SUP> derived
  by applying the cloud model, comparable to the highest chromospheric
  motions reported before. The Hα blueshifted broadening lasts for
  about six minutes and is temporally and spatially correlated with the
  start of a rising filament, which is later associated with the main
  phase of the flare as detected by the Atmosphere Imaging Assembly (AIA)
  onboard the Solar Dynamics Observatory (SDO). The potential importance
  of this Hα blueshifted broadening as a preflare chromospheric activity
  is briefly discussed within the context of the two-step eruption model.

Title: Fine-scale Photospheric Connections of Ellerman Bombs
Authors: Yang, Heesu; Chae, Jongchul; Lim, Eun-Kyung; Song, Donguk;
   Cho, Kyuhyoun; Kwak, Hannah; Yurchyshyn, Vasyl B.; Kim, Yeon-Han
Bibcode: 2016ApJ...829..100Y
Altcode:
  We investigate the photospheric and magnetic field structures
  associated with Ellerman bombs (EBs) using the 1.6 m New Solar
  Telescope at Big Bear Solar Observatory. The nine observed EBs were
  accompanied by elongated granule-like features (EGFs) that showed
  transverse motions prior to the EBs with an average speed of about
  3.8 km s<SUP>-1</SUP>. Each EGF consisted of a sub-arcsecond bright
  core encircled by a dark lane around its moving front. The bright
  core appeared in the TiO broadband filter images and in the far wings
  of the Hα and Ca II 8542 Å lines. In four EBs, the bi-directional
  expanding motion of the EGFs was identified in the TiO images. In
  those cases, the EGFs were found to be accompanied by an emerging flux
  (EF). In four other EBs, the EGF developed at the edge of a penumbra and
  traveled in the sunspot’s radial direction. The EGFs in these cases
  were identified as a moving magnetic feature (MMF). Our results show a
  clear connection among the magnetic elements, photospheric features, and
  EBs. This result suggests that the EBs result from magnetic reconnection
  forced by EFs or MMFs that are frequently manifested by EGFs.

Title: Solar Multiple Eruptions from a Confined Magnetic Structure
Authors: Lee, Jeongwoo; Liu, Chang; Jing, Ju; Chae, Jongchul
Bibcode: 2016ApJ...829L...1L
Altcode: 2017arXiv170804056L
  How eruption can recur from a confined magnetic structure is discussed
  based on the Solar Dynamics Observatory observations of the NOAA
  active region 11444, which produced three eruptions within 1.5 hr
  on 2012 March 27. The active region (AR) had the positive-polarity
  magnetic fields in the center surrounded by the negative-polarity fields
  around. Since such a distribution of magnetic polarity tends to form
  a dome-like magnetic fan structure confined over the AR, the multiple
  eruptions were puzzling. Our investigation reveals that this event
  exhibits several properties distinct from other eruptions associated
  with magnetic fan structures: (I) a long filament encircling the AR
  was present before the eruptions; (II) expansion of the open-closed
  boundary (OCB) of the field lines after each eruption was suggestive
  of the growing fan-dome structure, and (III) the ribbons inside the
  closed magnetic polarity inversion line evolved in response to the
  expanding OCB. It thus appears that in spite of multiple eruptions
  the fan-dome structure remained undamaged, and the closing back field
  lines after each eruption rather reinforced the fan-dome structure. We
  argue that the multiple eruptions could occur in this AR in spite of
  its confined magnetic structure because the filament encircling the AR
  was adequate for slipping through the magnetic separatrix to minimize
  the damage to its overlying fan-dome structure. The result of this
  study provides a new insight into the productivity of eruptions from
  a confined magnetic structure.

Title: Data Processing of the magnetograms for the Near InfraRed
    Imaging Spectropolarimeter at Big Bear Solar Observatory
Authors: Ahn, Kwangsu; Cao, Wenda; Shumko, Sergiy; Chae, Jongchul
Bibcode: 2016SPD....47.0207A
Altcode:
  We want to present the processing result of the vector magnetograms from
  the Near InfraRed Imaging Spectropolarimeter (NIRIS) at Big Bear Solar
  Observatory. The NIRIS is a successor of an old magnetograph system
  at BBSO, which equips with the new infrared detector and the improved
  Fabry-Perot filter system. While there are several upgrades to the new
  hardware, there are also some challenges as the data acquisition rate
  increases and we deal with the a larger detector array. The overall
  process includes dark and flat correction, image alignment, de-stretch,
  Stokes parameter selection, calibration of instrumental crosstalk,
  and Milne-Eddington inversion.

Title: Ultra-Narrow Negative Flare Front Observed in Helium-10830
    Å Using the1.6m New Solar Telescope
Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su,
   Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho,
   Kyuhyoun; Cho, Kyung-Suk; Gary, Dale E.; Wang, Haimin
Bibcode: 2016SPD....47.0633X
Altcode:
  Solar flares are sudden flashes of brightness on the Sun and are often
  associated with coronal mass ejections and solar energetic particles
  that have adverse effects on the near-Earth environment. By definition,
  flares are usually referred to as bright features resulting from excess
  emission. Using the newly commissioned 1.6-m New Solar Telescope at
  Big Bear Solar Observatory, we show a striking “negative” flare
  with a narrow but unambiguous “dark” moving front observed in He I
  10830 Å, which is as narrow as 340 km and is associated with distinct
  spectral characteristics in Hα and Mg II lines. Theoretically, such
  negative contrast in He I 10830 Å can be produced under special
  circumstances by nonthermal electron collisions or photoionization
  followed by recombination. Our discovery, made possible due to
  unprecedented spatial resolution, confirms the presence of the required
  plasma conditions and provides unique information in understanding
  the energy release and radiative transfer in solar flares.

Title: 2016 Total Solar Eclipse Expedition of KASI
Authors: Bong, Su-Chan; Choi, SeongHwan; Jang, Bi-Ho; Park, Jongyeob;
   Jeon, Young-Beom; Cho, Kyuhyoun; Chae, Jongchul
Bibcode: 2016SPD....47.0311B
Altcode:
  A total solar eclipse occurred on March 9 along the path through
  Indonesia and the Pacific. KASI organized an expedition team for total
  solar eclipse observation. The main purpose of this observation is to
  test the coronal temperature and outflow velocity diagnostics based
  on filter observation, which is proposed for the next generation
  coronagraph. In addition, various white light observations were
  tried. Although we could not get satisfactory data for the quantitative
  diagnostics due to system problem and weather, we could get some useful
  experimental data and nice white light images. We plan next expedition
  for 2017 total solar eclipse in USA.

Title: Oscillatory Response of the Solar Chromosphere to a Strong
    Downflow Event above a Sunspot
Authors: Kwak, Hannah; Chae, Jongchul; Song, Donguk; Kim, Yeon-Han;
   Lim, Eun-Kyung; Madjarska, Maria S.
Bibcode: 2016ApJ...821L..30K
Altcode: 2016arXiv160402252K
  We report three-minute oscillations in the solar chromosphere
  driven by a strong downflow event in a sunspot. We used the Fast
  Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the
  Interface Region Imaging Spectrograph (IRIS). The strong downflow
  event is identified in the chromospheric and transition region lines
  above the sunspot umbra. After the event, oscillations occur at the
  same region. The amplitude of the Doppler velocity oscillations is
  2 km s<SUP>-1</SUP> and gradually decreases with time. In addition,
  the period of the oscillations gradually increases from 2.7 to 3.3
  minutes. In the IRIS 1330 Å slit-jaw images, we identify a transient
  brightening near the footpoint of the downflow detected in the Hα+0.5
  Å image. The characteristics of the downflowing material are consistent
  with those of sunspot plumes. Based on our findings, we suggest that
  the gravitationally stratified atmosphere came to oscillate with a
  three-minute period in response to the impulsive downflow event as
  was theoretically investigated by Chae &amp; Goode.

Title: Ultra-narrow Negative Flare Front Observed in Helium-10830
    Å Using the 1.6 m New Solar Telescope
Authors: Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su,
   Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho,
   Kyuhyoun; Cho, Kyungsuk; Gary, Dale; Wang, Haimin
Bibcode: 2016ApJ...819...89X
Altcode: 2016arXiv160104729X
  Solar flares are sudden flashes of brightness on the Sun and are often
  associated with coronal mass ejections and solar energetic particles
  that have adverse effects on the near-Earth environment. By definition,
  flares are usually referred to as bright features resulting from excess
  emission. Using the newly commissioned 1.6 m New Solar Telescope at
  Big Bear Solar Observatory, we show a striking “negative” flare
  with a narrow but unambiguous “dark” moving front observed in He I
  10830 Å, which is as narrow as 340 km and is associated with distinct
  spectral characteristics in Hα and Mg II lines. Theoretically, such
  negative contrast in He I 10830 Å can be produced under special
  circumstances by nonthermal electron collisions or photoionization
  followed by recombination. Our discovery, made possible due to
  unprecedented spatial resolution, confirms the presence of the required
  plasma conditions and provides unique information in understanding
  the energy release and radiative transfer in astronomical objects.

Title: a New Method to Determine the Temperature of CMES Using a
    Coronagraph Filter System
Authors: Cho, Kyuhyoun; Chae, Jongchul; Lim, Eun-Kyung; Cho, Kyung-Suk;
   Bong, Su-Chan; Yang, Heesu
Bibcode: 2016JKAS...49...45C
Altcode: 2016arXiv160307047C
  The coronagraph is an instrument enables the investigation of faint
  features in the vicinity of the Sun, particularly coronal mass ejections
  (CMEs). So far coronagraphic observations have been mainly used to
  determine the geometric and kinematic parameters of CMEs. Here, we
  introduce a new method for the determination of CME temperature using
  a two filter (4025 A and 3934 A) coronagraph system. The thermal motion
  of free electrons in CMEs broadens the absorption lines in the optical
  spectra that are produced by the Thomson scattering of visible light
  originating in the photosphere, which affects the intensity ratio at two
  different wavelengths. Thus the CME temperature can be inferred from
  the intensity ratio measured by the two filter coronagraph system. We
  demonstrate the method by invoking the graduated cylindrical shell
  (GCS) model for the 3 dimensional CME density distribution and discuss
  its significance.

Title: Observations of a Series of Flares and Associated Jet-like
    Eruptions Driven by the Emergence of Twisted Magnetic Fields
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Park, Sung-Hong; Kim,
   Sujin; Cho, Kyung-Suk; Kumar, Pankaj; Chae, Jongchul; Yang, Heesu;
   Cho, Kyuhyoun; Song, Donguk; Kim, Yeon-Han
Bibcode: 2016ApJ...817...39L
Altcode: 2015arXiv151201330L
  We studied temporal changes of morphological and magnetic properties
  of a succession of four confined flares followed by an eruptive flare
  using the high-resolution New Solar Telescope (NST) operating at the Big
  Bear Solar Observatory (BBSO) and Helioseismic and Magnetic Imager (HMI)
  magnetograms and Atmospheric Image Assembly (AIA) EUV images provided by
  the Solar Dynamics Observatory (SDO). From the NST/Hα and the SDO/AIA
  304 Å observations we found that each flare developed a jet structure
  that evolved in a manner similar to evolution of the blowout jet: (1)
  an inverted-Y-shaped jet appeared and drifted away from its initial
  position; (2) jets formed a curtain-like structure that consisted
  of many fine threads accompanied by subsequent brightenings near
  the footpoints of the fine threads; and finally, (3) the jet showed
  a twisted structure visible near the flare maximum. Analysis of the
  HMI data showed that both the negative magnetic flux and the magnetic
  helicity have been gradually increasing in the positive-polarity region,
  indicating the continuous injection of magnetic twist before and during
  the series of flares. Based on these results, we suggest that the
  continuous emergence of twisted magnetic flux played an important role
  in producing successive flares and developing a series of blowout jets.

Title: Coronal Magnetic Structures for Homologous Eruptions
Authors: Lee, J.; Liu, C.; Jing, J.; Chae, J.
Bibcode: 2015AGUFMSH21C..05L
Altcode:
  Many studies have been made on homologous eruptions for their importance
  in understanding the flare energy build-up and release processes. We
  study the homologous eruptions that occurred in three active regions,
  NOAA 11444, 11283, and 12192, with emphasis on the coronal quantities
  derived from the nonlinear force-free field (NLFFF) extrapolation. The
  quantities include magnetic energy, electric current, and magnetic twist
  number, and decay index, computed from the high cadence photospheric
  vector magnetograms of the Helioseismic and Magnetic Imager (HMI) on
  board the Solar Dynamic Observatory (SDO). In addition, photospheric
  magnetic flux, flare ribbons and overlying field distribution are also
  examined to determine the changes associated with each eruption. As
  main results, we will present the difference between the homology of
  confined eruptions and that of eruptive ones, and variations of the
  coronal quantities with flare strength.

Title: Development of Space Science Instruments for Next Generation
    Small Satellite -1
Authors: KIM, H.; Sohn, J.; Lee, J.; Kang, S. B.; Choi, C.; Woo,
   C. H.; Seo, Y.; Woo, J.; Na, G. E.; Jo, G.; Min, K.; Seon, J.; Ryu,
   K.; Kang, K. I.; Chae, J. S.; Shin, G. H.
Bibcode: 2015AGUFMSA51C2413K
Altcode:
  A package of space science payloads is to be flown as a secondary
  payload on board the first satellite of the Next Generation Small
  Satellite-1 (NEXTSat-1) series of Korea, a microsatellite which is
  scheduled for launch in 2017 into the polar orbit. It consists of Space
  Radiation Detectors (SRD), which will measure the ring current and
  radiation belt particles in the subauroral regions, and Space Plasma
  Detectors (SPD), which will measure the ionospheric ions and electrons
  in the middle and low latitude regions. SRD consists of two instruments:
  Medium Energy Particle Detector (MEPD) will measure electrons and ions
  in the range of ~25 to ~400 keV, and High Energy Particle Detector
  (HEPD) will measure electrons of ~0.1 to ~2 MeV and ions up to ~20
  MeV. With two and three telescopes for MEPD and HEPD, respectively,
  together with many spectral bins, SRD, will discriminate the trapped and
  precipitating particles with high spectral resolution. SPD is composed
  of three conventional instruments: a Langmuir Probe (LP), a Retarding
  Potential Analyzer (RPA), and an Ion Drift Meter (IDM). LP of a planar
  shape will be used to determine the densities and temperatures of the
  ionospheric electrons, while RPA and IDM will determine the densities,
  temperatures, and the composition of the ionospheric ions as well as
  their drift velocities. With its high temporal resolution, SPD aims to
  observe substructures of plasma irregularities. This paper discusses
  the designs and scientific objectives of these instruments.

Title: Detection of a Fine-scale Discontinuity of Photospheric
    Magnetic Fields Associated with Solar Coronal Loop Brightenings
Authors: Song, Donguk; Chae, Jongchul; Park, Soyoung; Cho, Kyung-Suk;
   Lim, Eun-Kyung; Ahn, Kwangsu; Cao, Wenda
Bibcode: 2015ApJ...810L..16S
Altcode:
  We present the transient brightening of a coronal loop and an associated
  fine-scale magnetic discontinuity detected in the photosphere. Utilizing
  the high-resolution data taken with the Fast Imaging Solar Spectrograph
  and InfraRed Imaging Magnetograph of the New Solar Telescope at Big
  Bear Solar Observatory, we detect a narrow lane of intense horizontal
  magnetic field representing a magnetic discontinuity. It was visible
  as a dark lane partially encircling a pore in the continuum image,
  and was located near one of the footpoints of a small coronal loop
  that experienced transient brightenings. The horizontal field strength
  gradually increased before the loop brightening, and then rapidly
  decreased in the impulsive phase of the brightening, suggesting the
  increase of the magnetic non-potentiality at the loop footpoint and the
  sudden release of magnetic energy via magnetic reconnection. Our results
  support the nanoflare theory that coronal heating events are caused
  by magnetic reconnection events at fine-scale magnetic discontinuities.

Title: A Prestudy for the Development of a Compact Coronagraph
Authors: Bong, Su-Chan; Yang, Heesu; Cho, Kyuhyoun; Cho, Kyung-Suk;
   Lim, Eun-Kyung; Park, Young-Deuk; Chae, Jongchul
Bibcode: 2015IAUGA..2254511B
Altcode:
  We are conducting a prestudy for the development of a compact
  coronagraph. The coronagraph is comprised of the external occulter,
  lens, filter, and the CCD. We focus on the performance of the external
  occulter, and the measurement of the coronal temperature and velocity
  using a set of filters. We have tested the diffraction of a singlet
  occulter and a cone occulter using laser. Compared to the singlet
  occulter, the cone occulter gave rather symmetric, smooth and weak
  diffraction pattern. We also have calculated the Thomson scattering of
  the K corona to form coronal spectra in various temperature and velocity
  conditions. We found the optimized wavelength set (393.4, 399.0, 402.5,
  and 482.7 nm) for temperature and velocity measurement. We plan to
  build a prototype coronagraph and make a test observation during the
  total eclipse in 2016 without the occulter.

Title: Acoustic Waves Generated by a Disturbance in a
    Gravitationally-Stratified Medium
Authors: Chae, Jongchul; Goode, Phil
Bibcode: 2015IAUGA..2232493C
Altcode:
  Even though it is well-known from observations of the Sun that
  three-minute period chromospheric oscillations persist in the
  internetwork quiet regions and sunspot penumbrae, until now their
  origin and persistence has defied clear explanation. Here we provide
  a clear and simple explanation for it with a demonstration of how
  such oscillations at the chromosphere's critical frequency naturally
  arise in a gravitationally-stratified medium when it is disturbed. The
  largest-wavenumber components of a chromospheric disturbance produce
  the highest-frequency wave packets, which propagate out of the disturbed
  region at the group speed, which is close to the sound speed. Meanwhile,
  its smallest-wavenumber components develop into wave packets of
  frequencies close to the critical frequency that propagate at a group
  velocity that is much lower than the sound speed. Because of their
  low propagation speed, these wave packets with the natural frequency
  linger around the disturbed region and its surrounding regions for
  a long time, and it is these that one would observationally identify
  as the persistent, chromospheric three-minute oscillations. As well,
  according to our explanation, the power of the persistent chromospheric
  oscillations comes from disturbances with length scales that are greater
  than twice the pressure scale height in the source region and their
  frequencies are determined by the sound speed and the gravitational
  acceleration of the region.

Title: Acoustic Waves Generated by Impulsive Disturbances in a
    Gravitationally Stratified Medium
Authors: Chae, Jongchul; Goode, Philip R.
Bibcode: 2015ApJ...808..118C
Altcode:
  Even though it is well-known from observations of the Sun that
  three-minute period chromospheric oscillations persist in the
  internetwork quiet regions and sunspot umbrae, until now their
  origin and persistence has defied clear explanation. Here we provide
  a clear and simple explanation for it with a demonstration of how
  such oscillations at the chromosphere's cutoff frequency naturally
  arise in a gravitationally stratified medium when it is disturbed. The
  largest-wavenumber vertical components of a chromospheric disturbance
  produce the highest-frequency wave packets, which propagate out of
  the disturbed region at group speeds that are close to the sound
  speed. Meanwhile, the smallest-wavenumber components develop into
  wave packets of frequencies close to the acoustic cutoff frequency
  that propagate at group speeds that are much lower than the sound
  speed. Because of their low propagation speed, these low-frequency wave
  packets linger in the disturbed region and nearby, and thus, are the
  ones that an observer would identify as the persistent, chromospheric
  three-minute oscillations. We emphasize that we can account for the
  power of the persistent chromospheric oscillations as coming from the
  repeated occurrence of disturbances with length scales greater than
  twice the pressure scale height in the upper photosphere.

Title: Detection of Shock Merging in the Chromosphere of a Solar Pore
Authors: Chae, Jongchul; Song, Donguk; Seo, Minju; Cho, Kyung-Suk;
   Park, Young-Deuk; Yurchyshyn, Vasyl
Bibcode: 2015ApJ...805L..21C
Altcode:
  It was theoretically demonstrated that a shock propagating in the solar
  atmosphere can overtake another and merge with it. We provide clear
  observational evidence that shock merging does occur quite often in
  the chromosphere of sunspots. Using Hα imaging spectral data taken by
  the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope
  at the Big Bear Soar Observatory, we construct time-distance maps
  of line-of-sight velocities along two appropriately chosen cuts in
  a pore. The maps show a number of alternating redshift and blueshift
  ridges, and we identify each interface between a preceding redshift
  ridge and the following blueshift ridge as a shock ridge. The important
  finding of ours is that two successive shock ridges often merge with
  each other. This finding can be theoretically explained by the merging
  of magneto-acoustic shock waves propagating with lower speeds of about
  10 km s<SUP>-1</SUP> and those propagating at higher speeds of about
  16-22 km s<SUP>-1</SUP>. The shock merging is an important nonlinear
  dynamical process of the solar chromosphere that can bridge the gap
  between higher-frequency chromospheric oscillations and lower-frequency
  dynamic phenomena such as fibrils.

Title: Intensity and Doppler Velocity Oscillations in Pore Atmospheres
Authors: Cho, K. -S.; Bong, S. -C.; Nakariakov, V. M.; Lim, E. -K.;
   Park, Y. -D.; Chae, J. C.; Yang, H. -S.; Park, H. -M.; Yurchyshyn, V.
Bibcode: 2015ApJ...802...45C
Altcode:
  We have investigated chromospheric traveling features running across two
  merged pores from their centers at speeds of about 55 km s<SUP>-1</SUP>,
  in the active region AR 11828. The pores were observed on 2013 August
  24 by using high-time, spatial, and spectral resolution data from the
  Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope. We
  infer a line-of-sight (LOS) velocity by applying the lambdameter method
  to the Ca ii 8542 Å band and Hα band, and investigate intensity and
  LOS velocity changes at different wavelengths and different positions
  at the pores. We find that they have three-minute oscillations, and
  the intensity oscillation from the line center (0.0 \overset{\circ}A
  ) is preceded by that from the core (-0.3 \overset{\circ}A ) of the
  bands. There is no phase difference between the intensity and the
  LOS velocity oscillations at a given wavelength. The amplitude of LOS
  velocity from the near core spectra ({Δ }λ =0.10-0.21 \overset{\circ}A
  ) is greater than that from the far core spectra ({Δ }λ =0.24-0.36
  \overset{\circ}A ). These results support the interpretation of the
  observed wave as a slow magnetoacoustic wave propagating along the
  magnetic field lines in the pores. The apparent horizontal motion and
  a sudden decrease of its speed beyond the pores can be explained by
  the projection effect caused by inclination of the magnetic field with
  a canopy structure. We conclude that the observed wave properties of
  the pores are quite similar to those from the sunspot observations.

Title: Variations of the electron density in the low and middle
    latitude ionosphere due to high-speed solar wind streams observed
    by the DEMETER satellite
Authors: Kim, H. E.; Lee, E.; Kim, K. H.; Lee, D. H.; Ryu, K.; Chae,
   J.; Parrot, M.
Bibcode: 2014AGUFMSA11B3945K
Altcode:
  Earth's ionosphere varies very dynamically according to the geomagnetic
  activities and solar irradiance. Recently it has been studied that
  the plasma and neutral densities in the thermosphere and ionosphere
  show periodic oscillations with respect to the solar wind speed and Kp
  index during the declining phase of the solar cycle. In this study,
  we investigate the relationship between the electron density and
  the solar wind speed during the declining phase of the solar cycle
  using the observation from the Detection of Electro-Magnetic Emissions
  Transmitted from Earthquake Regions (DEMETER) satellite at the altitude
  of 660 km. The electron density near the dip equator tends to increase
  with the solar wind speed from January to April, but there is no clear
  tendency in the other times. Also, the electron density shows good
  relationship with the solar wind speed at the magnetic longitudes from
  240 to 300 degrees. However, there is poor relationship in the other
  longitudes. We will discuss the seasonal and longitudinal dependences
  of the electron density on the solar wind speed in the low and middle
  latitude ionosphere.

Title: Suspected seismo-ionospheric coupling observed by satellite
    measurements and GPS TEC related to the M7.9 Wenchuan earthquake of
    12 May 2008
Authors: Ryu, K.; Parrot, M.; Kim, S. G.; Jeong, K. S.; Chae, J. S.;
   Pulinets, S.; Oyama, K. -I.
Bibcode: 2014JGRA..11910305R
Altcode:
  Anomalous changes in the ionospheric conditions related to the
  Wenchuan earthquake of 12 May 2008 are investigated using electron
  density (N<SUB>e</SUB>) from Detection of Electro-Magnetic Emissions
  Transmitted from Earthquake Regions (DEMETER) and CHAMP satellites,
  electric field from DEMETER, and GPS-total electron content (TEC)
  maps. The normalized N<SUB>e</SUB> from the DEMETER satellite reveal
  that the previously reported TEC increments before the earthquake
  can be considered as fragments of the gradual equatorial ionization
  anomaly (EIA) enhancements near the epicenter longitude that began
  approximately 1 month before the earthquake and reached its maximum
  with an exceptionally large strength index 8 days prior to the
  main shock. This feature is indirectly confirmed through the CHAMP
  N<SUB>e</SUB> and GPS TEC data. Following the EIA intensity peak,
  disturbances in the N<SUB>e</SUB> and O<SUP>+</SUP> density were
  observed in the nightside. Based on the concurrent electric field and
  N<SUB>e</SUB> changes, it is suggested that EIA intensification could
  be triggered by the E field disturbances over the epicenter.

Title: Active Region Coronal Rain Event Observed by the Fast Imaging
    Solar Spectrograph on the NST
Authors: Ahn, Kwangsu; Chae, Jongchul; Cho, Kyung-Suk; Song, Donguk;
   Yang, Heesu; Goode, Philip R.; Cao, Wenda; Park, Hyungmin; Nah,
   Jakyung; Jang, Bi-Ho; Park, Young-Deuk
Bibcode: 2014SoPh..289.4117A
Altcode: 2014SoPh..tmp...98A
  The Fast Imaging Solar Spectrograph (FISS) is being operated on the New
  Solar Telescope of the Big Bear Solar Observatory. It simultaneously
  records spectra of Hα and Ca II 8542 Å lines, and this dual-spectra
  measurement provides an estimate of the temperature and nonthermal
  speed components. We observed a loop structure in AR 11305 using the
  FISS, SDO/AIA, and STEREO/EUVI in 304 Å, and found plasma material
  falling along the loop from a coronal height into the umbra of a
  sunspot, which accelerated up to 80 km s<SUP>−1</SUP>. We also
  observed C2 and C7 flare events near the loop. The temperature of the
  downflows was in the range of 10 000 - 33 000 K, increasing toward
  the umbra. The temperature of the flow varied with time, and the
  temperature near the footpoint rose immediately after the C7 flare,
  but the temperature toward the umbra remained the same. There seemed
  to be a temporal correlation between the amount of downflow material
  and the observed C-class flares. The downflows decreased gradually soon
  after the flares and then increased after a few hours. These high-speed
  red-shift events occurred continuously during the observations. The
  flows observed on-disk in Hα and Ca II 8542 Å appeared as fragmented,
  fuzzy condensed material falling from the coronal heights when seen
  off-limb with STEREO/EUVI at 304 Å. Based on these observations,
  we propose that these flows were an on-disk signature of coronal rain.

Title: Seismo-ionospheric coupling appearing as equatorial
    electron density enhancements observed via DEMETER electron density
    measurements
Authors: Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Pulinets, S.
Bibcode: 2014JGRA..119.8524R
Altcode:
  We report the processes and results of statistical analysis on
  the ionospheric electron density data measured by the Detection
  of Electro-Magnetic Emissions Transmitted from Earthquake Regions
  (DEMETER) satellite over a period of 6 years (2005-2010), in
  order to investigate the correlation between seismic activity and
  equatorial plasma density variations. To simplify the analysis,
  three equatorial regions with frequent earthquakes were selected and
  then one-dimensional time series analysis between the daily seismic
  activity indices and the equatorial ionization anomaly (EIA) intensity
  indices, which represent relative equatorial electron density increase,
  were performed for each region. The statistically significant values
  of the lagged cross-correlation function, particularly in the region
  with minimal effects of longitudinal asymmetry, indicate that some of
  the very large earthquakes with M &gt; 5.0 in the low-latitude region
  can accompany observable precursory and concurrent EIA enhancements,
  even though the seismic activity is not the most significant driver
  of the equatorial ionospheric evolution. The physical mechanisms of
  the seismo-ionospheric coupling is consistent with our observation,
  and the possibility of earthquake prediction using the EIA intensity
  variation is discussed.

Title: Magnetic-reconnection Generated Shock Waves as a Driver of
    Solar Surges
Authors: Yang, Heesu; Chae, Jongchul; Lim, Eun-Kyung; Lee, Kyoung-sun;
   Park, Hyungmin; Song, Dong-uk; Cho, Kyuhyoun
Bibcode: 2014ApJ...790L...4Y
Altcode:
  We found that a surge consists of multiple shock features. In our
  high-spatiotemporal spectroscopic observation of the surge, each shock
  is identified with the sudden appearance of an absorption feature at the
  blue wings of the Ca II 8542 Å line and Hα line that gradually shifts
  to the red wings. The shock features overlap with one another with
  the time interval of 110 s, which is much shorter than the duration
  of each shock feature, 300-400 s. This finding suggests that the
  multiple shocks might not have originated from a train of sinusoidal
  waves generated by oscillations and flows in the photosphere. As we
  found the signature of the magnetic flux cancelations at the base of
  the surge, we conclude that the multiple shock waves in charge of the
  surge were generated by the magnetic reconnection that occurred in
  the low atmosphere in association with the flux cancelation.

Title: Superpenumbral Fibrils Powered by Sunspot Oscillations
Authors: Chae, Jongchul; Yang, Heesu; Park, Hyungmin; Ajor Maurya,
   Ram; Cho, Kyung-Suk; Yurchysyn, Vasyl
Bibcode: 2014ApJ...789..108C
Altcode:
  It is still a mystery how the solar chromosphere can stand high above
  the photosphere. The dominant portion of this layer must be dynamically
  supported, as is evident by the common occurrence of jets such as
  spicules and mottles in quiet regions, and fibrils and surges in active
  regions. Hence, revealing the driving mechanism of these chromospheric
  jets is crucial for our understanding of how the chromosphere itself
  exists. Here, we report our observational finding that fibrils in the
  superpenumbra of a sunspot are powered by sunspot oscillations. We
  find patterns of outward propagation that apparently originate from
  inside the sunspot, propagate like running penumbral waves, and develop
  into the fibrils. Redshift ridges seen in the time-distance plots of
  velocity often merge, forming a fork-like pattern. The predominant
  period of these shock waves increases, often jumping with distance,
  from 3 minutes to 10 minutes. This short-to-long period transition
  seems to result from the selective suppression of shocks by the
  falling material of their preceding shocks. Based on our results,
  we propose that the fibrils are driven by slow shock waves with long
  periods that are produced by the merging of shock waves with shorter
  periods propagating along the magnetic canopy.

Title: Magnetic-Reconnection Generated Shock Waves as a Driver of
    Solar Surges
Authors: Yang, Heesu; Chae, Jongchul
Bibcode: 2014shin.confE.147Y
Altcode:
  We found that a surge consists of multiple shock features. In our high
  spatiotemporal spectroscopic observation of the surge using Fast Imaging
  Solar Spectrograph of the 1.6 meter New Solar Telescope at Big Bear
  Solar Observatory, each shock is identified with the sudden appearance
  of an absorption feature at the blue wings of the Ca ii 854.2nm line
  and H alpha line that gradually shifts to the red wings. The shock
  features are overlapped with one another with an time interval of
  110s, which is much shorter than the duration of each shock feature
  300 - 400s. This finding suggests that the multiple shocks may not
  have been originated from a train of sinusoidal waves generated by
  oscillations and flows in the photosphere. As we found the signature of
  the magnetic flux cancellations at the base of the surge, we conclude
  that the multiple shock waves in charge of the surge were generated
  by the magnetic reconnection in the low atmosphere associated with
  the flux cancellation.

Title: Multisatellite observations of an intensified equatorial
    ionization anomaly in relation to the northern Sumatra earthquake
    of March 2005
Authors: Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Oyama, K. -I.
Bibcode: 2014JGRA..119.4767R
Altcode:
  Here we report multisatellite observations of ionospheric disturbances
  in relation to the occurrence of the M8.7 northern Sumatra earthquake of
  28 March 2005. The DEMETER (Detection of Electro-Magnetic Emissions
  Transmitted from Earthquake Regions) and CHAMP (Challenging
  Minisatellite Payload) satellite data were investigated to find
  possible precursory and postevent phenomena. It was found that EIA
  (equatorial ionization anomaly) strength expressed in the apex height,
  derived from the CHAMP plasma density profile, was intensified along the
  orbits whose longitudes were close to the epicenter within about a week
  before and after occurrence of the earthquake. Increases in electron and
  O<SUP>+</SUP> density along the orbits close to the epicenter were also
  observed in the DEMETER measurements. The normalized equatorial plasma
  density derived from the DEMETER measurements showed intensification
  about a week before and after the earthquake reaching maximum the
  day after the shock and afterward disappearing. In addition, similar
  behavior of the EIA enhancements related to the M8.0 Pisco earthquake
  of 15 August 2007 was observed. Surveys of space weather and geomagnetic
  activities excluded the possibility that these fluctuations were caused
  by changes in space weather or by a geomagnetic storm. Statistical
  analyses of the longitudinal variation revealed that the EIA was
  enhanced in the west of the epicenter and reduced in the east of the
  epicenter, and this fits the "increased conductivity" model. Based on
  these observations, we proposed a revised view of seismo-ionospheric
  coupling in the region of the geomagnetic equator, to explain the EIA
  features observed in this study.

Title: Shock Waves As a Driver of Surges
Authors: Yang, Heesu; Chae, Jongchul; Park, Hyungmin; Lim, Eun-Kyung;
   Song, Dong-uk; Cho, Kyuhyoun
Bibcode: 2014cosp...40E3698Y
Altcode:
  We found that a surge consists of multiple shock features for a interval
  of 110 s with our high spatio-temporal spectroscopic observation using
  the Fast Imaging Solar Spectrograph (FISS). Each shock is identified
  with the sudden appearance of an absorption feature at the blue wing of
  the Ca ii line and Halpha line, indicating the upward motion of 20-40
  km s (-1) . Then the absorption feature gradually shifts to the red wing
  with a constant acceleration, reaching the downward motion of 20-40 km s
  (-1) within about 6 minutes. We also found magnetic flux cancellation
  and an Ellerman bomb near the foot point of the surge, suggesting
  that magnetic reconnection occurred in the low atmosphere. Our results
  suggest that the waves produced by energy release due to the magnetic
  reconnection in the low atmosphere propagates upward in the form of
  the shock waves, which drive the surge.

Title: Signals of solar cosmic ray flux variations inferred from
    the noise in raw CCD solar images taken by SOHO/EIT
Authors: Oh, Suyeon; Park, Hyungmin; Yi, Yu; Chae, Jongchul
Bibcode: 2014JGRA..119...88O
Altcode:
  The noise embedded in the raw data in one scientific discipline has
  sometimes been proven to be a valuable signal for another discipline,
  and there are examples throughout science history. The solar images
  taken by the solid state detectors (CCDs) of the Sun monitoring
  satellites are usually cleaned by removing the traces of cosmic
  rays on the raw CCD data files. Thus, while applying the method of
  removing the cosmic ray traces, we may be able to estimate the cosmic
  ray flux by counting the number of traces. The net cosmic ray flux is
  the sum of galactic cosmic rays and solar-originating particles. The
  latter are seen as highly transient flux changes related to solar
  eruptions. We can identify this kind of "cosmic ray" event from the
  association with phenomena revealed in processed solar images, and we
  show this using the data of SOHO/extreme ultraviolet imaging telescope
  (EIT). On the other hand, the estimated cosmic ray flux in the steady
  state is anticorrelated with solar cycle sunspot number. The profiles
  of estimated solar cosmic ray flux showing significant increase are
  found to be strongly correlated with the ground neutron monitor ground
  level enhancements. Additionally, the profile of estimated cosmic ray
  flux is consistent with that of the GOES P6 channel. It indicates that
  the particles with energy higher than 80 MeV may mainly produce the
  tracks on CCD of EIT. In conclusion, the raw solar images are valuable
  data for estimating both long-term cosmic ray variations and transient
  solar particles events.

Title: Spectral Inversion of the Hα Line for a Plasma Feature in
    the Upper Chromosphere of the Quiet Sun
Authors: Chae, Jongchul
Bibcode: 2014ApJ...780..109C
Altcode:
  We propose a generalization of Becker's cloud model (BCM): an embedded
  cloud model (ECM)—for the inversion of the core of the Hα line
  spectrum of a plasma feature either lying high above the forest
  of chromospheric features or partly embedded in the outermost part
  of this forest. The fundamental assumption of the ECM is that the
  background light incident on the bottom of the feature from below is
  equal to the ensemble-average light at the same height. This light
  is related to the observed ensemble-average light via the radiative
  transfer that is described by the four parameters newly introduced in
  addition to the original four parameters of the BCM. Three of these
  new parameters are independently determined from the observed rms
  contrast profile of the ensemble. We use the constrained χ<SUP>2</SUP>
  fitting technique to determine the five free parameters. We find that
  the ECM leads to the fairly good fitting of the observed line profiles
  and the reasonable inference of physical parameters in quiet regions
  where the BCM cannot. Our first application of this model to a quiet
  region of the Sun indicates that the model can produce the complete
  velocity map and Doppler width map of the region.

Title: Determination of Temperature in Solar Prominences/Filaments
    Using FISS Observations
Authors: Chae, Jongchul; Park, Hyungmin; Song, Donguk
Bibcode: 2014IAUS..300...85C
Altcode:
  Using the Fast Imaging Solar Spectrograph of the 1.6 meter New Solar
  Telescope at Big Bear, we simultaneously took the spectral profiles
  of the Hα line and the Ca ii line at 854.2 nm from prominences beyond
  the solar limb and filaments on the disk. The spectral data were fitted
  by the slab model of radiative transfer with constant source function,
  either with zero background intensity profile (in prominences) or with
  carefully constructed background intensity profile (in filaments). These
  observations with different perspectives and different analyses produced
  consistent results: temperature inside prominences/filaments ranges
  from 4000 to 20000 K with a mean of about 9500 K. We expect that this
  kind of observation and analysis with higher spatial resolution and
  higher temporal resolution will allow us to study in detail the thermal
  structure and evolution of plasma in prominences.

Title: Activity-related variations of high-degree p-mode amplitude,
    width, and energy in solar active regions
Authors: Maurya, R. A.; Ambastha, A.; Chae, J.
Bibcode: 2014A&A...561A.123M
Altcode: 2013arXiv1310.6458M
  Context. Solar energetic transients such as flares and coronal mass
  ejections occur mostly within active regions (ARs) and release large
  amounts of energy, which is expected to excite acoustic waves by
  transferring the mechanical impulse of the thermal expansion of the
  flare on the photosphere. On the other hand, strong magnetic fields of
  AR sunspots absorb the power of the photospheric oscillation modes. <BR
  /> Aims: We study the properties of high-degree p-mode oscillations in
  flaring and dormant ARs and compare them with those in corresponding
  quiet regions (QRs) to find the association of the mode parameters with
  magnetic- and flare-related activities. <BR /> Methods: We computed the
  mode parameters using the ring-diagram technique. The magnetic-activity
  indices (MAIs) of ARs and QRs were determined from the line-of-sight
  magnetograms. The flare indices (FIs) of ARs were obtained from the GOES
  X-ray fluxes. Mode parameters were corrected for foreshortening, duty
  cycle, and MAI using multiple non-linear regression. <BR /> Results:
  Our analysis of several flaring and dormant ARs observed during the
  Carrington rotations 1980-2109 showed a strong association of the mode
  amplitude, width, and energy with magnetic and flare activities,
  although their changes are combined effects of foreshortening,
  duty cycle, magnetic-activity, flare-activity, and measurement
  uncertainties. We find that the largest reduction in mode amplitude
  and background power of an AR are caused by the angular distance of
  the AR from the solar disc centre. After correcting the mode parameters
  for foreshortening and duty cycle, we find that the mode amplitudes of
  flaring and dormant ARs are lower than in corresponding QRs reducing
  with increasing MAI, suggesting a stronger mode power suppression in
  ARs with larger magnetic fields. The mode widths in ARs are larger
  than in corresponding QRs and increase with MAI, indicating shorter
  lifetimes of modes in ARs than in QRs. The variations in mode amplitude
  and width with MAI are not same in different frequency bands. The
  largest amplification (reduction) in mode amplitude (mode width) of
  dormant ARs is found in the five-minute frequency band. The average
  mode energy of both the flaring and dormant ARs is smaller than in
  their corresponding QRs, reducing with increasing MAI. But the average
  mode energy reduction rate in flaring ARs is smaller than in dormant
  ARs. Moreover, the increase in mode width rate in dormant (flaring)
  ARs is followed by a decrease (increase) in the amplitude variation
  rate. Furthermore, including the mode corrections for MAI shows that
  mode amplitude and mode energy of flaring ARs escalate with FI, while
  the mode width shows an opposite trend, suggesting excitations of modes
  and growth in their lifetimes by flares. The increase (decrease) in mode
  amplitude (width) is larger in the five-minute and higher-frequency
  bands. The enhancement in width variation rate is followed by a rapid
  decline in the amplitude variation rate.

Title: Temperature of Solar Prominences Obtained with the Fast Imaging
    Solar Spectrograph on the 1.6 m New Solar Telescope at the Big Bear
    Solar Observatory
Authors: Park, Hyungmin; Chae, Jongchul; Song, Donguk; Maurya, Ram
   Ajor; Yang, Heesu; Park, Young-Deuk; Jang, Bi-Ho; Nah, Jakyoung; Cho,
   Kyung-Suk; Kim, Yeon-Han; Ahn, Kwangsu; Cao, Wenda; Goode, Philip R.
Bibcode: 2013SoPh..288..105P
Altcode:
  We observed solar prominences with the Fast Imaging Solar Spectrograph
  (FISS) at the Big Bear Solar Observatory on 30 June 2010 and 15 August
  2011. To determine the temperature of the prominence material, we
  applied a nonlinear least-squares fitting of the radiative transfer
  model. From the Doppler broadening of the Hα and Ca II lines, we
  determined the temperature and nonthermal velocity separately. The
  ranges of temperature and nonthermal velocity were 4000 - 20 000 K and
  4 - 11 km s<SUP>−1</SUP>. We also found that the temperature varied
  much from point to point within one prominence.

Title: Velocities and Temperatures of an Ellerman Bomb and Its
    Associated Features
Authors: Yang, Heesu; Chae, Jongchul; Lim, Eun-Kyung; Park, Hyungmin;
   Cho, Kyuhyoun; Maurya, Ram Ajor; Song, Donguk; Kim, Yeon-Han; Goode,
   Philip R.
Bibcode: 2013SoPh..288...39Y
Altcode:
  We investigated the velocity and temperature characteristics of an
  Ellerman bomb (EB) and its associated features based on observations
  made with the Fast Imaging Solar Spectrograph (FISS) and a broadband
  TiO filter of the 1.6 meter New Solar Telescope at Big Bear Solar
  Observatory. In the TiO images of the photospheric level, we found a
  granular cell expanding in two opposite directions near the site of the
  EB. When one end of this granule reached the EB site, the transverse
  speed of the tip of the expanding granule rapidly decreased and the EB
  brightened. The wings of the Hα profile of the EB indicated that the
  EB was blueshifted up to 7 km s<SUP>−1</SUP>. About 260 s after the EB
  brightening, a surge was seen in absorption and varied from a blueshift
  of 20 km s<SUP>−1</SUP> to a redshift of 40 km s<SUP>−1</SUP> seen
  in the Hα and Ca II 8542 Å lines. From the Doppler absorption width
  of the two lines determined by applying the cloud model, we estimated
  the mean temperature of the surge material to be about 29000 K and the
  mean speed of nonthermal motion to be about 11 km s<SUP>−1</SUP>. We
  discuss the physical implications of our results in terms of magnetic
  reconnection and processes related to it.

Title: Fast Imaging Solar Spectrograph of the 1.6 Meter New Solar
    Telescope at Big Bear Solar Observatory
Authors: Chae, Jongchul; Park, Hyung-Min; Ahn, Kwangsu; Yang, Heesu;
   Park, Young-Deuk; Nah, Jakyoung; Jang, Bi Ho; Cho, Kyung-Suk; Cao,
   Wenda; Goode, Philip R.
Bibcode: 2013SoPh..288....1C
Altcode: 2012SoPh..tmp..248C
  For high resolution spectral observations of the Sun - particularly
  its chromosphere, we have developed a dual-band echelle spectrograph
  named Fast Imaging Solar Spectrograph (FISS), and installed it in a
  vertical optical table in the Coudé Lab of the 1.6 meter New Solar
  Telescope at Big Bear Solar Observatory. This instrument can cover any
  part of the visible and near-infrared spectrum, but it usually records
  the Hα band and the Ca II 8542 Å band simultaneously using two CCD
  cameras, producing data well suited for the study of the structure and
  dynamics of the chromosphere and filaments/prominences. The instrument
  does imaging of high quality using a fast scan of the slit across the
  field of view with the aid of adaptive optics. We describe its design,
  specifics, and performance as well as data processing

Title: Doppler Shifts of the Hα Line and the Ca II 854.2 nm Line
    in a Quiet Region of the Sun Observed with the FISS/NST
Authors: Chae, Jongchul; Park, Hyung-Min; Ahn, Kwangsu; Yang, Heesu;
   Park, Young-Deuk; Cho, Kyung-Suk; Cao, Wenda
Bibcode: 2013SoPh..288...89C
Altcode:
  The characteristics of Doppler shifts in a quiet region of the Sun
  are compared between the Hα line and the Ca II infrared line at 854.2
  nm. A small area of 16″×40″ was observed for about half an hour
  with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New
  Solar Telescope (NST) at Big Bear Solar Observatory. The observed area
  contains a network region and an internetwork region, and identified
  in the network region are fibrils and bright points. We infer Doppler
  velocity v<SUB>m</SUB> from each line profile at each individual point
  with the lambdameter method as a function of half wavelength separation
  Δλ. It is confirmed that the bisector of the spatially averaged Ca II
  line profile has an inverse C-shape with a significant peak redshift of
  + 1.8 km s<SUP>−1</SUP>. In contrast, the bisector of the spatially
  averaged Hα line profile has a C-shape with a small peak blueshift of
  − 0.5 km s<SUP>−1</SUP>. In both lines, the bisectors of bright
  network points are significantly redshifted not only at the line
  centers, but also at the wings. The Ca II Doppler shifts are found
  to be correlated with the Hα ones with the strongest correlation
  occurring in the internetwork region. Moreover, we find that here the
  Doppler shifts in the two lines are essentially in phase. We discuss
  the physical implications of our results in view of the formation of
  the Hα line and Ca II 854.2 nm line in the quiet region chromosphere.

Title: Chromospheric Sunspot Oscillations in Hα and Ca II 8542 Å
Authors: Maurya, Ram Ajor; Chae, Jongchul; Park, Hyungmin; Yang,
   Heesu; Song, Donguk; Cho, Kyuhyoun
Bibcode: 2013SoPh..288...73M
Altcode:
  We study chromospheric oscillations including umbral flashes and running
  penumbral waves in a sunspot of active region NOAA 11242 using scanning
  spectroscopy in Hα and Ca II 8542 Å with the Fast Imaging Solar
  Spectrograph (FISS) at the 1.6 meter New Solar Telescope at the Big Bear
  Solar Observatory. A bisector method is applied to spectral observations
  to construct chromospheric Doppler-velocity maps. Temporal-sequence
  analysis of these shows enhanced high-frequency oscillations inside
  the sunspot umbra in both lines. Their peak frequency gradually
  decreases outward from the umbra. The oscillation power is found to be
  associated with magnetic-field strength and inclination, with different
  relationships in different frequency bands.

Title: Study of Magnetic Helicity Injection in the Active Region NOAA
    9236 Producing Multiple Flare-associated Coronal Mass Ejection Events
Authors: Park, Sung-Hong; Kusano, Kanya; Cho, Kyung-Suk; Chae,
   Jongchul; Bong, Su-Chan; Kumar, Pankaj; Park, So-Young; Kim, Yeon-Han;
   Park, Young-Deuk
Bibcode: 2013ApJ...778...13P
Altcode: 2013arXiv1308.5774P
  To better understand a preferred magnetic field configuration and its
  evolution during coronal mass ejection (CME) events, we investigated
  the spatial and temporal evolution of photospheric magnetic fields in
  the active region NOAA 9236 that produced eight flare-associated CMEs
  during the time period of 2000 November 23-26. The time variations
  of the total magnetic helicity injection rate and the total unsigned
  magnetic flux are determined and examined not only in the entire
  active region but also in some local regions such as the main sunspots
  and the CME-associated flaring regions using SOHO/MDI magnetogram
  data. As a result, we found that (1) in the sunspots, a large amount
  of positive (right-handed) magnetic helicity was injected during most
  of the examined time period, (2) in the flare region, there was a
  continuous injection of negative (left-handed) magnetic helicity during
  the entire period, accompanied by a large increase of the unsigned
  magnetic flux, and (3) the flaring regions were mainly composed of
  emerging bipoles of magnetic fragments in which magnetic field lines
  have substantially favorable conditions for making reconnection with
  large-scale, overlying, and oppositely directed magnetic field lines
  connecting the main sunspots. These observational findings can also
  be well explained by some MHD numerical simulations for CME initiation
  (e.g., reconnection-favored emerging flux models). We therefore conclude
  that reconnection-favored magnetic fields in the flaring emerging flux
  regions play a crucial role in producing the multiple flare-associated
  CMEs in NOAA 9236.

Title: FISS Observations of Vertical Motion of Plasma in Tiny Pores
Authors: Cho, K. -S.; Bong, S. -C.; Chae, J.; Kim, Y. -H.; Park,
   Y. -D.; Katsukawa, Y.
Bibcode: 2013SoPh..288...23C
Altcode:
  Pores can be exploited for the understanding of the interaction
  between small-scale vertical magnetic field and the surrounding
  convective motions as well as the transport of mechanical energy into
  the chromosphere along the magnetic field. For better understanding of
  the physics of pores, we investigate tiny pores in a new emerging
  active region (AR11117) that were observed on 26 October 2010
  by the Solar Optical Telescope (SOT) on board Hinode and the Fast
  Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope
  (NST). The pores are compared with nearby small magnetic concentrations
  (SMCs), which have similar magnetic flux as the pores but do not
  appear dark. Magnetic flux density and Doppler velocities in the
  photosphere are estimated by applying the center-of-gravity method to
  the Hinode/Spectro-Polarimeter data. The line-of-sight motions in the
  lower chromosphere are determined by applying the bisector method to
  the wings of the Hα and the Ca II 8542 Å line simultaneously taken
  by the FISS. The coordinated observation reveals that the pores are
  filled with plasma which moves down slowly and are surrounded by
  stronger downflow in the photosphere. In the lower chromosphere, we
  found that the plasma flows upwards inside the pores while the plasma
  in the SMCs is always moving down. Our inspection of the Ca II 8542 Å
  line from the wing to the core shows that the upflow in the pores slows
  down with height and turns into downflow in the upper chromosphere
  while the downflow in the SMCs gains its speed. Our results are in
  agreement with the numerical studies which suggest that rapid cooling
  of the interior of the pores drives a strong downflow, which collides
  with the dense lower layer below and rebounds into an upflow.

Title: Connection Between Chromospheric Events and Photospheric
    Dynamics
Authors: Anđić, A.; Chae, J.; Park, H.; Yang, H.; Ahn, K.; Cao,
   W.; Park, Y. D.
Bibcode: 2013SoPh..288...55A
Altcode: 2012SoPh..tmp..232A
  We analyzed chromospheric events and their connection to oscillation
  phenomena and photospheric dynamics. The observations were done with the
  New Solar Telescope of Big Bear Solar Observatory using a broad-band
  imager at the wavelength of a TiO band and FISS spectrograph scanning
  Ca II and Hα spectral lines. The event in Ca II showed strong plasma
  flows and propagating waves in the chromosphere. The movement of
  the footpoints of flux tubes in the photosphere indicated flux tube
  entanglement and magnetic reconnection as a possible cause of the
  observed brightening and waves propagating in the chromosphere. An
  upward propagating train of waves was observed at the site of the
  downflow event in Hα. There was no clear relationship between
  photospheric waves and the Ca II and Hα events. Our observations
  indicate that chromospheric waves that were previously thought to
  originate from the photosphere may be generated by some events in the
  chromosphere as well.

Title: Global Coronal Seismology in the Extended Solar Corona through
    Fast Magnetosonic Waves Observed by STEREO SECCHI COR1
Authors: Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman,
   Leon; Davila, Joseph M.; Chae, Jongchul; Zhang, Jie
Bibcode: 2013ApJ...776...55K
Altcode:
  We present global coronal seismology for the first time, which allows
  us to determine inhomogeneous magnetic field strength in the extended
  corona. From the measurements of the propagation speed of a fast
  magnetosonic wave associated with a coronal mass ejection (CME)
  and the coronal background density distribution derived from the
  polarized radiances observed by the STEREO SECCHI COR1, we determined
  the magnetic field strengths along the trajectories of the wave at
  different heliocentric distances. We found that the results have an
  uncertainty less than 40%, and are consistent with values determined
  with a potential field model and reported in previous works. The
  characteristics of the coronal medium we found are that (1) the density,
  magnetic field strength, and plasma β are lower in the coronal hole
  region than in streamers; (2) the magnetic field strength decreases
  slowly with height but the electron density decreases rapidly so that
  the local fast magnetosonic speed increases while plasma β falls off
  with height; and (3) the variations of the local fast magnetosonic
  speed and plasma β are dominated by variations in the electron
  density rather than the magnetic field strength. These results imply
  that Moreton and EIT waves are downward-reflected fast magnetosonic
  waves from the upper solar corona, rather than freely propagating
  fast magnetosonic waves in a certain atmospheric layer. In addition,
  the azimuthal components of CMEs and the driven waves may play an
  important role in various manifestations of shocks, such as type II
  radio bursts and solar energetic particle events.

Title: Helicity injection by flux motions and its role in flare
    and CMEs
Authors: Panditi, Vemareddy; Ambastha, A.; Maurya, R.; Chae, J.;
   Ambstha, A.; Maurya, R. A.; Chae, J.
Bibcode: 2013SPD....4430003P
Altcode:
  An investigation of helicity injection by photospheric shear motions
  is carried out for two active regions (ARs), NOAA 11158 and 11166,
  using line-of-sight magnetic field observations obtained from
  the Helioseismic and Magnetic Imager on board the Solar Dynamics
  Observatory. We derived the horizontal velocities in the ARs from the
  differential affine velocity estimator (DAVE) technique. Persistent
  strong shear motions at maximum velocities in the range of 0.6-0.9
  km s-1 along the magnetic polarity inversion line and outward flows
  from the peripheral regions of the sunspots were observed in the two
  ARs. The helicities injected in NOAA 11158 and 11166 during their
  six-day evolution period were estimated as 14.16x10$^42$ Mx$^2$
  and 9.5x10$^42$ Mx$^2$, respectively. The estimated injection rates
  decreased up to 13% by increasing the time interval between the
  magnetograms from 12 minutes to 36 minutes, and increased up to 9%
  by decreasing the DAVE window size from 21x18 to 9x6 pixel$^2$,
  resulting in 10% variation in the accumulated helicity. In both
  ARs, the flare-prone regions (R2) had inhomogeneous helicity flux
  distribution with mixed helicities of both signs and coronal mass
  ejection (CME) prone regions had almost homogeneous distribution of
  helicity flux dominated by a single sign. The temporal profiles of
  helicity injection showed impulsive variations during some flares/CMEs
  due to negative helicity injection into the dominant region of positive
  helicity flux. A quantitative analysis reveals a marginally significant
  association of helicity flux with CMEs but not flares in AR 11158,
  while for the AR 11166, we find a marginally significant association
  of helicity flux with flares but not CMEs, providing evidence of the
  role of helicity injection at localized sites of the events. These
  short-term variations of helicity flux are further discussed in
  view of possible flare-related effects. This study suggests that flux
  motions and spatial distribution of helicity injection are important to
  understanding the complex nature of the magnetic flux system of the AR,
  and how it can lead to conditions favorable for eruptive events.

Title: Helicity Injection by the Shearing Motion of Fluxes in Relation
    to Flares and Coronal Mass Ejections
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.; Chae, J.
Bibcode: 2013enss.confE...8V
Altcode:
  An investigation of helicity injection by photospheric shear motions is
  carried out for two active regions (ARs), NOAA 11158 and 11166, using
  line-of-sight magnetic field observations obtained from the Helioseismic
  and Magnetic Imager on board the Solar Dynamics Observatory. We derived
  the horizontal velocities in the ARs from the differential affine
  velocity estimator (DAVE) technique. Persistent strong shear motions at
  maximum velocities in the range of 0.6-0.9 km s^{-1} along the magnetic
  polarity inversion line and outward flows from the peripheral regions
  of the sunspots were observed in the two ARs. The helicities injected
  in NOAA 11158 and 11166 during their six-day evolution period were
  estimated as 14.16x10^{42} Mx^2 and 9.5×10^{42} Mx^2, respectively. The
  estimated injection rates decreased up to 13% by increasing the time
  interval between the magnetograms from 12 minutes to 36 minutes, and
  increased up to 9% by decreasing the DAVE window size from 21×18 to
  9×6 pixel2, resulting in 10% variation in the accumulated helicity. In
  both ARs, the flare-prone regions (R2) had inhomogeneous helicity
  flux distribution with mixed helicities of both signs and coronal
  mass ejection (CME) prone regions had almost homogeneous distribution
  of helicity flux dominated by a single sign. The temporal profiles of
  helicity injection showed impulsive variations during some flares/CMEs
  due to negative helicity injection into the dominant region of positive
  helicity flux. A quantitative analysis reveals a marginally significant
  association of helicity flux with CMEs but not flares in AR 11158,
  while for the AR 11166, we find a marginally significant association
  of helicity flux with flares but not CMEs, providing evidence of the
  role of helicity injection at localized sites of the events. These
  short-term variations of helicity flux are further discussed in
  view of possible flare-related effects. This study suggests that flux
  motions and spatial distribution of helicity injection are important to
  understanding the complex nature of the magnetic flux system of the AR,
  and how it can lead to conditions favorable for eruptive events.

Title: Chromospheric Waves and Oscillations in Sunspots
Authors: Maurya, R. A.; Chae, J.
Bibcode: 2013enss.confE..45M
Altcode:
  We studied the chromospheric oscillations in and around a sunspot
  of the active region NOAA 11242 using high spectral and spatial
  resolution observations in the spectral lines Hα and Ca II 8542Å
  obtained from the Fast Imaging Solar Spectrograph (FISS) of 1.6 meter
  New Solar Telescope (NST) at Big Bear Solar Observatory. A suitable
  bisector method is applied to the spectral observations, to construct
  the chromospheric Doppler Velocity maps. Time series analysis of
  Doppler maps, in both the spectral bands, revealed enhanced high
  frequency oscillations inside the umbra of the sunspot. The frequency
  of oscillations gradually decreases from the umbra to outward. We have
  found clear evidence of two boundaries for the peak power frequency
  transformation, one of which occurs close to the umbral and penumbral
  boundary, and the other near the penumbral and super-penumbral boundary
  of the sunspot. The oscillation power is found to be associated with
  magnetic field strength and inclination, although they showed different
  relationships in different frequency bands.

Title: Chromospheric Sunspot Oscillations in H-alpha and Ca II 8542A
Authors: Ajor Maurya, Ram; Chae, Jongchul; Park, Hyungmin; Yang,
   Heesu; Song, Donguk; Cho, Kyuhyoun
Bibcode: 2013arXiv1302.1234A
Altcode:
  We study chromospheric oscillations including umbral flashes and
  running penumbral waves in a sunspot of active region (AR) using
  scanning spectroscopy in H-alpha and Ca II 8542A, with the Fast Imaging
  Solar Spectrograph (FISS) at the 1.6 meter New Solar Telescope at
  Big Bear Solar Observatory. A bisector method is applied to spectral
  observations to construct chromospheric Doppler velocity maps. Temporal
  sequence analysis of these shows enhanced high-frequency oscillations
  inside the sunspot umbra in both lines. Their peak frequency gradually
  decreases outward from the umbra. The oscillation power is found to be
  associated with magnetic-field strength and inclination, with different
  relationships in different frequency bands.

Title: Solar Cosmic Ray Flux Variation Estimated from the Raw Solar
    Images Taken by SOHO/EIT
Authors: Oh, Suyeon; Park, Hyungmin; Chae, Jongchul; Yi, Yu
Bibcode: 2013ICRC...33.3476O
Altcode:
  The solar images are taken by the CCD detectors of the Sun monitoring
  satellites such as SOHO, TRACE, STEREO, SDO, and so on. The solar images
  are constructed after removing the traces of cosmic rays on the raw CCD
  data files. Thus, while applying the method of removing the cosmic rays
  traces, we can estimate the cosmic rays flux by counting the number
  of traces. The cosmic ray flux in the steady state might be the sum
  of the solar and galactic cosmic rays. However, the abrupt change in
  the flux could be assumed to be originated from the Sun. Therefore,
  we can identify the solar origins of the sudden solar cosmic ray flux
  changes from the phenomena shown in the processed solar images. The
  results using the data of SOHO/EIT are presented. The estimated cosmic
  ray flux in the steady state is the anti-correlated with sunspot
  numbers, which shows the minima in cosmic ray flux at the solar cycle
  maxima defined by the sunspot numbers. The profiles of estimated solar
  cosmic ray associated with ground level enhancements observed by the
  ground neutron monitor have the significant increase in the cosmic
  ray flux with good correlation. Thus, the solar images are valuable
  data useful in estimating the solar cosmic ray long term and transient
  flux variations.

Title: On the Injection of Helicity by the Shearing Motion of Fluxes
    in Relation to Flares and Coronal Mass Ejections
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.; Chae, J.
Bibcode: 2012ApJ...761...86V
Altcode: 2012arXiv1202.5195V
  An investigation of helicity injection by photospheric shear motions is
  carried out for two active regions (ARs), NOAA 11158 and 11166, using
  line-of-sight magnetic field observations obtained from the Helioseismic
  and Magnetic Imager on board the Solar Dynamics Observatory. We derived
  the horizontal velocities in the ARs from the differential affine
  velocity estimator (DAVE) technique. Persistent strong shear motions at
  maximum velocities in the range of 0.6-0.9 km s<SUP>-1</SUP> along the
  magnetic polarity inversion line and outward flows from the peripheral
  regions of the sunspots were observed in the two ARs. The helicities
  injected in NOAA 11158 and 11166 during their six-day evolution
  period were estimated as 14.16 × 10<SUP>42</SUP> Mx<SUP>2</SUP> and
  9.5 × 10<SUP>42</SUP> Mx<SUP>2</SUP>, respectively. The estimated
  injection rates decreased up to 13% by increasing the time interval
  between the magnetograms from 12 minutes to 36 minutes, and increased
  up to 9% by decreasing the DAVE window size from 21 × 18 to 9 ×
  6 pixel<SUP>2</SUP>, resulting in 10% variation in the accumulated
  helicity. In both ARs, the flare-prone regions (R2) had inhomogeneous
  helicity flux distribution with mixed helicities of both signs and
  coronal mass ejection (CME) prone regions had almost homogeneous
  distribution of helicity flux dominated by a single sign. The temporal
  profiles of helicity injection showed impulsive variations during
  some flares/CMEs due to negative helicity injection into the dominant
  region of positive helicity flux. A quantitative analysis reveals
  a marginally significant association of helicity flux with CMEs but
  not flares in AR 11158, while for the AR 11166, we find a marginally
  significant association of helicity flux with flares but not CMEs,
  providing evidence of the role of helicity injection at localized
  sites of the events. These short-term variations of helicity flux
  are further discussed in view of possible flare-related effects. This
  study suggests that flux motions and spatial distribution of helicity
  injection are important to understanding the complex nature of the
  magnetic flux system of the AR, and how it can lead to conditions
  favorable for eruptive events.

Title: Three-dimensional Structure and Evolution of
    Extreme-ultraviolet Bright Points Observed by STEREO/SECCHI/EUVI
Authors: Kwon, Ryun-Young; Chae, Jongchul; Davila, Joseph M.; Zhang,
   Jie; Moon, Yong-Jae; Poomvises, Watanachak; Jones, Shaela I.
Bibcode: 2012ApJ...757..167K
Altcode:
  We unveil the three-dimensional structure of quiet-Sun EUV bright
  points and their temporal evolution by applying a triangulation method
  to time series of images taken by SECCHI/EUVI on board the STEREO twin
  spacecraft. For this study we examine the heights and lengths as the
  components of the three-dimensional structure of EUV bright points
  and their temporal evolutions. Among them we present three bright
  points which show three distinct changes in the height and length:
  decreasing, increasing, and steady. We show that the three distinct
  changes are consistent with the motions (converging, diverging,
  and shearing, respectively) of their photospheric magnetic flux
  concentrations. Both growth and shrinkage of the magnetic fluxes
  occur during their lifetimes and they are dominant in the initial
  and later phases, respectively. They are all multi-temperature
  loop systems which have hot loops (~10<SUP>6.2</SUP> K) overlying
  cooler ones (~10<SUP>6.0</SUP> K) with cool legs (~10<SUP>4.9</SUP>
  K) during their whole evolutionary histories. Our results imply that
  the multi-thermal loop system is a general character of EUV bright
  points. We conclude that EUV bright points are flaring loops formed by
  magnetic reconnection and their geometry may represent the reconnected
  magnetic field lines rather than the separator field lines.

Title: Ca II Transient Brightenings Associated with Canceling
    Magnetic Features
Authors: Park, Soyoung; Chae, Jongchul
Bibcode: 2012SoPh..280..103P
Altcode: 2012SoPh..tmp..158P
  We analyzed transient Ca II H brightening associated with small-scale
  canceling magnetic features (CMFs) in the quiet Sun near disk center
  using Ca II H filter images and Na D<SUB>1</SUB> magnetograms
  of Hinode/SOT. We found that in most Ca II brightening events
  related to CMFs the Ca II H intensity peaks after the magnetic flux
  cancellation. Moreover, the brightening tends to appear as a pair
  of bright points of similar size and brightness overlying a magnetic
  bipole. Then a new opposite polarity fragment moves to them and cancels
  out. These results imply that magnetic reconnection takes place there
  and is responsible for CMFs.

Title: Rates of Magnetic Flux Cancellation Measured with Hinode/SOT
Authors: Park, S.; Chae, J.; Litvinenko, Y. E.
Bibcode: 2012ASPC..454...59P
Altcode:
  The specific cancellation rate of canceling magnetic features,
  defined as the rate of flux cancellation divided by the interface
  length, is an observational quantity of magnetic reconnection model
  in the low atmosphere. This value gives an accurate estimate of the
  electric field in the reconnecting current sheet. We have measured
  the specific rates using the magnetograms taken by the Solar Optical
  Telescope (SOT)/Hinode. As a result, the specific rates determined
  with SOT turned out to be systematically higher —about four times—
  than those based on the data obtained by the Michelson Doppler Imager
  (MDI) aboard the SOHO. This higher value is mainly due to the higher
  resolution and better sensitivity of the SOT, resulting in magnetic
  fluxes up to five times larger than those obtained from the MDI. The
  higher rates of flux cancellation correspond to either faster inflows
  or stronger magnetic fields of the inflow region in the current sheet,
  which may have important consequences for the physics of photospheric
  magnetic reconnection.

Title: The Formation of a Magnetic Channel by Emergence of
    Current-Carrying Magnetic Fields
Authors: Lim, E. -K.; Chae, J.; Jing, J.; Wang, H.; Wiegelmann, T.
Bibcode: 2012ASPC..454..185L
Altcode:
  The term magnetic channel indicates a series of polarity reversals
  separating elongated flux threads with opposite polarities. We studied
  the formation process of the magnetic channel in AR 10930 using time
  sequence SP data taken by SOT/Hinode. As a result, we detected both
  upflows (-0.5 to -1.0 km s<SUP>-1</SUP>) and downflows (+1.5 to +2.0 km
  s<SUP>-1</SUP>) within the channel site, and a pair of strong vertical
  current threads of opposite polarity along the channel. We also analyzed
  coronal magnetic fields computed from the non-linear force-free field
  extrapolation, and found that the current density in the lower corona
  increased as the channel structure evolved. These findings support
  the idea that the magnetic channel represents the emergence of the
  twisted flux tube.

Title: First Stereoscopic Determinations of Heights and Their
    Variations of EUV Bright Points Using SECCHI EUVI aboard STEREO
Authors: Kwon, R. -Y.; Chae, J.
Bibcode: 2012ASPC..454..163K
Altcode:
  We measure the heights of an EUV BPs observed by EUVI onboard the
  STEREO, and their time variation using a stereoscopic method developed
  by Kwon, Chae, Zhang (2010). The lifetime of the BP was 25 h. There is
  a tendency that the height of the BP is the highest at the formation
  phase and it decreases through its temporal evolution while the
  intensity is the strongest in the latter half of its lifetime. There
  is strong correlation between height and length which implies that BP
  is a group of semi-circular loops. Our results strongly suggest that
  a BP originates from magnetic reconnection due to the interaction
  between converging opposite magnetic poles.

Title: Waves in the Solar Chromosphere using FISS and SDO
Authors: Ajor Maurya, Ram; Chae, Jongchul; Park, Hyungmin
Bibcode: 2012cosp...39.1204A
Altcode: 2012cosp.meet.1204A
  Waves in the solar atmosphere are believed to play a crucial role in
  heating the chromosphere and corona. To explore the characteristic
  properties of waves in different chromospheric features, e.g.,
  sunspot, plages, etc., we analyzed the high resolution observational
  data provided by the Fast Imaging Solar Spectrometer (FISS) and Solar
  Dynamic Observatory (SDO). The high spatial and temporal resolution
  multi-wavelength observations provided by these instruments enable us
  to sample the chromosphere at different heights. The spectral data
  provided by the FISS are used to derive physical parameters, viz.,
  temperature, Doppler velocity, etc., which help us to understand the
  wave excitation mechanism in different chromospheric features. We
  have studied the running penumbral waves by constructing Doppler
  images from the spectral observations in different wavelength bands
  of H-alpha and Ca II obtained from the FISS. Details of our findings
  will be presented in the paper.

Title: The Occurrence and Speed of CMEs Related to Two Characteristic
    Evolution Patterns of Helicity Injection in Their Solar Source Regions
Authors: Park, Sung-Hong; Cho, Kyung-Suk; Bong, Su-Chan; Kumar,
   Pankaj; Chae, Jongchul; Liu, Rui; Wang, Haimin
Bibcode: 2012ApJ...750...48P
Altcode: 2012arXiv1203.1690P
  Long-term (a few days) variation of magnetic helicity injection
  was calculated for 28 solar active regions that produced 47 coronal
  mass ejections (CMEs) to find its relationship to the CME occurrence
  and speed using SOHO/MDI line-of-sight magnetograms. As a result, we
  found that the 47 CMEs can be categorized into two different groups by
  two characteristic evolution patterns of helicity injection in their
  source active regions, which appeared for ~0.5-4.5 days before their
  occurrence: (1) a monotonically increasing pattern with one sign of
  helicity (Group A 30 CMEs in 23 active regions) and (2) a pattern
  of significant helicity injection followed by its sign reversal
  (Group B 17 CMEs in 5 active regions). We also found that CME speed
  has a correlation with average helicity injection rate with linear
  correlation coefficients of 0.85 and 0.63 for Group A and Group B,
  respectively. In addition, these two CME groups show different
  characteristics as follows: (1) the average CME speed of Group B
  (1330 km s<SUP>-1</SUP>) is much faster than that of Group A (870
  km s<SUP>-1</SUP>), (2) the CMEs in Group A tend to be single events
  whereas those in Group B mainly consist of successive events, and (3)
  flares related to the CMEs in Group B are relatively more energetic
  and impulsive than those in Group A. Our findings therefore suggest
  that the two CME groups have different pre-CME conditions in their
  source active regions and different CME characteristics.

Title: Magnetic Reconnection in the Photosphere and Chromosphere
Authors: Chae, J.
Bibcode: 2012ASPC..455..187C
Altcode:
  Recent studies based on Hinode and high resolution ground-based
  observations have produced significant results that shed more light
  on the physical property of reconnection processes occurring in the
  photosphere and chromosphere. For better insights on this issue,
  I will review relevant published results together with previous
  results, focusing on five questions: (1) Is flux cancellation a result
  of magnetic reconnection? (2) At what atmospheric levels does such
  reconnection occur? (3) How does magnetic flux retract? (4) How does
  plasma respond to reconnection? (5) Is reconnection responsible for
  the chromospheric and coronal heating?

Title: Automatic Solar Filament Segmentation and Characterization
Authors: Yuan, Y.; Shih, F. Y.; Jing, J.; Wang, H.; Chae, J.
Bibcode: 2011SoPh..272..101Y
Altcode: 2011SoPh..tmp..131Y; 2011SoPh..tmp..187Y; 2011SoPh..tmp..256Y
  This paper presents a generic method to automatically segment and
  characterize solar filaments from various Hα full-disk solar images,
  obtained by different solar observatories, with different dynamic
  ranges and statistical properties. First, a cascading Hough circle
  detector is designed to find the center location and radius of the
  solar disks. Second, polynomial surface fitting is adopted to correct
  unbalanced luminance. Third, an adaptive thresholding method is put
  forward to segment solar filaments. Finally, for each piece of a solar
  filament, its centroid location, area, and length are characterized, in
  which morphological thinning and graph theory are used for identifying
  the main skeletons of filaments. To test the performance of the proposed
  methods, a dataset composed of 125 Hα images is considered. These
  images were obtained by four solar observatories from January 2000
  to May 2010, one image per month. Experimental results show that the
  accuracy rate is above 95% as measured by filament number and above 99%
  as measured by filament area, indicating that only a few tiny filaments
  are not detected.

Title: Substructure of quiet sun bright points
Authors: Andic, Aleksandra; Chae, Jongchul; Goode, Phillip R.
Bibcode: 2011IAUS..273..339A
Altcode: 2010arXiv1012.2080A
  Since photospheric bright points (BPs) were first observed, there has
  been a question as to how are they structured. Are they just single
  flux tubes or a bundle of the flux-tubes? Surface photometry of the
  quiet Sun (QS) has achieved resolution close to 0.1'' with the New Solar
  Telescope at Big Bear Solar Observatory. This resolution allowed us to
  detect a richer spectrum of BPs in the QS. The smallest BPs we observed
  with TiO 705.68 nm were 0.13'', and we were able to resolve individual
  components in some of the BPs clusters and ribbons observed in the QS,
  showing that they are composed of the individual BPs. Average size of
  observed BPs was 0.22''.

Title: Active Region High Velocity Events Observed by Fast Imaging
    Solar Spectrograph on the NST
Authors: Ahn, Kwangsu; Chae, J.; Nah, J.; Park, H.; Jang, B.; Yang,
   H.; Park, Y.; Cao, W.; Goode, P. R.
Bibcode: 2011SPD....42.1904A
Altcode: 2011BAAS..43S.1904A
  The Fast Imaging Solar Spectrograph (FISS) is the only
  spectrograph-based instrument on the NST that is currently
  operational. With a high spectral resolution of 1.4 x 10<SUP>5</SUP>
  and simultaneous dual spectral band imaging, this instrument can
  accurately determine the physical parameters of chromospheric features
  --- filaments, jets and so on. Initial observations captured several
  peculiar dynamic events that showed high line-of-sight velocities
  of the order of 20 km s<SUP>-1</SUP> in the vicinity of sunspots. We
  expect that FISS will provide a better understanding of the physics
  in the chromosphere with the aid of the unprecedentedly high spatial
  resolution of NST.

Title: Propagating Transverse Wave In A Spicule Observed By The
    Hinode Sot
Authors: Kim, Yeon-Han; Bong, S.; Cho, K.; Park, Y.; Cho, I.; Chae, J.
Bibcode: 2011SPD....42.0306K
Altcode: 2011BAAS..43S.0306K
  We examined the wave signatures in a spicule observed by the Hinode SOT
  to present a quantitative and clear evidence of propagating transverse
  waves. Especially, we estimated the propagation wave speed in the
  spicule observed on 2008 June 3 in the north polar limb of the Sun. For
  this, we made time-slice stacks at different height of the spicule axis
  using time series images of the spicule. All time-slice stacks for 9
  different heights show oscillation patterns with a period of about 130
  s. We also investigated the cross-correlation among time-slice stacks
  to estimate the phase difference of the oscillation with height and
  its propagating speed. We found that the mean phase delay over the
  height difference of 3000 km is about 13 s. This result suggests that
  the oscillation is a propagating transverse wave and the propagating
  speed is about 220 km s<SUP>-1</SUP>. In addition, we found that the
  estimated speeds increased from 100 to 230 km s<SUP>-1</SUP> over 5000
  km height range and this is well explained by the density variation
  along the spicule structure.

Title: Chromospheric Response At The Photospheric Dynamic
Authors: Andic, Aleksandra; Chae, J.; Park, H.; Yang, H.
Bibcode: 2011SPD....42.1735A
Altcode: 2011BAAS..43S.1735A
  We analysed the event in the chromosphere and its connection to
  the photo- spheric dynamic. The observations were done at New Solar
  Telescope at the Big Bear Solar Observatory using the photometry in TiO
  spectral line and FISS spec- trograph scanning Ca II and Hα spectral
  lines. <P />The event showed strong plasma flows and propagating
  oscillations that coin- cided with the photospheric dynamic. The
  movement of the footprints of the flux tubes in photosphere indicated
  a possible flux tube entanglement and mag- netic reconnection that
  caused observed brightening. The waves, originating in the photosphere,
  were propagating prior the event. The reconnection itself caused
  additional burst of the oscillations originating at the place of the
  reconnection. This event are complex and contain both jets and the
  oscillatory propagation.

Title: Tiny Pores Observed by New Solar Telescope and Hinode
Authors: Cho, KyungSuk; Bong, S.; Chae, J.; Kim, Y.; Park, Y.; Ahn,
   K.; Katsukawa, Y.
Bibcode: 2011SPD....42.1903C
Altcode: 2011BAAS..43S.1903C
  Seoul National University and Korea Astronomy and Space Science
  Institute installed Fast Imaging Solar Spectrograph (FISS) in the
  Cude room of the 1.6 m New Solar Telescope (NST) at Big Bear Solar
  Observatory on May 14, 2010. FISS is a unique system that can do
  imaging of H-alpha and Ca II 8542 band simultaneously, which is quite
  suitable for studying of dynamics of chromosphere. To investigate the
  relationship between the photospheric and low-chromospheric motions at
  the pore region, we took a coordinate observation with NST/FISS and
  Hinode/SOT for new emerging active region (AR11117) on October 26,
  2010. In the observed region, we could find two tiny pores and two
  small magnetic concentrations (SMCs), which have similar magnetic
  flux with the pores but do not look dark. Magnetic flux density and
  Doppler velocities at the photosphere are estimated by applying the
  center-of-gravity (COG) method to the HINODE/spectropolarimeter (SP)
  data. The line-of-sight motions above the photosphere are determined
  by adopting the bisector method to the wing spectra of Ha and CaII
  8542 lines. As results, we found the followings. (1)There are upflow
  motion on the pores and downflow motion on the SMCs. (2)Towards the
  CaII 8542 line center, upflow motion decrease and turn to downward
  motion in pores, while the speed of down flow motion increases in
  the SMCs. (3)There is oscillating motion above pores and the SMCs,
  and this motion keep its pattern along the height. (4) As height
  increase, there is a general tendency of the speed shift to downward
  on pores and the SMCs. In this poster, we will present preliminary
  understanding of the coupling of pore dynamics between the photosphere
  and the low-chromosphere.

Title: Response of Granulation to Small-scale Bright Features in
    the Quiet Sun
Authors: Anđić, A.; Chae, J.; Goode, P. R.; Cao, W.; Ahn, K.;
   Yurchyshyn, V.; Abramenko, V.
Bibcode: 2011ApJ...731...29A
Altcode: 2011arXiv1102.3404A
  We detected 2.8 bright points (BPs) per Mm<SUP>2</SUP> in the quiet
  Sun with the New Solar Telescope at Big Bear Solar Observatory, using
  the TiO 705.68 nm spectral line at an angular resolution ~0farcs1 to
  obtain a 30 minute data sequence. Some BPs formed knots that were
  stable in time and influenced the properties of the granulation
  pattern around them. The observed granulation pattern within ~3''
  of knots presents smaller granules than those observed in a normal
  granulation pattern, i.e., around the knots a suppressed convection
  is detected. Observed BPs covered ~5% of the solar surface and were
  not homogeneously distributed. BPs had an average size of 0farcs22,
  they were detectable for 4.28 minutes on average, and had an averaged
  contrast of 0.1% in the deep red TiO spectral line.

Title: Development of the Fast Imaging Solar Spectrograph for 1.6
    m New Solar Telescope
Authors: Nah, Ja-Kyoung; Chae, Jong-Chul; Park, Young-Deuk; Park,
   Hyung-Min; Jang, Bi-Ho; Ahn, Kwang-Su; Yang, Hee-Su; Cho, Kyung-Suk;
   Kim, Yeon-Han; Kim, Kwang-Dong; Cao, Wenda; Gorceix, Nicolas; Goode,
   Philip. R.
Bibcode: 2011PKAS...26...45N
Altcode:
  No abstract at ADS

Title: Recent activities of solar astronomers in Korea
Authors: Cho, K. -S.; Chae, J.; Moon, Y. J.; Choe, G. S.
Bibcode: 2011ASInC...2..383C
Altcode:
  At present, about twenty PhDs are carrying out education, research, and
  observation in the field of solar astronomy in Korea. The history and
  recent activities of the Korean solar community are briefly reviewed
  in this paper. We expect that the current efforts of Korean solar
  astronomers contribute to the promotion of cooperative solar research
  in the Asian-Pacific countries.

Title: Fast Imaging Solar Spectrograph System in New Solar Telescope
Authors: Park, Y. -D.; Kim, Y. H.; Chae, J.; Goode, P. R.; Cho, K. S.;
   Park, H. M.; Nah, J. K.; Jang, B. H.
Bibcode: 2010nspm.conf..189P
Altcode:
  In 2004, Big Bear Solar Observatory in California, USA launched
  a project for construction of the world's largest aperture solar
  telescope (D = 1.6m) called New Solar Telescope(NST). University
  of Hawaii (UH) and Korea Astronomy and Space Science Institute(KASI)
  partly collaborate on the project. NST is a designed off-axis parabolic
  Gregorian reflector with very high spatial resolution(0.07 arcsec
  at 5000A) and is equipped with several scientific instruments such as
  Visible Imaging Magnetograph (VIM), InfraRed Imaging Magnetograph IRIM),
  and so on. Since these scientific instruments are focused on studies of
  the solar photosphere, we need a post-focus instrument for the NST to
  study the fine structures and dynamic patterns of the solar chromosphere
  and low Transition Region (TR) layer, including filaments/prominences,
  spicules, jets, micro flares, etc. For this reason, we developed and
  installed a fast imaging solar spectrograph(FISS) system on the NST
  withadvantages of achieving compact design with high spectral resolution
  and small aberration as well as recording many solar spectral lines in
  a single and/or dual band mode. FISS was installed in May, 2010 and now
  we carry out a test observation. In this talk, we introduce the FISS
  system and the results of the test observation after FISS installation.

Title: Tiny Pores observed by HINODE/SOT
Authors: Cho, K.; Bong, S.; Chae, J.; Kim, Y.; Park, Y.
Bibcode: 2010AGUFMSH11B1647C
Altcode:
  The study of pores, small penumbraless sunspots, can give us a chance to
  understand how strong magnetic fields interact with convective motions
  in the photosphere. For a better understanding of this interaction, we
  investigate the temporal variation of several tiny pores smaller than
  2“. These pores were observed by the Solar Optical Telescope (SOT)
  onboard Hinode on 2006 December 29. We have analyzed the high resolution
  spectropolarimetric (SP) data and the G-band filtergrams taken during
  the observation. Magnetic flux density and Doppler velocities of the
  pores are estimated by applying the center of gravity (COG) method to
  the SP data. The horizontal motions in and around the pores are tracked
  by adopting the Nonlinear Affine Velocity Estimator (NAVE) method to
  the G-band filter images. As results, we found the followings. (1)
  Darkness of pores is positively correlated with magnetic flux
  density. (2) Downflows always exist inside and around the pores. (3)
  The speed of downflows inside the pores is negatively correlated with
  their darkness. (4) The pores are surrounded by strong downflows. (5)
  Brightness changes of the pores are correlated with the divergence
  of mass flow (correlation coefficient &gt; 0.9). (6) The pores in the
  growing phase are associated with the converging flow pattern and the
  pores in the decay phase with the diverging flow pattern. Our results
  support the idea that a pore grows as magnetic flux density increases
  due to the convergence of ambient mass flow and it decays with the
  decrease of the flux density due to the diverging mass flow.

Title: A small-scale H-alpha eruption in the north polar limb of
    the Sun observed by New Solar Telescope
Authors: Kim, Y. -H.; Park, Y. -D.; Bong, S. -Ch.; Cho, K. -S.;
   Chae, J.
Bibcode: 2010nspm.conf...73K
Altcode:
  The 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory
  (BBSO) is the recently constructed world's largest optical solar
  telescope on the ground. Up to date it has been partly operated,
  i.e., observations that have been made at Nasmyth focus only without
  adaptive optic (AO) system. The AO system is planned to be installed
  this summer. Using the NST, we have observed the north polar limb
  in H-alpha line center wavelength on 2009 August 26. A remarkable
  H-alpha eruption was observed from 18:20 UT to 18:45 UT with a
  relatively slower speed of about 10 km/s in its early stage. The
  eruption was then slightly accelerated up to 20-30 km/s and appeared
  to be deflected along the pre-existing magnetic field. The eruption
  also showed several interesting characteristics such as bifurcation,
  rotation, horizontal oscillation, and direction and thickness changes
  of its structure during its evolution. In this talk, we report on the
  observational properties of the small-scale eruption observed by the
  NST and discuss their implications for magnetic reconnection.

Title: Tiny Pores Observed by Hinode/Solar Optical Telescope
Authors: Cho, Kyung-Suk; Bong, Su-Chan; Chae, Jongchul; Kim, Yeon-Han;
   Park, Young-Deuk
Bibcode: 2010ApJ...723..440C
Altcode:
  The study of pores, small penumbraless sunspots, can give us a chance to
  understand how strong magnetic fields interact with convective motions
  in the photosphere. For a better understanding of this interaction,
  we investigate the temporal variation of several tiny pores smaller
  than 2''. These pores were observed by the Solar Optical Telescope on
  board Hinode on 2006 December 29. We have analyzed the high-resolution
  spectropolarimetric (SP) data and the G-band filtergrams taken during
  the observation. Magnetic flux density and Doppler velocities of the
  pores are estimated by applying the center-of-gravity method to the
  SP data. The horizontal motions in and around the pores are tracked
  by adopting the nonlinear affine velocity estimator method to the
  G-band filter images. As a result, we found the following. (1) The
  darkness of the pores is positively correlated with the magnetic flux
  density. (2) Downflows always exist inside and around the pores. (3)
  The speed of downflows inside the pores is negatively correlated with
  their darkness. (4) The pores are surrounded by strong downflows. (5)
  Brightness changes of the pores are correlated with the divergence
  of mass flow (correlation coefficient &gt;0.9). (6) The pores in
  the growing phase are associated with the converging flow pattern
  and the pores in the decay phase with the diverging flow pattern. Our
  results support the idea that a pore grows as the magnetic flux density
  increases due to the convergence of ambient mass flow and it decays
  with the decrease of the flux density due to the diverging mass flow.

Title: Chromospheric Signatures of Small-scale Flux Emergence as
    Observed with New Solar Telescope and Hinode Instruments
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Chae,
   J.; Cao, W.; Andic, A.; Ahn, K.
Bibcode: 2010ApJ...722.1970Y
Altcode: 2011arXiv1102.1034Y
  With the ever-increasing influx of high-resolution images of the solar
  surface obtained at a multitude of wavelengths, various processes
  occurring at small spatial scales have become a greater focus of our
  attention. Complex small-scale magnetic fields have been reported that
  appear to have enough stored energy to heat the chromosphere. While
  significant progress has been made in understanding small-scale
  phenomena, many specifics remain elusive. We present here a detailed
  study of a single event of disappearance of a magnetic dipole and
  associated chromospheric activity. Based on New Solar Telescope Hα
  data and Hinode photospheric line-of-sight magnetograms and Ca II
  H images, we report the following. (1) Our analysis indicates that
  even very small dipoles (elements separated by about 0farcs5 or less)
  may reach the chromosphere and trigger non-negligible chromospheric
  activity. (2) Careful consideration of the magnetic environment where
  the new flux is deposited may shed light on the details of magnetic
  flux removal from the solar surface. We argue that the apparent
  collision and disappearance of two opposite polarity elements may
  not necessarily indicate their cancellation (i.e., reconnection,
  emergence of a "U" tube, or submergence of Ω loops). In our case, the
  magnetic dipole disappeared by reconnecting with overlying large-scale
  inclined plage fields. (3) Bright points (BPs) seen in off-band Hα
  images are very well correlated with the Ca II H BPs, which in turn
  are cospatial with G-band BPs. We further speculate that, in general,
  Hα BPs are expected to be cospatial with photospheric BPs; however,
  a direct comparison is needed to refine their relationship.

Title: Time Evolution of Coronal Magnetic Helicity in the Flaring
    Active Region NOAA 10930
Authors: Park, Sung-Hong; Chae, Jongchul; Jing, Ju; Tan, Changyi;
   Wang, Haimin
Bibcode: 2010ApJ...720.1102P
Altcode: 2010arXiv1008.1558P
  To study the three-dimensional (3D) magnetic field topology and its
  long-term evolution associated with the X3.4 flare of 2006 December 13,
  we investigate the coronal relative magnetic helicity in the flaring
  active region (AR) NOAA 10930 during the time period of December
  8-14. The coronal helicity is calculated based on the 3D nonlinear
  force-free magnetic fields reconstructed by the weighted optimization
  method of Wiegelmann, and is compared with the amount of helicity
  injected through the photospheric surface of the AR. The helicity
  injection is determined from the magnetic helicity flux density proposed
  by Pariat et al. using Solar and Heliospheric Observatory/Michelson
  Doppler Imager magnetograms. The major findings of this study are the
  following. (1) The time profile of the coronal helicity shows a good
  correlation with that of the helicity accumulation by injection through
  the surface. (2) The coronal helicity of the AR is estimated to be -4.3
  × 10<SUP>43</SUP> Mx<SUP>2</SUP> just before the X3.4 flare. (3) This
  flare is preceded not only by a large increase of negative helicity,
  -3.2 × 10<SUP>43</SUP> Mx<SUP>2</SUP>, in the corona over ~1.5 days
  but also by noticeable injections of positive helicity through the
  photospheric surface around the flaring magnetic polarity inversion
  line during the time period of the channel structure development. We
  conjecture that the occurrence of the X3.4 flare is involved with
  the positive helicity injection into an existing system of negative
  helicity.

Title: Patterns of Flows in an Intermediate Prominence Observed
    by Hinode
Authors: Ahn, Kwangsu; Chae, Jongchul; Cao, Wenda; Goode, Philip R.
Bibcode: 2010ApJ...721...74A
Altcode:
  The investigation of plasma flows in filaments/prominences gives
  us clues to understanding their magnetic structures. We studied
  the patterns of flows in an intermediate prominence observed by
  Hinode/SOT. By examining a time series of Hα images and Ca II H images,
  we have found horizontal flows in the spine and vertical flows in
  the barb. Both of these flows have a characteristic speed of 10-20 km
  s<SUP>-1</SUP>. The horizontal flows displayed counterstreaming. Our
  detailed investigation revealed that most of the moving fragments in
  fact reversed direction at the end point of the spine near a footpoint
  close to the associated active region. These returning flows may be
  one possible explanation of the well-known counterstreaming flows
  in prominences. In contrast, we have found vertical flows—downward
  and upward—in the barb. Most of the horizontal flows in the spine
  seem to switch into vertical flows when they approach the barb,
  and vice versa. We propose that the net force resulting from a small
  deviation from magnetohydrostatic equilibrium, where magnetic fields
  are predominantly horizontal, may drive these patterns of flow. In the
  prominence studied here, the supposed magnetohydrostatic configuration
  is characterized by magnetic field lines sagging with angles of 13°
  and 39° in the spine and the barb, respectively.

Title: The Formation of a Magnetic Channel by the Emergence of
    Current-carrying Magnetic Fields
Authors: Lim, Eun-Kyung; Chae, Jongchul; Jing, Ju; Wang, Haimin;
   Wiegelmann, Thomas
Bibcode: 2010ApJ...719..403L
Altcode: 2010arXiv1009.0420L
  A magnetic channel—a series of polarity reversals separating elongated
  flux threads with opposite polarities—may be a manifestation of
  a highly non-potential magnetic configuration in active regions. To
  understand its formation, we have carried out a detailed analysis of
  the magnetic channel in AR 10930 using data taken by the Solar Optical
  Telescope/Hinode. As a result, we found upflows (-0.5 to -1.0 km
  s<SUP>-1</SUP>) and downflows (+1.5 to +2.0 km s<SUP>-1</SUP>) inside
  and at both tips of the thread, respectively, and a pair of strong
  vertical currents of opposite polarity along the channel. Moreover,
  our analysis of the nonlinear force-free fields constructed from the
  photospheric magnetic field indicates that the current density in the
  lower corona may have gradually increased as a result of the continuous
  emergence of the highly sheared flux along the channel. With these
  results, we suggest that the magnetic channel originates from the
  emergence of the twisted flux tube that has formed below the surface
  before the emergence.

Title: Productivity of Solar Flares and Magnetic Helicity Injection
    in Active Regions
Authors: Park, Sung-hong; Chae, Jongchul; Wang, Haimin
Bibcode: 2010ApJ...718...43P
Altcode: 2010arXiv1005.3416P
  The main objective of this study is to better understand how magnetic
  helicity injection in an active region (AR) is related to the occurrence
  and intensity of solar flares. We therefore investigate the magnetic
  helicity injection rate and unsigned magnetic flux, as a reference. In
  total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr
  averaged helicity injection rate and unsigned magnetic flux are compared
  with the flare index and the flare-productive probability in the next
  24 hr following a measurement. In addition, we study the variation of
  helicity over a span of several days around the times of the 19 flares
  above M5.0 which occurred in selected strong flare-productive ARs. The
  major findings of this study are as follows: (1) for a sub-sample of
  91 large ARs with unsigned magnetic fluxes in the range from (3-5)
  × 10<SUP>22</SUP> Mx, there is a difference in the magnetic helicity
  injection rate between flaring ARs and non-flaring ARs by a factor
  of 2; (2) the GOES C-flare-productive probability as a function of
  helicity injection displays a sharp boundary between flare-productive
  ARs and flare-quiet ones; (3) the history of helicity injection
  before all the 19 major flares displayed a common characteristic:
  a significant helicity accumulation of (3-45) × 10<SUP>42</SUP>
  Mx<SUP>2</SUP> during a phase of monotonically increasing helicity over
  0.5-2 days. Our results support the notion that helicity injection is
  important in flares, but it is not effective to use it alone for the
  purpose of flare forecast. It is necessary to find a way to better
  characterize the time history of helicity injection as well as its
  spatial distribution inside ARs.

Title: Oscillatory Behavior in the Quiet Sun Observed with the New
    Solar Telescope
Authors: Anđić, A.; Goode, P. R.; Chae, J.; Cao, W.; Ahn, K.;
   Yurchyshyn, V.; Abramenko, V.
Bibcode: 2010ApJ...717L..79A
Altcode: 2010arXiv1007.0272A
  Surface photometry of the quiet Sun has achieved an angular resolution
  of 0farcs1 with the New Solar Telescope at Big Bear Solar Observatory,
  revealing that a disproportionate fraction of the oscillatory events
  appear above observed bright point-like structures. During the tracking
  of these structures, we noted that the more powerful oscillatory events
  are cospatial with them, indicating that observed flux tubes may be
  the source of many observed oscillatory events.

Title: Non-Hydrostatic Support of Plasma in the Solar Chromosphere
    and Corona
Authors: Chae, Jong-Chul
Bibcode: 2010JKAS...43...55C
Altcode:
  No abstract at ADS

Title: Dynamics of Vertical Threads and Descending Knots in a
    Hedgerow Prominence
Authors: Chae, Jongchul
Bibcode: 2010ApJ...714..618C
Altcode:
  The existence and behavior of vertical fine structures of
  plasma—threads and knots—are a significant observational clue
  to understanding the magnetic structure and dynamics of quiescent
  prominences on the quiet Sun. Based on the equation of motion in ideal
  MHD, we reason that the non-hydrostatic support of plasma against
  gravity in general requires either the motion of plasma with a high
  value of downward acceleration (dynamical support) or the role of
  horizontal magnetic fields (magnetic support). By carefully tracking
  the motion of several bright threads seen in a hedgerow prominence
  observed by the Solar Optical Telescope aboard Hinode, we confirm that
  these threads are essentially static and stable, which negates the
  dynamic support. The application of the Kippenhahn-Schlüter solution
  suggests that they may be supported by sagged magnetic field lines with
  a sag angle of about 43°. We also track several bright descending
  knots and find that their descending speeds range from 10 to 30 km
  s<SUP>-1</SUP>, with a mean value of 16 km s<SUP>-1</SUP>, and their
  vertical accelerations from -0.10 to 0.10 km s<SUP>-2</SUP>, with a
  mean of practically zero. This finding suggests that these knots are
  basically supported by horizontal magnetic fields against gravity even
  when they descend, and the complex variations of their descending speeds
  should be attributed to small imbalances between gravity and the force
  of magnetic tension. Furthermore, some knots are observed to impulsively
  get accelerated downward from time to time. We conjecture that these
  impulsive accelerations are a result of magnetic reconnection and the
  subsequent interchange of magnetic configuration between a knot and its
  surrounding structure. It is proposed that this process of reconnection
  and interchange not only initiates the descending motion of the knots,
  but also allows knots to keep falling long distance through the medium
  permeated by horizontal magnetic fields.

Title: Stereoscopic Determination of Heights of Extreme Ultraviolet
    Bright Points Using Data Taken by SECCHI/EUVI Aboard STEREO
Authors: Kwon, Ryun-Young; Chae, Jongchul; Zhang, Jie
Bibcode: 2010ApJ...714..130K
Altcode:
  We measure the heights of EUV bright points (BPs) above the solar
  surface by applying a stereoscopic method to the data taken by the Solar
  TErrestrial RElations Observatory/SECCHI/Extreme UltraViolet Imager
  (EUVI). We have developed a three-dimensional reconstruction method
  for point-like features such as BPs using the simple principle that
  the position of a point in the three-dimensional space is specified as
  the intersection of two lines of sight. From a set of data consisting
  of EUVI 171 Å, 195 Å, 284 Å, and 304 Å images taken on 11 days
  arbitrarily selected during a period of 14 months, we have identified
  and analyzed 210 individual BPs that were visible on all four passband
  images and smaller than 30 Mm. The BPs seen in the 304 Å images have
  an average height of 4.4 Mm, and are often associated with the legs
  of coronal loops. In the 171 Å, 195 Å, and 284 Å images the BPs
  appear loop-shaped, and have average heights of 5.1, 6.7, and 6.1 Mm,
  respectively. Moreover, there is a tendency that overlying loops are
  filled with hotter plasmas. The average heights of BPs in 171 Å, 195
  Å, and 284 Å passbands are roughly twice the corresponding average
  lengths. Our results support the notion that an EUV BP represents a
  system of small loops with temperature stratification like flaring
  loops, being consistent with the magnetic reconnection origin.

Title: Highest Resolution Observations of the Quietest Sun
Authors: Goode, Philip R.; Yurchyshyn, Vasyl; Cao, Wenda; Abramenko,
   Valentyna; Andic, Aleksandra; Ahn, Kwangsu; Chae, Jongchul
Bibcode: 2010ApJ...714L..31G
Altcode:
  Highest resolution observations made with the new 1.6 m aperture solar
  telescope in Big Bear Solar Observatory during this time of historic
  inactivity on the Sun reveal new insights into the small-scale dynamics
  of the Sun's photosphere. The telescope's unprecedented resolution
  enabled us to observe that the smallest scale photospheric magnetic
  field seems to come in isolated points in the dark intergranular lanes,
  rather than the predicted continuous sheets confined to the lanes, and
  the unexpected longevity of the bright points implies a deeper anchoring
  than predicted. Further, we demonstrated for the first time that the
  photospheric plasma motion and magnetic fields are in equipartition
  over a wide dynamic range, and both cascade energy to ever-smaller
  scales according to classical Kolmogorov turbulence theory. Finally,
  we discovered tiny jet-like features originating in the dark lanes that
  surround the ubiquitous granules that characterize the solar surface.

Title: New Solar Telescope Observations of Magnetic Reconnection
    Occurring in the Chromosphere of the Quiet Sun
Authors: Chae, Jongchul; Goode, P. R.; Ahn, K.; Yurchysyn, V.;
   Abramenko, V.; Andic, A.; Cao, W.; Park, Y. D.
Bibcode: 2010ApJ...713L...6C
Altcode:
  Magnetic reconnection is a process in which field-line connectivity
  changes in a magnetized plasma. On the solar surface, it often
  occurs with the cancellation of two magnetic fragments of opposite
  polarity. Using the 1.6 m New Solar Telescope, we observed the
  morphology and dynamics of plasma visible in the Hα line, which is
  associated with a canceling magnetic feature (CMF) in the quiet Sun. The
  region can be divided into four magnetic domains: two pre-reconnection
  and two post-reconnection. In one post-reconnection domain, a small
  cloud erupted, with a plane-of-sky speed of 10 km s<SUP>-1</SUP>,
  while in the other one, brightening began at points and then tiny
  bright loops appeared and subsequently shrank. These features support
  the notion that magnetic reconnection taking place in the chromosphere
  is responsible for CMFs.

Title: Magnetic Activity on the Sun Revealed by Hinode/SOT (Keynote)
Authors: Chae, J.; Park, S.
Bibcode: 2009ASPC..415..101C
Altcode:
  Hinode observations have given us an unprecedented opportunity for
  understanding fine-scale magnetic activities on the Sun. The data
  produced by the Solar Optical Telescope (SOT) are particularly useful
  in the investigation of the interaction between magnetic field and
  plasma in the photosphere and chromosphere, opening the new era
  of observational magnetohydrodynamics (MHD). As an illustration,
  we would like to introduce new results and questions in three topics
  we have worked on. One is the nature of magnetic reconnection in the
  chromosphere as manifest in the flux cancellation observed in the
  photosphere. Our new result is that the rates of flux cancellation
  determined from Hinode/SOT are much higher than those determined from
  SOHO/MDI. Another topic is the determination of scale-dependent magnetic
  diffusivity in the photosphere, which seems to be closely related to
  the turbulent cascade of magnetoconvection. Finally, we will present our
  finding of a pattern of horizontal flows in a quiescent prominence that
  consists of a number of vertical threads. We think this flow pattern
  is an important clue to solving the mystery of vertical threads and
  downflows along the threads in quiescent prominences.

Title: NST observations of H alpha features and the non-hydrostatic
    support of the solar chromosphere
Authors: Chae, J.
Bibcode: 2009AGUFMSH51A1258C
Altcode:
  The existence of many structures of cool plasma in the solar
  chromosphere that extend much above the pressure scale height suggests
  that these structures are supported against gravity by mechanisms other
  than hydrostatic support. One possible mechanism is magnetic support,
  and the other is dynamic support. To reveal which is the dominant
  mechanism of non-hydrostatic support of chromospheric plasma, we have
  taken high resolution images of the chromosphere at the limb and on
  the disk by using the New Solar Telescope (NST) at Big Bear. We will
  report different kinds of chromospheric features/events which may hold
  a key to this problem.

Title: Rates of Photospheric Magnetic Flux Cancellation Measured
    with Hinode
Authors: Park, Soyoung; Chae, Jongchul; Litvinenko, Yuri E.
Bibcode: 2009ApJ...704L..71P
Altcode:
  Photospheric magnetic flux cancellation on the Sun is generally
  believed to be caused by magnetic reconnection occurring in the
  low solar atmosphere. Individual canceling magnetic features are
  observationally characterized by the rate of flux cancellation. The
  specific cancellation rate, defined as the rate of flux cancellation
  divided by the interface length, gives an accurate estimate of the
  electric field in the reconnecting current sheet. We have determined
  the specific cancellation rate using the magnetograms taken by the
  Solar Optical Telescope (SOT) aboard the Hinode satellite. The specific
  rates determined with SOT turned out to be systematically higher than
  those based on the data taken by the Michelson Doppler Imager (MDI)
  aboard the Solar and Heliospheric Observatory. The median value of
  the specific cancellation rate was found to be 8 × 10<SUP>6</SUP>
  G cm s<SUP>-1</SUP>—a value four times that obtained from the MDI
  data. This big difference is mainly due to a higher angular resolution
  and better sensitivity of the SOT, resulting in magnetic fluxes up
  to five times larger than those obtained from the MDI. The higher
  rates of flux cancellation correspond to either faster inflows or
  stronger magnetic fields of the reconnection inflow region, which may
  have important consequences for the physics of photospheric magnetic
  reconnection.

Title: The Rotating Sunspot in AR 10930
Authors: Min, Soonyoung; Chae, Jongchul
Bibcode: 2009SoPh..258..203M
Altcode:
  We study the pattern and behavior of a rotating sunspot in Active Region
  10930. The rotational angular speed has been extracted from the apparent
  motions of the sunspot determined by applying a new optical technique -
  called non-linear affine velocity estimator (NAVE) - to high-resolution
  G-band images taken by the Solar Optical Telescope (SOT) onboard the
  Hinode satellite. The structure and dynamics of coronal loops in this
  active region have been examined using the images obtained by the X-Ray
  Telescope (XRT) and the spectral data taken by the Extreme-ultraviolet
  Imaging Spectrometer (EIS), both also onboard Hinode. Our results are
  summarized as follows: i) The small sunspot of positive polarity rotated
  counterclockwise about its center by 540° during the period of five
  days. ii) Its angular velocity varied with the azimuth angle as well
  as the radial distance, being affected by the asymmetric shape of the
  umbra. iii) The angular velocity increased up to 8° h<SUP>−1</SUP>
  until 13 December as the sunspot grew, and then decreased rapidly down
  to 3° h<SUP>−1</SUP> on the next day as the sunspot decayed. iv)
  The coronal loops that connected the two sunspots became sigmoidal in
  shape. v) The coronal emissions from the regions around the rotating
  sunspot were blueshifted, which may indicate the expansion of the
  coronal loops. Our results suggest that the rotation of the sunspot
  may be closely related to the dynamic development of emerging twisted
  magnetic fields.

Title: A Comparison of the Initial Speed of Coronal Mass Ejections
    with the Magnetic Flux and Magnetic Helicity of Magnetic Clouds
Authors: Sung, S. -K.; Marubashi, K.; Cho, K. -S.; Kim, Y. -H.; Kim,
   K. -H.; Chae, J.; Moon, Y. -J.; Kim, I. -H.
Bibcode: 2009ApJ...699..298S
Altcode:
  To investigate the relationship between the speed of a coronal mass
  ejection (CME) and the magnetic energy released during its eruption,
  we have compared the initial speed of CMEs (V <SUB>CME</SUB>) and the
  two parameters of their associated magnetic clouds (MC), magnetic
  flux (F <SUB>MC</SUB>), and magnetic helicity per unit length
  (|H <SUB>MC</SUB>|/L), for 34 pairs of CMEs and MCs. The values
  of these parameters in each MC have been determined by fitting
  the magnetic data of the MC to the linear force-free cylindrical
  model. As a result, we found that there are positive correlations
  between V <SUP>2</SUP> <SUB>CME</SUB> and F <SUB>MC</SUB>, and
  between V <SUP>2</SUP> <SUB>CME</SUB> and |H <SUB>MC</SUB>|/L. It
  is also found that the kinetic energy of CMEs (E <SUB>CME</SUB>)
  is correlated with F <SUB>MC</SUB> and |H <SUB>MC</SUB>|/L of the
  associated MC. In contrast, we found no significant correlation between
  langV <SUB>MC</SUB>rang<SUP>2</SUP> and F <SUB>MC</SUB>, nor between
  langV <SUB>MC</SUB>rang<SUP>2</SUP> and |H <SUB>MC</SUB>|/L. Our
  results support the notion that the eruption of a CME is related to
  the magnetic helicity of the source active region.

Title: Estimation of Errors in the Transverse Velocity Vectors
    Determined from HINODE/SOT Magnetograms Using the NAVE Technique
Authors: Chae, Jong-Chul; Moon, Yong-Jae
Bibcode: 2009JKAS...42...61C
Altcode:
  No abstract at ADS

Title: Return Flows in a Counter-streaming Prominence
Authors: Ahn, Kwangsu; Chae, J.; Goode, P.
Bibcode: 2009SPD....40.1008A
Altcode:
  It is known that the fine structures of filaments/prominences show
  counter-streaming motion. We found that the counter-streaming could be
  an outcome of return flows at the edge of filaments/prominences. We
  picked an intermediate prominence that showed a dominant horizontal
  motion. The trajectories of the plasma fragments in this prominence
  showed that most of the plasma in this prominence changed their
  direction near the edge of prominence structure. This implies that
  the counter-streaming may be represented by plasma which move back and
  forth along the horizontal magnetic field lines. We assumed that there
  could be magnetic pillar-like structures near the edge, so that they
  could increase magnetic pressure near the edge, pulling the plasma
  back to the original position.

Title: Chirality of Intermediate Filaments and Magnetic Helicity of
    Active Regions
Authors: Lim, Eun-Kyung; Chae, J.
Bibcode: 2009SPD....40.0912L
Altcode:
  Filaments that form either between or around active regions (ARs)
  are called intermediate filaments. Even though there have been many
  theoretical studies, the origin of the chirality of filaments is still
  unknown. We investigated how intermediate filaments are related to their
  associated ARs, especially from the point of view of magnetic helicity
  and the orientation of polarity inversion lines (PILs). The chirality
  of filaments has been determined based on the orientations of barbs
  observed in the full-disk Hα images taken at Big Bear Solar Observatory
  during the rising phase of solar cycle 23. The sign of magnetic helicity
  of ARs has been determined using S/inverse-S shaped sigmoids from Yohkoh
  SXT images. As a result, we have found a good correlation between the
  chirality of filaments and the magnetic helicity sign of ARs. Among
  45 filaments, 42 filaments have shown the same sign as helicity sign
  of nearby ARs. It has been also confirmed that the role of both the
  orientation and the relative direction of PILs to ARs in determining
  the chirality of filaments is not significant, against a theoretical
  prediction. These results suggest that the chirality of intermediate
  filaments may originate from magnetic helicity of their associated ARs.

Title: Signatures of Sweet-Parker magnetic reconnection in the
    solar chromosphere
Authors: Litvinenko, Y. E.; Chae, J.
Bibcode: 2009A&A...495..953L
Altcode:
  Aims: Predicted and observed signatures of magnetic reconnection in
  the solar chromosphere are discussed. <BR />Methods: Compressible
  reconnection scalings for the Sweet-Parker current sheet in the
  chromosphere are derived, which generalize earlier treatments by
  including both the Lorentz force and the pressure gradient in the
  reconnection outflow as possible drivers of reconnection jets. The
  theoretical scalings were tested against the measured speed,
  density, and temperature of an extreme-ultraviolet jet, observed
  with TRACE. Model predictions for the reconnection jet parameters as
  functions of height above the solar photosphere were computed. <BR
  />Results: The predicted variation of reconnection jet parameters with
  height appears to correspond to the observed wide range of parameters
  of chromospheric jet-like features.

Title: Chirality of Intermediate Filaments and Magnetic Helicity of
    Active Regions
Authors: Lim, Eun-Kyung; Chae, Jongchul
Bibcode: 2009ApJ...692..104L
Altcode: 2009arXiv0901.0360L
  Filaments that form either between or around active regions (ARs)
  are called intermediate filaments. Even though there have been many
  theoretical studies, the origin of the chirality of filaments is still
  unknown. We investigated how intermediate filaments are related to their
  associated ARs, especially from the point of view of magnetic helicity
  and the orientation of polarity inversion lines (PILs). The chirality
  of filaments has been determined based on the orientations of barbs
  observed in full-disk Hα images taken at Big Bear Solar Observatory
  during the rising phase of solar cycle 23. The sign of magnetic helicity
  of ARs has been determined using S/inverse-S shaped sigmoids from Yohkoh
  SXT images. As a result, we have found good correlation between the
  chirality of filaments and the magnetic helicity sign of ARs. Among
  45 filaments, 42 filaments have shown the same sign as helicity sign
  of nearby ARs. It has been also confirmed that the role of both the
  orientation and the relative direction of PILs to ARs in determining
  the chirality of filaments is not significant, against a theoretical
  prediction. These results suggest that the chirality of intermediate
  filaments may originate from magnetic helicity of their associated ARs.

Title: Magnetic Helicity Injection during the Formation of AN
    Intermediate Filament
Authors: Jeong, Hye-Won; Chae, Jong-Chul; Moon, Y. J.
Bibcode: 2009JKAS...42....9J
Altcode:
  No abstract at ADS

Title: A Test of Three Optical Flow Techniques—LCT, DAVE, and NAVE
Authors: Chae, Jongchul; Sakurai, Takashi
Bibcode: 2008ApJ...689..593C
Altcode:
  A time sequence of high-quality images currently produced by
  high-resolution observations either from the ground or in space may
  be utilized to determine the transverse flow field on the plane of
  the sky with the help of optical flow techniques. We have examined the
  performance of three different methods—a well-known technique called
  local correlation tracking (LCT), a recently developed technique called
  the differential affine velocity estimator (DAVE), and a new technique
  called the nonlinear affine velocity estimator (NAVE)—using three
  kinds of image data: mapping-based synthetic images, a set of MHD
  simulation data, and real images (magnetograms) taken by the Solar
  Optical Telescope on board Hinode. We have generalized the model
  equation of image evolution by adding to the continuity equation a
  source term that is proportional to the image value. Synthetic images
  were constructed based on the analytical solution of this equation
  with different velocity profiles: uniform, affine, or nonaffine. The
  tests with the synthetic data indicated that NAVE is very good at
  detecting subpixel motions, superpixel motions, and nonuniform
  motions, while LCT is not good at detecting nonuniform motions,
  especially around critical points, and the performance of DAVE is
  degraded in the presence of superpixel motions. In all the methods,
  the performance became worse as the velocity field deviated more from
  an affine one. We also found that the MHD simulation data we used
  are not quite suited for discriminating between the three methods,
  maybe because the data do not contain enough structural information
  to be used for tracing. In contrast, the determination of velocity
  fields from the real image data was somewhat sensitive to the technique
  adopted. The technique of NAVE with the source term produced velocity
  fields that are the most consistent with the data.

Title: Persistent Horizontal Flows and Magnetic Support of Vertical
    Threads in a Quiescent Prominence
Authors: Chae, Jongchul; Ahn, Kwangsoo; Lim, Eun-Kyung; Choe, G. S.;
   Sakurai, Takashi
Bibcode: 2008ApJ...689L..73C
Altcode:
  There has been some controversy as to whether the magnetic fields
  of vertical threads seen in quiescent prominences are predominantly
  vertical or horizontal. We report finding special patterns of flow in
  a quiescent prominence observed by the Solar Optical Telescope aboard
  Hinode. This prominence is a small hedgerow prominence composed of many
  vertical threads. To one side of it, we found a pattern of persistent
  horizontal flows of Hα-emitting plasma. These flows originated from a
  region in the chromosphere, rose to coronal heights, and then extended
  horizontally for a long distance until they reached the main body of
  the prominence. In the higher altitudes the flows either moved across
  vertical threads or lifted them up, while in the lower altitudes
  they often formed bright blobs of plasma and shed them, resulting in
  a sudden change of flow direction from horizontal to vertical. The
  observed persistent horizontal flows support a configuration of
  initially horizontal magnetic fields, and our results appear to
  be consistent with the traditional theory that vertical threads in
  quiescent prominences are stacks of plasma supported against gravity
  by the sagging of initially horizontal magnetic field lines.

Title: The Variation of Relative Magnetic Helicity around Major Flares
Authors: Park, Sung-Hong; Lee, Jeongwoo; Choe, G. S.; Chae, Jongchul;
   Jeong, Hyewon; Yang, Guo; Jing, Ju; Wang, Haimin
Bibcode: 2008ApJ...686.1397P
Altcode: 2010arXiv1004.2856P
  We have investigated the variation of magnetic helicity over a span
  of several days around the times of 11 X-class flares which occurred
  in seven active regions (NOAA 9672, 10030, 10314, 10486, 10564, 10696,
  and 10720) using the magnetograms taken by the Michelson Doppler Imager
  (MDI) on board the Solar and Heliospheric Observatory (SOHO). As a
  major result we found that each of these major flares was preceded
  by a significant helicity accumulation, (1.8-16) × 10<SUP>42</SUP>
  Mx<SUP>2</SUP> over a long period (0.5 to a few days). Another finding
  is that the helicity accumulates at a nearly constant rate, (4.5-48)
  × 10<SUP>40</SUP> Mx<SUP>2</SUP> hr<SUP>-1</SUP>, and then becomes
  nearly constant before the flares. This led us to distinguish the
  helicity variation into two phases: a phase of monotonically increasing
  helicity and the following phase of relatively constant helicity. As
  expected, the amount of helicity accumulated shows a modest correlation
  with time-integrated soft X-ray flux during flares. However, the
  average helicity change rate in the first phase shows even stronger
  correlation with the time-integrated soft X-ray flux. We discuss the
  physical implications of this result and the possibility that this
  characteristic helicity variation pattern can be used as an early
  warning sign for solar eruptions.

Title: Determination of Magnetic Diffusivity from High-Resolution
    Solar Magnetograms
Authors: Chae, Jongchul; Litvinenko, Yuri E.; Sakurai, Takashi
Bibcode: 2008ApJ...683.1153C
Altcode:
  The magnetic diffusivity in the solar photosphere is determined by
  applying a new method to the magnetic induction equation. The magnetic
  field evolution is specified by a time sequence of high-resolution
  magnetograms of plage regions, taken by Hinode/SOT and SOHO/MDI. The
  mean value of magnetic diffusivity determined from SOT magnetograms with
  the smallest pixel size of 116 km is about 0.87 +/- 0.08 km<SUP>2</SUP>
  s<SUP>-1</SUP>. This is the smallest value that has been empirically
  determined so far. High-resolution and full-disk MDI magnetograms with
  the pixel sizes of 440 and 1400 km yielded larger values of 4.4 +/-
  0.4 and 18 +/- 7.4 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The
  measured diffusivity values at different length scales are consistent
  with a turbulent cascade that ends at a resistive dissipation scale of
  about 30 km. The results suggest that turbulent magnetic diffusivity
  should be taken into account in the analysis of the observed rate of
  magnetic flux cancellation in the photosphere.

Title: Capability of the Fast Imaging Solar Spectrograph on NST/BBSO
    for Observing Filaments/Prominences at the Spectral Lines Hα,
    Ca II 8542, and Ca II K
Authors: Ahn, Kwang-Su; Chae, Jong-Chul; Park, Hyung-Min; Nah,
   Jak-Young; Park, Young-Deuk; Jang, Bi-Ho; Moon, Yong-Jae
Bibcode: 2008JKAS...41...39A
Altcode:
  No abstract at ADS

Title: Magnetic Twist of EUV Coronal Loops Well-traced in TRACE
Images: Evidence for Magnetic Reconnection Origin of Coronal Loops?
Authors: Kwon, Ryun Young; Chae, Jongchul
Bibcode: 2008ApJ...677L.141K
Altcode:
  The measurements of magnetic twist of EUV coronal loops for 14 loops are
  presented here. EUV coronal loops are thin, EUV-emitting structures of
  hot plasma tracing magnetic field lines in the corona. The constriction
  of plasma into a loop without dispersion may be explained if the
  magnetic field of the loop is twisted. On the basis of this idea,
  Chae and Moon developed a method of determining magnetic twist of
  coronal loops by analyzing coronal images and photospheric magnetograms
  together. By applying this method to as many coronal loops observed
  by TRACE 171 Å as possible, we attempt to determine a statistically
  meaningful value of magnetic twist of coronal loops for the first
  time. We have selected a number of conspicuous loops which are bright
  enough and well separated from other adjacent loops on TRACE EUV
  images. We have constructed and examined coronal magnetic fields of
  selected active regions containing the loops with consideration of the
  projection effect, and we can identify 14 coronal loops whose magnetic
  field lines are well represented by a linear force-free field. We
  have found that these loops have absolute twist values from 0.22π to
  1.73π, which suggests that the absolute winding number of EUV coronal
  loop may be mostly less than one turn. Our results support the idea
  that EUV coronal loops may be a product of magnetic reconnection of
  magnetic flux tubes.

Title: Spatial Distribution of Magnetic Reconnection in the 2006
    December 13 Solar Flare as Observed by Hinode
Authors: Jing, Ju; Chae, Jongchul; Wang, Haimin
Bibcode: 2008ApJ...672L..73J
Altcode:
  A massive two-ribbon flare and its source magnetic field region were
  well captured by the Solar Optical Telescope (SOT) on board Hinode
  in the Ca II H spectral line and by the Spectro-Polarimeter of SOT,
  respectively. Using the high-resolution Hinode data sets, we compare
  the spatial distribution of the local magnetic reconnection rate and
  the energy release rate along the ribbons with that of G-band kernels
  that serve as a proxy for the primary energy release. The G-band kernels
  spatially coincide with the maximum of both modeled quantities, which
  gives strong support for the reconnection model. We also investigate
  the magnitude scaling correlation between the ribbon separation speed
  V<SUB>r</SUB> and magnetic field strength B<SUB>n</SUB> at four 2
  minute time bins around the maximum phase of the flare. It is found that
  V<SUB>r</SUB> is weakly and negatively correlated with B<SUB>n</SUB>. An
  empirical relation of V<SUB>r</SUB> propto B<SUB>n</SUB><SUP>-0.15</SUP>
  is obtained at the flare peak time with an correlation coefficient
  ~-0.33. The correlation is weaker at other time bins.

Title: Determination of Magnetic Diffusivity from High Resolution
    Solar Magnetograms
Authors: Chae, Jongchul; Litvinenko, Yuri E.; Sakurai, Takashi
Bibcode: 2008cosp...37..482C
Altcode: 2008cosp.meet..482C
  The magnetic diffusivity in the solar photosphere is determined by
  applying a model of magnetic induction to high resolution magnetograms
  of plage regions, taken by HINODE/SOT and SOHO/MDI. The mean value
  of magnetic diffusivity determined from SOT magnetograms with the
  smallest pixel size of 116 km is about 0.84±0.34 km2 s-1 . This is
  the smallest value that has been empirically determined so far. High
  resolution and full-disk MDI magnetograms with the pixel sizes of 440
  and 1400 km yielded larger values of 4.5±1.4 km2 s-1 and 13±10 km2
  s-1 , respectively. The measured diffusivity values at different length
  scales are consistent with a turbulent cascade that ends at a resistive
  dissipation scale of about 25 km. The results suggest that turbulent
  magnetic diffusivity should be taken into account in the analysis of
  the observed rate of magnetic flux cancellation in the photosphere.

Title: Magnetic Twist of EUV Coronal Loops Observed by TRACE:
    Evidence for Magnetic Reconnection Origin of Coronal Loops?
Authors: Chae, Jongchul
Bibcode: 2008cosp...37..483C
Altcode: 2008cosp.meet..483C
  The measurements of magnetic twist of EUV coronal loops for 14
  loops are presented here. EUV coronal loops are thin and emitting
  structures of hot plasma tracing magnetic field line in the corona. The
  constriction of plasma into a loop without dispersion may be explained
  if the magnetic field of the loop is twisted. On the basis of this
  idea, Chae and Moon (2005) developed a method of determining magnetic
  twist of coronal loops by analyzing coronal images and photospheric
  magnetograms together. By applying this method to as many coronal
  loops observed by TRACE 171˚ as possible, we attempt to determine a
  statistically meaningful A value of magnetic twist of coronal loops for
  the first time. We have selected a number of conspicuous loops which
  are bright enough and well separated from other adjacent loops on TRACE
  EUV images. We have constructed and examined coronal magnetic fields
  of selected active regions containing the loops with consideration of
  the projection effect, and we could identify 14 coronal loops whose
  magnetic field line is well represented by a linear force free field. We
  have found that these loops have absolute twist values from 0.22 π to
  1.73 π, which suggest that the absolute winding number of EUV coronal
  loop may be mostly less than one turn. Our results support the idea
  that EUV coronal loops may be a product of magnetic reconnection of
  magnetic flux tubes.

Title: Relationship between CME initial speed and magnetic helicity
    of magnetic clouds
Authors: Sung, S.; Marubashi, K.; Kim, K.; Cho, K.; Moon, Y.; Chae, J.
Bibcode: 2007AGUFMSH31A0228S
Altcode:
  In order to understand the relationship between solar and interplanetary
  phenomena, we have examined the initial properties of coronal mass
  ejections (CMEs) and magnetic helicity of magnetic clouds (MCs) for 24
  CME- MC pairs. MCs are fitted with the linear force-free cylindrical
  model to obtain MC parameters (orientation, size, magnetic field
  magnitude, impact parameter, chirality, etc). The relative helicity
  per unit length of MC is calculated by \frac{HMC}{L}=\frac{4π
  B02}{α}\int0RJ12(α r)rdr. Comparing the square of CME initial speeds
  (VCME2) with the magnetic helicities (HMC, we find that there is a
  positive correlation between VCME2 and HMC, and the linear correlation
  coefficient (CC) between the two parameters is 0.52. We obtain a better
  correlation (CC=0.61) for 17 events whose impact parameter (the shortest
  distance of the satellite to the MC axis normalized by MC radius)
  is less than 0.5. Considering that the magnetic force in a flux rope
  is intimately related to magnetic helicity, our result supports that
  the magnetic force is responsible for the CME eruption. From this
  result we suggest that the high speed CME is associated with large
  magnetic helicity.

Title: Magnetic Helicity Injection in Active Regions
Authors: Jeong, Hyewon; Chae, Jongchul
Bibcode: 2007ApJ...671.1022J
Altcode:
  Magnetic helicity is now regarded as an important physical quantity in
  understanding solar magnetic activities. We have studied the injection
  of magnetic helicity through the photosphere of four active regions
  during the long periods of their lifetimes. The rate of helicity
  injection was determined as a function of time in each active region
  by applying the local correlation tracking (LCT) method to full-disk,
  96 minute cadence magnetograms taken by SOHO MDI. As a result, we have
  found that most helicity was intensively injected while active regions
  emerged and grew, suggesting that magnetic flux emergence may be the
  major process of helicity injection. In all the active regions studied,
  the rate of helicity injection during flux emergence was initially
  low, increased and stayed high for a while, and then became low again,
  while magnetic flux steadily increased at a more or less constant rate
  all the time. Flux cancellation, as a minor process, resulted in some
  loss of coronal magnetic helicity, or inverse helicity injection. The
  contribution of differential rotation to helicity injection was found
  to be insignificant in these active regions. It was also found that
  the magnetic helicity budget of an active region strongly depends on
  its average magnetic flux.

Title: Small-scale X-ray/EUV Jets seen in Hinode XRT and TRACE
Authors: Kim, Y.; Moon, Y.; Cho, K.; Bong, S.; Park, Y.; Sakurai,
   T.; Chae, J.
Bibcode: 2007AGUFMSH53A1061K
Altcode:
  In this study, we present the morphological and kinematic
  characteristics of three small-scale X-ray/EUV jets that are
  simultaneously observed by the X-ray telescope (XRT) onboard Hinode
  (Solar-B) and the TRACE. For this study, we examined all XRT movies
  with a thin Al/Poly filter from 2006 October 20 to April 8 to look
  for small-scale X-ray eruptions and then found 34 eruptions. Next we
  took a look at the corresponding TRACE 171/195 {Å} images associated
  with these X-ray eruptions. As a result, we found three simultaneous
  X-ray and EUV jets and their major characteristics can be summarized
  as follows : (1) They all have no association with major flares. (2)
  From the comparison between XRT and TRACE observations, we found that
  they have similar characteristics in terms of projected speed, lifetime,
  and size. (3) Their sizes range from 4 × 105 to 5 × 105 km. (4) Their
  projected speeds are estimated to be 180-310 km s-1 with an average
  speed of about 250 km s- 1 (5) Their lifetimes lie in the range of 100
  to 600 s. (6) From the comparison between the XRT images with the SOHO
  MDI maps for two events, all they are associated with the parasitic
  polarity region. These characteristics are similar to the previous
  observations for X-ray jets by the Yohkoh SXT but quite different
  from EUV jets associated with Hα surges. In addition, from the EIS
  four spectral lines for the last event, we found blueshift (up to -64
  km s-1) and redshift (up to 20 km s-1) motions as well as nonthermal
  velocities ranging from 57 to 106 km s-1 at the jet footpoint. We
  note a tendency : the hotter the maximum ionization temperature is,
  the larger the area of blueshift region is. These characteristics
  are consistent with a typical jet model that includes the magnetic
  reconnection between open coronal fields and emerging magnetic fields.

Title: Analysis of Korean Historical Comet Records
Authors: Park, So-Yeon; Chae, Jong-Chul
Bibcode: 2007PKAS...22..151P
Altcode:
  No abstract at ADS

Title: Initial Results on Line-of-Sight Field Calibrations of SP/NFI
    Data Taken by SOT/Hinode
Authors: Chae, Jongchul; Moon, Yong-Jae; Park, Young-Deuk; Ichimoto,
   Kiyoshi; Sakurai, Takashi; Suematsu, Yoshinori; Tsuneta, Saku;
   Katsukawa, Yukio; Shimizu, Toshifumi; Shine, Richard A.; Tarbell,
   Theodore D.; Title, Alan M.; Lites, Bruce; Kubo, Masahito; Nagata,
   Shin'ichi; Yokoyama, Takaaki
Bibcode: 2007PASJ...59S.619C
Altcode:
  We present initial results on the line-of-sight field calibration
  of the two kinds of Stokes I and V data taken by the Solar Optical
  Telescope on the satellite Hinode: spectral profiles of Stokes I and V
  parameters recorded on the Spectro-polarimeter (SP), and monochromatic
  images of the same parameters recorded on the Narrow-band Filter Imager
  (NFI). By applying the center-of-gravity method to the SP data of
  AR10930 taken on 2006 December 11, we determined the line-of-sight field
  at every location in the active region. As a result, we found that the
  line-of-sight field strength ranges up to 2kG in plages, even without
  taking into account the filling factor, and up to 3.5kG or higher values
  inside the umbra of the major sunspot. We calibrated the NFI data in
  reference to the field determined from the SP data. In regions outside
  the sunspots and the penumbral regions, we adopted a linear relation,
  B<SUB>||</SUB> = βV / I, between the circular polarization, V / I,
  and the line-of-sight field strength, B<SUB>||</SUB>, and obtained β =
  23.5kG in regions outside the sunspots, and β = 12.0kG in penumbral
  regions. In umbral regions of sunspots, a first-order polynomial was
  adopted to model the reversal of the polarization signal over the
  field strength.

Title: Two-Step Reconnections in a C3.3 Flare and Its Preflare
    Activity Observed by Hinode XRT
Authors: Kim, Sujin; Moon, Young-Jae; Kim, Khan-Hyuk; Kim, Yeon-Han;
   Sakurai, Takashi; Chae, Jongchul; Kim, Kap-Sung
Bibcode: 2007PASJ...59S.831K
Altcode:
  We investigated the evolution of a C3.3 impulsive flare and its
  preflare activity, which occurred in NOAA Active Region 10923 on 2006
  November 12, using Hinode X-Ray Telescope (XRT) data. For an extensive
  investigation, we also used GOES X-ray flux, TRACE 171Å, and SOHO MDI
  data. Examining the time-series of the XRT and TRACE images, we can
  identify the following evolutionary sequences: (1) There were three
  bundles of loops along the sheared polarity inversion line forming a
  sigmoidal structure during the preflare phase. (2) Preflare brightening
  occurred between two upper-loop bundles, and they consequently formed
  one larger bundle. (3) The main flare occurred near the location
  where this new loop bundle and the third bundle met together. (4) As a
  result, a single stacked loop structure was formed. This morphological
  evolution of the X-ray loops is quite consistent with a tether-cutting
  model involving a single-bipole explosion. Our result shows that the
  preflare and the main flare in this event are a two-step reconnection
  process, which strongly suggests that the preflare activity plays an
  important role in triggering the main flare.

Title: Hinode SP Vector Magnetogram of AR10930 and Its
    Cross-Comparison with MDI
Authors: Moon, Yong-Jae; Kim, Yeon-Han; Park, Young-Deuk; Ichimoto,
   Kiyoshi; Sakurai, Takashi; Chae, Jongchul; Cho, Kyung Suk; Bong,
   Suchan; Suematsu, Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimojo,
   Masumi; Shimizu, Toshifumi; Shine, Richard A.; Tarbell, Theodore D.;
   Title, Alan M.; Lites, Bruce; Kubo, Masahito; Nagata, Shin'ichi;
   Yokoyama, Takaaki
Bibcode: 2007PASJ...59S.625M
Altcode:
  We present one Hinode Spectropolarimeter (SP) magnetogram of AR 10930
  that produced several major flares. The inversion from Stokes profiles
  to magnetic field vectors was made using the standard Milne-Eddington
  code. We successfully applied the Uniform Shear Method for resolving
  the 180° ambiguity to the magnetogram. The inversion gave very strong
  magnetic field strengths (near 4500 gauss) for a small portion of area
  in the umbra. Considering that the observed V-profile of 6301.5Å was
  well-fitted as well as a direct estimation of the Zeeman splitting
  results in 4300-4600 gauss, we think that the field strengths
  should not be far from the actual value. A cross-comparison of the
  Hinode SP and SOHO MDI high resolution flux densities shows that the
  MDI flux density could be significantly underestimated by about a
  factor of two. In addition, it has a serious negative correlation
  (the so-called Zeeman saturation effect) with the Hinode SP flux
  density for umbral regions. Finally, we could successfully obtain
  a recalibrated MDI magnetogram that has been corrected for the
  Zeeman saturation effect using not only a pair of MDI intensity and
  magnetogram data simultaneously observed, but also the relationship
  from the cross-comparison between the Hinode SP and MDI flux densities.

Title: Small-Scale X-Ray/EUV Jets Seen in Hinode XRT and TRACE
Authors: Kim, Yeon-Han; Moon, Young-Jae; Park, Young-Deuk; Sakurai,
   Takashi; Chae, Jongchul; Cho, Kyung Suk; Bong, Su-Chan
Bibcode: 2007PASJ...59S.763K
Altcode:
  We present the morphological and kinematic characteristics of three
  small-scale X-ray/EUV jets simultaneously observed by the Hinode
  XRT and the TRACE. For this, we examined all XRT movies with a thin
  Al/Poly filter from 2006 October 20 to 2007 April 8, and then found
  34 small-scale eruptions. We next took a look at the corresponding
  TRACE 171/195Å images associated with the eruptions. As a result,
  we found three simultaneous X-ray and EUV jets. For two different
  bands, they have similar characteristics in terms of the projected
  speed (90-310kms<SUP>-1</SUP>), lifetime (100-2000s), and size
  (1.1-5×10<SUP>5</SUP>km). These characteristics are similar to the
  previous results by the Yohkoh SXT, but are quite different from EUV
  jets associated with Hα surges. From the EUV Imaging Spectrometer,
  four spectral lines for the last event, we found blueshift (up to
  -64kms<SUP>-1</SUP>) and redshift (up to 20kms<SUP>-1</SUP>) motions as
  well as nonthermal velocities ranging from 57 to 106kms<SUP>-1</SUP>
  at the jet footpoint. We note a tendency: the hotter the maximum
  ionization temperature is, the smaller the area of blueshift region
  is. These characteristics are consistent with a typical jet model
  that includes the magnetic reconnection between open coronal fields
  and emerging magnetic fields.

Title: Chromospheric Magnetic Reconnection
Authors: Chae, J.
Bibcode: 2007ASPC..369..243C
Altcode:
  There has been increasing observational evidence that magnetic
  reconnection often occurs in the low atmosphere of the sun. I
  will present a brief review of our recent observational results on
  canceling magnetic features in the photosphere and jet-like events
  in the chromosphere and discuss the expected physical properties of
  magnetic reconnection occurring in the photosphere and chromosphere
  based on an adiabatic current sheet model of Sweet-Parker type. A
  special attention is paid to the temperature-speed relation in jet-like
  events in the chromosphere, and the need of anomalous resistivity in
  the model of chromospheric magnetic reconnection.

Title: Evolutionary Characteristics of Magnetic Helicity Injection
    in Active Regions
Authors: Jeong, H.; Chae, J.
Bibcode: 2007ASPC..369..167J
Altcode:
  Magnetic helicity is now regarded as an important physical quantity
  in understanding the magnetic activities of solar active regions
  such as flares and coronal mass ejections. A common wisdom is that
  magnetic helicity is transported from the interior to the corona,
  and then to the interplanetary space. In the present study, we are
  interested in examining the temporal behavior of helicity injection
  through the photospheric boundary that divides the interior and
  the corona. Specifically we aim to see whether magnetic helicity
  is supplied to the corona in a more or less steady way or not. We
  determined the rate of helicity injection in each active region applying
  Chae's method to the full-disk, 96 minute-cadence magnetograms taken by
  SOHO/MDI. Using these data, each active region could be followed without
  interruption for about 5 days while it was away from the limb. Some
  active regions were followed at next rotations, too. We found that
  magnetic helicity was supplied intensively during the period of flux
  emergence, especially during the growth of active regions. The amount
  of helicity injected during the growth period ranged from 1.7×10^{42}
  Mx^{2} to 43×10^{42} Mx^{2}, depending on the active region flux. These
  values are much larger than the estimated contributions of differential
  rotation at the photospheric level. Our result suggests that most of
  the magnetic helicity in active regions may be supplied for several
  days during the early phase of active region evolution.

Title: Magnetic Twist of EUV Coronal Loops Observed by TRACE
Authors: Kwon, R. -Y.; Chae, J.
Bibcode: 2007ASPC..369..299K
Altcode:
  The constriction of plasma into a loop without dispersion may be
  explained if the magnetic field of the loop is twisted. Based on this
  idea, Chae and Moon (2005) developed a method of determining magnetic
  twist of coronal loops by analyzing coronal images and photospheric
  magnetograms together. We attempt to determine the number distribution
  of magnetic twist of coronal loops, by expanding their method to more
  number of EUV loops observed by TRACE 171 Å. Preliminary results we
  have obtained from three loops indicate that these loops have twist
  values from 1.5π to 2.5π, which suggests that the winding number of
  EUV coronal loop may be around one.

Title: Low Atmosphere Reconnections Associated with a Filament
    Eruption
Authors: Moon, Y. -J.; Chae, J.; Park, Y. D.
Bibcode: 2007ASPC..369..425M
Altcode:
  We present preflare activity associated with an eruptive flare. For
  this work we have analyzed high temporal (about 1 minute) and spatial
  (about 1 arcsec) resolution images taken by SOHO/MDI, BBSO H-alpha
  centerline and blue wing, and TRACE 1600 UV images. We found that
  there were several transient brightenings seen around the preflare
  phase. They took place near one footpoint of the filament and were
  associated with cancelling magnetic features (CMFs) as well as
  recurrent EUV ejections. The flux variations suggest that the flux
  cancellation may have been driven by the flux emergence and/or shearing
  motions. The above results imply that the preflare activity is caused
  by low-atmospheric reconnections. For this event, we estimated the
  ejection speeds of the associated filament ranging from 10 to 160 km/s
  for the first twenty minutes. It is noted that the initiation of the
  filament eruption (as defined by the rise speed of about 10 km/s) was
  coincident with the preflare activity characterized by UV brightenings
  and CMFs. Our results support that the initiation of the filament
  eruption be physically related to low-atmosphere magnetic reconnection.

Title: Determination of Magnetic Helicity of a Solar Active Region
    Using the Linear Force-Free Field Model
Authors: Lim, E. -K.; Jeong, H.; Chae, J.
Bibcode: 2007ASPC..369..175L
Altcode:
  We aim to measure the helicity of the coronal magnetic field
  of an active region based on the linear force-free field(LFFF)
  assumption. With a value of the force-free α, the coronal field is
  constructed from the extrapolation of SOHO/MDI magnetograms, and the
  constructed field lines are compared with the coronal loops in the EUV
  images taken by SOHO/EIT. The force-free field that best fits the loops
  is used to calculate the helicity of the active region. By applying this
  method to the solar active region AR 10696 during its first rotation,
  we have examined the temporal variation of the magnetic helicity,
  and have compared it with the accumulated amount of the helicity
  transferred to the corona through the photosphere which was determined
  independently. Our results are summarized as follows. 1) The magnetic
  field of the active region is not fully LFF. The force-free α varies
  from loop to loop, with a deviation of 30 to 45%, which gives us a
  very conservative estimate of the uncertainty in the coronal helicity
  determined using the LFF model. 2) The measured value of the coronal
  magnetic helicity was close to the accumulated amount of injected
  helicity with a discrepancy of 10∼30%. 3) The coronal magnetic
  helicity decreased after CMEs occurred, with the amount of decrease
  being close to what may have been carried away by the CMEs. Our results
  support that the LFF field extrapolation method can be used to infer
  the magnetic helicity of an active region within an uncertainty of a
  few tens of percent.

Title: Hα Spectral Properties of Velocity Threads Constituting a
    Quiescent Solar Filament
Authors: Chae, Jong-Chul; Park, Hyung-Min; Park, Young-Deuk
Bibcode: 2007JKAS...40...67C
Altcode:
  No abstract at ADS

Title: Flux Pile-up Magnetic Reconnection in the Solar Photosphere
Authors: Litvinenko, Yuri E.; Chae, Jongchul; Park, So-Young
Bibcode: 2007ApJ...662.1302L
Altcode:
  Magnetic reconnection in the temperature minimum region of the
  solar photosphere, observationally manifested as canceling magnetic
  features, is considered. Flux pile-up reconnection in the Sweet-Parker
  current sheet is analyzed. It is shown that the standard Sweet-Parker
  reconnection rate in the photosphere is too slow to explain the observed
  cancellation. Flux pile-up reconnection scalings, however, are shown
  to be in agreement with the speeds of canceling magnetic fragments,
  magnetic fields in the fragments, and the rates of magnetic flux
  cancellation, derived from SOHO MDI data. Pile-up factors in the range
  between 1 and 5 and local reconnecting magnetic fields of a few hundred
  G are calculated for the analyzed canceling features. The analysis
  shows that flux pile-up is a likely mechanism for adjusting the local
  parameters of reconnecting current sheets in the photosphere and for
  sustaining the reconnection rates that are determined by large-scale
  supergranular flows. The upward mass flux in the reconnection jet,
  associated with a large canceling feature, is predicted to exceed
  10<SUP>15</SUP> g hr<SUP>-1</SUP>. Hence, cancellation in a few
  photospheric patches over several hours can lead to the formation of
  a solar filament in the corona.

Title: A Check for Consistency between Different Magnetic Helicity
    Measurements Based on the Helicity Conservation Principle
Authors: Lim, Eun-Kyung; Jeong, Hyewon; Chae, Jongchul; Moon, Yong-Jae
Bibcode: 2007ApJ...656.1167L
Altcode:
  Magnetic helicity is a useful quantity in characterizing the magnetic
  systems of solar active regions. The purpose of the present work is
  to check for consistency between the local correlation tracking (LCT)
  method used to measure helicity injection through the photosphere, and
  the linear force-free field (LFFF) method used to determine helicity
  in the corona, based on the principle of helicity conservation in
  the solar corona. We have calculated the amount of magnetic helicity
  injected through the photosphere during the first disk passage of AR
  10696 using the LCT method initially described by Chae. We have also
  measured the coronal magnetic helicity as a function of time using the
  LFFF method. With a value for the force-free α, the coronal field
  is constructed from the extrapolation of the Solar and Heliospheric
  Observatory (SOHO) MDI magnetograms, then compared with the coronal
  loops in the EUV images taken by the SOHO EIT. The force-free α that
  best fits the loops is used to calculate the coronal helicity. From a
  careful comparison of different helicity measurements during each time
  interval, we have reached the core conclusion that our measurements
  follow the helicity conservation principle with an uncertainty of ~15%
  and hence support the consistency between the two different methods
  with the same amount of uncertainty.

Title: Measurements of magnetic helicity injected through the solar
    photosphere
Authors: Chae, Jongchul
Bibcode: 2007AdSpR..39.1700C
Altcode:
  The amount of magnetic helicity injected into the corona through
  the photosphere can be measured by inferring the apparent motion
  of photospheric footpoints of fieldlines from a time series of
  line-of-sight magnetograms, as originally proposed by [Chae, J.,
  2001. Observational determination of the rate of magnetic helicity
  transport through the solar surface via the horizontal motion of
  field line footpoints. Astrophysical Journal 560, L95-L98]. In this
  paper, we present a revised version of Chae's original method by
  adopting a better proxy for the flux density of magnetic helicity
  that was proposed by [Pariat, E., Démoulin, P., Berger, M.A.,
  2005. Photospheric flux density of magnetic helicity. Astronomy
  and Astrophysics 439, 1191-1203]. Moreover it is allowed to choose
  either the old technique of local correlation tracking (LCT) or the
  new method called the different affine velocity estimator (DAVE)
  method that was developed by [Schuck, P. W., 2006. Tracking magnetic
  footpoints with the magnetic induction equation. Astrophysical Journal
  646, 1358-1391.] for inferring transverse velocity. We have applied
  the revised method using the DAVE method to a set of 96-min cadence,
  full-disk MDI magnetograms for AR 10696 and compared the results with
  those obtained using the LCT method. As a result, we have found that
  the helicity measurements using the DAVE method yield systematically
  higher values of helicity injection than those using the LCT method,
  but the discrepancy is moderately small, being less than 10%.

Title: Magnetic helicity comparison between coronal magnetic field
    of an active region and interplanetary magnetic cloud
Authors: Sung, S.; Chae, J.; Lim, E.; Kim, K.
Bibcode: 2006AGUFMSH33B0410S
Altcode:
  We investigate several interplanetary magnetic cloud events associated
  with halo coronal mass ejections to compare the content of helicity
  in magnetic clouds with the coronal magnetic helicity variation after
  coronal mass ejections occurred. We use a cylindrically symmetric
  constant-alpha force-free model to derive magnetic helicity of magnetic
  cloud events by determining the parameters as magnetic cloud orientation
  and radius, magnetic magnitude, and helicity sign. For the helicity
  of the coronal magnetic field of an active region, we also assume
  the linear force-free field. The result of this study provide the
  information whether the magnetic helicity is conserved or not between
  sun and near Earth (1 AU).

Title: Progress on the 1.6-meter New Solar Telescope at Big Bear
    Solar Observatory
Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.;
   Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter,
   R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.;
   Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A.
Bibcode: 2006SPIE.6267E..0AD
Altcode: 2006SPIE.6267E..10D
  The New Solar Telescope (NST) project at Big Bear Solar Observatory
  (BBSO) now has all major contracts for design and fabrication in place
  and construction of components is well underway. NST is a collaboration
  between BBSO, the Korean Astronomical Observatory (KAO) and Institute
  for Astronomy (IfA) at the University of Hawaii. The project will
  install a 1.6-meter, off-axis telescope at BBSO, replacing a number
  of older solar telescopes. The NST will be located in a recently
  refurbished dome on the BBSO causeway, which projects 300 meters into
  the Big Bear Lake. Recent site surveys have confirmed that BBSO is
  one of the premier solar observing sites in the world. NST will be
  uniquely equipped to take advantage of the long periods of excellent
  seeing common at the lake site. An up-to-date progress report will
  be presented including an overview of the project and details on the
  current state of the design. The report provides a detailed description
  of the optical design, the thermal control of the new dome, the optical
  support structure, the telescope control systems, active and adaptive
  optics systems, and the post-focus instrumentation for high-resolution
  spectro-polarimetry.

Title: Two Phases of Helicity Variation Around Major Flares
Authors: Park, Sung-Hong; Chae, J.; Jeong, H.; Choe, G.; Lee, J.;
   Yang, G.; Jing, J.; Wang, H.
Bibcode: 2006SPD....37.2201P
Altcode: 2006BAAS...38..249P
  We have investigated the magnetic helicity injection rates in three
  active regions (NOAA 10484, 10486 and 10696) around the times of four
  X-class flares using the MDI/SOHO magnetograms. In all cases, the
  total magnetic flux of the individual active region changed little
  with time, and the helicity variation is directly related to the
  variation of field line winding. This also justifies our measurement of
  magnetic helicity injection rates using a local correlation tracking
  method. Our analysis reveals that there were two distinct phases of
  helicity variation around those flares. In the first phase that starts
  a few days before the flare onset, the helicity accumulates at a nearly
  constant rate. The second phase usually starts 3-12 hours before the
  flare onset and lasts until 3-20 hours after the flare. During this
  phase, the helicity injection rate is negligible and the magnitude
  of helicity remains almost constant or increases only slightly. This
  characteristic pattern in the helicity evolution may imply a physical
  link between magnetic winding and flare occurrence, and could be used
  as an early warning sign of impending flares.

Title: Imaging Spectroscopy of a Solar Filament Using a Tunable
    Hα Filter
Authors: Chae, Jongchul; Park, Young-Deuk; Park, Hyung-Min
Bibcode: 2006SoPh..234..115C
Altcode:
  Observations using a narrow band Hα filter still remain one of the
  best ways to investigate the fine structures and internal dynamics of
  solar filaments. Hα observations, however, have been usually carried
  out with the peak response of the filter fixed at a single wavelength,
  usually at the centerline, in which the investigation is limited to the
  Hα morphology and its time evolution. In this paper, we demonstrate
  that the Hα spectroscopy that takes Hα images successively at several
  wavelengths is a useful tool in the study of solar filaments on the
  solar disk. Our observation of a filament was carried out on August 3,
  2004 at Big Bear Solar Observatory using the 10-inch refractor. The
  Lyot Hα filter was successively tuned to five wavelengths: −0.6,
  −0.3, 0.0, +0.3, and +0.6 Å from the Hα line center. Each set
  of wavelength scan took 15 s. After several steps of data reduction,
  we have constructed a five-wavelength spectral profile of intensity
  contrast at every spatial point. The contrast profile at each spatial
  point inside the filament was reasonably well fit by the cloud model
  as far as the contrast is high enough, and allowed us to construct the
  maps of τ<SUB>0</SUB>, v, Δ λ<SUB>D</SUB> and S in the filament. We
  also found that the line center method that is often used, always
  yields line-of-sight velocities that are systematically lower than the
  cloud model fit. Our result suggests that taking Hα images at several
  wavelengths using a tunable filter provides an effective way of deriving
  physically meaningful parameters of solar filaments. Particularly
  constructing the time sequence of v maps appears to be a useful tool
  for the study of internal dynamics, like counterstreaming, in filaments.

Title: Measurements of Magnetic Helicity Injected through the
    Photosphere and Magnetic Helicity Content in the Corona
Authors: Chae, J.; Jeong, H.; Lim, E.
Bibcode: 2006cosp...36..880C
Altcode: 2006cosp.meet..880C
  Magnetic helicity is a useful quantity in characterizing the magnetic
  connection of the solar interior surface corona and the interplanetary
  space It is a common wisdom that magnetic helicity is transferred from
  the interior to the corona and then is expelled out of the Sun in
  the form of coronal mass ejections From observations it is possible
  to independently measure the accumulated amount of magnetic helicity
  transferred through the photopshere the content of magnetic helicity in
  the corona and the amount magnetic helicity carried away by coronal mass
  ejections Chae 2001 fisrt proposed that the magnetic helicity injected
  into the corona through the photopshere is determined from the local
  correlation tracking of of magnetic fieldline footpoints The magnetic
  helicity content of the corona is inferred from the three dimensional
  structure of coronal magnetic field which is usually constructed
  using the extrapolation of magnetic field The simplest extrapolation
  model that can be used to determine magnetic helicity is a linear
  force-free field We have applied the two indepdent approaches to the
  active region 10696 to indepently determine the accumulated magnetic
  helicity injected through the photosphere and the coronal magnetic
  helicity content as functions of time Our results are as follows 1
  most magnetic helicity was supplied intensively during the period
  of flux emergence especially during the growth of active regions The
  helicity injected in the early five days was about 2 times 10 43 Mx
  2 2 The linear force-free assumption is not

Title: Spatio-Spectral Maximum Entropy Method: II. Solar Microwave
    Imaging Spectroscopy
Authors: Bong, Su-Chan; Lee, Jeong-Woo; Gary, Dale E.; Yun, Hong-Sik;
   Chae, Jong-Chul
Bibcode: 2005JKAS...38..445B
Altcode:
  No abstract at ADS

Title: Magnetic Twist of an Extreme-Ultraviolet Coronal Loop Inferred
    from Plasma Constriction
Authors: Chae, Jongchul; Moon, Yong-Jae
Bibcode: 2005ApJ...629.1110C
Altcode:
  Magnetic twist is a very likely way of constricting coronal plasma
  into loops. An attempt is made to determine the magnetic twist
  that can explain the constriction of coronal loops indirectly
  from observations. We decompose the coronal magnetic field into a
  large-scale magnetic field and a small-scale magnetic field. The
  large-scale field is assumed to be force-free, but the small-scale
  field is not. We derive a magnetohydrostatic equation describing the
  relationship between the small-scale field variation and the pressure
  variation across the loop. We adopt a simple flux rope model with the
  following properties. (1) There exists a close physical relationship
  between the twist-creating process and the plasma-injecting process that
  keeps the axial field constant as the loop forms. (2) The large-scale
  force-free field is so close to the current-free configuration that
  its associated current is negligible in the plasma constriction. (3)
  Pressure peaks on the loop axis and monotonically decreases with the
  distance from the axis. This flux tube model is characterized by three
  independent parameters: axial field strength, peak pressure excess, and
  loop width. The peak pressure excess and the loop width are determined
  from an analysis of the EUV data taken by TRACE, and an estimate of the
  axial field strength is found from the linear force-free extrapolation
  of the photospheric magnetic field observed by SOHO MDI. By applying
  this method to a specific coronal loop, we have found that the magnetic
  twist on the loop axis is about 1.5π, and the twist per unit length
  is more concentrated near its top than near its footpoints. This twist
  value has been obtained using the simplifying assumption of uniform
  axial field strength. In the case where the axial field is stronger
  inside the loop than in the surroundings, the twist will turn out to
  be greater than 1.5π, since the twist is required to constrict not
  only the plasma but also the magnetic flux. On the other hand, if the
  axial field is weaker than that in the surroundings, a smaller twist
  may be enough to constrict the plasma.

Title: New extrapolation method for coronal mass ejection onset
    time estimation
Authors: Moon, Y. -J.; Cho, K. -S.; Chae, Jongchul; Choe, G. S.; Kim,
   Y. -H.; Bong, Su-Chan; Park, Y. -D.
Bibcode: 2005JGRA..110.7103M
Altcode: 2005JGRA..11007103M
  The onset time of a coronal mass ejection (CME) is usually extrapolated
  from its speed in a coronagraph using the constant speed method. In
  this study, we present a new empirical method for extrapolating
  the onset times of flare-associated CMEs. For this we reexamined
  seven well-observed CME-flare events whose initial eruption speeds
  are estimated to be about a few tens of kilometers per second from
  LASCO C1 coronagraph or loop displacements seen in SOHO/EIT and TRACE
  images. In this study, the CME onset time is assumed to be the earliest
  observable time of eruption from these images. We estimated the onset
  time differences between the CMEs and the associated flares observed
  in soft X rays. We then compared them with the onset time differences
  estimated by the constant speed extrapolation method from LASCO C2
  positions. It is noted that there is a certain quadratic relation
  between the CME speed first observed in the LASCO C2 field of view
  and the observed CME travel time from near the solar surface to the
  C2 field of view in units of the travel time estimated by the constant
  speed method. This empirical relation thus enables us to determine the
  onset times of CMEs without any assumption in CME kinematics. We have
  applied the new empirical method to 91 flare-associated CMEs that were
  accompanied by type II bursts. The onset time difference for these
  events as well as the well-observed events shows that in most cases
  (about 80%) the CME initiation precedes the onset of the associated
  flare. This result provides an important clue to the mechanism and
  relation of CMEs and flares.

Title: a Method for Determining Magnetic Helicity of Solar Active
    Regions from Soho/mdi Magneto Grams
Authors: Chae, Jongchul; Jeong, Hyewon
Bibcode: 2005JKAS...38..295C
Altcode:
  No abstract at ADS

Title: The Magnetic Structure of Filament Barbs
Authors: Chae, Jongchul; Moon, Yong-Jae; Park, Young-Deuk
Bibcode: 2005ApJ...626..574C
Altcode:
  There is a controversy about how features protruding laterally from
  filaments, called barbs, are magnetically structured. On 2004 August 3,
  we observed a filament that had well-developed barbs. The observations
  were performed using the 10 inch refractor of the Big Bear Solar
  Observatory. A fast camera was employed to capture images at five
  different wavelengths of the Hα line and successively record them
  on the basis of frame selection. The terminating points of the barbs
  were clearly discernable in the Hα images without any ambiguity. The
  comparison of the Hα images with the magnetograms taken by SOHO
  MDI revealed that the termination occurred above the minor polarity
  inversion line dividing the magnetic elements of the major polarity
  and those of the minor polarity. There is also evidence that the flux
  cancellation proceeded on the polarity inversion line. Our results
  together with similar other recent observations support the idea that
  filament barbs are cool matter suspended in local dips of magnetic
  field lines, formed by magnetic reconnection in the chromosphere.

Title: The New Solar Telescope at Big Bear Solar Observatory -
    A Progress Report
Authors: Denker, C.; Cao, W.; Chae, J.; Coulter, R.; Kuhn, J. R.;
   Marquette, W. H.; Moon, Y.; Park, Y.; Ren, D.; Tritschler, A.; Varsik,
   J. R.; Wang, H.; Yang, G.; Shoumko, S.; Goode, P. R.
Bibcode: 2005AGUSMSP43A..07D
Altcode:
  The New Solar Telescope (NST) is a new 1.6-meter, off-axis telescope
  for the Big Bear Solar Observatory (BBSO) in California. The NST is
  collaboration between BBSO, the Korean Astronomical Observatory (KAO)
  and Institute for Astronomy (IfA) at the University of Hawaii. BBSO
  is an ideal site for high-spatial resolution observations, since this
  mountain-lake site provides consistent seeing conditions with extended
  periods of excellent seeing from sunrise to sunset. These unique seeing
  characteristics make BBSO ideally suited for combined high-resolution
  campaigns and synoptic observations, which are essential for studies
  of solar activity and space weather. In this progress report, we
  present the latest information on the optical design, the optical
  support structure, the telescope control system and the requisite
  instrumentation for the telescope. Acknowledgements: This work has been
  supported by NSF under grants ATM-0236945, ATM-0342560, MRI-0320540,
  and Air Force DURIP F-49620-03-1-0271.

Title: New Geoeffective Parameters of Very Fast Halo Coronal Mass
Authors: Moon, Y.; Cho, K.; Dryer, M.; Kim, Y.; Bong, S.; Chae, J.;
   Park, Y.
Bibcode: 2005AGUSMSH23A..01M
Altcode:
  We have examined the physical characteristics of very fast coronal
  mass ejections (CMEs) and their geoeffective parameters. For this we
  consider SOHO/LASCO CMEs whose speeds are larger than 1300 km s-1. By
  examining all SOHO/EIT and SOHO/LASCO images of the CMEs, we selected
  38 front-side very fast CMEs and then examined their associations with
  solar activity such as X-ray flares and Type II bursts. As a result,
  we found that among these frontside fast CMEs, 25 are halo (or full
  halo) CMEs with span of 360 degrees; 12 are partial halo CMEs with
  span greater than 130 degrees; only 1 is broadside CME with span of 53
  degrees. There are 13 events that are shock deflected CMEs: 6 are full
  halo CMEs and 7 are partial halo CMEs. It is found that about 60 %
  (23/38) CMEs were ejected from the western hemisphere. We also note
  that these very fast CMEs have very high associations with other solar
  activities: all the CMEs are associated with X-ray flares (X-12, M-23,
  C-3), and about 80 % of the CMEs (33/38) were accompanied by Type II
  bursts. For the examination of CME geoeffectiveness, we select 12 halo
  CMEs whose longitudes are less than 40 degrees, which are thought to
  be the most plausible candidates of geoeffective CMEs. Then we examine
  the relationship between their CME physical parameters (mass, column
  density, location of an associated flare, and direction) and the Dst
  index. Especially, a CME direction parameter, which is defined as the
  maximum ratio of its shorter front from solar disk center and its longer
  one, is proposed as a new geoeffective parameter. Its major advantage
  is that it can be directly estimated from coronagraph observation. It
  is found that while the location of the associated flare has a poor
  relationship with the Dst index, the new direction parameter has a
  relatively good relationship. In addition, the column density of a CME
  also has a comparable good correlation with the Dst index. Noting that
  the CME column density is strongly affected by the direction of a CME,
  our results imply that the CME direction seems to be the most important
  parameter that controls the geoeffectiveness of very fast halo CMEs.

Title: New Geoeffective Parameters of Very Fast Halo Coronal Mass
    Ejections
Authors: Moon, Y. -J.; Cho, K. -S.; Dryer, M.; Kim, Y. -H.; Bong,
   Su-chan; Chae, Jongchul; Park, Y. D.
Bibcode: 2005ApJ...624..414M
Altcode:
  We have examined the physical characteristics of very fast coronal mass
  ejections (CMEs) and their geoeffective parameters. For this we consider
  SOHO LASCO CMEs whose speeds are larger than 1300 km s<SUP>-1</SUP>. By
  examining all SOHO EIT and SOHO LASCO images of the CMEs, we selected
  38 front-side very fast CMEs and then examined their associations with
  solar activity such as X-ray flares and type II bursts. As a result,
  we found that among these front-side fast CMEs, 25 are halo (or full
  halo) CMEs with span of 360°, 12 are partial halo CMEs with span
  greater than 130°, and only one is a broadside CME, with a span of
  53°. There are 13 events that are shock-deflected CMEs: six are full
  halo CMEs, and seven are partial halo CMEs. It is found that about 60%
  (23/38) CMEs were ejected from the western hemisphere. We also note
  that these very fast CMEs have very high associations with other solar
  activities: all the CMEs are associated with X-ray flares (X-12, M-23,
  C-3), and about 80% of the CMEs (33/38) were accompanied by type II
  bursts. For the examination of CME geoeffectiveness, we select 12 halo
  CMEs whose longitudes are less than 40°, which are thought to be the
  most plausible candidates of geoeffective CMEs. Then we examine the
  relation between their CME physical parameters (mass, column density,
  location of an associated flare, and direction) and the Dst index. In
  particular, a CME direction parameter, which is defined as the maximum
  ratio of its shorter front from solar disk center and its longer one,
  is proposed as a new geoeffective parameter. Its major advantage is
  that it can be directly estimated from coronagraph observation. It
  is found that while the location of the associated flare has a poor
  correlation with the Dst index, the new direction parameter has a
  relatively good correlation. In addition, the column density of a CME
  also has a comparable good correlation with the Dst index. Noting that
  the CME column density is strongly affected by the direction of a CME,
  our results imply that the CME direction seems to be the most important
  parameter that controls the geoeffectiveness of very fast halo CMEs.

Title: Technique for Inferring Magnetic Helicity of Active Regions
Authors: Chae, Jongchul; Moon, Yong-Jae
Bibcode: 2005HiA....13..109C
Altcode:
  The magnetic helicity content of a coronal volume may change over time
  at the presence of surface flows. When phtospheric magnetic fields are
  predominantly vertical it is possible to determine the rate of change of
  magnetic helicity using a time series of longitudinal magnetograms only
  since one can determine the horizontal component of velocity by tracking
  the displacements of magnetic flux fragments using the technique of
  local correlation (LCT). This technique has turned out to be very
  useful in revealing significant helicity changes that are associated
  with prominence formation and major flares. When magnetic fields are
  not vertical it is crucial to determine the vertical component of
  velocity too. A clever way of inferring it from the induction equation
  and the LCT-determined horizontal velocity has been proposed. However
  the results should be interpreted with a caution since the LCT may
  not yield even the correct value of the horizontal velocity component
  when magnetic fields are inclined to the vertical. Alternatively we are
  trying to make use of the full Stokes profile data taken by the NSO/ASP
  to determine the velocity vectors as well as magnetic field vectors.

Title: Preliminary Feasibility Study of the Solar Observation Payloads
    for STSAT-CLASS Satellites
Authors: Moon, Yong-Jae; Cho, Kyung-Seok; Jin, Ho; Chae, Jong-Chul;
   Lee, Sung-Ho; Seon, Kwang-Il; Kim, Yeon-Han; Park, Young-Deuk
Bibcode: 2004JASS...21..329M
Altcode:
  In this paper, we present preliminary feasibility studies on three
  types of solar observation payloads for future Korean Science and
  Technology Satellite (STSAT) programs. The three candidates are (1)
  an UV imaging telescope, (2) an UV spectrograph, and (3) an X-ray
  spectrometer. In the case of UV imaging telescope, the most important
  constraint seems to be the control stability of a satellite in order
  to obtain a reasonably good spatial resolution. Considering that
  the current pointing stability estimated from the data of the Far
  ultraviolet Imaging Spectrograph (FIMS) onboard the Korean STSAT-1, is
  around 1 arc minutes/sec, we think that it is hard to obtain a spatial
  resolution sufficient for scientific research by such an UV Imaging
  Telescope. <P />For solar imaging missions, we realize that an image
  stabilization system, which is composed of a small guide telescope
  with limb sensor and a servo controller of secondary mirror, is quite
  essential for a very good pointing stability of about 0.1 arcsec. An UV
  spectrograph covering the solar full disk seems to be a good choice in
  that there is no risk due to poor pointing stability as well as that it
  can provide us with valuable UV spectral irradiance data valuable for
  studying their effects on the Earth's atmosphere and satellites. The
  heritage of the FIMS can be a great advantage of developing the UV
  spectrograph. Its main disadvantage is that two major missions are in
  operation or scheduled. Our preliminary investigations show that an
  X-ray spectrometer for the full disk Sun seems to be the best choice
  among the three candidates. The reasons are : (1) high temporal and
  spectral X-ray data are very essential for studying the acceleration
  process of energetic particles associated with solar flares, (2)
  we have a good heritage of X-ray detectors including a rocket-borne
  X-ray detector, (3) in the case of developing countries such as India
  and Czech, solar X-ray spectrometers were selected as their early
  stage satellite missions due to their poor pointing stabilities, and
  (4) there is no planned major mission after currently operating Reuven
  Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) mission. Finally,
  we present a preliminary design of a solar X-ray spectrometer covering
  soft X-ray (2 keV) to gamma ray (10 MeV).

Title: Determination of magnetic helicity content of solar active
    regions from SOHO/MDI magnetograms
Authors: Chae, Jongchul; Moon, Yong-Jae; Park, Young-Deuk
Bibcode: 2004SoPh..223...39C
Altcode:
  Chae (2001) first proposed a method of self-consistently determining the
  rate of change of magnetic helicity using a time series of longitudinal
  magnetograms only, such as taken by SOHO/MDI. Assuming that magnetic
  fields in the photosphere are predominantly vertical, he determined
  the horizontal component of velocity by tracking the displacements
  of magnetic flux fragments using the technique of local correlation
  tracking (LCT). In the present paper, after briefly reviewing the
  recent advance in helicity rate measurement, we argue that the LCT
  method can be more generally applied even to regions of inclined
  magnetic fields. We also present some results obtained by applying
  the LCT method to the active region NOAA 10365 under emergence during
  the observable period, which are summarized as follows. (1) Strong
  shearing flows were found near the polarity inversion line that were
  very effective in helicity injection. (2) Both the magnetic flux and
  helicity of the active region steadily increased during the observing
  period, and reached 1.2 × 10<SUP>22</SUP> Mx and 8 ×10<SUP>42</SUP>
  Mx<SUP>2</SUP>, respectively, 4.5 days after the birth of the active
  region. (3) The corresponding ratio of the helicity to the square of the
  magnetic flux, 0.05, is roughly compatible with the values determined
  by other studies using linear-force-free modeling. (4) A series of
  flares took place while the rate of helicity injection was high. (5)
  The choice of a smaller window size or a shorter time interval in
  the LCT method resulted in a bigger value of the LCT velocity and a
  bigger value of the temporal fluctuation of the helicity rate. (6)
  Nevertheless when averaged over a time period of about one hour or
  longer, the average rate of helicity became about the same within about
  10%, almost irrespective of the chosen window size and time interval,
  indicating that short-lived, fluctuating flows may be insignificant in
  transferring magnetic helicity. Our results suggest that the LCT method
  may be applied to 96-minute cadence full-disk MDI magnetograms or other
  data of similar kind, to provide a practically useful, if not perfect,
  way of monitoring the magnetic helicity content of active regions as
  a function of time.

Title: Flat-Fielding of Solar Hα Observations Using Relatively
    Shifted Images
Authors: Chae, Jongchul
Bibcode: 2004SoPh..221....1C
Altcode:
  A new algorithm is proposed to determine the flat pattern from a
  set of relatively shifted images. It simultaneously searches for the
  flat pattern, the object image, the light levels, and optionally the
  relative displacements that optimize the sum of the error squares. We
  have applied the method to real Hα observations, and examined in detail
  the dependence of the accuracy of the solution on the iteration number,
  the light level change, the dither pattern, and the noise. It has been
  found that the method can produce a flat pattern with an error down
  to 0.25% of the mean level in Hα observations with low noise.

Title: Flat-Fielding of Solar Magnetograph Observations Using
    Relatively Shifted Images
Authors: Chae, Jongchul
Bibcode: 2004SoPh..221...15C
Altcode:
  I present a method to correct solar magnetograms for a non-uniform
  detector pattern that depends on the sense of light polarization. The
  application to Big Bear Solar Observatory magnetograph observations
  demonstrates that the determination of a flat pattern can be done at
  an accuracy imposed by the photon noise in the raw magnetograms.

Title: Low Atmosphere Reconnections Associated with AN Eruptive
    Solar Flare
Authors: Moon, Y. -J.; Chae, Jongchul; Choe, G. S.; Wang, Haimin;
   Park, Y. D.; Cheng, C. Z.
Bibcode: 2004JKAS...37...41M
Altcode:
  No abstract at ADS

Title: Observational Evidence of Magnetic Flux Submergence in Flux
    Cancellation Sites
Authors: Chae, Jongchul; Moon, Yong-Jae; Pevtsov, Alexei A.
Bibcode: 2004ApJ...602L..65C
Altcode:
  Using high-resolution vector magnetograms of NOAA Active Region
  10043, observed on 2002 July 26 with the Advanced Stokes Polarimeter
  and low-order adaptive optics system, we studied the magnetic field
  topology and line-of-sight velocities in two flux cancellation sites. We
  found that the magnetic field is near horizontal at the place where
  two opposite polarities cancel each other. In addition, we observed
  significant downflows of about 1 km s<SUP>-1</SUP> near the polarity
  reversal line, where the field is horizontal. We interpret these
  observations as the direct evidence of the magnetic flux submergence of
  concave-down (Ω-shaped) magnetic loop at the flux cancellation sites.

Title: Small-Scale Hα Dynamic Features Supported by Chromo Spheric
    Magnetic Reconnection
Authors: Lee, Sangwoo; Yun, Hong Sik; Chae, Jongchul; Goode, Philip R.
Bibcode: 2003JKAS...36S..21L
Altcode:
  No abstract at ADS

Title: Magnetic Helicity Changes of Solar Active Regions by
    Photospheric Horizontal Motions
Authors: Moon, Y. -J.; Chae, Jongchul; Park, Y. D.
Bibcode: 2003JKAS...36S..37M
Altcode:
  No abstract at ADS

Title: Observational Tests of Chromospheric Magnetic Reconnection
Authors: Chae, Jongchul; Moon, Yong-Jae; Park, So-Young
Bibcode: 2003JKAS...36S..13C
Altcode:
  No abstract at ADS

Title: Pre-flare Activity, Canceling Magnetic Features, and Filament
    Initiation associated with an X-class Flare
Authors: Moon, Y. -J.; Chae, J.; Choe, G. S.; Wang, H.; Park, Y. D.
Bibcode: 2003SPD....34.1611M
Altcode: 2003BAAS...35R.834M
  We have examined the relationship among pre-flare brightenings,
  canceling magnetic features (CMFs), and filament initiation associated
  with an X1.8 flare that occurred in NOAA AR 9236 on November 24,
  2000. For this, we have inspected high temporal (about 1 minute)
  and spatial (about 1 arcsec) resolutions of SOHO/MDI, BBSO Hα , and
  TRACE 1600 Å UV images. Major results are as follows. First, these
  pre-flare brightenings are the most clearly seen in the TRACE 1600 Å
  images rather than in BBSO Hα with very weak corresponding features
  in SOHO/EIT images. Second, two major pre-flare brightenings near one
  of the filament footpoints are exactly located on CMFs seen in the
  MDI images. Third, recurrent small-scale TRACE UV eruptive events,
  which may be interpreted as upward outflows associated with the low
  atmosphere magnetic reconnection, took place just at the site of <P
  />the CMFs. Fourth, these CMFs show a common tendency of flux change:
  first flux emergence and then flux cancellation. Fifth, the abrupt
  UV enhancement of one major pre-flare brightening is responsible for
  the flare precursor in the GOES X-ray curve. It is very interesting
  to note that such an enhancement is coincident with the starting of
  the eruption, which is about 20 minutes earlier than the starting
  time of hard X-ray flaring. Our results support an idea that the low
  atmosphere reconnection, supported by CMFs and pre-flare brightenings,
  play important role in triggering the filament eruption. <P />This
  work has been supported by NASA grants NAG5-10894 and NAG5-7837,
  by a MURI grant of AFOSR, and by NRL M10104000059-01J000002500 of
  Korean government.

Title: Magnetic Helicity Pumping by Twisted Flux Tube Expansion
Authors: Chae, Jongchul; Moon, Y. -J.; Rust, D. M.; Wang, Haimin;
   Goode, Philip R.
Bibcode: 2003JKAS...36...33C
Altcode:
  No abstract at ADS

Title: The Formation of a Prominence in NOAA Active Region
    8668. II. Trace Observations of Jets and Eruptions Associated with
    Canceling Magnetic Features
Authors: Chae, Jongchul
Bibcode: 2003ApJ...584.1084C
Altcode:
  Our previous study has shown that the formation of a reverse S-shaped
  filament in NOAA active region 8668 was closely associated with a
  large canceling magnetic feature. In the present paper we investigate
  the response of the upper atmosphere at the region of this canceling
  magnetic feature. The UV and EUV data taken by the Transition
  Region and Coronal Explorer (TRACE) reveal that a series of jets
  and small eruptions took place there during the formation of the
  prominence. Plasma in each jet originated from a single site of flux
  cancellation and moved in opposite directions at a transverse speed of
  80-250 km s<SUP>-1</SUP> across the plane of the sky. Plasma eruptions
  showing complex morphology and dynamics started from two or more sites
  of flux cancellation and appear to have the same physical origin as the
  jets. The two filter ratio technique indicates that the EUV-emitting
  plasma in the jets and eruptions have transition-region temperatures of
  (2-3)×10<SUP>5</SUP> K. It is also found from emission-measure analysis
  that the electron density is (0.7-1.9)×10<SUP>10</SUP> cm<SUP>-3</SUP>
  and that each jet carries plasma mass of (1.7-4.6)×10<SUP>13</SUP>
  g and each eruption carries additional mass of (9-25)×10<SUP>13</SUP>
  g. Our results are consistent with the current pictures that (1) flux
  cancellation observed in the photosphere is a consequence of magnetic
  reconnection occurring in the chromosphere and (2) that a series of
  such magnetic reconnection events is able to supply the mass necessary
  for the formation of a solar prominence.

Title: Magnetic helicity change rate associated with three X-class
    eruptive flares
Authors: Moon, Y. -J.; Chae, Jongchul; Wang, Haimin; Park, Y. D.
Bibcode: 2003AdSpR..32.1953M
Altcode:
  In this paper we have examined the temporal evolution of magnetic
  helicity change rate associated with three X-class eruptive flares that
  occurred on November 24, 2000. By analyzing a set of 1 minute cadence
  high-resolution magnetograms taken by Michelson Doppler Imager (MDI)
  on board Solar and Heliospheric Observatory (SOHO), we have determined
  the rates of magnetic helicity transport via horizontal photospheric
  motions. Then we have compared the impulsive variations of helicity
  injection rate with an initial eruption speed profile of a filament
  associated with a X1.8 flare. As a result, we have found (1) that the
  impulsive variations of magnetic helicity change rate were strongly
  correlated with only three X-class flarings, (2) that the eruption of
  the filament started about 10 minutes before the impulsive variation
  of the helicity change rate, and (3) that horizontal velocity kernels
  were located between Ha two flaring ribbons. Thus we suggest that
  the observed impulsive helicity change is not a cause of the eruptive
  solar flare but its result, i.e., photospheric response to the coronal
  field restructuring.

Title: Techniques for Inferring Active Region Magnetic Helicity
Authors: Chae, Jongchul; Moon, Yong-Jae
Bibcode: 2003IAUJD...3E..25C
Altcode:
  The magnetic helicity content of a coronal volume may change over time
  at the presence of surface flows. When phtospheric magnetic fields are
  predominantly vertical it is possible to determine the rate of change of
  magnetic helicity using a time series of longitudinal magnetograms only
  since one can determine the horizontal component of velocity by tracking
  the displacements of magnetic flux fragments using the technique of
  local correlation (LCT). This technique has turned out to be very
  useful in revealing significant helicity changes that are associated
  with prominence formation and major flares. When magnetic fields are
  not vertical it is crucial to determine the vertical component of
  velocity too. A clever way of inferring it from the induction equation
  and the LCT-determined horizontal velocity has been proposed. However
  the results should be interpreted with a caution since the LCT may
  not yield even the correct value of the horizontal velocity component
  when magnetic fields are inclined to the vertical. Alternatively we are
  trying to make use of the full Stokes profile data taken by the NSO/ASP
  to determine the velocity vectors as well as magnetic field vectors.

Title: Coronal Loops Heated by Magnetohydrodynamic Turbulence. I. A
    Model of Isobaric Quiet-Sun Loops with Constant Cross Sections
Authors: Chae, Jongchul; Poland, Arthur I.; Aschwanden, Markus J.
Bibcode: 2002ApJ...581..726C
Altcode:
  Several recent papers have presented new observational results
  indicating that many coronal loops in active regions are nearly
  isothermal. It is expected that quiet-Sun loops may have similar thermal
  structures, since quiet-Sun differential emission measures look similar
  to those in active regions. In the quiet Sun, it is well known from
  observations that the nonthermal velocity inferred from the excess
  broadening of a line over thermal broadening reaches a peak of about
  30 km s<SUP>-1</SUP> around 3×10<SUP>5</SUP> K and then decreases
  with temperature, having a value of about 20 km s<SUP>-1</SUP> at
  1×10<SUP>6</SUP> K. In the present work, we make the assumption
  that the observed nonthermal velocities are a manifestation of
  magnetohydrodynamic (MHD) turbulence and present a model of static,
  isobaric coronal loops heated by turbulence. Instead of solving the
  MHD equations, we adopt simple energy spectra in MHD turbulence and
  infer the heating rate as a function of temperature from the observed
  nonthermal velocities. By solving the steady state energy equation
  of a loop in which temperature monotonically increases with height,
  we obtain the following results: (1) The heating rate is predominantly
  near the footpoints and decreases with the loop arc length. (2) There
  is a critical temperature above which the loop cannot be maintained
  in a steady state. (3) The loop is denser and is more isothermal than
  uniformly heated loops, being compatible with recent observations. (4)
  The theoretical differential emission measures are in good agreement
  with the empirical values at temperatures above 10<SUP>5</SUP> K. Below
  this temperature, we still have a large discrepancy. (5) It is possible
  to explain the observed strong correlation between intensity and
  nonthermal velocity of a spectral line in the quiet Sun. Our results
  support the idea that quasi-statically driven MHD turbulence of the
  direct current (DC) type in the stratified medium (transition region
  and corona) is a viable mechanism for coronal heating.

Title: Impulsive Variations of the Magnetic Helicity Change Rate
    Associated with Eruptive Flares
Authors: Moon, Y. -J.; Chae, Jongchul; Wang, Haimin; Choe, G. S.;
   Park, Y. D.
Bibcode: 2002ApJ...580..528M
Altcode:
  In this paper, we investigate impulsive variations of the magnetic
  helicity change rate associated with eruptive solar flares (three
  X class flares and one M class flare) accompanying halo coronal
  mass ejections. By analyzing four sets of 1 minute cadence full-disk
  magnetograms taken by the Michelson Doppler Imager on board the Solar
  and Heliospheric Observatory, we have determined the rates of magnetic
  helicity transport due to horizontal photospheric motions. We have found
  that magnetic helicity of the order of 10<SUP>41</SUP> Mx<SUP>2</SUP>
  was impulsively injected into the corona around the flaring peak time
  of all the flares. We also found that there is a positive correlation
  between the impulsively injected magnetic helicity and the X-ray peak
  flux of the associated flare. The impulsive helicity variations are
  attributed to horizontal velocity kernels localized near the polarity
  inversion lines. Finally, we report that there is a close spatial
  proximity between the horizontal velocity kernels and Hα bright points.

Title: Flare Activity and Magnetic Helicity Injection by Photospheric
    Horizontal Motions
Authors: Moon, Y. -J.; Chae, Jongchul; Choe, G. S.; Wang, Haimin;
   Park, Y. D.; Yun, H. S.; Yurchyshyn, Vasyl; Goode, Philip R.
Bibcode: 2002ApJ...574.1066M
Altcode:
  We present observational evidence that the occurrence of homologous
  flares in an active region is physically related to the injection of
  magnetic helicity by horizontal photospheric motions. We have analyzed
  a set of 1 minute cadence magnetograms of NOAA AR 8100 taken over a
  period of 6.5 hr by the Michelson Doppler Imager on board the Solar
  and Heliospheric Observatory. During this observing time span, seven
  homologous flares took place in the active region. We have computed
  the magnetic helicity injection rate into the solar atmosphere by
  photospheric shearing motions and found that a significant amount of
  magnetic helicity was injected during the observing period. In a strong
  M4.1 flare, the magnetic helicity injection rate impulsively increased
  and peaked at the same time as the X-ray flux. The flare X-ray flux
  integrated over the X-ray emission time strongly correlates with the
  magnetic helicity injected during the flaring interval. The integrated
  X-ray flux is found to be a logarithmically increasing function of
  the injected magnetic helicity. Our results suggest that injection of
  helicity and abrupt increase of helicity magnitude play a significant
  role in flare triggering.

Title: Statistical Evidence for Sympathetic Flares
Authors: Moon, Y. -J.; Choe, G. S.; Park, Y. D.; Wang, Haimin;
   Gallagher, Peter T.; Chae, Jongchul; Yun, H. S.; Goode, Philip R.
Bibcode: 2002ApJ...574..434M
Altcode:
  Sympathetic flares are a pair of flares that occur almost simultaneously
  in different active regions, not by chance, but because of some
  physical connection. In this paper statistical evidence for the
  existence of sympathetic flares is presented. From GOES X-ray flare
  data, we have collected 48 pairs of near simultaneous flares whose
  positional information and Yohkoh soft X-ray telescope images
  are available. To select the active regions that probably have
  sympathetic flares, we have estimated the ratio R of actual flaring
  overlap time to random-coincidence overlap time for 38 active region
  pairs. We have then compared the waiting-time distributions for the
  two different groups of active region pairs (R&gt;1 and R&lt;1) with
  corresponding nonstationary Poisson distributions. As a result, we
  find a remarkable overabundance of short waiting times for the group
  with R&gt;1. This is the first time such strong statistical evidence
  has been found for the existence of sympathetic flares. To examine
  the role of interconnecting coronal loops, we have also conducted
  the same analysis for two subgroups of the R&gt;1 group: one with
  interconnecting X-ray loops and the other without. We do not find any
  statistical evidence that the subgroup with interconnecting coronal
  loops is more likely to produce sympathetic flares than the subgroup
  without. For the subgroup with loops, we find that sympathetic flares
  favor active region pairs with transequatorial loops.

Title: The Origin of Mass, Magnetic Flux, and Magnetic Helicity in
    a Solar Prominence
Authors: Chae, J.; Yun, H. S.; Moon, Y. -J.; Wang, H.; Goode, P.
Bibcode: 2002AAS...200.3715C
Altcode: 2002BAAS...34..697C
  Solar prominences are cloud-like cool and dense plasma supported by
  highly non-potential, and very likely twisted magnetic fields in the
  corona against the gravity. Therefore, the supply of mass, magnetic
  flux, and magnetic helicity is the necessary condition for the formation
  of solar prominences. We have been doing a series of case studies on
  the formation of a prominence in active region NOAA 8668. As a result,
  we have found a series of jets in Hα and EUV at the region where
  significant amounts of magnetic fluxes of opposite polarity canceled
  each other. We also found the existence of non-differential-rotation
  photospheric shearing motion that prevailed during the period of
  prominence formation. Both the magnetic flux associated with flux
  cancellation, and magnetic helicity injected by the shearing motion
  were more than enough for the formation of the prominence. Our results
  support that chromospheric magnetic reconnection is in charge of
  supplying mass and magnetic flux, and photospheric shearing motion
  is in charge of supplying magnetic helicity. This work was supported
  by the US-Korea Cooperative Science Program (KOSEF 995-0200-002-2,
  NSF INT-98-16267), the NASA grant NAG 5-10894 and the the National
  Research Laboratory project M10104000059-01J000002500 and the BK21
  project of the Korean Government.

Title: Magnetic Helicity Injection By Transient Photospheric Shear
    Flows in Flares and Prominences
Authors: Yun, H. S.; Chae, J.; Moon, Y. -J.; Wang, H.; Goode, P. R.
Bibcode: 2002AAS...200.3716Y
Altcode: 2002BAAS...34..697Y
  There has been increasing interest in magnetic helicity since it is
  a well-conserved measure of the non-potentiality of solar magnetic
  fields. Magnetic helicity in the solar corona may change when magnetic
  helicity is transported either across the photosphere or out of the
  Sun. Of our specific interest is the magnetic helicity change due to
  transient shear flows in the photosphere. We have developed a method
  of determining its rate from a time series of magnetograms, and have
  applied it to several active regions. We present one example showing
  that transient shear flows may inject significant amount of magnetic
  helicity for several days during the formation of a prominence,
  and other examples showing that magnetic helicity injection by
  shear flows may occur impulsively during strong flares. We do not
  know the physical nature of transient shear flows, but there is a
  possibility that they may represent the photospheric velocity field
  of low frequency, large-scale torsional Alfvén waves passing through
  the solar surface. This work was supported by the US-Korea Cooperative
  Science Program (KOSEF 995-0200-002-2, NSF INT-98-16267), and the the
  National Research Laboratory project M10104000059-01J000002500 and
  the BK21 project of the Korean Government.

Title: Flux Cancellation Rates and Converging Speeds of Canceling
    Magnetic Features
Authors: Chae, Jongchul; Moon, Yong-Jae; Wang, Haimin; Yun, H. S.
Bibcode: 2002SoPh..207...73C
Altcode:
  Canceling magnetic features are commonly believed to result from
  magnetic reconnection in the low atmosphere. According to the
  Sweet-Parker type reconnection model, the rate of flux cancellation
  in a canceling magnetic feature is related to the converging speed of
  each pole. To test this prediction observationally, we have analyzed
  the time variation of two canceling magnetic features in detail using
  the high-resolution magnetograms taken by the Michelson Doppler Imager
  (MDI) on the Solar and Heliospheric Observatory (SOHO). As a result,
  we have obtained the rate and converging speed of flux cancellation
  in each feature: 1.3×10<SUP>18</SUP> Mx hr<SUP>−1</SUP> (or
  1.1×10<SUP>6</SUP> G cm s<SUP>−1</SUP> per unit contact length) and
  0.35 km s<SUP>−1</SUP> in the smaller one, and 3.5×10<SUP>18</SUP>
  Mx hr<SUP>−1</SUP> (1.2×10<SUP>6</SUP> G cm s<SUP>−1</SUP>) and
  0.27 km s<SUP>−1</SUP> in the bigger one. The observed speeds are
  found to be significantly bigger than the theoretically expected ones,
  but this discrepancy can be resolved if uncertainty factors such as
  low area filling factor of magnetic flux and low electric conductivity
  are taken into account.

Title: Flare Activity and Magnetic Helicity Injection By Photospheric
    Horizontal Motions
Authors: Moon, Y. -J.; Chae, J.; Choe, G.; Wang, H.; Park, Y. D.;
   Yun, H. S.; Yurchyshyn, V.; Goode, P. R.
Bibcode: 2002AAS...200.2002M
Altcode: 2002BAAS...34..673M
  We present observational evidence that the occurrence of homologous
  flares in an active region is physically related to the injection
  of magnetic helicity by horizontal photospheric motions. We have
  analyzed a set of 1 minute cadence magnetograms of NOAA AR 8100 taken
  over a period of 6.5 hours by Michelson Doppler Imager (MDI) on board
  Solar and Heliospheric Observatory (SOHO). During this observing time
  span, seven homologous flares took place in the active region. We have
  computed the magnetic helicity injection rate into the solar atmosphere
  by photospheric shearing motions, and found that a significant amount
  of magnetic helicity was injected during the observing period. In a
  strong M4.1 flare, the magnetic helicity injection rate impulsively
  increased and peaked at the same time as the X-ray flux did. The flare
  X-ray flux integrated over the X-ray emission time strongly correlates
  with the magnetic helicity injected during the flaring interval. The
  integrated X-ray flux is found to be a logarithmically increasing
  function of the injected magnetic helicity. Our results suggest that
  injection of helicity and abrupt increase of helicity magnitude play
  a significant role in flare triggering. This work has been supported
  by NASA grants NAG5-10894 and NAG5-7837, by MURI grant of AFOSR, by
  the US-Korea Cooperative Science Program (NSF INT-98-16267), by NRL
  M10104000059-01J000002500 of the Korean government, and by the BK 21
  project of the Korean government.

Title: Temperatures of Extreme-Ultraviolet-emitting Plasma Structures
    Observed by the Transition Region and Coronal Explorer
Authors: Chae, Jongchul; Park, Young-Deuk; Moon, Yong-Jae; Wang,
   Haimin; Yun, H. S.
Bibcode: 2002ApJ...567L.159C
Altcode:
  The Transition Region and Coronal Explorer has revealed, in
  unprecedented detail, various kinds of EUV-emitting plasma structures
  in the solar upper atmosphere. The filter ratio 195 Å/171 Å has been
  conventionally used to determine the plasma temperatures, but this
  method has a shortcoming in that it may not yield a unique temperature
  value for a given ratio. Therefore, we introduce a new method employing
  two filter ratios (195 Å/171 Å and 284 Å/195 Å). It is demonstrated
  that this color-color method is effective in determining a wide range
  of unambiguous plasma temperatures. We have obtained a temperature of
  1×10<SUP>6</SUP> K for a loop that is bright in 171 Å but hardly
  visible in 284 Å, a higher temperature of 2×10<SUP>6</SUP> K for
  a loop that is clearly visible in 195 and 284 Å but not in 171 Å,
  and a transition-region temperature of 2.5×10<SUP>5</SUP> K for a
  low-lying loop that is clearly visible in all the EUV wavelengths. In
  addition, we have found that ``moss'' structures have temperatures
  of around 1×10<SUP>6</SUP> K and that EUV jets have temperatures of
  about 2.5×10<SUP>5</SUP> K.

Title: Chromospheric Magnetic Reconnection on the Sun
Authors: Chae, Jongchul; Choi, Byung-Kyu; Park, Min-Ju
Bibcode: 2002JKAS...35...59C
Altcode:
  No abstract at ADS

Title: Dip-Like Magnetic Field Structure Seen in Solar Prominences
Authors: Yun, H. S.; Lee, S.; Chae, J.; Kim, J. H.; Park, Y. D.; Kim,
   S. E.; Goode, P. R.; Wang, H.
Bibcode: 2002stma.conf..103Y
Altcode:
  No abstract at ADS

Title: Magnetic helicity injection associated with solar flares
Authors: Moon, Y.; Chae, J.; Wang, H.; Choe, G.; Park, Y.
Bibcode: 2002cosp...34E.471M
Altcode: 2002cosp.meetE.471M
  We have examined the characteristics of magnetic helicity injections
  associated with solar flares. We have analyzed a set of 1 minute
  cadence magnetograms of NOAA AR 8100 taken over a period of 6.5 hours
  by Michelson Doppler Imager (MDI) on board Solar and Heliospheric
  Observatory (SOHO). During this observing time span, seven homologous
  flares took place in the active region. We have computed the magnetic
  helicity injection rate into the solar atmosphere by photospheric
  shearing motions, and found that a significant amount of magnetic
  helicity was injected during the observing period. In a strong M4.1
  flare, the magnetic helicity injection rate impulsively increased and
  peaked at the same time as the X-ray flux did. It is also noted that
  the GOES X-ray flux integrated over the X-ray emission time strongly
  correlates with the magnetic helicity injected during the flaring
  interval.

Title: Inter-Active Region Connection of Sympathetic Flaring on 2000
    February 17
Authors: Wang, Haimin; Chae, Jongchul; Yurchyshyn, Vasyl; Yang, Guo;
   Steinegger, Michael; Goode, Philip
Bibcode: 2001ApJ...559.1171W
Altcode:
  We have analyzed high-resolution Hα full disk data from Big
  Bear Solar Observatory (BBSO); magnetograph and EUV data from the
  Michelson Doppler Imager, Large Angle and Spectrometric Coronagraph,
  and Extreme Ultraviolet Imaging Telescope on board SOHO; and Yohkoh
  soft X-ray data of 2000 February 17. Two sympathetic M-class solar
  flares erupted in succession in NOAA Active Region 8869 and 8872,
  respectively. The eruption from AR 8872 was followed by an extremely
  symmetric halo coronal mass ejection (CME). We demonstrate the loop
  activation, which appears to be the consequence of the first flare in
  AR 8869 and the cause of the second flare in AR 8872. The activation
  started in the form of a surge just after a filament eruption and its
  associated flare in AR 8869. The surge quickly turned into a set of
  disturbances that propagated at a speed of about 80 km s<SUP>-1</SUP>
  toward the other active region AR 8872. The second flare followed in
  less than an hour after the arrival of the disturbances at AR 8872. The
  moving disturbances appeared in absorption in both Hα and EUV 195
  Å images. The disturbances may represent mass transfer, which had
  a significant velocity component perpendicular to the field lines
  and, hence, caused the transport of field lines. In this case, the
  disturbances may be considered to be a special kind of surge, which we
  may call a ``sweeping closed-loop surge.'' We also demonstrated large
  area dimmings associated with the CME in three active regions. The
  dimming started from AR 8869 and AR 8872 and was extended to AR 8870,
  which was on the opposite side of the solar equator. We believe that
  both the activation of inter-active region loops and the large-scale
  dimming are the signatures of large-scale restructuring associated
  with the CME.

Title: The Formation of a Prominence in Active Region NOAA
    8668. I. SOHO/MDI Observations of Magnetic Field Evolution
Authors: Chae, Jongchul; Wang, Haimin; Qiu, Jiong; Goode, Philip R.;
   Strous, Louis; Yun, H. S.
Bibcode: 2001ApJ...560..476C
Altcode:
  We have studied the evolution of the photospheric magnetic field in
  active region NOAA 8668 for 3 days while the formation of a reverse
  S-shaped filament proceeded. From a set of full-disk line-of-sight
  magnetograms taken by the Michelson Doppler Imager (MDI) on board
  the Solar and Heliospheric Observatory (SOHO), we have found a
  large canceling magnetic feature that was closely associated with
  the formation of the filament. The positive flux of the magnetic
  feature was initially 1.5×10<SUP>21</SUP> Mx and exponentially
  decreased with an e-folding time of 28 hr throughout the period of
  observations. We also have determined the transverse velocities of
  the magnetic flux concentrations in the active region by applying
  local correlation tracking. As a result, a persistent pattern of shear
  motion was identified in the neighborhood of the filament. The shear
  motion had a speed of 0.2-0.5 km s<SUP>-1</SUP> and fed negative
  magnetic helicity of -3×10<SUP>42</SUP> Mx<SUP>2</SUP> into the
  coronal volume during an observing run of 50 hr at an average rate
  of -6×10<SUP>40</SUP> Mx<SUP>2</SUP> hr<SUP>-1</SUP>. This rate is
  an order of magnitude higher than the rate of helicity change due to
  the solar differential rotation. The magnetic flux of the field lines
  created by magnetic reconnection and the magnetic helicity generated
  by the photospheric shear motion are much more than enough for the
  formation of the filament. Based on this result, we conjecture that the
  filament formation may be the visible manifestation of the creation
  of a much bigger magnetic structure that may consist of a flux rope
  and an overlying sheared arcade.

Title: Are Non-thermal Motions in the Solar Corona Evidence for
    Coronal Heating by MHD Turbulence?
Authors: Chae, Jongchul
Bibcode: 2001APS..DPPFM1005C
Altcode:
  Recent solar observations suggest that the solar outer atmosphere is
  turbulent. In the present talk, I focus on the SOHO/SUMER observations
  of non-thermal motions --- unresolved plasma motions that are required
  to explain the line width excess over thermal broadening --- of
  UV/EUV emitting plasma whose temperature ranges from 10^4 to 10^6
  K. It has been found from a thorough investigation of the quiet Sun
  that the most probable speed of non-thermal motion depends on the
  formation temperature of the spectral lines: it is smaller than 10 km
  s<SUP>-1</SUP> in the chromosphere (T&lt;2 × 10^4 K), reaches a peak
  value of 30 km s<SUP>-1</SUP> in the transition region ( 3 × 10^5 K),
  and decreases to about 20 km s<SUP>-1</SUP> in the low corona (T&gt;10^6
  K). Non-thermal motions are essentially isotropic and remain unresolved
  at a spatial resolution of 1000 km and at a temporal resolution of a
  few tens of seconds. Moreover, a careful examination of profiles of the
  S VI line formed at 2 × 10^5 K has revealed that a fraction of the
  line-emitting plasma has non-thermal motions of 50 km s<SUP>-1</SUP>
  or higher values. Non-thermal motions were also measured in each
  of several spatially resolved loops in an active region. Some loops
  have the most probable speed of 20 km s<SUP>-1</SUP>, others have a
  much bigger value of 50 km s<SUP>-1</SUP>, suggesting that non-thermal
  motion is an intrinsic property of a loop as temperature is. Non-thermal
  motions may represent either one of or a combination of three different
  kinds of physical processes: 1) a superposition of laminar flows along
  very small magnetic loops, 2) MHD waves, especially Alfvénic waves,
  and 3) MHD turbulence. Our results seem to be more compatible with the
  last explanation than the others, and to support the coronal heating
  by MHD turbulence.

Title: Observational Determination of the Rate of Magnetic Helicity
    Transport through the Solar Surface via the Horizontal Motion of
    Field Line Footpoints
Authors: Chae, Jongchul
Bibcode: 2001ApJ...560L..95C
Altcode:
  Magnetic helicity may be transported to the solar corona through the
  solar surface either via the passage of helical magnetic field lines
  from below or via the shuffling of footpoints of preexisting coronal
  field lines. In this Letter, we show how to observationally determine
  the rate of magnetic helicity transport via photospheric footpoint
  shuffling from a time series of line-of-sight magnetograms. Our
  approach is not confined to the previously known shear motions,
  such as differential rotation, but can be exploited to search for the
  possible existence of physically significant shear motions other than
  differential rotation. We have applied the method to a 40 hr run of
  high-resolution magnetograms of a small active region (NOAA Active
  Region 8011) taken by the Michelson Doppler Imager on board the Solar
  and Heliospheric Observatory. In this region, we find that the rate
  of magnetic helicity transport oscillates with periods of 1 to several
  hours. Our result suggests that the time-series analysis of the helicity
  transport rate might be a useful observational diagnostic for the role
  of photospheric flows in the evolution of coronal magnetic fields in
  solar active regions.

Title: A Steady Flow Model for the Differential Emission Measure in
    the Solar Quiet Region
Authors: Bong, S.; Chae, J.; Yun, H.; Lee, J.
Bibcode: 2001AGUSM..SH41B21B
Altcode:
  With high quality UV spectroscopy from the SoHO spacecraft, the
  physical structure of the solar Transition Region (TR) is of renewed
  interest. We have investigated the thermodynamic structure of the TR
  using a one dimensional magnetic tube model constrained to Raymond
  &amp; Doyle's Differential Emission Measure (DEM) in the average quiet
  sun. We have included the effect of the expansion of magnetic flux
  tube and a heating which is required in addition to conductive heat,
  convective energy and radiative cooling. From the resulting heating
  and flux tube geometry, we also investigated upflows probable in the
  transition region. To reproduce the Doppler shift of UV lines measured
  using SoHO/SUMER (Chae, Yun, &amp; Poland 1998), flux tube needs to
  expand rapidly above T=10<SUP>5</SUP> K at a rate of radius increase
  up to (7.4x 10<SUP>-2</SUP> km<SUP>-1</SUP>)~ r<SUB>4.1</SUB> where
  r<SUB>4.1</SUB> is the radius at log T = 4.1. To balance the energy,
  an energy supply by more than (9.3x 10<SUP>4</SUP> erg cm<SUP>-2</SUP>
  s<SUP>-1</SUP>)~π r<SUB>4.1</SUB><SUP>2</SUP> is required at the region
  between 1.3x 10<SUP>4</SUP> K and 2.5x 10<SUP>4</SUP> K regardless
  of filling factor, suggesting a local heating in the chromosphere. As
  for upflows, in subsonic flow cases, a model with the same additional
  energy loss as in a downflow is probable. Also, supersonic flows could
  be easily made and, in this case, supersonic upflows could carry extra
  energy to corona without increasing DEM, showing the possibility that
  upflows play a role in corona heating. This work was supported by
  the Basic Science Research Institute Program, Ministry of Education
  (BSRI-98-5408) and by the BK21 Project of the Korean Government.

Title: Inter-Active Region Connection of Sympathetic Flaring on 2000
    February 17
Authors: Wang, H.; Chae, J.; Yurchyshyn, V.; Yang, G.; Steinegger,
   M.; Goode, P. R.
Bibcode: 2001AGUSM..SP42A03W
Altcode:
  We have analyzed high resolution Hα full disk data from Big Bear
  Solar Observatory (BBSO), magnetograph and EUV data from MDI, LASCO
  and EIT on board SOHO, and Yohkoh soft X-ray data of February 17,
  2000. Two sympathetic M-class solar flares erupted in succession
  in NOAA 8869 and 8872, respectively. The eruption from AR 8872 was
  followed by an extremely symmetric halo CME. We demonstrate a new
  kind of loop activation, which appears to be the consequence of
  the first flare in AR 8869 and the cause of the second flare in
  AR 8872. The activation started in the form of a surge just after
  a filament eruption and its associated flare in AR 8869. The surge
  quickly turned into a set of disturbances that propagated at a speed of
  about 80 km/s toward the other active region AR 8872. The second flare
  followed in less than an hour after the arrival of the disturbances
  at AR 8872. The moving disturbances appeared in absorption in both
  Hα and EUV 195A images. The disturbances may represent mass transfer
  which had a significant velocity component perpendicular to the field
  lines and, hence, caused the transport of field lines. In this case,
  the disturbances may be considered to be a special kind of surge,
  which we may call a "sweeping closed-loop surge". Alternatively, the
  disturbances may represent fronts of compressive magnetohydrodynamic
  waves that were driven by the surge. We also demonstrated large area
  dimmings associated with the CME in three active regions. The dimming
  started from ARs 8869 and 8872, and was extended to AR 8870 which was
  on the opposite side of the solar equator. We believe that both the
  activation of inter-active region loops and the large scale dimming are
  the signatures of large scale re-structuring associated with the CME.

Title: Results from the Big Bear Solar Observatory's New Digital
    Vector Magnetograph
Authors: Spirock, T. J.; Denker, C.; Varsik, J.; Shumko, S.; Qiu,
   J.; Gallagher, P.; Chae, J.; Goode, P.; Wang, H.
Bibcode: 2001AGUSM..SP51B06S
Altcode:
  During the past several years the Big Bear Solar Observatory has
  been involved in an aggressive program to modernize the observatory's
  instrumentation. At the forefront of this effort has been the upgrade
  of the observatory's digital vector magnetograph (DVMG), which has been
  recently integrated into the observatory's daily observing program. The
  DVMG, which is mounted on the observatory's 25 cm vacuum refractor,
  is a highly sensitive, high cadence magnetograph which studies the
  FeI line at 630.1 nm. An easy to use GUI observing tool has been
  written to aid instrument development and data acquisition. This
  tool automatically calibrates the data and generates near real-time
  vector magnetograms which will aid space weather forecasting and the
  support of space weather missions. Also, our plan is to integrate the
  DVMG data into the HESSI Synoptic Archive. The very sensitive quiet
  Sun magnetograms, produced by the DVMG, will aid the study of small
  scale magnetic reconnection at the intranetwork level and its possible
  contribution to the coronal heating problem. Quiet sun longitudinal and
  active region vector magnetograms will be presented. Image quality,
  such as bias, cross-talk, noise levels and sensitivity, will be
  discussed in addition to the improvements gained in post processing
  such as image selection and image alignment.

Title: Small Magnetic Bipoles Emerging in a Filament Channel
Authors: Chae, Jongchul; Martin, Sara F.; Yun, H. S.; Kim, Junghoon;
   Lee, Sangwoo; Goode, Philip R.; Spirock, Tom; Wang, Haimin
Bibcode: 2001ApJ...548..497C
Altcode:
  Observations have shown that quiescent prominences or filaments have a
  hemispheric magnetic pattern of chirality. Motivated by the question
  of whether the filament chirality is of subsurface origin or not,
  we have studied small magnetic bipoles that emerged in a quiescent
  filament channel at latitude N45°. During our 5 day observing run,
  performed in 1999 October, a huge filament erupted and reformed shortly
  in the same filament channel. Using high-cadence, long-integration
  line-of-sight magnetograms taken at Big Bear Solar Observatory, we
  identified a total of 102 bipoles that showed an average total flux
  of 2.8×10<SUP>19</SUP> Mx, an average separation of 7400 km at the
  time of full development, and an emergence rate of 430 hr<SUP>-1</SUP>
  per the entire solar surface area. These properties indicate that most
  of the bipoles are ephemeral regions. The most important finding in
  the present study is that the magnetic axes of the bipoles emerging in
  the filament channel are systematically oriented; a negative (trailing)
  pole is observed to be located preferentially to the south-east of its
  companion positive (leading) pole. This preferred orientation does not
  match either the Hale law of active region orientation or a theory that
  attributes the axial field of a filament to emerging bipoles. We propose
  two possible subsurface field configurations of bipoles consistent with
  the observed preferential orientation and discuss physical implications
  of our results for understanding filament magnetic fields.

Title: The Big Bear Solar Observatory's Digital Vector Magnetograph
Authors: Spirock, T.; Denker, C.; Chen, H.; Chae, J.; Qiu, J.; Varsik,
   J.; Wang, H.; Goode, P. R.; Marquette, W.
Bibcode: 2001ASPC..236...65S
Altcode: 2001aspt.conf...65S
  No abstract at ADS

Title: A Rapid Change in Magnetic Connectivity Observed Before
    Filament Eruption and Its Associated Flare
Authors: Kim, Jung-Hoon; Yun, H. S.; Lee, Sangwoo; Chae, Jongchul;
   Goode, Philip R.; Wang, Haimin
Bibcode: 2001ApJ...547L..85K
Altcode:
  To gain insight to the cause of filament eruptions and flares on
  the Sun, we observed a filament that erupted in active region NOAA
  8597. The observations consisted of Hα filtergrams at three wavelengths
  (line center and +/-0.5 Å) and line-of-sight magnetograms. All
  were taken on 1999 June 24 at Big Bear Solar Observatory. We found
  from the time sequence of Hα images that the filament eruption was
  preceded by a rapid change in connectivity in a bundle of filament
  threads. The thread bundle was initially sharply curved near its one
  end of the filament and suddenly flipped and then became straight in
  the new orientation. The flipped segment of the thread bundle swept
  over a 100<SUP>''</SUP>×50<SUP>''</SUP> area on the solar surface in
  about half an hour. At the latter stage of the connectivity change,
  we observed a downward draining of material along the thread bundle
  that had a transverse component of 50 km s<SUP>-1</SUP>. After that,
  the filament body split into two parallel parts, one part erupted
  while the other part remained, and the two-ribbon flare occurred. We
  also found canceling magnetic features in the vicinity of the initial
  location of the thread end, which displayed a flux decrease during the
  Hα connectivity change. Our results show clear and direct evidence
  that magnetic reconnection takes place in the low atmosphere prior to
  eruption. This preeruption reconnection seems to be very different
  from a posteruption coronal reconnection, which is believed to lead
  to a two-ribbon flare.

Title: Dynamics of Quiet Sun Magnetic Fields
Authors: Denker, C.; Spirock, T.; Varsik, J. R.; Chae, J.; Marquette,
   W. H.; Wang, H.; Goode, P. R.
Bibcode: 2001ASPC..236..463D
Altcode: 2001aspt.conf..463D
  No abstract at ADS

Title: Dynamical Characteristics of Small-Scale Hα Upflow Events
    on the Quiet Sun
Authors: Lee, Chik-Yin; Chae, Jongchul; Wang, Haimin
Bibcode: 2000ApJ...545.1124L
Altcode:
  Studies of small-scale dynamical features on the quiet Sun are crucial
  for understanding the energetics and mass supply in the chromosphere
  and corona. Recent works by Wang and coworkers revealed the existence
  of numerous short-lived upflow events in Hα on the quiet Sun. In
  this paper we examine in detail the dynamical characteristics of these
  Hα upflow events based on Hα spectrograph observations and compare
  them with those of elongated dark mottles, which are often considered
  to be the disk counterpart of limb spicules. Our observations were
  performed at the Big Bear Solar Observatory on 1997 August 26 using
  the Littrow Spectrograph on the 65 cm reflector. We repeated drift
  scans of a quiet Sun region, which produced a four-dimensional (x, y,
  t, λ) data array. We examine the spectral, temporal, and morphological
  characteristics of upflow events and determine their physical parameters
  like size, lifetime, birthrate, line-of-sight velocity, Doppler width,
  and optical thickness. Our results show that upflow events appear
  different from dark mottles in that (1) most of the line profiles of
  upflow events show absorption in the blue wing only, while those of
  dark mottles show absorptions in both wings, (2) the typical optical
  thickness of upflow events is smaller than that of dark mottles, and
  (3) unlike dark mottles, upflow events do not have returning flows at
  the same site. We discuss possible physical relationships among upflow
  events, elongated dark mottles, and spicules as observed at the limb.

Title: Steady Flow Model of a Magnetic Flux Tube Constrained to
    Observed Differential Emission Measure
Authors: Bong, Su-Chan; Chae, Jongchul; Yun, Hong Sik
Bibcode: 2000JKAS...33..159B
Altcode:
  We have investigated one dimensional steady flow model of a typical
  magnetic flux tube in the solar transition region constrained
  to observed Differential Emission Measure (DEM) for the average
  quiet-Sun deduced by Raymond &amp; Doyle (1981) with a flux tube
  geometry conforming to Doppler shifts of UV lines measured by Chae,
  Yun &amp; Poland (1998). Because local heating and filling factor in the
  transition region are not well known, we considered two extreme cases,
  one characterized by the filling factor = 1 ("filled-up model") and
  the other set by local heating = 0 ("not-heated model"). We examined
  how much the heating is required for the flux tube by recomputing
  a model through adjustment of the filling factor in such a way that
  "not-heated model" accounts for the observed DEM.

Title: The Magnetic Helicity Sign of Filament Chirality
Authors: Chae, Jongchul
Bibcode: 2000ApJ...540L.115C
Altcode:
  A solar prominence has either dextral or sinistral chirality depending
  on its axial field direction. We determine the magnetic helicity
  sign of filaments using high-resolution observations performed
  by Transition Region And Coronal Explorer. At EUV wavelengths,
  filaments sometimes appear as mixtures of bright threads and dark
  threads. This characteristic has enabled us to discern overlying threads
  and underlying ones and to determine the sign of magnetic helicity
  based on the assumption that the helicity sign of two crossing thread
  segments is the same as that of the filament. Our results support the
  notion that dextral filaments have negative magnetic and that sinistral
  filaments have positive helicity.

Title: High-Resolution Hα Observations of Proper Motion in NOAA 8668:
    Evidence for Filament Mass Injection by Chromospheric Reconnection
Authors: Chae, Jongchul; Denker, Carsten; Spirock, Tom J.; Wang,
   Haimin; Goode, Philip R.
Bibcode: 2000SoPh..195..333C
Altcode:
  There have been two different kinds of explanations for the source
  of cool material in prominences or filaments: coronal condensations
  from above and cool plasma injections from below. In this paper, we
  present observational results which support filament mass injection
  by chromospheric reconnection. The observations of an active filament
  in the active region NOAA 8668 were performed on 17 August 1999 at a
  wavelength of Hα−0.6 Å using the 65 cm vacuum reflector, a Zeiss Hα
  birefringent filter, and a 12-bit SMD digital camera of Big Bear Solar
  Observatory. The best image was selected every 12 s for an hour based
  on a frame selection algorithm. All the images were then co-aligned and
  corrected for local distortion due to the seeing. The time-lapse movie
  of the data shows that the filament was undergoing ceaseless motion. The
  Hα flow field has been determined as a function of time using local
  correlation tracking. Time-averaged flow patterns usually trace local
  magnetic field lines, as inferred from Hα fibrils and line-of-sight
  magnetograms. An interesting finding is a transient flow field in a
  system of small Hα loops, some of which merge into the filament. The
  flow is associated with a cancelling magnetic feature which is located
  at one end of the loop system. Initially a diverging flow with speeds
  below 10 km s<SUP>−1</SUP> is visible at the flux cancellation
  site. The flow is soon directed along the loops and accelerated up
  to 40 km s<SUP>−1</SUP> in a few minutes. Some part of the plasma
  flow then merges into and moves along the filament. This kind of
  transient flow takes place several times during the observations. Our
  results clearly demonstrate that reconnection in the photosphere and
  chromosphere is a likely way to supply cool material to a filament,
  as well as re-organizing the magnetic field configuration, and, hence,
  is important in the formation of filaments.

Title: Extreme-Ultraviolet Flare Loop Emissions in an Eruptive Event
Authors: Qiu, Jiong; Wang, Haimin; Chae, Jongchul; Goode, Philip R.
Bibcode: 2000SoPh..194..269Q
Altcode:
  The TRACE/BBSO joint campaign on 27 September 1998 observed an eruptive
  flare event which lasted for half an hour. The observation covered
  several ultraviolet (UV) and extreme-ultraviolet (EUV) lines and Hα
  center and off-band emissions with very high spatial resolution. We find
  the EUV emissions in different stages of the flare display different
  characteristics. (1) During the `pre-flare' phase, when the SXR output
  was weak, we observed simultaneous impulsive HXR peak at 25-100
  keV and strong EUV emission. (2) In the impulsive phase, when Hα,
  UV and SXR emissions were rising to the maxima, the EUV emission was
  very weak. (3) During the main phase, when SXR emission was decaying,
  a peak in the EUV emission was observed which was substantially delayed
  by 7 min compared to emissions from other wavelengths. Based on our
  observations, we propose that the `pre-flare' phase in this event was
  a separate energy release process rather than a mere pre-cursor of the
  flare, and it is likely that the `pre-flare' EUV emission was due to
  weak in situ heating of low-lying coronal loops. The mechanism of the
  EUV emission in the main phase is investigated. It is suggested that
  the delayed EUV emission may come from cooling of SXR loops.

Title: Orientation of Emerging Bipoles in a Filament Channel
Authors: Chae, J.; Goode, P. R.; Spirock, T. J.; Wang, H.; Martin,
   S. F.; Yun, H. S.; Kim, Jung-Hoon; Lee, Sangwoo
Bibcode: 2000SPD....31.0405C
Altcode: 2000BAAS...32R.835C
  Observations have shown that quiescent prominences or filaments have
  a hemispheric magnetic pattern of chirality or handedness. Motivated
  by the question of whether the filament chirality is of sub-surface
  origin or not, we have studied magnetic bipoles emerging in a quiescent
  filament channel at latitude N45° . During our 5 day observing run
  performed in 1999 October, a huge filament erupted and another began to
  form in the same filament channel. Using high cadence deep line-of-sight
  magnetograms, we identified a total of 102 small emerging bipoles,
  which display the following statistical properties: 1) an average flux
  of 1.2x 10<SUP>19</SUP> Mx and an average separation of 7200 km; 2) an
  inferred global emergence frequency of 600 hr<SUP>-1</SUP> all over the
  solar surface; and 3) a preferred orientation that a negative (trailing)
  pole is located at the south-east of the companion positive (leading)
  pole. The majority of the bipoles appear to be ephemeral regions which
  are systematically smaller than those previously studied with Kitt
  Peak full disk daily magnetograms. The preferred orientation of these
  bipoles differs greatly from both the filament axial field direction
  and the active region polarity law. We conclude that factors other than
  the Hale polarity law are the cause of asymmetry in the orientation of
  small bipoles having total magnetic fluxes below 2 x 10<SUP>19</SUP> Mx.

Title: Observational Evidence for Magnetic Dips in Solar Prominences
Authors: Lee, Sangwoo; Yun, H. S.; Kim, Jung-Hoon; Chae, J.; Goode,
   P. R.; Choe, G. S.
Bibcode: 2000SPD....31.0148L
Altcode: 2000BAAS...32R.809L
  It has been a long-standing mystery in the study of the Sun how cool and
  dense plasma material in prominences can be supported against gravity. A
  common wisdom has been to assume magnetic field configurations with
  magnetic dips which supply an upward magnetic tension. A number of
  proposed theoretical models have regarded magnetic dips as a supporting
  mechanism of the dense plasma material. Nevertheless, the existence
  of magnetic dips in prominences has a scant observational underpinning
  mainly because of the difficulty in determining 3-D magnetic fields in
  prominences. For the first time, we report observational evidence for
  magnetic dips based on the mass motion seen in prominences. We have
  found an oscillatory overshooting out of a prominence body, which is
  very naturally explained as mass motion along dipped magnetic field
  lines sagging under gravity.

Title: A Rapid Magnetic Connectivity Change Observed Before a
    Filament Eruption
Authors: Kim, Jung-Hoon; Yun, H. S.; Lee, Sangwoo; Chae, J.; Goode,
   P. R.
Bibcode: 2000SPD....31.0267K
Altcode: 2000BAAS...32Q.823K
  It has been a mystery what causes a solar prominence eruption. To get an
  insight on this problem, we observed an active region filament eruption
  in Hα lines (line center, +/- 0.5 { Angstroms}) and longitudinal
  magnetograms at Big Bear Solar Observatory. The cadence is about 1
  minute each for Hα and magnetogram. During 8 hours of observing run,
  we covered complete phases of the filament eruption and an associated
  two-ribbon flare. From Hα movies, we found a rapid connectivity
  change in a filament thread before its eruption. The thread was
  initially highly curved. It suddenly became straightened due to the
  rotation of its end. The duration of change was about 30 minutes and
  the rotated thread swept 100{\arcsec}x50{\arcsec} area on the solar
  surface. After this connectivity change, the filament body split into
  two parts, one part erupted, and the two-ribbon flare occurred. Being
  associated with the connectivity change, transverse mass motion of about
  50 km/s was observed in Hα along the newly connected field lines, and
  a cancelling magnetic feature was observed in the vicinity where the
  connectivity changed. Flux cancellation began before the connectivity
  change, and continued while the connectivity change proceeded. Within 2
  hours, the flux decreased by the amount of about 2.0x 10<SUP>20</SUP>
  Mx. These observational results clearly give direct evidence that
  magnetic reconnection takes place prior to eruption. This reconnection
  is distinct from the post-eruption reconnection which is believed to
  lead to the two-ribbon flare.

Title: Active Region Loops Observed with SUMER on Board the SOHO
Authors: Chae, Jongchul; Wang, Haimin; Qiu, Jiong; Goode, Philip R.;
   Wilhelm, Klaus
Bibcode: 2000ApJ...533..535C
Altcode:
  We study the emission and dynamical characteristics of transition region
  temperature plasmas in magnetic loops by analyzing a high-resolution,
  limb observation of the active region NOAA 7962. The observations were
  performed by the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) instrument on board the Solar and Heliospheric Observatory
  (SOHO). The SUMER observation produced a set of raster scans of the
  region, in the four lines, H I Lyβ λ1025, O VI λλ1032, 1038,
  and C II λ1037. The data are used to construct intensity, velocity,
  and line width maps of the active region, from which more than 10
  well-resolved loops are identified and classified into four different
  groups. We determine several physical parameters of the loops in each
  group such as diameter, length, temperature, line-of-sight plasma
  velocity, and nonthermal line broadening. Our results indicate that
  both kinds of temperature variations exist in active region loops:
  variations from loop to loop and variations along each loop. It is
  also found that there is a distinction between stationary loops and
  dynamic loops. The dynamic loops have large bulk motions and large
  nonthermal line broadenings. Some of the dynamic loops display large
  velocity shears with the sign of line-of-sight velocities changing
  across the loop axes. These velocity shears appear to represent
  rotational motions around the loop axes with velocities of up to 50 km
  s<SUP>-1</SUP>. There are indications that nonthermal line broadening
  is the result of magnetohydrodynamic turbulence inside the loops. Based
  on our observations, we postulate that when loops erupt, some of the
  kinetic and magnetic energy cascades down to turbulent energy which
  would be dissipated as heat.

Title: Nonpotential Broadening of UV Lines Observed at the Limb of
    the Quiet Sun
Authors: Lee, Hyunsook; Yun, Hong Sik; Chae, Jongchul
Bibcode: 2000JKAS...33...57L
Altcode:
  We have done a spectroscopic study of the solar transition region
  using high resolution UV &amp; EUV data obtained by SUMER) on board
  SOHO. Optically thin and conspicuous emission lines observed at the
  solar limb are carefully selected to acquire average values of physical
  parameters for the quiet region as a function of radial distance. Our
  main results found from the present study can be summarized as
  follows. 1) Nonthermal velocities estimated from various UV lines
  do not decrease with height at least within one total line intensity
  scale height above the limb. 2) Nonthermal velocity distribution with
  temperature is very similar to that of the disk center, in the sense
  that its peak is located around 2E+5 K, but the value is systematically
  larger than that of the disk. 3) It is found that nonthermal velocity
  is inversely proportional to quadratic root of electron density up to
  about 10 arc seconds above the limb, i.e. ~ Ne**(-1/4), implying that
  the observed nonthermal broadening can be attributed to Alfven waves
  passing through the medium. 4) Electron density estimated from the O
  V 629/760 line ratio is found to range from about 1e+10 cm-3 to 2e+10
  cm-3 in the transition region.

Title: Comparison of Transient Network Brightenings and Explosive
    Events in the Solar Transition Region
Authors: Chae, Jongchul; Wang, Haimin; Goode, Philip R.; Fludra,
   Andrzej; Schühle, Udo
Bibcode: 2000ApJ...528L.119C
Altcode:
  The relation between transient network brightenings, known as blinkers,
  and explosive events is examined based on coordinated quiet Sun
  observations in the transition region line O V λ630 recorded by
  the Coronal Diagnostic Spectrometer (CDS), in the transition region
  line Si IV λ1402 recorded by the Solar Ultraviolet Measurements of
  Emitted Radiation (SUMER) instrument, and in photospheric magnetograms
  taken by the Big Bear Solar Observatory videomagnetograph. From these
  observations, we find that (1) explosive events, which are traditionally
  defined as features with very broad UV line profiles, tend to keep
  away from the centers of network brightenings and are mostly located
  at the edges of such brightenings, (2) CDS blinkers consist of many
  small-scale, short-lived SUMER ``unit brightening events'' with a
  size of a few arcseconds and a lifetime of a few minutes, and most
  importantly (3) each SUMER unit brightening event is characterized by
  a UV line profile that is not as broad as those of explosive events,
  but still has significantly enhanced wings. Our results imply that,
  like explosive events, individual unit brightening events involve high
  velocities, and, hence, blinkers may have the same physical origin
  as explosive events. It is likely that transient network brightenings
  and explosive events are both due to magnetic reconnection--but with
  different magnetic geometries.

Title: Counter-streaming Mass Flow and Transient Brightening in
    Active Region Loops
Authors: Qiu, Jiong; Wang, Haimin; Chae, Jongchul; Goode, Philip R.
Bibcode: 1999SoPh..190..153Q
Altcode:
  An active region loop system was observed in a decaying active region
  for three hours by TRACE and BBSO in a joint campaign on September
  27, 1998. Continuous mass motion was seen in Hα offband filtergrams
  throughout the three hours, and some UV loops were exhibited transient
  brightenings. We find that: (1) cool material was flowing along the
  loops at a speed of at least 20 km s<SUP>−1</SUP>. Further, in Hα red
  and blue wings, we see mass motion along different loops in opposite
  directions. This is the first report of a counter-streaming pattern
  of mass motion in an Hα loop system. (2) Transient brightenings
  of different UV loops at different times were observed at C iv 1550
  Å. These brightened UV loops were located in the same region and at
  the same altitudes as the Hα loops. The observations show a clear
  correlation between the transient brightenings of UV loops and mass
  motion in Hα loops. (3) Both footpoints of the loop system were
  located in regions of mixed magnetic polarities. Frequent micro-flares
  at one footpoint of the loops with small-scale brightenings spreading
  along the loop leg were observed before the brightening and rising
  of one C iv loop. Similar to the case of a filament, the continuous
  mass motion along the loops seems important for maintaining the cool
  Hα loop system at coronal height. There may be an indication that the
  mass motion in cool Hα loops and the correlated transient brightening
  of the active region loops were due to the small-scale chromospheric
  magnetic reconnection at the footpoint regions of the loop system.

Title: Non-Coplanar Magnetic Reconnection as a Magnetic Twist Origin
Authors: Chae, Jongchul
Bibcode: 1999JKAS...32..137C
Altcode:
  Recent studies show the importance of understanding three-dimensional
  magnetic reconnection on the solar surface. For this purpose, I consider
  non-coplanar magnetic reconnection, a simple case of three-dimensional
  reconnection driven by a collision of two straight flux tubes which
  are not on the same plane initially. The relative angle theta between
  the two tubes characterizes such reconnection, and can be regarded
  as a measure of magnetic shear. The observable characteristics of
  non-coplanar reconnection are compared between the two cases of small
  and large angles. An important feature of the non-coplanar reconnection
  is that magnetic twist can be produced via the re-ordering of field
  lines. This is a consequence of the conversion of mutual helicity
  into self helicities by reconnection. It is shown that the principle
  of energy conservation when combined with the production of magnetic
  twist puts a low limit on the relative angle between two flux tubes for
  reconnection to occur. I provide several observations supporting the
  magnetic twist generation by reconnection, and discuss its physical
  implications for the origin of magnetic twist on the solar surface
  and the problem of coronal heating.

Title: Small-Scale Dynamics on the Quiet Sun
Authors: Wang, H.; Chae, J.; Lee, C. -Y.
Bibcode: 1999ESASP.446..695W
Altcode: 1999soho....8..695W
  No abstract at ADS

Title: Studies of Microflares and C5.2 flare of 27 September 1998
Authors: Wang, Haimin; Chae, Jongchul; Qiu, Jiong; Lee, Chik-Yin;
   Goode, Philip R.
Bibcode: 1999SoPh..188..365W
Altcode:
  On 27 September 1998, Big Bear Solar Observatory (BBSO) and Transition
  Region and Coronal Explorer (TRACE) coordinated observations from
  16:00 to 19:00 UT to study properties of microflares in AR NOAA
  No. 8340. Fortuitously, a C5.2 flare occurred at 16:30 UT in this active
  region. Hα and magnetograph movies were obtained at BBSO; C iv 1550
  Å, Fe ix 171 Å, and Fe xii 195 Å movies were obtained by TRACE;
  both with a cadence about 1 min. In this paper, we concentrate on the
  study of magnetic properties of 70 C iv microflares, as well as their
  relationship to the C5.2 flare. We obtained the following results: (1)
  We found two kinds of microflares: microflares of transient brightenings
  with a time scale of 1 to 5 min (impulsive events) and microflares
  lasting half an hour or longer (persistent events). Ninety percent of
  the microflares are impulsive events. Most of the event in this category
  are associated with well defined magnetic neutral lines, but some are
  found in non-neutral line areas. All of seven persistent events are
  found at parasitic magnetic configurations with inclusions of small
  magnetic flux within dominant magnetic flux of opposite polarity. (2)
  More than a third of the impulsive microflares occurred near the C5.2
  flare site indicating that a local instability is responsible for both
  the C5.2 flare and microflares. This indirectly supports the avalanche
  theory of flare energy release, which implies that a big flare may be
  spatially associated with many small flares.

Title: Extreme-Ultraviolet Jets and Hα Surges in Solar Microflares
Authors: Chae, J.; Qiu, J.; Wang, H.; Goode, P. R.
Bibcode: 1999AAS...194.7906C
Altcode: 1999BAAS...31..963C
  We analyzed simultaneous EUV data from the Transition Region And
  Coronal Explorer (TRACE) and Hα data from Big Bear Solar Observatory
  (BBSO). In the active region studied, we found several EUV jets that
  repeatedly occurred where pre-existing magnetic flux was canceled by
  newly emerging flux of opposite polarity. The jets look like, but are
  usually smaller and shorter lived than Yohkoh soft X-ray jets. The EUV
  jets have a typical size of 4000-10,000 km, a transverse velocity of
  50-100 km s(-1) , and a lifetime of 2-4 minutes. Each of the jets was
  ejected from a loop-like bright EUV emission patch at the moment when
  the patch reached its peak emission. We also found dark Hα surges
  that are correlated with these jets. A careful comparison, however,
  revealed that the Hα jets are not cospatial with the EUV jets. Instead,
  the EUV jets are are identified with bright jetlike features in the Hα
  line center, which are distinct from dark surges. Our results support
  a picture in which Hα surges and EUV jets represent different kinds
  of plasma ejection --- cool and hot plasma ejections along different
  field lines --- which must be dynamically connected to each other. We
  emphasize the importance of observed flux cancellation and a small
  erupting filament in understanding the acceleration mechanisms of EUV
  jets and Hα surges. This work is partially supported by NSF under
  grant ATM-97-14796 and NASA under grants NAG5-4919, NAG5-7349, and
  NAG5-7350 to BBSO.

Title: Dynamical Characteristics of Hα Fine Features on the Quiet Sun
Authors: Lee, C. -Y.; Wang, H.; Chae, J.
Bibcode: 1999AAS...194.2306L
Altcode: 1999BAAS...31..861L
  The Littrow spectrograph in the Big Bear Solar Observatory (BBSO) is an
  unique grating system which can produce a 4-dimensional (x,y,lambda ,t)
  data array. We are mainly interested in studying Hα fine features like
  upflow events, spicules/fibrils, and dark grains by means of constructed
  spectroheligrams. We have found from upflow events: (1) The typical
  profile indicates a spectral character in which absorption is only
  observed in the blue wing. (2) The line-center optical thickness
  is lower than that of spicules. (3) The motion has no receding
  phase as seen in Hα as shown by Doppler signals. The lifetime,
  size, and velocity of upflow events are found to be 1.4 minutes,
  2.5 arcsec (FWHM), and 15 km s(-1) respectively. Dark grains may be
  considered to be the least energetic upflow events in the sense that
  its lifetime and size are about half that of upflow events. The total
  birthrate is estimated to be 200 s(-1) , which is about one third of
  that of explosive events. The association of the magnetic origin of
  explosive events has been reported by a previous study on the use of
  BBSO/magnetograms and SOHO/SUMER UV images. The electron temperature
  (10(4) K) and density (10(10) cm(-3) ) of upflow events can easily be
  found. The global particle and kinetic energy flux are determined to be
  10(15) cm(-2) s(-1) and 10(5) ergs cm(-2) s(-1) respectively. Judged by
  the favorable amount of particle flux, we propose a scenario in that
  the predominant downflow observed in UV is due to hot and diffusive
  returning material of Hα upflow events. Comparisons with TRACE/EUV
  images are in process.

Title: Modeling of Solar Transition Region Outflows
Authors: Poland, A. I.; Chae, J.
Bibcode: 1999AAS...194.9312P
Altcode: 1999BAAS...31..990P
  The problem of observing outflow of material from the Sun has been an
  interesting issue in solar physics for several decades. The problem is
  that we know material flows from the Sun since there is a solar wind
  measured at Earth and in interplanetary space. However, observations in
  the chromosphere, transition region, and lower corona show mostly inflow
  with almost no outflow. In a recent paper by Hassler and coworkers it
  was shown that there is a significant outflow at network boundaries
  as seen in NeVIII (Te 800,000K), but no significant outflows have been
  observed at other temperatures. In our earlier work we demonstrated why
  one would expect to see only inflows below 100,000K. The energy balance
  between conduction, radiation, and enthalpy resulted in gradients
  being too steep to observe outflowing material. We have extended that
  work to 1,000,000K and included the observed effects of the spreading
  magnetic field with temperature. These new calculation results seem
  to be in agreement with the observations and indicate that outflows
  should only be observable in the 800,000K range.

Title: Ultraviolet Flare Loop Systems in an Eruptive Event
Authors: Qiu, J.; Wang, H.; Chae, J.; Lee, C.; Goode, P. R.
Bibcode: 1999AAS...194.7904Q
Altcode: 1999BAAS...31..963Q
  The BBSO/TRACE joint campaign on September 27, 1998 observed an
  eruptive flare event which lasted for half an hour. The observation
  covered several ultraviolet lines from transition region and Hα
  line center and off-band emissions from chromosphere with high
  spatial resolution which allows detailed study on the flare plasma
  at wide temperature range. Various flare loop systems are found in
  the active region depicting different scenarios of the event. The
  flare was started by low atmosphere explosive reconnection which
  triggered vehement loop eruption, heating of both large scale and
  low-lying pre-existent loops, and mass ejection of both hot (up to
  10(6) K) and cool (10(4) K) plasmas. Due to reconnection of open field
  lines, new flaring loop archade was formed after the eruption and was
  clearly seen in EUV emissions. From high resolution UV, EUV and Hα
  filtergrams, fine structure of both low-lying and coronal loops can be
  identified. The multi-wavelength observations on this event enable us
  to distinguish different mechanisms of energy transfer in different
  loop systems displaying different radiative and dynamic behaviours,
  and to investigate the early stage of the flare when lower atmosphere
  instability is essential in triggering the major flare and the relation
  between lower and higher atmospheres is complex. This work is supported
  by NSF under grants ATM-9628862 and ATM-9713359, and NASA under grants
  NAG5-5036 and NAG5-7085, and ONR under grant N00014-97-1-1037.

Title: Studies of Microflares and C5.2 Flare of September 27, 1998
Authors: Wang, H.; Qiu, J.; Chae, J.; Lee, C.; Goode, P.
Bibcode: 1999AAS...194.7907W
Altcode: 1999BAAS...31..964W
  On September 27, 1998, Big Bear Solar Observatory (BBSO) and Transition
  Region and Coronal Explorer (TRACE) coordinated observations from
  16:00 to 19:00 UT to study properties of microflares on AR NOAA
  #8340. Fortuitously, a C5.2 flare occurred at 16:30UT in this active
  region. Hα and magnetograph movies were obtained at BBSO; CIV 1550
  Angstroms, FeIX 171 Angstroms, and FeXII 195 Angstroms movies were
  obtained by TRACE; both with a cadence about 1 minute. In this
  paper, we concentrate on the study of magnetic properties of 70
  CIV microflares, as well as their relationship to the C5.2 flare. We
  obtained the following results: (1) We found two kinds of microflares:
  (a) microflares of transient brightenings with a time scale of
  1 to 5 minutes (impulsive events). 90% of the microflares are of
  this form. Most of the events in this category are associated with
  well defined magnetic neutral lines, although a few of them are not
  located near a neutral line; and (b) microflares lasting half an hour
  or longer (persistent events). Seven events in three clusters belong to
  this category. All three sites are associated with a dominant magnetic
  polarity plus a very small element of opposite polarity. (2) More than
  a third of the impulsive microflares occurred near the C5.2 flare site
  indicating that a local instability is responsible for both the C5.2
  flare and microflares. This indirectly support the avalanche theory of
  flare energy release, which predicts that a big flare may be associated
  with many small flares. Based on the morphologies of those events, we
  postulate that the persistent events may be due to loop interaction;
  while impulsive events may be associated with sheared loop structure.

Title: Extreme-Ultraviolet Jets and Hα Surges in Solar Microflares
Authors: Chae, Jongchul; Qiu, Jiong; Wang, Haimin; Goode, Philip R.
Bibcode: 1999ApJ...513L..75C
Altcode:
  We analyzed simultaneous EUV data from the Transition Region and Coronal
  Explorer and Hα data from Big Bear Solar Observatory. In the active
  region studied, we found several EUV jets that repeatedly occurred where
  pre-existing magnetic flux was ``canceled'' by newly emerging flux of
  opposite polarity. The jets look like Yohkoh soft X-ray jets, but are
  smaller and shorter lived than X-ray jets. They have a typical size
  of 4000-10,000 km, a transverse velocity of 50-100 km s<SUP>-1</SUP>,
  and a lifetime of 2-4 minutes. Each of the jets was ejected from a
  looplike bright EUV emission patch at the moment that the patch reached
  its peak emission. We also found dark Hα surges that are correlated
  with these jets. A careful comparison, however, revealed that the Hα
  surges are not cospatial with the EUV jets. Instead, the EUV jets are
  identified with bright jetlike features in the Hα line center. Our
  results support a picture in which Hα surges and EUV jets represent
  different kinds of plasma ejection--cool and hot plasma ejections along
  different field lines--which must be dynamically connected to each
  other. We emphasize the importance of observed flux cancellation and
  a small erupting filament in understanding the acceleration mechanisms
  of EUV jets and Hα surges.

Title: Evidence for non-potential magnetic fields in the quiet Sun
Authors: Woodard, M. F.; Chae, Jongchul
Bibcode: 1999SoPh..184..239W
Altcode:
  A comparison of BBSO Hα centerline filtergrams and videomagnetograms
  was made to investigate the existence of non- potential magnetic fields
  in the quiet Sun near magnetic network. We use the fibril structure
  in the Hα images as a proxy for the horizontal chromospheric magnetic
  field which we compare with the horizontal field obtained by potential
  extrapolation of the observed, line-of-sight photospheric field. The
  quiet-Sun field was found to be consistently and significantly
  non-potential in each of the three fields of view studied. A
  transient extreme ultraviolet (EUV) brightening, known as a blinker,
  occurred during the observations of a region where the field is highly
  non-potential, suggesting a connection between magnetic reconnection
  and non-potentiality.

Title: Small-Scale Magnetic Reconnection in the Quiet Sun
Authors: Chae, J.
Bibcode: 1999ASPC..183..375C
Altcode: 1999hrsp.conf..375C
  No abstract at ADS

Title: Stray-Light Effect on Magnetograph Observations
Authors: Chae, Jongchul; Yun, Hong Sik; Sakurai, Takashi; Ichimoto,
   Kiyoshi
Bibcode: 1998SoPh..183..229C
Altcode:
  To examine the stray-light effect in magnetograph observations, we
  have determined the point spread functions of the vector magnetograph
  mounted on the Japanese Solar Flare Telescope based on two indirect
  methods, one analyzing the solar limb intensity profile, and the
  other using the Fourier power spectra of photospheric intensity
  distributions. Point spread functions consist of two parts: a blurring
  part which describes seeing and small-spread-angle stray light, and
  a scattering part which describes large-spread-angle stray light. The
  FWHM spatial resolution is typically 3.0'', and the amount of scattered
  light is about 15% on clear days. We find that the blurring part is
  well described by a Moffat function whose Fourier transform is given
  by an exponential function. Our results indicate that polarization
  measurements of low-intensity magnetic elements like sunspots may be
  significantly underestimated due to the large-spread-angle stray light,
  and polarization measurements of magnetic elements which are smaller
  than 5-7'' appear to be disturbed by small-spread-angle stray light.

Title: Stray-light correction in magnetograph observations using
    the maximum entropy method
Authors: Chae, Jongchul; Yun, Hong Sik; Sakurai, Takashi; Ichimoto,
   Kiyoshi
Bibcode: 1998SoPh..183..245C
Altcode:
  We have developed a method of stray-light correction which is applicable
  to filter-based magnetograph observations. Stray-light-corrected Stokes
  images are obtained by performing the deconvolution of observed Stokes
  images by the point spread function which is determined from the Stokes
  I image. For image deconvolution, the maximum entropy principle is
  used to guarantee that intensity should be positive and polarization
  degrees should be less than unity. We present an iterative algorithm
  for the maximum entropy method, which seeks the solution in Fourier
  space and thus accomplishes fast convergence. We find that our method
  is effective in correcting stray light which has a spread angle greater
  than the full width at half maximum of the point spread function. We
  also discuss the effect of stray light on magnetograph calibration.

Title: Comparison of Prominences in Hα and He II 304 Å
Authors: Wang, Haimin; Chae, Jongchul; Gurman, Joseph B.; Kucera,
   Therese A.
Bibcode: 1998SoPh..183...91W
Altcode:
  In this letter, we bring attention to prominences which show different
  morphology in Hα and He ii 304 Å, as observed simultaneously by
  BBSO and EIT on board SOHO. Those two lines have been thought to
  represent similar chromospheric structures although they are formed at
  significantly different temperatures. We give two examples representing
  two kinds of anomaly: (1) prominences showing strong Hα emissions in
  the lower part and strong He ii emissions in the upper part, and (2)
  erupting prominences showing extensive He ii emission, but nothing in
  Hα. Our results indicate that a part or the whole of a prominence may
  be too hot to emit Hα radiation, possibly due to heating or thermal
  instability. Please note that these are not just two isolated cases,
  many other prominences show the similar differences in Hα and He ii
  304 Å.

Title: SUMER Measurements of Nonthermal Motions: Constraints on
    Coronal Heating Mechanisms
Authors: Chae, Jongchul; Schühle, Udo; Lemaire, Philippe
Bibcode: 1998ApJ...505..957C
Altcode:
  We have determined nonthermal velocities in the quiet Sun at
  temperatures between 10<SUP>4</SUP> K and 2 × 10<SUP>6</SUP> K by
  measuring the widths of a number of EUV and far-ultraviolet (FUV)
  lines taken with SUMER on board the SOHO spacecraft. The broadenings
  owing to the SUMER instrument and the finite opacity in each line
  have been carefully examined. The nonthermal velocity at temperatures
  below 2 × 10<SUP>4</SUP> K is smaller than 10 km s<SUP>-1</SUP>. The
  velocity increases with temperature, reaches a peak value of 30
  km s<SUP>-1</SUP> around 3 × 10<SUP>5</SUP> K, and then decreases
  with the temperature. The coronal nonthermal velocity is about 20 km
  s<SUP>-1</SUP>. There exists a strong correlation between intensity
  and nonthermal velocity at temperatures 2 × 10<SUP>4</SUP>-1 ×
  10<SUP>5</SUP> K. The correlation at higher temperatures weakens as
  temperature increases. Furthermore, there is a spatial correlation
  between the nonthermal velocities inferred from a set of any two lines
  with temperatures below 2 × 10<SUP>5</SUP> K. Neither significant
  center-to-limb variation nor meaningful dependence on the integration
  time was found from the measured nonthermal velocities. We have
  discovered the existence of high-velocity components in the observed
  S VI λ933.4 line profiles. The average nonthermal velocity and
  intensity fraction of this S VI line high-velocity component are found
  to be 55 km s<SUP>-1</SUP> and 0.25, respectively. <P />Observational
  characteristics of nonthermal motions carry some problems that should be
  solved when interpreting observed nonthermal motions in terms of either
  unresolved loop flows or Alfvén waves. The isotropic and very small
  scale nature of the observed nonthermal motions appears to be suited to
  the MHD turbulence interpretation of nonthermal motions. The turbulent
  heating rates inferred from the measured nonthermal motions can account
  for the radiative loss throughout the transition region and corona if
  the nonthermal motions are truly turbulent motions whose mechanical
  energy is injected at a scale of 1000 km (Kolmogorov-type turbulence)
  or 15 km (Kraichnan-type turbulence). The existence of high-velocity
  components at temperatures 6 × 10<SUP>4</SUP>-2 × 10<SUP>5</SUP>
  K appears as observational evidence supporting nanoflare heating at
  these temperatures.

Title: Chromospheric Upflow Events Associated with Transition Region
    Explosive Events
Authors: Chae, Jongchul; Wang, Haimin; Lee, Chik-Yin; Goode, Philip
   R.; Schühle, Udo
Bibcode: 1998ApJ...504L.123C
Altcode:
  Transition region explosive events are considered to be a manifestation
  of small-scale magnetic reconnection ubiquitously occurring--even in
  the quiet Sun. In this paper, we report a close association between
  transition region explosive events and chromospheric upflow events seen
  in Hα. From a comparison of the Big Bear Solar Observatory (BBSO)
  Hα spectrograph data and the Solar and Heliospheric Observatory
  (SOHO) / Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  data, we found a succession of chromospheric upflow events at sites
  where repeated explosive events occurred. Individual chromospheric
  events appear as compact dark features that are best visible in
  Hα-0.5 Å and that have a size of 2"-3" and a lifetime of 1-2
  minutes. They are characterized by an upward motion of 15-30 km
  s<SUP>-1</SUP>, a temperature of 10<SUP>4</SUP> K, a mass density
  of 1×10<SUP>-13</SUP> g, and a nonthermal velocity less than 10
  km s<SUP>-1</SUP>. Unlike spicules, which display descending motion
  following their ascending phase, these upflow events are not followed
  by noticeable redshifts. ``Hα jets'' at -1.0 Å studied by Wang et
  al. appear to be a special case of this kind of chromospheric upflow
  event. The physical characteristics of chromospheric upflow events and
  their close association with transition region explosive events suggest
  that chromospheric upflow events may be the manifestation of cool plasma
  material flowing into magnetically diffusive regions, while explosive
  events represent hot plasma material flowing out of the same regions.

Title: Photospheric Magnetic Field Changes Associated with Transition
    Region Explosive Events
Authors: Chae, Jongchul; Wang, Haimin; Lee, Chik-Yin; Goode, Philip
   R.; Schühle, Udo
Bibcode: 1998ApJ...497L.109C
Altcode:
  From a comparison of the Solar and Heliospheric Observatory SUMER
  spectral data and a time series of Big Bear Solar Observatory
  magnetograms, we present observational clues to the physical origin of
  transition region explosive events. First, explosive events rarely occur
  in the interior of strong magnetic flux concentrations but rather are
  preferentially found in regions with weak and mixed polarity fluxes that
  display magnetic neutral lines. Second, the majority of explosive events
  happen during the ``cancellation'' of photospheric magnetic flux. Third,
  there is a strong tendency for explosive events to occur repeatedly, as
  bursts, while local photospheric magnetic flux continuously decreases
  because of cancellation. These results strongly support the idea that
  transition region explosive events are a manifestation of magnetic
  reconnection occurring in the quiet Sun. Furthermore, one may infer from
  the third result that the explosive events represent repetitive fast
  magnetic reconnections in the transition region, which are initiated
  by slow magnetic reconnections occurring beneath.

Title: Dynamical Characteristics of the Quiet Transition Region:
    Spatial Correlation Studies of H I 931 and S VI 933 UV Lines
Authors: Yun, Hong Sik; Chae, Jong Chul; Poland, A. J.
Bibcode: 1998JKAS...31....1Y
Altcode:
  To understand the basic physics underlying large spatial fluctuations
  of intensity and Doppler shift, we have investigated the dynamical
  charctersitics of the transition region of the quiet sun by analyzing
  a raster scan of high resolution UV spectral band containing H
  Lyman lines and a S VI line. The spectra were taken from a quiet
  area of 100" X 100" located near the disk center by SUMER on board
  SOHO. The spectral band ranges from 906 A to 950 A with spatial and
  spectral resolution of 1" and 0.044 A, respectively. The parameters of
  individual spectral lines were determined from a single Gaussian fit
  to each spectral line. Then, spatial correlation analyses have been
  made among the line parameters. Important findings emerged from the
  present analysis are as follows. (1) The integrated intensity maps of
  the observed area of H I 931 line (1 X 10^4 K) and S VI 933 line (2 X
  10^5 K) look very similar to each other with the same characterstic
  size of 5". An important difference, however, is that the intensity
  ratio of brighter network regions to darker cell regions is much
  larger in S VI 933 line than that in H I 931 line. (2) Dynamical
  features represented by Doppler shifts and line widths are smaller
  than those features seen in intensity maps. The features are found
  to be changing rapidly with time within a time scale shorter than the
  integration time, 110 seconds, while the intensity structure remains
  nearly unchanged during the same time interval. (3) The line intensity
  of S VI is quite strongly correlated with that of H I lines, but the
  Doppler shift correlation between the two lines is not as strong as
  the intensity correlation. The correlation length of the intensity
  structure is found to be about 5.7"(4100 km), which is at least 3 times
  larger than that of the velocity structure. These findings support the
  notion that the basic unit of the transition region of the quiet sun
  is a loop-like structure with a size of a few 10^3 km, within which
  a number of unresolved smaller velocity structures are present.

Title: Temperature Dependence of Ultraviolet Line Average Doppler
    Shifts in the Quiet Sun
Authors: Chae, J.; Yun, H. S.; Poland, A. I.
Bibcode: 1998ApJS..114..151C
Altcode:
  The existence of prevailing redshifts in the UV lines formed in the
  solar transition region raises an important question concerning its
  physical origin and its role in the mass and energy balance of the
  outer solar atmosphere. A series of UV spectral lines observed by
  SUMER has been analyzed to obtain the spatial average of Doppler
  shifts in the quiet Sun as a function of temperature. The UV lines
  used for the analysis cover temperatures ranging from 10<SUP>4</SUP>
  to 10<SUP>6</SUP> K. The wavelength calibration has been done in
  reference to the coolest chromospheric lines such as neutral lines
  of silicon and sulfur. The positioning of the line center in blended
  lines has been made by employing a constrained multi-Gaussian fitting
  technique. The error in the measured average of the Doppler shifts is
  estimated to be smaller than 1 km s<SUP>-1</SUP>. <P />Our results show
  that the average Doppler shift at the base of the transition region is
  about 1-2 km s<SUP>-1</SUP>, increasing with temperature with a peak
  value of 11 km s<SUP>-1</SUP> near T = 2.3 × 10<SUP>5</SUP> K. Then
  it decreases but remains still above zero (5 km s<SUP>-1</SUP> in
  Ne VIII lines and 4 km s<SUP>-1</SUP> in Mg X lines). We find that
  this behavior can be explained by the dominance of emission from
  plasma flowing downward from the upper hot region to the lower cool
  region along flux tubes with varying cross section. Assuming that
  pressure and mass flux are constant along a flux tube, the cross
  section of a typical flux tube has been estimated as a function of
  temperature. It turns out that the cross section is nearly constant
  below T = 10<SUP>5</SUP> K and then expands by a factor of about 30 at
  T = 10<SUP>6</SUP> K. This behavior is fairly well represented by an
  analytical functional form, A(T)/A(T<SUB>h</SUB>) = [1 + (Γ<SUP>2</SUP>
  - 1)(T/T<SUB>h</SUB>)<SUP>ν</SUP>]<SUP>1/2</SUP>/Γ with parameters
  of T<SUB>h</SUB> = 10<SUP>6</SUP> K, Γ = 30, and ν = 3.6.

Title: Effects of Non-LTE Radiative Loss and Partial Ionization on
    the Structure of the Transition Region
Authors: Chae, J.; Yun, H. S.; Poland, A. I.
Bibcode: 1997ApJ...480..817C
Altcode:
  In this paper we address the question of how non-LTE radiative losses
  with partial ionization of hydrogen and helium affects the energetics
  and structure of the solar transition region. To accomplish this we
  have constructed theoretical models of a thin rigid magnetic flux
  tube with a steady material flow, which is embedded vertically in
  the solar atmosphere. These models include the effects of material
  flow, conduction, non-LTE radiative transfer in H and He, and partial
  ionization. We find from this study that the effect of non-LTE radiative
  transfer with partial ionization is significant near the base of the
  transition region at temperatures less than 2.5 × 10<SUP>4</SUP>
  K. This leads to a 1 order of magnitude increase in the differential
  emission measure in comparison with the optically thin approximation
  with complete ionization in the low (less than 2.5 × 10<SUP>4</SUP> K)
  temperature regime. Above this region the non-LTE and opacity effects
  are small. In the upflow case the conductive and convective energy
  processes dominate to such a large extent that non-LTE radiative
  process and partial ionization are not important. <P />In this work
  we also confirm the previous work of other authors who provided the
  explanation for why downflowing transition region material is much
  more visible than upflowing material. We present the results in a
  manner that gives a good physical understanding as to why this occurs.

Title: Power Spectra of Solar Network and Non-Network Fields
Authors: Lee, Jeongwoo; Chae, J. -C.; Yun, H. S.; Zirin, H.
Bibcode: 1997SoPh..171..269L
Altcode: 1997SoPh..171..269J
  We report new properties of solar magnetic fields in a quiet region
  as found from their magnetic power spectra. The power spectra of
  network and intranetwork fields (non-network fields) are separately
  calculated from a Big Bear magnetogram obtained with moderately high
  spatial resolution of 1.5 arc sec and a high sensitivity reaching 2
  Mx cm<SUP>-2</SUP>. The effect of seeing on the power spectrum has
  been corrected using Fried's (1966) Modulation Transfer Function
  with the seeing parameter determined in our previous analysis of
  the magnetogram. As a result, it is found that the two-dimensional
  power spectra of network and non-network fields appear in a form: Γ(
  ≲ ≲ <SUB>1</SUB>) ∼ <SUP>-1</SUP> and Γ( ≳ <SUB>1</SUB>)
  ∼ <SUP>-3.5</SUP>. Here <SUB>0</SUB> ≈ 0.47 Mm<SUP>-1</SUP>
  for network fields and <SUB>0</SUB> ≈ 0.69 Mm<SUP>-1</SUP> for
  non-network fields, the latter of which corresponds to the size
  of mesogranulation; <SUB>1</SUB> ≈ 3.0 Mm<SUP>-1</SUP> for both,
  which is about the size of a large granule. The network field spectrum
  below <SUB>0</SUB> appears nearly flat, whereas that of non-network
  fields instead decreases towards lower wave numbers as Γ( ) ∼
  <SUP>1.3</SUP>. The turnover behavior of magnetic field spectra around
  <SUB>1</SUB> coincides with that found for the velocity power spectrum,
  which may justify the kinetic approach taken in previous theoretical
  studies of the solar magnetic power spectra.

Title: The Effect of Seeing on Solar Magnetic Flux Measurements
Authors: Lee, Jeongwoo; Chae, J. -C.; Yun, H. S.; Zirin, H.
Bibcode: 1997SoPh..171...35L
Altcode: 1997SoPh..171...35J
  We investigate the influence of seeing upon measurement of magnetic flux
  of photospheric fields. For this purpose we quantify seeing variation
  in one day's observation at Big Bear Solar Observatory in terms of
  the Fried function, a Modulation Transfer Function for the atmospheric
  seeing. The temporal variation of seeing quality is compared with that
  of magnetic flux measured in a quiet region with size 5' × 4' near
  the solar disk center. A good correlation is found between the seeing
  change and apparent evolution of magnetic flux values, implying, as a
  possibility, that magnetic flux measurement might have been modulated
  by seeing. Based on a simple model of ensembles of Gaussian magnetic
  elements we argue that even the net flux as well as the total flux
  can change due to seeing variation if the magnetograph has a finite
  detection threshold and if the intrinsic fluxes in one and the other
  polarities are unbalanced.

