Author name code: brajsa
ADS astronomy entries on 2022-09-14
author:"Brajsa, Roman" 
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Title: The quiet Sun at mm Wavelengths as Seen by ALMA
Authors: Alissandrakis, Costas; Bastian, Timothy; Brajša, Roman
Bibcode: 2022arXiv220902569A
Altcode:
  Solar observations at sub-mm, mm and cm wavelengths offer a
  straightforward diagnostic of physical conditions in the solar
  atmosphere because they yield measurement of brightness temperature
  which, for optically thick features, equals intrinsic temperature -
  much unlike solar diagnostics in other spectral ranges. The Atacama
  Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a
  new, hitherto underexplored, spectral window for studying the enigmatic
  solar chromosphere. In this review we discuss initial ALMA studies of
  the quiet chromosphere that used both single-dish and compact-array
  interferometric observing modes. We present results on the temperature
  structure of the chromosphere, comparison with classic empirical models
  of the chromosphere, and observations of the chromospheric network and
  spicules. Furthermore, we discuss what may be expected in the future,
  since the ALMA capabilities continuously expand and improve towards
  higher angular resolution, wavelength coverage, and polarization
  measurement for magnetometry.

Title: Variation in solar differential rotation and activity in the
    period 1964-2016 determined by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Jurkić, T.;
   Brajša, R.; Skokić, I.; Sudar, D.; Ruždjak, D.; Hržina, D.;
   Pötzi, W.; Hanslmeier, A.; Veronig, A. M.
Bibcode: 2022A&A...663A..24P
Altcode: 2022arXiv220407396P
  <BR /> Aims: Theoretical calculations predict an increased equatorial
  rotation and more pronounced differential rotation (DR) during
  the minimum of solar magnetic activity. However, the results of
  observational studies vary, some showing less and some more pronounced
  DR during the minimum of solar magnetic activity. Our study aims to gain
  more insight into these discrepancies. <BR /> Methods: We determined
  the DR parameters A and B (corresponding to the equatorial rotation
  velocity and the gradient of the solar DR, respectively) by tracing
  sunspot groups in sunspot drawings of the Kanzelhöhe Observatory
  for Solar and Environmental Research (KSO; 1964-2008, for solar
  cycles 20-23) and KSO white-light images (2009-2016, for solar cycle
  24). We used different statistical methods and approaches to analyse
  variations in DR parameters related to the cycle and to the phase of
  the solar cycle, together with long-term related variations. <BR />
  Results: The comparison of the DR parameters for individual cycles
  obtained from the KSO and from other sources yield statistically
  insignificant differences for the years after 1980, meaning that the
  KSO sunspot group data set is well suited for long-term cycle to cycle
  studies. The DR parameters A and B show statistically significant
  periodic variability. The periodicity corresponds to the solar cycle
  and is correlated with the solar activity. The changes in A related
  to solar cycle phase are in accordance with previously reported
  theoretical and experimental results (higher A during solar minimum,
  lower A during the maximum of activity), while changes in B differ
  from the theoretical predictions as we observe more negative values
  of B, that is, a more pronounced differential rotation during activity
  maximum. The main result of this paper for the long-term variations in
  A is the detection of a phase shift between the activity flip (in the
  1970s) and the equatorial rotation velocity flip (in the early 1990s),
  during which both A and activity show a secular decreasing trend. This
  indicates that the two quantities are correlated in between 1970 and
  1990. Therefore, the theoretical model fails in the phase-shift time
  period that occurs after the modern Gleissberg maximum, while in the
  time period thereafter (after the 1990s), theoretical and experimental
  results are consistent. The long-term variations in B in general yield
  an anticorrelation of B and activity, as a rise of B is observed during
  the entire time period (1964-2016) we analysed, during which activity
  decreased, with the exception of the end of solar cycle 22 and the
  beginning of solar cycle 23. <BR /> Conclusions: We study for the first
  time the variation in solar DR and activity based on 53 years of KSO
  data. Our results agree well with the results related to the solar cycle
  phase from corona observations. The disagreement of the observational
  results for B and theoretical studies may be due to the fact that we
  analysed the period immediately after the modern Gleissberg maximum,
  where for the phase-shift period, A versus activity also entails a
  result that differs from theoretical predictions. Therefore, studies
  of rotation versus activity with data sets encompassing the Gleissberg
  extremes should include separate analyses of the parts of the data set
  in between different flips (e.g., before the activity flip, between
  the activity and the rotation flip, and after the rotation flip).

Title: A Genetic Algorithm to Model Solar Radio Active Regions From
    3D Magnetic Field Extrapolations
Authors: de Oliveira e Silva, Alexandre José; Selhorst, Caius Lucius;
   Costa, Joaquim E. R.; Simões, Paulo J. A.; Giménez de Castro,
   Carlos Guillermo; Wedemeyer, Sven; White, Stephen M.; Brajša, Roman;
   Valio, Adriana
Bibcode: 2022FrASS...9.1118D
Altcode: 2022arXiv220503385S; 2022arXiv220503385J
  In recent decades our understanding of solar active regions (ARs)
  has improved substantially due to observations made with better
  angular resolution and wider spectral coverage. While prior AR
  observations have shown that these structures were always brighter
  than the quiet Sun at centimeter wavelengths, recent observations
  at millimeter and submillimeter wavelengths have shown ARs with well
  defined dark umbrae. Given this new information, it is now necessary to
  update our understanding and models of the solar atmosphere in active
  regions. In this work, we present a data-constrained model of the AR
  solar atmosphere, in which we use brightness temperature measurements
  of NOAA 12470 at three radio frequencies: 17, 100 and 230 GHz. The
  observations at 17 GHz were made by the Nobeyama Radioheliograph (NoRH),
  while the observations at 100 and 230 GHz were obtained by the Atacama
  Large Millimeter/submillimeter Array (ALMA). Based on our model, which
  assumes that the radio emission originates from thermal free-free and
  gyroresonance processes, we calculate radio brightness temperature
  maps that can be compared with the observations. The magnetic field at
  distinct atmospheric heights was determined in our modelling process by
  force-free field extrapolation using photospheric magnetograms taken by
  the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
  Observatory (SDO). In order to determine the best plasma temperature
  and density height profiles necessary to match the observations,
  the model uses a genetic algorithm that modifies a standard quiet Sun
  atmospheric model. Our results show that the height of the transition
  region (TR) of the modelled atmosphere varies with the type of region
  being modelled: for umbrae the TR is located at 1080 ± 20 km above
  the solar surface; for penumbrae, the TR is located at 1800 ± 50 km;
  and for bright regions outside sunspots, the TR is located at 2000 ±
  100 km. With these results, we find good agreement with the observed
  AR brightness temperature maps. Our modelled AR can be used to estimate
  the emission at frequencies without observational coverage.

Title: The Solar Activity Monitor Network - SAMNet
Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang,
   Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.;
   Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša,
   Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez,
   Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.;
   Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu,
   Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer,
   James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen,
   Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz,
   Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili,
   Teimuraz; Zuccarello, Francesca
Bibcode: 2022JSWSC..12....2E
Altcode:
  The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a
  future UK-led international network of ground-based solar telescope
  stations. SAMNet, at its full capacity, will continuously monitor
  the Sun's intensity, magnetic, and Doppler velocity fields at
  multiple heights in the solar atmosphere (from photosphere to upper
  chromosphere). Each SAMM sentinel will be equipped with a cluster of
  identical telescopes each with a different magneto-optical filter (MOFs)
  to take observations in K I, Na D, and Ca I spectral bands. A subset
  of SAMM stations will have white-light coronagraphs and emission line
  coronal spectropolarimeters. The objectives of SAMNet are to provide
  observational data for space weather research and forecast. The goal
  is to achieve an operationally sufficient lead time of e.g., flare
  warning of 2-8 h and provide many sought-after continuous synoptic
  maps (e.g., LoS magnetic and velocity fields, intensity) of the lower
  solar atmosphere with a spatial resolution limited only by seeing or
  diffraction limit, and with a cadence of 10 min. The individual SAMM
  sentinels will be connected to their master HQ hub where data received
  from all the slave stations will be automatically processed and flare
  warning issued up to 26 h in advance.

Title: A prediction for the 25th solar cycle maximum amplitude
Authors: Brajša, Roman; Verbanac, Giuli; Bandić, Mario; Hanslmeier,
   Arnold; Skokić, Ivica; Sudar, Davor
Bibcode: 2022AN....34313960B
Altcode: 2022arXiv220311293B
  The minimum-maximum method, belonging to the precursor class of the
  solar activity forecasting methods, is based on a linear relationship
  between relative sunspot number in the minimum and maximum epochs of
  solar cycles. In the present analysis, we apply a modified version of
  this method using data not only from the minimum year, but also from
  a couple of years before and after the minimum. The revised 13-month
  smoothed monthly total sunspot number data set from Sunspot Index and
  Long-term Solar Observations/SIDC is used. Using data for solar cycle
  nos. 1-24 the largest correlation coefficient (CC) is obtained when
  correlating activity level 3 years before solar cycle minimum with the
  subsequent maximum (CC=0.82), independent of inclusion or exclusion
  of the solar cycle no. 19. For the next solar maximum of the cycle
  no. 25, we predict: Rmax=121±33. Our results indicate that the next
  solar maximum (of the cycle no. 25) will be of the similar amplitude
  as the previous one, or even something lower. This is in accordance
  with the general middle-term lowering of the solar activity after the
  secular maximum in the 20th century and consistent with the Gleissberg
  period of the solar activity. The reliability of the "3 years before
  the minimum" predictor is experimentally justified by the largest CC
  and verified with the Student t-test. It is satisfactorily explained
  with the two empirical well-known findings: the extended solar cycle
  and the Waldmeier effect. Finally, we successfully reproduced the
  maxima of the last four solar cycles, nos. 21-25, using the 3 years
  before the minimum method.

Title: On the Determination of the Solar Rotation Elements i, {\Omega}
    and Period using Sunspot Observations by Ruđer Bošković in 1777
Authors: Husak, Mirko; Brajša, Roman; Špoljarić, Dragan
Bibcode: 2022arXiv220302289H
Altcode:
  In September 1777, Ruđer Bošković observed sunspots for
  six days. Based on these measurements, he used his own methods to
  calculate the elements of the solar rotation, the longitude of the
  node, the inclination of the solar equator and the period. He published
  a description of the methods, the method of observation and detailed
  instructions for calculations in the second chapter of the fifth part of
  the Opera in 1785. In this paper, Bošković original calculations and
  repeated calculations by his procedure are published. By analysing the
  input quantities, procedures, and results, the input quantities of the
  error, and the calculation results are discussed. The reproduction of
  Bošković calculations is successfully reproduced and we obtained very
  similar results. The conclusion proposes a relationship of Bošković
  research with modern astronomy.

Title: Solar rotation elements $i, \Omega$ and period determined
    using sunspot observations by Ruđer Bošković in 1777
Authors: Husak, M.; Brajša, R.; ŠPoljarić, D.
Bibcode: 2022arXiv220311745H
Altcode:
  Ruđer Bošković developed methods for determination of solar
  rotation elements: the solar equator inclination i, the longitude
  of the node {\Omega} and the period of solar rotation. In his last
  work Opera pertinentia ad opticam et astronomiam, published in 1785,
  in the chapter Opuscule II he described his methods, the formulae
  with figure descriptions and an example for calculation of the solar
  rotation elements with detailed numerical explanation using his own
  observations performed in September 1777. The original numerical
  procedure was performed using logarithmic formulae. In present work
  we give a description of the original results of R. Bošković and
  compare them with our recalculated values.

Title: Determination of the Solar Rotation Elements and Period from
    Ruđer Bo\vsković's Sunspot Observations in 1777
Authors: Roša, D.; Hržina, D.; Husak, M.; Brajša, R.; Špoljarić,
   D.; Skokić, I.; Maričić, D.; Šterc, F.; Romštajn, I.
Bibcode: 2021simi.conf...86R
Altcode:
  This paper focuses on the observations of sunspots made by Ruđer
  Bo\vsković in 1777. We derived the expressions needed to calculate
  the elements of the Sun's rotation and period from observations. We
  used modern ephemeris data in the processing of the observation
  results. Obtained results are very similar to Bo\vsković's original
  calculations. In addition to historical significance, they also provide
  scientifically valuable data on the Sun's differential rotation,
  which plays a significant role in generating and maintaining solar
  magnetic activity.

Title: ALMA small-scale features in the quiet Sun and active regions
Authors: Brajša, R.; Skokić, I.; Sudar, D.; Benz, A. O.; Krucker,
   S.; Ludwig, H. -G.; Saar, S. H.; Selhorst, C. L.
Bibcode: 2021A&A...651A...6B
Altcode: 2021arXiv210503644B
  <BR /> Aims: The main aim of the present analysis is to decipher (i)
  the small-scale bright features in solar images of the quiet Sun and
  active regions obtained with the Atacama Large Millimeter/submillimeter
  Array (ALMA) and (ii) the ALMA correspondence of various known
  chromospheric structures visible in the Hα images of the Sun. <BR
  /> Methods: Small-scale ALMA bright features in the quiet Sun region
  were analyzed using single-dish ALMA observations (1.21 mm, 248 GHz)
  and in an active region using interferometric ALMA measurements (3
  mm, 100 GHz). With the single-dish observations, a full-disk solar
  image is produced, while interferometric measurements enable the
  high-resolution reconstruction of part of the solar disk, including
  the active region. The selected quiet Sun and active regions are
  compared with the Hα (core and wing sum), EUV, and soft X-ray images
  and with the magnetograms. <BR /> Results: In the quiet Sun region,
  enhanced emission seen in the ALMA is almost always associated with a
  strong line-of-sight magnetic field. Four coronal bright points were
  identified, while other small-scale ALMA bright features are most likely
  associated with magnetic network elements and plages. In the active
  region, in 14 small-scale ALMA bright features randomly selected and
  compared with other images, we found five good candidates for coronal
  bright points, two for plages, and five for fibrils. Two unclear cases
  remain: a fibril or a jet, and a coronal bright point or a plage. A
  comparison of the Hα core image and the 3 mm ALMA image of the analyzed
  active region showed that the sunspot appears dark in both images
  (with a local ALMA radiation enhancement in sunspot umbra), the four
  plage areas are bright in both images and dark small Hα filaments are
  clearly recognized as dark structures of the same shape also in ALMA.

Title: Magnetic structure above solar active regions
Authors: Brajša, R.; Skokić, I.; Sudar, D.
Bibcode: 2020CEAB...44....1B
Altcode:
  ALMA images of the whole solar disk (single-dish measurements, 248
  GHz, $\lambda = 1.21$ mm) and of an active region (interferometric
  measurements, 100 GHz, $\lambda$ = 3.0 mm) are compared with LOS
  photospheric magnetograms and potential field source surface model of
  extrapolated magnetic field in the solar chromosphere and corona. While
  a general magnetic structure is consistent with ALMA observations,
  a detailed analysis and comparison with ALMA small-scale features is
  not possible with the model used and requires a more detailed magnetic
  field extrapolation model, which is left for a future work.

Title: Correlation between the solar magnetic field strength and
    the millimeter brightness temperature
Authors: Skokić, I.; Sudar, D.; Brajša, R.
Bibcode: 2020CEAB...44....2S
Altcode: 2022arXiv220311747S
  Images of the Sun at millimeter wavelengths obtained by ALMA show
  a significant correspondence with the magnetograms. In this paper,
  we investigate this correspondence by comparing ALMA full-disk solar
  image taken at 1.2 mm with a SDO/HMI magnetogram and analyze their
  correlation. It is found that chromospheric network and active regions
  show a positive correlation where brightness temperature is increasing
  with the line-of-sight magnetic field strength, while sunspots have a
  negative correlation. Quiet Sun regions do not show any dependence
  of the brightness temperature with the magnetic field. Thermal
  bremsstrahlung is given as the best explanation for the observed
  correlations.

Title: Centre-to-Limb Brightness Variations from the Atacama Large
    Millimeter-Submillimeter Array (ALMA) Full-Disk Solar Images
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O.
Bibcode: 2019SoPh..294..163S
Altcode:
  Science Verification (SV) data of solar observations with the Atacama
  Large Millimeter-submillimeter Array (ALMA) telescope have been
  released to the scientific community. Understanding the centre-to-limb
  brightness function is necessary to compare features in full-disk
  images. Our goals are to find the empirical centre-to-limb brightness
  functions in two available spectral bands and create flattened
  images with centre-to-limb brightness variations removed. We used a
  second-order polynomial fit of the cosine of incidence angle to data
  points as a function of radial distance to the centre of the solar
  disk. The method also includes iterative removal of outliers based
  on the inter-quartile range. Fitting functions for all available
  images proved to describe the data adequately with comparatively
  small errors in the fitting coefficients. In both bands we found
  brightening towards the limb, which is a consequence of the increase
  in electron temperature with radial distance in this region of the
  solar atmosphere. This study found that the brightness temperature
  [T<SUB>b</SUB>] of an active region has about 180 K difference between
  estimates with and without the limb brightening at radial distance
  ≈0.75 <SUB>R⊙</SUB> in Band 6. We also made flattened images with
  limb brightening removed. The limb-brightening effect in ALMA images
  is significant enough (of the order of 10% for Band 3 and about 15%
  in Band 6) that it cannot be neglected in further analyses. Since the
  effect of the side lobes was not included in this study, these values
  probably represent the lower limit of the limb brightening. The shape
  of the limb-brightening function can also be used to constrain electron
  densities and temperatures in various layers of the solar atmosphere.

Title: Centre to limb brightness variations from ALMA full disk
    solar images
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O.
Bibcode: 2019arXiv190908952S
Altcode:
  Science Verification (SV) data of solar observations with Atacama Large
  Millimeter-submillimeter Array (ALMA) telescope were released to the
  scientific community. Understanding the centre to limb brightness
  function is necessary to compare features in full disk images. Our
  goals are to find the empirical centre to limb brightness functions
  in two available spectral bands and create flattened images with
  centre to limb brightness variations removed. We used second-order
  polynomial fit of the cosine of incidence angle to data points as
  a function of radial distance to the centre of the solar disk. The
  method also includes iterative removal of outliers based on the
  interquartile range. Fitting functions for all available images proved
  to adequately describe the data with comparatively small errors in the
  fitting coefficients. In both bands we found brightening towards the
  limb which is a consequence of increase in electron temperatures with
  radial distance in this region of the solar atmosphere. This study
  found that the $T_{b}$ of an active region has about 180 K difference
  between with and without the limb brightening at radial distance
  $\approx$0.75$R_{\odot}$ in Band 6. We also made flattened images with
  limb brightening removed. The limb brightening effect in ALMA images
  is significant enough (of the order of 10% for Band 3 and about 15%
  in Band 6) that it can not be neglected in further analyses. Since the
  effect of the side lobes was not included in this study, these values
  probably represent the lower limit of the limb brightening. The shape
  of the limb brightening function can also be used to constrain electron
  densities and temperatures in various layers of the solar atmosphere.

Title: Turbulent Diffusion Derived from the Motions of SDO/AIA
    Coronal Bright Points
Authors: Skokić, I.; Brajša, R.; Sudar, D.; Ruždjak, D.; Saar, S. H.
Bibcode: 2019ApJ...877..142S
Altcode:
  Diffusion of magnetic elements on the Sun has an important role
  in current solar dynamo models as a part of the mechanism for
  redistribution of the magnetic field and as an important part for
  maintaining the solar activity cycle. The main goal is to determine the
  character of solar magnetic diffusivity and a value of the diffusion
  coefficient by analyzing the motions of coronal bright points (CBPs)
  within the frame of the random walk model. We tracked positions of
  CBPs in Solar Dynamics Observatory/Atmospheric Imaging Assembly images
  for a period of 5 months and examined their displacement spectrum. We
  calculated spectral index and diffusion coefficient from the spectrum
  and investigated their variation with temporal and spatial scale. For
  the first time, variations of the spectral index with heliographic
  latitude and time were analyzed. Our results indicate subdiffusion with
  the spectral index γ = 0.70 ± 0.01 and the corresponding diffusion
  coefficient with a value decreasing from 400 to 100 km<SUP>2</SUP>
  s<SUP>-1</SUP> for temporal scales of 10<SUP>3</SUP>-10<SUP>5</SUP>
  s and spatial scales of (1.5-7) × 10<SUP>3</SUP> km. Seemingly
  random variations around the mean value of spectral index were found,
  with peak-to-peak amplitudes &lt;0.30 with time and &lt;0.10 with
  latitude. The main conclusion is that CBP motions are consistent with
  a subdiffusion process.

Title: ALMA Solar Ephemeris Generator
Authors: Skokić, I.; Brajša, R.
Bibcode: 2019arXiv190408263S
Altcode:
  An online software tool for the easy preparation of ephemerides of the
  solar surface features is presented. It was developed as a helper tool
  for the preparation of observations of the Sun with the Atacama Large
  Millimeter/submillimeter Array (ALMA), but it can be used at other
  observatories as well. The tool features an easy to use point-and-click
  graphical user interface with the possibility to enter or adjust input
  parameters, while the result is a table of predicted positions in the
  celestial equatorial coordinate system, suitable for import into the
  ALMA Observing Tool software. The tool has been successfully used for
  the preparation and execution of solar observations with ALMA.

Title: Polar Brightening in ALMA full-disk solar images
Authors: Sudar, D.; Skokić, I.; Brajša, R.
Bibcode: 2019CEAB...43....1S
Altcode:
  We have analysed polar brightening effect in two images recorded by
  the ALMA telescope in 2015 in Bands 3 ($\lambda=2.8$ mm, $\nu=107$
  GHz) and 6 ($\lambda=1.2$ mm, $\nu=248$ GHz). After removing the limb
  brightening effect we found that the amplitude of variations is $\approx
  180$ K in both Bands.

Title: Solar Polar Brightening and Radius at 100 and 230 GHz Observed
    by ALMA
Authors: Selhorst, Caius L.; Simões, Paulo J. A.; Brajša, Roman;
   Valio, Adriana; Giménez de Castro, C. G.; Costa, Joaquim E. R.;
   Menezes, Fabian; Rozelot, Jean Pierre; Hales, Antonio S.; Iwai,
   Kazumasa; White, Stephen
Bibcode: 2019ApJ...871...45S
Altcode: 2018arXiv181112158S
  Polar brightening of the Sun at radio frequencies has been studied
  for almost 50 years and yet a disagreement persists between solar
  atmospheric models and observations. Some observations reported
  brightening values much smaller than the expected values obtained from
  the models, with discrepancies being particularly large at millimeter
  wavelengths. New clues to calibrate the atmospheric models can be
  obtained with the advent of the Atacama Large Millimeter/submillimeter
  Array (ALMA) radio interferometer. In this work, we analyzed the lower
  limit of the polar brightening observed at 100 and 230 GHz by ALMA,
  during its Science Verification period, 2015 December 16-20. We find
  that the average polar intensity is higher than the disk intensity
  at 100 and 230 GHz, with larger brightness intensities at the south
  pole in eight of the nine maps analyzed. The observational results
  were compared with calculations of the millimetric limb brightening
  emission for two semi-empirical atmospheric models, FAL-C and SSC. Both
  models presented larger limb intensities than the average observed
  values. The intensities obtained with the SSC model were closer to the
  observations, with polar brightenings of 10.5% and 17.8% at 100 and
  230 GHz, respectively. This discrepancy may be due to the presence of
  chromospheric features (like spicules) at regions close to the limb.

Title: Photospheric and chromospheric observations with solar
    telescope at Hvar Observatory
Authors: Calogovic, J.; Brajsa, Roman; Vrsnak, Bojan; Dumbovic,
   Mateja; Skokic, Ivica
Bibcode: 2018cosp...42E.496C
Altcode:
  The double solar telescope at the Hvar Observatory consists of two
  Carl Zeiss refractors, one with 217 mm objective diameter used for
  photospheric observations and the second one with 130 mm objective used
  for chromospheric observations. Hvar solar telescope aims to produce
  the high-resolution and high-cadence imaging of active regions on the
  Sun using a field of view of about 11 arcmin for the photosphere and
  7 arcmin for the chromosphere. The modern Pulnix TM-4200GE 12-bit 4
  megapixel CCD cameras recording seven frames per second together with
  the software that automatically selects the sharpest frames allow
  to study the rapid changes on the Sun in great detail. High-cadence
  ground-based observations are an important tool to identify and study
  solar flares, filaments and other solar phenomena that are associated
  with coronal mass ejections and their propagation to the Earth. Aiming
  to improve the space weather forecasts using ground-based observations,
  we compiled the catalogue of Hvar solar telescope observations in the
  solar cycle 24. In addition, expansion of this catalogue in future
  will be used for comparison with ALMA-SSALMON observations. This work
  has been supported by the Croatian Science Foundation project 6212
  "Solar and Stellar Variability" (SOLSTEL).

Title: Observations of the solar chromosphere with ALMA and comparison
    with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
   Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
   Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
Bibcode: 2018csss.confE..37B
Altcode: 2018arXiv181207293B
  In this work we use solar observations with the ALMA radio telescope
  at the wavelength of 1.21 mm. The aim of the analysisis to improve
  understanding of the solar chromosphere, a dynamic layer in the
  solar atmosphere between the photosphere andcorona. The study has
  an observational and a modeling part. In the observational part
  full-disc solar images are analyzed.Based on a modied FAL atmospheric
  model, radiation models for various observed solar structures are
  developed. Finally, theobservational and modeling results are compared
  and discussed.

Title: First analysis of solar structures in 1.21 mm full-disc ALMA
    image of the Sun
Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta,
   M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.;
   Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.
Bibcode: 2018A&A...613A..17B
Altcode: 2017arXiv171106130B
  Context. Various solar features can be seen in emission or absorption
  on maps of the Sun in the millimetre and submillimetre wavelength
  range. The recently installed Atacama Large Millimetre/submillimetre
  Array (ALMA) is capable of observing the Sun in that wavelength range
  with an unprecedented spatial, temporal and spectral resolution. To
  interpret solar observations with ALMA, the first important step is to
  compare solar ALMA maps with simultaneous images of the Sun recorded in
  other spectral ranges. <BR /> Aims: The first aim of the present work
  is to identify different structures in the solar atmosphere seen in the
  optical, infrared, and EUV parts of the spectrum (quiet Sun, active
  regions, prominences on the disc, magnetic inversion lines, coronal
  holes and coronal bright points) in a full-disc solar ALMA image. The
  second aim is to measure the intensities (brightness temperatures) of
  those structures and to compare them with the corresponding quiet Sun
  level. <BR /> Methods: A full-disc solar image at 1.21 mm obtained on
  December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and
  compared with full-disc solar images from the same day in Hα line, in
  He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4
  nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness
  temperatures of various structures are determined by averaging over
  corresponding regions of interest in the calibrated ALMA image. <BR />
  Results: Positions of the quiet Sun, active regions, prominences on
  the disc, magnetic inversion lines, coronal holes and coronal bright
  points are identified in the ALMA image. At the wavelength of 1.21
  mm, active regions appear as bright areas (but sunspots are dark),
  while prominences on the disc and coronal holes are not discernible
  from the quiet Sun background, despite having slightly less intensity
  than surrounding quiet Sun regions. Magnetic inversion lines appear as
  large, elongated dark structures and coronal bright points correspond
  to ALMA bright points. <BR /> Conclusions: These observational results
  are in general agreement with sparse earlier measurements at similar
  wavelengths. The identification of coronal bright points represents
  the most important new result. By comparing ALMA and other maps,
  it was found that the ALMA image was oriented properly and that the
  procedure of overlaying the ALMA image with other images is accurate
  at the 5 arcsec level. The potential of ALMA for physics of the solar
  chromosphere is emphasised.

Title: Meridional Motions and Reynolds Stress Determined by Using
    Kanzelhöhe Drawings and White Light Solar Images from 1964 to 2016
Authors: Ruždjak, Domagoj; Sudar, Davor; Brajša, Roman; Skokić,
   Ivica; Poljančić Beljan, Ivana; Jurdana-Šepić, Rajka; Hanslmeier,
   Arnold; Veronig, Astrid; Pötzi, Werner
Bibcode: 2018SoPh..293...59R
Altcode: 2018arXiv180401344R
  Sunspot position data obtained from Kanzelhöhe Observatory for
  Solar and Environmental Research (KSO) sunspot drawings and white
  light images in the period 1964 to 2016 were used to calculate the
  rotational and meridional velocities of the solar plasma. Velocities
  were calculated from daily shifts of sunspot groups and an iterative
  process of calculation of the differential rotation profiles was used
  to discard outliers. We found a differential rotation profile and
  meridional motions in agreement with previous studies using sunspots as
  tracers and conclude that the quality of the KSO data is appropriate
  for analysis of solar velocity patterns. By analyzing the correlation
  and covariance of meridional velocities and rotation rate residuals
  we found that the angular momentum is transported towards the solar
  equator. The magnitude and latitudinal dependence of the horizontal
  component of the Reynolds stress tensor calculated is sufficient to
  maintain the observed solar differential rotation profile. Therefore,
  our results confirm that the Reynolds stress is the dominant mechanism
  responsible for transport of angular momentum towards the solar equator.

Title: Exploring the Sun with ALMA
Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu,
   B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson,
   H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić,
   I.; Wedemeyer, S.; White, S. M.; Yan, Y.
Bibcode: 2018Msngr.171...25B
Altcode:
  The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory
  opens a new window onto the Universe. The ability to perform continuum
  imaging and spectroscopy of astrophysical phenomena at millimetre and
  submillimetre wavelengths with unprecedented sensitivity opens up new
  avenues for the study of cosmology and the evolution of galaxies, the
  formation of stars and planets, and astrochemistry. ALMA also allows
  fundamentally new observations to be made of objects much closer
  to home, including the Sun. The Sun has long served as a touchstone
  for our understanding of astrophysical processes, from the nature of
  stellar interiors, to magnetic dynamos, non-radiative heating, stellar
  mass loss, and energetic phenomena such as solar flares. ALMA offers
  new insights into all of these processes.

Title: A comparison of solar ALMA observations and model based
    predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
   D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
   A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
   Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
Bibcode: 2018CEAB...42....1B
Altcode:
  The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
  capable of observing the Sun in the wavelength range from 0.3 mm to 10
  mm with an unprecedented spatial, temporal and spectral resolution. The
  first aim of the present work is to identify different structures
  in the solar atmosphere (quiet Sun, active regions, filaments on the
  disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
  obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
  with full disc solar images from the same day in the Hα line (Cerro
  Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
  21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
  areas, active regions, filaments on the disc, and coronal holes are
  identified in the ALMA image. To interpret solar observations with ALMA
  it is important to compare the measured and calculated intensities
  of various solar structures. So, the second aim of this work is to
  calculate the intensity (brightness temperature) for those structures
  (quiet Sun, active regions, filaments on the disc, and coronal holes)
  for a broad wavelength range (from 0.3 mm to 10 mm), closely related
  to that of the ALMA, and to compare the results with available
  ALMA observations. Thermal bremsstrahlung is the dominant radiation
  mechanism for explanation of the observed phenomena. A procedure for
  calculating the brightness temperature for a given wavelength and
  model atmosphere, which integrates the radiative transfer equation
  for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
  active regions appear as bright areas, while filaments on the disc and
  coronal holes are not discernible from the quiet Sun background. The
  models generally agree with the observed results: Active regions are
  bright primarily due to higher densities, filaments can appear bright,
  dark or not at all and coronal holes cannot be easily identified.

Title: A Relationship Between the Solar Rotation and Activity Analysed
    by Tracing Sunspot Groups
Authors: Ruždjak, Domagoj; Brajša, Roman; Sudar, Davor; Skokić,
   Ivica; Poljančić Beljan, Ivana
Bibcode: 2017SoPh..292..179R
Altcode: 2017arXiv171103723R
  The sunspot position published in the data bases of the Greenwich
  Photoheliographic Results (GPR), the US Air Force Solar Optical
  Observing Network and National Oceanic and Atmospheric Administration
  (USAF/NOAA), and of the Debrecen Photoheliographic Data (DPD) in the
  period 1874 to 2016 were used to calculate yearly values of the solar
  differential-rotation parameters A and B . These differential-rotation
  parameters were compared with the solar-activity level. We found that
  the Sun rotates more differentially at the minimum than at the maximum
  of activity during the epoch 1977 - 2016. An inverse correlation between
  equatorial rotation and solar activity was found using the recently
  revised sunspot number. The secular decrease of the equatorial rotation
  rate that accompanies the increase in activity stopped in the last part
  of the twentieth century. It was noted that when a significant peak
  in equatorial rotation velocity is observed during activity minimum,
  the next maximum is weaker than the previous one.

Title: Solar differential rotation in the period 1964-2016 determined
    by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
   Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
   Veronig, A.; Skokić, I.; Wöhl, H.
Bibcode: 2017A&A...606A..72P
Altcode:
  Context. Kanzelhöhe Observatory for Solar and Environmental Research
  (KSO) provides daily multispectral synoptic observations of the Sun
  using several telescopes. In this work we made use of sunspot drawings
  and full disk white light CCD images. <BR /> Aims: The main aim of
  this work is to determine the solar differential rotation by tracing
  sunspot groups during the period 1964-2016, using the KSO sunspot
  drawings and white light images. We also compare the differential
  rotation parameters derived in this paper from the KSO with those
  collected fromf other data sets and present an investigation of the
  north - south rotational asymmetry. <BR /> Methods: Two procedures
  for the determination of the heliographic positions were applied: an
  interactive procedure on the KSO sunspot drawings (1964-2008, solar
  cycles Nos. 20-23) and an automatic procedure on the KSO white light
  images (2009-2016, solar cycle No. 24). For the determination of the
  synodic angular rotation velocities two different methods have been
  used: a daily shift (DS) method and a robust linear least-squares fit
  (rLSQ) method. Afterwards, the rotation velocities had to be converted
  from synodic to sidereal, which were then used in the least-squares
  fitting for the solar differential rotation law. A comparison of
  the interactive and automatic procedures was performed for the
  year 2014. <BR /> Results: The interactive procedure of position
  determination is fairly accurate but time consuming. In the case
  of the much faster automatic procedure for position determination,
  we found the rLSQ method for calculating rotational velocities to
  be more reliable than the DS method. For the test data from 2014,
  the rLSQ method gives a relative standard error for the differential
  rotation parameter B that is three times smaller than the corresponding
  relative standard error derived for the DS method. The best fit solar
  differential rotation profile for the whole time period is ω(b) =
  (14.47 ± 0.01)-(2.66 ± 0.10)sin<SUP>2</SUP>b (deg/day) for the DS
  method and ω(b) = (14.50 ± 0.01)-(2.87 ± 0.12)sin<SUP>2</SUP>b
  (deg/day) for the rLSQ method. A barely noticeable north - south
  asymmetry is observed for the whole time period 1964-2016 in the
  present paper. Rotation profiles, using different data sets, presented
  by other authors for the same time periods and the same tracer types,
  are in good agreement with our results. <BR /> Conclusions: The KSO
  data set used in this paper is in good agreement with the Debrecen
  Photoheliographic Data and Greenwich Photoheliographic Results and is
  suitable for the investigation of the long-term variabilities in the
  solar rotation profile. Also, the quality of the KSO sunspot drawings
  has gradually increased during the last 50 yr.

Title: Identification of features in solar ALMA images and comparison
    with solar atmospheric models
Authors: Skokić, I.; Brajša, R.; Sudar, D.; Kuhar, M.; Benz, A. O.
Bibcode: 2017simi.conf..121S
Altcode:
  Various solar features were identified in the full-disc single-dish ALMA
  images taken at wavelength of 1.2 and 2.8 mm and compared with Hα, Ca
  II K and EUV images and magnetograms. Assuming thermal bremsstrahlung
  as the dominant radiation mechanism, several models were constructed
  to calculate the brightness temperature of various solar features
  (quiet and active solar regions, filaments and coronal holes) in a
  wavelength range from 0.3 to 10 mm. It is found that model predictions
  are in a qualitative agreement with ALMA images where active regions
  appear brighter, while filaments and coronal holes are not discernible
  from the quiet Sun level. It is also found that in ALMA images regions
  around magnetic neutral lines appear darker than the quiet Sun. Models
  predict a critical frequency below which filaments should appear in
  absorption and above it in emission.

Title: Solar Commissioning Observations of the Sun with ALMA
Authors: White, Stephen M.; Shimojo, Masumi; Bastian, Timothy S.;
   Iwai, Kazumasa; Hales, Antonio; Brajsa, Roman; Skokic, Ivica; Kim,
   Sujin; Hudson, Hugh S.; Loukitcheva, Maria; Wedemeyer, Sven
Bibcode: 2017SPD....4820402W
Altcode:
  PI-led science observations have commenced with the Atacama
  Large Millimeter-submillimeter Array (ALMA) following an extensive
  commissioning effort. This talk will summarize that effort and discuss
  some of the scientific results derived from the commissioning data. As
  the solar cycle declines, ALMA observations will mainly address
  chromospheric science topics. Examples of data obtained during
  commissioning, both from the interferometer and from single-dish
  observations, will be presented. The temperatures of the layers that
  ALMA is most sensitive to have been determined for the two frequency
  bands currently used for solar observations. Curious behavior in a
  sunspot umbra and an observations of a small chromospheric ejection
  will be discussed.

Title: Solar research with ALMA: Czech node of European ARC as your
    user-support infrastructure
Authors: Bárta, M.; Skokić, I.; Brajša, R.; Czech ARC Node Team
Bibcode: 2017simi.conf..127B
Altcode:
  ALMA (Atacama Large Millimeter/sub-millimeter Array) is by far the
  largest project of current ground-based observational facilities
  in astronomy and astrophysics. It is built and operated in the
  world-wide cooperation (ESO, NRAO, NAOJ) at altitude of 5000m in the
  desert of Atacama, Chile. Because of its unprecedented capabilities,
  ALMA is considered as a cutting-edge research device in astrophysics
  with potential for many breakthrough discoveries in the next decade
  and beyond. In spite it is not exclusively solar-research dedicated
  instrument, science observations of the Sun are now possible and has
  recently started in the observing Cycle 4 (2016-2017). <P />In order to
  facilitate user access to this top-class, but at the same moment very
  complicated device to researchers lacking technical expertise, a network
  of three ALMA Regional Centers (ARCs) has been formed in Europe, North
  America, and East Asia as a user-support infrastructure and interface
  between the observatory and users community. After short introduction
  to ALMA the roles of ARCs and hint how to utilize their services will
  be presented, with emphasis to the specific (and in Europe unique)
  mission of the Czech ARC node in solar research with ALMA. Finally,
  peculiarities of solar observations that demanded the development
  of the specific Solar ALMA Observing Modes will be discussed and the
  results of Commissioning and Science Verification observing campaigns
  (solar ALMA maps) will be shown.

Title: A comparison of solar ALMA maps with solar images obtained
    at other wavelengths
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold;
   Kuhar, Matej; White, Stephen M.
Bibcode: 2017SPD....4820403B
Altcode:
  We use recently released Commissioning and Science Verification
  data of the Sun from the observing campaigns perfomed with the ALMA
  radio telescope in December 2014 and in December 2015. The dataset
  consists of calibrated maps of the Sun recorded in ALMA observing
  band 3 (corresponding to a wavelength of 3 mm) and band 6 (1.2 mm)
  which show both bright and dark areas and a background of highly
  structured pattern. Solar ALMA maps are compared with images in EUV
  (SDO/AIA), H-alpha (NISP, Cerro Tololo) and He 1083 nm (NSO/SOLIS),
  as well as with magnetograms (SDO/HMI) recorded at times closest
  to the ALMA observations. With a special software the images
  are overlapped and a correspondence of identified structures is
  checked in both ways. The visibility of active regions, sunspots,
  inversion lines of global magnetic field, prominences on the disc,
  coronal holes and coronal bright points is investigated in ALMA
  images at mm wavelengths. Single-dish ALMA images of the Sun reveal
  large-scale structures in the solar atmosphere, while high resolution
  interferometric images are used to analyse the fine-scale chromospheric
  structure. The intensities (the brightness temperatures) of identified
  structures were determined and compared with selected model-based
  predictions.

Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric
    Imaging
Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.;
   Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.;
   Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.;
   Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder,
   S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.;
   Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y.
Bibcode: 2017SoPh..292...87S
Altcode: 2017arXiv170403236S
  Observations of the Sun at millimeter and submillimeter wavelengths
  offer a unique probe into the structure, dynamics, and heating of the
  chromosphere; the structure of sunspots; the formation and eruption
  of prominences and filaments; and energetic phenomena such as jets
  and flares. High-resolution observations of the Sun at millimeter and
  submillimeter wavelengths are challenging due to the intense, extended,
  low-contrast, and dynamic nature of emission from the quiet Sun,
  and the extremely intense and variable nature of emissions associated
  with energetic phenomena. The Atacama Large Millimeter/submillimeter
  Array (ALMA) was designed with solar observations in mind. The
  requirements for solar observations are significantly different from
  observations of sidereal sources and special measures are necessary
  to successfully carry out this type of observations. We describe the
  commissioning efforts that enable the use of two frequency bands,
  the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum
  interferometric-imaging observations of the Sun with ALMA. Examples of
  high-resolution synthesized images obtained using the newly commissioned
  modes during the solar-commissioning campaign held in December 2015
  are presented. Although only 30 of the eventual 66 ALMA antennas
  were used for the campaign, the solar images synthesized from the
  ALMA commissioning data reveal new features of the solar atmosphere
  that demonstrate the potential power of ALMA solar observations. The
  ongoing expansion of ALMA and solar-commissioning efforts will continue
  to enable new and unique solar observing capabilities.

Title: Solar differential rotation in the period 1964 - 2016
    determined by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
   Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
   Veronig, A.; Skokić, I.; Wöhl, H.
Bibcode: 2017arXiv170707886P
Altcode:
  The main aim of this work is to determine the solar differential
  rotation by tracing sunspot groups during the period 1964-2016, using
  the Kanzelhöhe Observatory for Solar and Environmental Research
  (KSO) sunspot drawings and white light images. Two procedures for
  the determination of the heliographic positions were applied: an
  interactive procedure on the KSO sunspot drawings (1964 - 2008, solar
  cycles nos. 20 - 23) and an automatic procedure on the KSO white light
  images (2009 - 2016, solar cycle no. 24). For the determination of the
  synodic angular rotation velocities two different methods have been
  used: a daily shift (DS) method and a robust linear least-squares fit
  (rLSQ) method. Afterwards, the rotation velocities had to be converted
  from synodic to sidereal, which were then used in the least-squares
  fitting for the solar differential rotation law. For the test
  data from 2014, we found the rLSQ method for calculating rotational
  velocities to be more reliable than the DS method. The best fit solar
  differential rotation profile for the whole time period is $\omega(b)$
  = (14.47 $\pm$ 0.01) - (2.66 $\pm$ 0.10) $\sin^2b$ (deg/day) for the
  DS method and $\omega(b)$ = (14.50 $\pm$ 0.01) - (2.87 $\pm$ 0.12)
  $\sin^2b$ (deg/day) for the rLSQ method. A barely noticeable north -
  south asymmetry is observed for the whole time period 1964 - 2016
  in the present paper. Rotation profiles, using different data sets
  (e.g. Debrecen Photoheliographic Data, Greenwich Photoheliographic
  Results), presented by other authors for the same time periods and the
  same tracer types, are in good agreement with our results. Therefore,
  the KSO data set is suitable for the investigation of the long-term
  variabilities in the solar rotation profile.

Title: Meridional Motion and Reynolds Stress from Debrecen
    Photoheliographic Data
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Poljančić
   Beljan, Ivana; Wöhl, Hubertus
Bibcode: 2017SoPh..292...86S
Altcode: 2017arXiv170500912S
  The Debrecen Photoheliographic Data catalogue is a continuation of
  the Greenwich Photoheliographic Results providing daily positions of
  sunspots and sunspot groups. We analyse the data for sunspot groups
  focussing on meridional motions and transfer of angular momentum towards
  the solar equator. Velocities are calculated with a daily shift method
  including an automatic iterative process of removing the outliers. Apart
  from the standard differential rotation profile, we find meridional
  motion directed towards the zone of solar activity. The difference in
  measured meridional flow in comparison to Doppler measurements and some
  other tracer measurements is interpreted as a consequence of different
  flow patterns inside and outside of active regions. We also find a
  statistically significant dependence of meridional motion on rotation
  velocity residuals confirming the transfer of angular momentum towards
  the equator. Analysis of horizontal Reynolds stress reveals that the
  transfer of angular momentum is stronger with increasing latitude
  up to about 40<SUP>∘</SUP>, where there is a possible maximum in
  absolute value.

Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota,
   A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales,
   A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki,
   W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.;
   Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.;
   Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann,
   G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.
Bibcode: 2017SoPh..292...88W
Altcode: 2017arXiv170504766W
  The Atacama Large Millimeter/submillimeter Array (ALMA) radio
  telescope has commenced science observations of the Sun starting
  in late 2016. Since the Sun is much larger than the field of view
  of individual ALMA dishes, the ALMA interferometer is unable to
  measure the background level of solar emission when observing the
  solar disk. The absolute temperature scale is a critical measurement
  for much of ALMA solar science, including the understanding of energy
  transfer through the solar atmosphere, the properties of prominences,
  and the study of shock heating in the chromosphere. In order to provide
  an absolute temperature scale, ALMA solar observing will take advantage
  of the remarkable fast-scanning capabilities of the ALMA 12 m dishes
  to make single-dish maps of the full Sun. This article reports on the
  results of an extensive commissioning effort to optimize the mapping
  procedure, and it describes the nature of the resulting data. Amplitude
  calibration is discussed in detail: a path that uses the two loads in
  the ALMA calibration system as well as sky measurements is described
  and applied to commissioning data. Inspection of a large number of
  single-dish datasets shows significant variation in the resulting
  temperatures, and based on the temperature distributions, we derive
  quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at
  λ =1.3 mm. These values have statistical uncertainties of about 100
  K, but systematic uncertainties in the temperature scale that may be
  significantly larger. Example images are presented from two periods
  with very different levels of solar activity. At a resolution of about
  25<SUP>″</SUP>, the 1.3 mm wavelength images show temperatures on
  the disk that vary over about a 2000 K range. Active regions and plages
  are among the hotter features, while a large sunspot umbra shows up as
  a depression, and filament channels are relatively cool. Prominences
  above the solar limb are a common feature of the single-dish images.

Title: Hvar Observatory - First 45 Years
Authors: Brajša, R.
Bibcode: 2017CEAB...41....1B
Altcode:
  Hvar Observatory is the only professional astrophysical observatory
  in the Republic of Croatia. It is one of departments of the Faculty
  of Geodesy, University of Zagreb and the main activities of Hvar
  Observatory are scientific research in astronomy and astrophysics and
  education of young scientists in these research areas. Four telescopes
  are installed at Hvar Observatory, for observations of the Sun, the
  bodies of the solar system, stars and galaxies. Besides the astronomical
  and astrophysical research, geodetic and geophysical measurements
  are also systematically performed at Hvar Observatory. In this paper
  we briefly describe the foundation of Hvar Observatory in the year
  1972 and activities of the Observatory in the last 45 years. Also,
  the telescopes of Hvar Observatory, scientific research and public
  outreach are presented.

Title: Extreme Space Weather in Extra-Solar Systems - a Flare
    Alert Program
Authors: Hanslmeier, A.; Leitzinger, M.; Greimel, R.; Odert, P.;
   Ratzka, T.; Brajša, R.; Guenther, E. W.; Korhonen, H.; Pribulla, T.;
   Šlechta, M.; Vida, K.; Güdel, M.; Heinzel, P.; Lammer, H.; Ribas, I.
Bibcode: 2017CEAB...41...67H
Altcode:
  Highly energetic stellar activity phenomena, such as outbreaks of
  radiations (flares) and mass expulsions into the helio-/astro-sphere
  (coronal mass ejections/CMEs), may have a severe impact on
  the atmospheric evolution of planets. Stellar flare have been
  studied for decades now and their typical parameters are determined
  statistically. However, observations of stellar CMEs are rare, yielding
  only a handful of detections so far. The detection of CMEs on stars
  demands more observational effort than the detection flares, because
  the circumstellar environment cannot be spatially resolved like in the
  Solar System. The most convincing detections up to now were found as
  Doppler-shifted Balmer line extra-emission/absorption features emerging
  close to flare events, indicating the rise end ejection of prominence
  material embedded in the CME core. Dedicated programs aiming for a
  statistical determination of occurrence rates and the parameters of
  stellar CMEs are still lacking. Therefore, we propose an innovative
  and efficient observational approach to search for and characterize
  CMEs on Sun-like and late-type pre-main sequence and main sequence
  stars to determine stellar CME parameters and their occurrence rates
  as a function of stellar spectral type and age, as well as establish
  a stellar flare/CME association rate, for the first time ever.

Title: Solar Observations with the Atacama Large
    Millimeter/submillimeter Array (ALMA)
Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen,
   B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.;
   Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.;
   Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA
   Solar Development Team
Bibcode: 2016ASPC..504..327K
Altcode:
  The Atacama Large Millimeter/Submillimeter Array (ALMA) is a
  joint North American, European, and East Asian project that opens
  the mm-sub mm wavelength part of the electromagnetic spectrum for
  general astrophysical exploration, providing high-resolution imaging
  in frequency bands currently ranging from 84 GHz to 950 GHz (300
  microns to 3 mm). It is located in the Atacama desert in northern
  Chile at an elevation of 5000 m. Despite being a general purpose
  instrument, provisions have been made to enable solar observations
  with ALMA. Radiation emitted at ALMA wavelengths originates mostly
  from the chromosphere, which plays an important role in the transport
  of matter and energy, and the in heating the outer layers of the solar
  atmosphere. Despite decades of research, the solar chromosphere remains
  a significant challenge: both to observe, owing to the complicated
  formation mechanisms of currently available diagnostics; and to
  understand, as a result of the complex nature of the structure and
  dynamics of the chromosphere. ALMA has the potential to change the
  scene substantially as it serves as a nearly linear thermometer at
  high spatial and temporal resolution, enabling us to study the complex
  interaction of magnetic fields and shock waves and yet-to-be-discovered
  dynamical processes. Moreover, ALMA will play an important role in
  the study of energetic emissions associated with solar flares at
  sub-THz frequencies.

Title: Solar Science with the Atacama Large Millimeter/Submillimeter
    Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
   Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
   B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
   P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
   A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
   Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
   D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
   der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
   Selhorst, C. L.; Barta, M.
Bibcode: 2016SSRv..200....1W
Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
  The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
  powerful tool for observing the Sun at high spatial, temporal, and
  spectral resolution. These capabilities can address a broad range
  of fundamental scientific questions in solar physics. The radiation
  observed by ALMA originates mostly from the chromosphere—a complex
  and dynamic region between the photosphere and corona, which plays a
  crucial role in the transport of energy and matter and, ultimately,
  the heating of the outer layers of the solar atmosphere. Based on
  first solar test observations, strategies for regular solar campaigns
  are currently being developed. State-of-the-art numerical simulations
  of the solar atmosphere and modeling of instrumental effects can help
  constrain and optimize future observing modes for ALMA. Here we present
  a short technical description of ALMA and an overview of past efforts
  and future possibilities for solar observations at submillimeter and
  millimeter wavelengths. In addition, selected numerical simulations
  and observations at other wavelengths demonstrate ALMA's scientific
  potential for studying the Sun for a large range of science cases.

Title: Meridional motions and Reynolds stress from SDO/AIA coronal
    bright points data
Authors: Sudar, D.; Saar, S. H.; Skokić, I.; Poljančić Beljan,
   I.; Brajša, R.
Bibcode: 2016A&A...587A..29S
Altcode: 2016arXiv160102406S
  Context. It is possible to detect and track coronal bright points (CBPs)
  in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA)
  images. A combination of high resolution and high cadence provides
  a wealth of data that can be used to determine velocity flows on the
  solar surface with very high accuracy. <BR /> Aims: We derived a very
  accurate solar rotation profile and investigated meridional flows,
  torsional oscillations, and horizontal Reynolds stress based on ≈6
  months of SDO/AIA data. <BR /> Methods: We used a segmentation algorithm
  to detect CBPs in SDO/AIA images. We also used invariance of the solar
  rotation profile with central meridian distance (CMD) to determine
  the height of CBPs in the 19.3 nm channel. <BR /> Results: The best
  fit solar rotation profile is given by ω(b) = (14.4060 ± 0.0051 +
  (-1.662 ± 0.050)sin<SUP>2</SUP>b + (-2.742 ± 0.081)sin<SUP>4</SUP>b)°
  day<SUP>-1</SUP>. The height of CBPs in the SDO/AIA 19.3 nm channel was
  found to be ≈6500 km. Meridional motion is predominantly poleward for
  all latitudes, while solar velocity residuals show signs of torsional
  oscillations. Horizontal Reynolds stress was found to be smaller than in
  similar works, but still showed transfer of angular momentum towards the
  solar equator. <BR /> Conclusions: Most of the results are consistent
  with Doppler measurements rather than tracer measurements. The fairly
  small calculated value of horizontal Reynolds stress might be due to
  the particular phase of the solar cycle. Accuracy of the calculated
  rotation profile indicates that it is possible to measure changes in
  the profile as the solar cycle evolves. Analysis of further SDO/AIA CBP
  data will also provide a better understanding of the temporal behaviour
  of the rotation velocity residuals, meridional motions, and Reynolds
  stress. <P />Table 1 is only available at the CDS via anonymous ftp to
  <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A29">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A29</A>

Title: An Application of the Random Walk Model to Proper Motions of
    Coronal Bright Points from SDO Data
Authors: Skokić, I.; Sudar, D.; Saar, S. H.; Brajša, R.;
   Poljančić-Beljan, I.
Bibcode: 2016CEAB...40...23S
Altcode:
  Atmospheric Imaging Assembly (AIA) images from the Solar Dynamics
  Observatory (SDO) were used to follow the motions of coronal bright
  points (CBPs) in the period 1 January - 19 May 2011 with a cadence of
  10 minutes. This resulted in a data set of 80966 CBPs with measured
  lifetimes and mean velocities which were used in a random walk model
  to calculate the diffusion coefficient, D. The results show that D has
  a value of ≈260 km^2 s^{-1} for CBPs with lifetime below 6 hours,
  decreasing to ≈170 km^2 s^{-1} for lifetimes above 12 hours, with
  a mean value of ≈230 km^2 s^{-1}.

Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
   Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
   Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
   M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
   Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
   V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
   P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
   A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
Bibcode: 2016arXiv160100587W
Altcode:
  This document was created by the Solar Simulations for the Atacama
  Large Millimeter Observatory Network (SSALMON) in preparation of
  the first regular observations of the Sun with the Atacama Large
  Millimeter/submillimeter Array (ALMA), which are anticipated to start
  in ALMA Cycle 4 in October 2016. The science cases presented here
  demonstrate that a large number of scientifically highly interesting
  observations could be made already with the still limited solar
  observing modes foreseen for Cycle 4 and that ALMA has the potential
  to make important contributions to answering long-standing scientific
  questions in solar physics. With the proposal deadline for ALMA Cycle
  4 in April 2016 and the Commissioning and Science Verification campaign
  in December 2015 in sight, several of the SSALMON Expert Teams composed
  strategic documents in which they outlined potential solar observations
  that could be feasible given the anticipated technical capabilities
  in Cycle 4. These documents have been combined and supplemented
  with an analysis, resulting in recommendations for solar observing
  with ALMA in Cycle 4. In addition, the detailed science cases also
  demonstrate the scientific priorities of the solar physics community
  and which capabilities are wanted for the next observing cycles. The
  work on this White Paper effort was coordinated in close cooperation
  with the two international solar ALMA development studies led by
  T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
  further updated until the beginning of Cycle 4 in October 2016. In
  particular, we plan to adjust the technical capabilities of the solar
  observing modes once finally decided and to further demonstrate the
  feasibility and scientific potential of the included science cases by
  means of numerical simulations of the solar atmosphere and corresponding
  simulated ALMA observations.

Title: VizieR Online Data Catalog: Time and positions of coronal
    bright points (Sudar+, 2016)
Authors: Sudar, D.; Saar, S. H.; Skokic, I.; Poljancic Beljan, I.;
   Brajsa, R.
Bibcode: 2016yCat..35870029S
Altcode:
  Positional information about CBPs detected by the segmentation
  algorithm are presented. For each CBP time in Julian days (JD) and x
  and y coordinates in pixels are given. <P />(1 data file).

Title: Solar Simulations for the Atacama Large Millimeter Observatory
    Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.;
   Shimojo, M.
Bibcode: 2015ASPC..499..341W
Altcode: 2015arXiv150206379W
  The Atacama Large Millimeter/submillimeter Array (ALMA) will
  be a valuable tool for observing the chromosphere of our Sun at
  (sub-)millimeter wavelengths at high spatial, temporal and spectral
  resolution and as such has great potential to address long-standing
  scientific questions in solar physics. In order to make the best use
  of this scientific opportunity, the Solar Simulations for the Atacama
  Large Millimeter Observatory Network has been initiated. A key goal
  of this international collaboration is to support the preparation and
  interpretation of future observations of the Sun with ALMA.

Title: SSALMON - The Solar Simulations for the Atacama Large
    Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
   H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
   B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
   Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
   Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
   A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
Bibcode: 2015AdSpR..56.2679W
Altcode: 2015arXiv150205601W
  The Solar Simulations for the Atacama Large Millimeter Observatory
  Network (SSALMON) was initiated in 2014 in connection with two ALMA
  development studies. The Atacama Large Millimeter/submillimeter Array
  (ALMA) is a powerful new tool, which can also observe the Sun at
  high spatial, temporal, and spectral resolution. The international
  SSALMONetwork aims at co-ordinating the further development of solar
  observing modes for ALMA and at promoting scientific opportunities
  for solar physics with particular focus on numerical simulations,
  which can provide important constraints for the observing modes and
  can aid the interpretation of future observations. The radiation
  detected by ALMA originates mostly in the solar chromosphere - a
  complex and dynamic layer between the photosphere and corona, which
  plays an important role in the transport of energy and matter and the
  heating of the outer layers of the solar atmosphere. Potential targets
  include active regions, prominences, quiet Sun regions, flares. Here,
  we give a brief overview over the network and potential science cases
  for future solar observations with ALMA.

Title: Solar ALMA Observations - A New View of Our Host Star
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Shimojo,
   M.; Hales, A.; Yagoubov, P.; Hudson, H.
Bibcode: 2015ASPC..499..345W
Altcode: 2015arXiv150206397W
  ALMA provides the necessary spatial, temporal and spectral resolution to
  explore central questions in contemporary solar physics with potentially
  far-reaching implications for stellar atmospheres and plasma physics. It
  can uniquely constraint the thermal and magnetic field structure in
  the solar chromosphere with measurements that are highly complementary
  to simultaneous observations with other ground-based and space-borne
  instruments. Here, we highlight selected science cases.

Title: The Atacama Large Millimeter/Submillimeter Array: a New Asset
    for Solar and Heliospheric Physics
Authors: Bastian, Timothy S.; Barta, Miroslav; Brajsa, Roman; Chen,
   Bin; De Pontieu, Bart; Fleishman, Gregory; Gary, Dale; Hales, Antonio;
   Hills, Richard; Hudson, Hugh; Iwai, Kazamasu; Shimojo, Masumi; White,
   Stephen; Wedemeyer, Sven; Yan, Yihua
Bibcode: 2015IAUGA..2257295B
Altcode:
  The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint
  North American, European, and East Asian interferometric array that
  opens the mm-submm wavelength part of the electromagnetic spectrum
  for general astrophysical exploration, providing high-resolution
  imaging in frequency bands ranging from 86 to 950 GHz. Despite being
  a general purpose instrument, provisions have been made to enable
  solar observations with ALMA. Radiation emitted at ALMA wavelengths
  originates mostly from the chromosphere, which plays an important
  role in the transport of energy and matter and the heating of the
  outer layers of the solar atmosphere. In this paper we describe
  recent efforts to ensure that ALMA can be usefully exploited by
  the scientific community to address outstanding questions in solar
  physics. We summarize activities under North American and European
  ALMA development studies, including instrument testing, calibration
  and imaging strategies, a science simulations. With the support of
  solar observations, ALMA joins next-generation groundbased instruments
  that can be used alone or in combination with other ground-based and
  space-based instruments to address outstanding questions in solar
  and heliospheric physics. Opportunities for the wider community to
  contribute to these efforts will be highlighted.

Title: SSALMON - The Solar Simulations for the Atacama Large
    Millimeter Observatory Network
Authors: Wedemeyer, Sven; Bastian, Timothy S.; Brajsa, Roman; Barta,
   Miroslav
Bibcode: 2015IAUGA..2257466W
Altcode:
  The Atacama Large Millimeter/submillimeter Array (ALMA) provides
  a new powerful tool for observing the solar chromosphere at high
  spatial, temporal, and spectral resolution, which will allow for
  addressing fundamental scientific questions. Based on first solar test
  observations, observing strategies for regular solar campaigns are
  currently under development. State-of-the-art numerical simulations of
  the solar atmosphere and modeling of instrumental effects can help in
  this respect, constraining and optimizing future observing modes for
  ALMA. On September 1st, 2014, the Solar Simulations for the Atacama
  Large Millimeter Observatory Network (SSALMON) has been initiated
  with the aim to co-ordinate related activities and to promote the
  scientific potential of ALMA observations of the Sun. The network
  is connected to two currently ongoing ALMA development studies. As
  of March 18th, 57 scientists from 15 countries have joined the
  international SSALMONetwork. Among the affiliations are NRAO, ESO,
  NAOJ, the Czech ALMA ARC node at Ondrejov, ESA and many more. Since
  March 2015, we are building up expert teams, which work on specific
  tasks in preparation of future regular ALMA observations (expected to
  start in late 2016) and their interpretation. Registration and more
  information at http://www.ssalmon.uio.no.

Title: Solar ALMA observations - A revolutionizing new view at our
    host star
Authors: Wedemeyer, Sven; Brajsa, Roman; Bastian, Timothy S.; Barta,
   Miroslav; Hales, Antonio; Yagoubov, Pavel; Hudson, Hugh; Loukitcheva,
   Maria; Fleishman, Gregory
Bibcode: 2015IAUGA..2256732W
Altcode:
  Observations of the Sun with the Atacama Large Millimeter/submillimeter
  Array (ALMA) have a large potential for revolutionizing our
  understanding of our host star with far reaching implications
  for stars in general. The radiation emitted at ALMA wavelengths
  originates mostly from the chromosphere - a complex and dynamic layer
  between the photosphere and the corona, which plays an important
  role in the transport of energy and matter and the heating of the
  outer layers of the solar atmosphere.Despite decades of intensive
  research, the chromosphere is still elusive and challenging to
  observe owing to the complicated formation mechanisms of currently
  available diagnostics. ALMA will change the scene substantially as
  it serves as a nearly linear thermometer at high spatial, temporal,
  and spectral resolution, enabling us to study the complex interaction
  of magnetic fields and shock waves and yet-to-be-discovered dynamical
  processes. Furthermore, radio recombination and molecular lines
  may have great diagnostic potential but need to be investigated
  first. These unprecedented capabilities promise important new findings
  for a large range of topics in solar physics including the structure,
  dynamics and energy balance of quiet Sun regions, active regions and
  sunspots, flares and prominences. As a part of ongoing development
  studies, an international network has been initiated, which aims at
  defining and preparing key solar science with ALMA through simulation
  studies: SSALMON -- Solar Simulations for the Atacama Large Millimeter
  Observatory Network (http://ssalmon.uio.no). Here, we give an overview
  of potential science cases.

Title: Steps towards a high precision solar rotation profile:
    Results from SDO/AIA coronal bright point data
Authors: Sudar, D.; Skokić, I.; Brajša, R.; Saar, S. H.
Bibcode: 2015A&A...575A..63S
Altcode: 2015arXiv150101285S
  Context. Coronal bright points (CBP) are ubiquitous small brightenings
  in the solar corona associated with small magnetic bipoles. <BR /> Aims:
  We derive the solar differential rotation profile by tracing the motions
  of CBPs detected by the Atmospheric Imaging Assembly (AIA) instrument
  aboard the Solar Dynamics Observatory (SDO). We also investigate
  problems related to the detection of CBPs resulting from instrument
  and detection algorithm limitations. <BR /> Methods: To determine
  the positions and identification of CBPs we used a segmentation
  algorithm. A linear fit of their central meridian distance and latitude
  vs time was used to derive velocities. <BR /> Results: We obtained
  906 velocity measurements in a time interval of only 2 days. The
  differential rotation profile can be expressed as ω<SUB>rot</SUB> =
  (14.47° ± 0.10° + (0.6° ± 1.0°) sin<SUP>2</SUP>(b) = (-4.7° ±
  1.7°) sin<SUP>4</SUP>(b)) d<SUP>-1</SUP>. Our result is in agreement
  with other work and it comes with reasonable errors in spite of the
  very short time interval used. This was made possible by the higher
  sensitivity and resolution of the AIA instrument compared to similar
  equipment as well as high cadence. The segmentation algorithm also
  played a crucial role by detecting so many CBPs, which reduced the
  errors to a reasonable level. <BR /> Conclusions: Data and methods
  presented in this paper show a great potential for obtaining very
  accurate velocity profiles, both for rotation and meridional motion and,
  consequently, Reynolds stresses. The amount of CBP data that could be
  obtained from this instrument should also provide a great opportunity
  to study changes of velocity patterns with a temporal resolution of
  only a few months. Other possibilities are studies of evolution of
  CBPs and proper motions of magnetic elements on the Sun.

Title: A comparison between the observed and predicted amplitude of
    the 24<SUP>th</SUP> solar cycle
Authors: Brajša, R.; Verbanac, G.; Sudar, D.; Skokić, I.; Žic,
   T.; Hanslmeier, A.; Wöhl, H.; Roth, M.; Mursula, K.; Zhang, L.
Bibcode: 2015CEAB...39..135B
Altcode:
  In present work we compared the measured and predicted amplitudes of
  the 24<SUP>th</SUP> solar cycle. The modified minimum--maximum method,
  belonging to the precursor class of methods, was applied to the smoothed
  monthly sunspot number values (the ``old'' data set, used before the
  change introduced on July 1<SUP>st</SUP>, 2015). The maximum of the
  24<SUP>th</SUP> solar cycle occurred in April 2014 with an amplitude of
  R=82 and this observed value is very close to our mean predicted value
  R=83. The maximum was significantly weaker than in several previous
  cycles. Additionally, a curious solar activity minimum of 2008,
  between the solar cycles no.~23 and no.~24 was analysed, as well as
  the shape of the maximum profile. The maximum of the 24<SUP>th</SUP>
  solar cycle had a double-peak, the second one being higher than the
  first one. The obtained results represent a strong indication that
  the minimum--maximum method is a reliable tool for the solar cycle
  prediction, using data available already 3 years before the preceding
  minimum of solar activity.

Title: Solar velocity field determined tracking coronal bright points
Authors: Brajša, R.; Sudar, D.; Skokić, I.; Saar, S. H.; Žic, T.
Bibcode: 2015CEAB...39...21B
Altcode:
  Preliminary data from Atmospheric Imaging Assembly (AIA) instrumenton
  board Solar Dynamics Observatory (SDO) satellite were used to determine
  solar differential rotation and related phenomena. A segmentation
  algorithm, which uses multiple AIA channels in search for intensity
  enhancements in EUV and X-ray parts of the spectrum compared to the
  background intensity, was applied to obtain positional information of
  coronal bright points (CBPs). More than 60000 position measurements
  of more than 10000 identified CBPs from the period 1 - 2 January 2011
  were analyzed. Rotational and meridional velocities were determined
  by tracking identified CBPs and various filters were used to exclude
  erroneous results. Also, proper motions of CBPs were calculated from
  rotation velocity residuals and meridional velocities. Proper motions
  of CBPs were investigated using a random walk model and the diffusion
  constant was calculated. These results were compared with the previous
  ones obtained by other instruments and methods (especially with the
  SOHO-EIT and Hinode data) and a striking agreement of the obtained
  diffusion constant with results from other studies was found.

Title: Future mmVLBI Research with ALMA: A European vision
Authors: Tilanus, R. P. J.; Krichbaum, T. P.; Zensus, J. A.; Baudry,
   A.; Bremer, M.; Falcke, H.; Giovannini, G.; Laing, R.; van Langevelde,
   H. J.; Vlemmings, W.; Abraham, Z.; Afonso, J.; Agudo, I.; Alberdi,
   A.; Alcolea, J.; Altamirano, D.; Asadi, S.; Assaf, K.; Augusto, P.;
   Baczko, A-K.; Boeck, M.; Boller, T.; Bondi, M.; Boone, F.; Bourda,
   G.; Brajsa, R.; Brand, J.; Britzen, S.; Bujarrabal, V.; Cales, S.;
   Casadio, C.; Casasola, V.; Castangia, P.; Cernicharo, J.; Charlot,
   P.; Chemin, L.; Clenet, Y.; Colomer, F.; Combes, F.; Cordes, J.;
   Coriat, M.; Cross, N.; D'Ammando, F.; Dallacasa, D.; Desmurs, J-F.;
   Eatough, R.; Eckart, A.; Eisenacher, D.; Etoka, S.; Felix, M.; Fender,
   R.; Ferreira, M.; Freeland, E.; Frey, S.; Fromm, C.; Fuhrmann, L.;
   Gabanyi, K.; Galvan-Madrid, R.; Giroletti, M.; Goddi, C.; Gomez, J.;
   Gourgoulhon, E.; Gray, M.; di Gregorio, I.; Greimel, R.; Grosso, N.;
   Guirado, J.; Hada, K.; Hanslmeier, A.; Henkel, C.; Herpin, F.; Hess,
   P.; Hodgson, J.; Horns, D.; Humphreys, E.; Hutawarakorn Kramer, B.;
   Ilyushin, V.; Impellizzeri, V.; Ivanov, V.; Julião, M.; Kadler, M.;
   Kerins, E.; Klaassen, P.; van 't Klooster, K.; Kording, E.; Kozlov,
   M.; Kramer, M.; Kreikenbohm, A.; Kurtanidze, O.; Lazio, J.; Leite,
   A.; Leitzinger, M.; Lepine, J.; Levshakov, S.; Lico, R.; Lindqvist,
   M.; Liuzzo, E.; Lobanov, A.; Lucas, P.; Mannheim, K.; Marcaide, J.;
   Markoff, S.; Martí-Vidal, I.; Martins, C.; Masetti, N.; Massardi,
   M.; Menten, K.; Messias, H.; Migliari, S.; Mignano, A.; Miller-Jones,
   J.; Minniti, D.; Molaro, P.; Molina, S.; Monteiro, A.; Moscadelli,
   L.; Mueller, C.; Müller, A.; Muller, S.; Niederhofer, F.; Odert,
   P.; Olofsson, H.; Orienti, M.; Paladino, R.; Panessa, F.; Paragi,
   Z.; Paumard, T.; Pedrosa, P.; Pérez-Torres, M.; Perrin, G.; Perucho,
   M.; Porquet, D.; Prandoni, I.; Ransom, S.; Reimers, D.; Rejkuba, M.;
   Rezzolla, L.; Richards, A.; Ros, E.; Roy, A.; Rushton, A.; Savolainen,
   T.; Schulz, R.; Silva, M.; Sivakoff, G.; Soria-Ruiz, R.; Soria, R.;
   Spaans, M.; Spencer, R.; Stappers, B.; Surcis, G.; Tarchi, A.; Temmer,
   M.; Thompson, M.; Torrelles, J.; Truestedt, J.; Tudose, V.; Venturi,
   T.; Verbiest, J.; Vieira, J.; Vielzeuf, P.; Vincent, F.; Wex, N.;
   Wiik, K.; Wiklind, T.; Wilms, J.; Zackrisson, E.; Zechlin, H.
Bibcode: 2014arXiv1406.4650T
Altcode:
  Very long baseline interferometry at millimetre/submillimetre
  wavelengths (mmVLBI) offers the highest achievable spatial
  resolution at any wavelength in astronomy. The anticipated inclusion
  of ALMA as a phased array into a global VLBI network will bring
  unprecedented sensitivity and a transformational leap in capabilities
  for mmVLBI. Building on years of pioneering efforts in the US and
  Europe the ongoing ALMA Phasing Project (APP), a US-led international
  collaboration with MPIfR-led European contributions, is expected to
  deliver a beamformer and VLBI capability to ALMA by the end of 2014
  (APP: Fish et al. 2013, arXiv:1309.3519). This report focuses on
  the future use of mmVLBI by the international users community from
  a European viewpoint. Firstly, it highlights the intense science
  interest in Europe in future mmVLBI observations as compiled from
  the responses to a general call to the European community for future
  research projects. A wide range of research is presented that includes,
  amongst others: - Imaging the event horizon of the black hole at the
  centre of the Galaxy - Testing the theory of General Relativity an/or
  searching for alternative theories - Studying the origin of AGN jets
  and jet formation - Cosmological evolution of galaxies and BHs, AGN
  feedback - Masers in the Milky Way (in stars and star-forming regions) -
  Extragalactic emission lines and astro-chemistry - Redshifted absorption
  lines in distant galaxies and study of the ISM and circumnuclear gas -
  Pulsars, neutron stars, X-ray binaries - Testing cosmology - Testing
  fundamental physical constants

Title: Validity of the Relations Between the Synodic and Sidereal
    Rotation Velocities of the Sun
Authors: Skokić, I.; Brajša, R.; Roša, D.; Hržina, D.; Wöhl, H.
Bibcode: 2014SoPh..289.1471S
Altcode: 2013arXiv1310.0778S
  Existing methods for conversion between synodic and sidereal
  rotation velocities of the Sun are tested for validity using
  state-of-the-art ephemeris data. We found that some of them agree well
  with ephemeris calculations while others show a discrepancy of almost
  0.01<SUP>∘</SUP> day<SUP>−1</SUP>. This discrepancy is attributed
  to a missing factor and a new corrected relation is given.

Title: Tracing sunspot groups to determine angular momentum transfer
    on the Sun
Authors: Sudar, D.; Skokić, I.; Ruždjak, D.; Brajša, R.; Wöhl, H.
Bibcode: 2014MNRAS.439.2377S
Altcode: 2014MNRAS.tmp..355S; 2014arXiv1401.5641S
  In this paper, our goal is to investigate Reynolds stress and to
  check whether it is plausible that this is responsible for angular
  momentum transfer towards the solar equator. We have also analysed
  meridional velocity, rotation velocity residuals and correlation
  between the velocities. We have used the position measurements of
  sunspot groups from the Greenwich Photographic Result and the Solar
  Observing Optical Network/United States Air Force/National Oceanic
  and Atmospheric Administration data bases, covering the period
  1878-2011. In order to calculate the velocities, we used the daily
  motion of sunspot groups. The sample was also limited to ±58° in the
  central meridian distance in order to avoid solar limb effects. We have
  mainly investigated velocity patterns depending on the solar cycle phase
  and latitude. We have found that the meridional motion of sunspot groups
  is towards the centre of activity from all available latitudes and in
  all phases of the solar cycle. The range of meridional velocities is
  ±10 m s<SUP>-1</SUP>. Horizontal Reynolds stress is negative at all
  available latitudes and indicates that there is a minimum value (q ≈
  -3000 m<SUP>2</SUP> s<SUP>-2</SUP>) located at b ≈ ±30°. In our
  convention, this means that angular momentum is transported towards
  the solar equator, in agreement with the observed rotational profile
  of the Sun.

Title: An analysis of the solar differential rotation from the
    Kanzelhöhe sunspot drawings
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Čargonja, M.;
   Brajša, R.; Hržina, D.; Pötzi, W.; Hanslmeier, A.
Bibcode: 2014CEAB...38...87P
Altcode:
  We present here the results of the behaviour of the solar differential
  rotation during solar cycles no. 20 and no. 22, derived from Kanzelhöhe
  sunspot drawings (Kanzelhöhe Observatory for Solar and Environmental
  Research, University of Graz, Austria). The positions of sunspot groups
  were determined using a special software Sungrabber. Sunspot groups were
  identified with the help of the Greenwich Photoheliographic Results
  (GPR) and Debrecen Photoheliographic Data (DPD) databases, covering
  solar cycles no. 20 and no. 22, respectively. In order to calculate
  the sidereal angular rotation rate ω and subsequently solar rotation
  parameters A and B we used two procedures: a) daily motion of sunspot
  groups and b) linear least-square fit from the function CMD(t) for each
  tracer, where CMD denotes the Central Meridian Distance. The sample
  was limited to ±58° in CMD in order to avoid solar limb effects. We
  mainly investigated velocity patterns depending on the solar cycle
  phase and latitude.

Title: Preliminary results on the solar rotation determined tracing
    SDO/AIA coronal bright points
Authors: Brajša, R.; Sudar, D.; Skokič, I.; Saar, S. H.
Bibcode: 2014CEAB...38..105B
Altcode:
  In this paper we present preliminary results on the solar differential
  rotation measured tracing coronal bright points in SDO/AIA images. An
  automatic recognition method was applied to the series of images taken
  in the test period, 1-2 January 2011. Coronal bright points are suitable
  tracers for the determination of the solar differential rotation,
  because they are localized objects which are very well distributed
  over solar disc. Results presented in this paper show that the SDO/AIA
  data are very useful for that aim, due to the high spatial and temporal
  resolution of the images.

Title: High-latitude opportunities for flow measurements with the
    EUI instrument onboard Solar Orbiter
Authors: Gissot, Samuel; Brajsa, Roman
Bibcode: 2014cosp...40E1000G
Altcode:
  The Solar Orbiter mission will offer a unique out-of-ecliptic
  vantage point which represents an excellent opportunity to address
  the cyclic nature of solar magnetic activity and key questions
  for our understanding of solar dynamo such as transport of flux at
  high latitudes and the properties of the polar magnetic field. Our
  current knowledge of solar activity at high latitudes is limited
  by the ecliptic position of past and current instruments so that
  characterizing the solar flows remains difficult because of this
  ecliptic viewing angle. This is a major limitation to our knowledge
  of meridional circulation and differential rotation at all latitudes
  and radii. During the out-of-the-ecliptic phase of the mission,
  Solar Orbiter will reach heliographic latitudes of 25(°) during the
  nominal mission and as high as 34(°) during the extended mission and
  thus contribute to new constraints and understanding for solar dynamo
  models. Following past work on tracer tracking of coronal bright points
  and the inter-instrument measurements of flows, we will present the
  lessons learned to address these issues using the Solar Orbiter EUI and
  PHI remote sensing instruments. In particular, we will present a method
  for the detection and tracking of high-latitude tracers from which one
  can derive requirements on the specific high solar inclination science
  windows of Solar Orbiter. We will illustrate how this will contribute
  to refine our current knowledge of differential rotation and meridional
  flows and discuss how the successive Solar Orbiter passes at perihelion
  could extend these solar activity indices over cycle time scales.

Title: The chaotic solar cycle. II. Analysis of cosmogenic
    <SUP>10</SUP>Be data
Authors: Hanslmeier, A.; Brajša, R.; Čalogović, J.; Vršnak,
   B.; Ruždjak, D.; Steinhilber, F.; MacLeod, C. L.; Ivezić, Ž.;
   Skokić, I.
Bibcode: 2013A&A...550A...6H
Altcode: 2014arXiv1402.2776H
  Context. The variations of solar activity over long time intervals using
  a solar activity reconstruction based on the cosmogenic radionuclide
  <SUP>10</SUP>Be measured in polar ice cores are studied. <BR /> Aims:
  The periodicity of the solar activity cycle is studied. The solar
  activity cycle is governed by a complex dynamo mechanism. Methods
  of nonlinear dynamics enable us to learn more about the regular
  and chaotic behavior of solar activity. In this work we compare
  our earlier findings based on <SUP>14</SUP>C data with the results
  obtained using <SUP>10</SUP>Be data. <BR /> Methods: By applying
  methods of nonlinear dynamics, the solar activity cycle is studied
  using solar activity proxies that have been reaching into the past
  for over 9300 years. The complexity of the system is expressed by
  several parameters of nonlinear dynamics, such as embedding dimension
  or false nearest neighbors, and the method of delay coordinates is
  applied to the time series. We also fit a damped random walk model,
  which accurately describes the variability of quasars, to the solar
  <SUP>10</SUP>Be data and investigate the corresponding power spectral
  distribution. The periods in the data series were searched by the
  Fourier and wavelet analyses. <BR /> Results: The solar activity on the
  long-term scale is found to be on the edge of chaotic behavior. This
  can explain the observed intermittent period of longer lasting solar
  activity minima. Filtering the data by eliminating variations below
  a certain period (the periods of 380 yr and 57 yr were used) yields a
  far more regular behavior of solar activity. A comparison between the
  results for the <SUP>10</SUP>Be data with the <SUP>14</SUP>C data shows
  many similarities. Both cosmogenic isotopes are strongly correlated
  mutually and with solar activity. Finally, we find that a series of
  damped random walk models provides a good fit to the <SUP>10</SUP>Be
  data with a fixed characteristic time scale of 1000 years, which is
  roughly consistent with the quasi-periods found by the Fourier and
  wavelet analyses. <BR /> Conclusions: The time series of solar activity
  proxies used here clearly shows that solar activity behaves differently
  from random data. The unfiltered data exhibit a complex dynamics that
  becomes more regular when filtering the data. The results indicate
  that solar activity proxies are also influenced by other than solar
  variations and reflect solar activity only on longer time scales.

Title: Observing the Sun with ALMA
Authors: Benz, A. O.; Brajsa, R.; Shimojo, M.; Karlicky, M.; Testi, L.
Bibcode: 2012IAUSS...6E.205B
Altcode:
  The Atacama Large Millimeter Array (ALMA) is in the commissioning
  phase for solar observations. A filter reduces the solar radiation
  to a level suitable for solar observations. First observations
  with one antenna have mapped the Sun by scanning. The results look
  promising. The image of the quiet chromosphere shows large spatial
  variations in emissivity. Interferometry is much more demanding and
  not yet achieved. The current state and problems will be summarized. It
  is clear that solar ALMA observations will take more developing time,
  but will eventually be possible. The goal is subarcsecond resolution
  of the quiet and active submillimeter continuum radiation originating
  in the chromosphere and possibly in the flaring corona. A limiting
  factor will be the temporal variability of the solar emission.

Title: Solar Hα and white light telescope at Hvar Observatory
Authors: Čalogović, J.; Dumbović, M.; Novak, N.; Vršnak, B.;
   Brajša, R.; Pötzi, W.; Hirtenfellner-Polanec, W.; Veronig, A.;
   Hanslmeier$, A.; Klvaňa, M.; Ambrož, P.
Bibcode: 2012CEAB...36...83C
Altcode:
  Recently, the double solar telescope at Hvar Observatory was equipped
  with the fourth generation of acquisition hardware and software. It
  provides a valuable instrument to study rapid changes of chromospheric
  and photospheric features in great detail. The telescope consists of
  two Carl Zeiss refractors (photosphere d=217mm, chromosphere d=130mm)
  mounted as one unit on a German parallax mounting. Using a field
  of view of about 7 and 11 arcmin, it aims to produce high-resolution
  high-cadence imaging of active regions on the Sun. New Pulnix TM-4200GE
  12-bit CCD cameras allow to obtain time series with a cadence up to
  30 images per minute.

Title: A relationship between the solar rotation and activity in the
    period 1998-2006 analysed by tracing small bright coronal structures
    in SOHO-EIT images
Authors: Jurdana-Šepić, R.; Brajša, R.; Wöhl, H.; Hanslmeier,
   A.; Poljančić, I.; Svalgaard, L.; Gissot, S. F.
Bibcode: 2011A&A...534A..17J
Altcode:
  <BR /> Aims: The study aims to find a relationship between the rotation
  of the small bright coronal structures (SBCS) described by the solar
  rotation parameters and indices of solar activity on monthly and yearly
  temporal scales. <BR /> Methods: We analyse precise measurements of
  the solar differential rotation determined by tracing SBCS in SOHO-EIT
  images and compare the derived solar rotation parameters with the
  status of solar activity in the period 1998 - 2006. Full-disc solar
  images obtained with the Extreme ultraviolet Imaging Telescope (EIT)
  on board the Solar and Heliospheric Observatory (SOHO) were used to
  analyse solar differential rotation determined by tracing SBCS. An
  automatic method to identify and track the SBCS in EIT full-disc images
  with a six hour cadence is applied. We performed a statistical analysis
  of the monthly and yearly values of solar sidereal rotation velocity
  parameters A and B (corresponding to the equatorial rotation velocity
  and the gradient of the solar differential rotation, respectively)
  as a function of various solar activity indices. <BR /> Results:
  The dependence of the solar rotation on the phase of the solar cycle
  was found. It is clearly visible for the solar rotation parameter A,
  whilst the results are not conclusive for parameter B. The relationship
  between the solar rotation and activity, expressed by the monthly
  relative sunspot number, the smoothed monthly relative sunspot number,
  the yearly relative sunspot number, and the interdiurnal variability
  (IDV) index was investigated. The statistically significant correlation
  was found for the solar rotation parameter A, whilst a very low and
  insignificant correlation was obtained for the rotation parameter
  B. <BR /> Conclusions: During the maximum of the solar cycle 23 and
  just after it, the equatorial solar rotation velocity was lower than
  in other phases of the cycle, when there was less activity. This is
  consistent with other observational findings, obtained by different
  tracers and methods.

Title: Differences in heliographic positions and rotation velocities
    of sunspot groups from various observatories
Authors: Poljančić, I.; Brajša, R.; Hržina, D.; Wöhl, H.;
   Hanslmeier, A.; Pötzi, W.; Baranyi, T.; Özgüç, A.; Singh, J.;
   Ruždjak, V.
Bibcode: 2011CEAB...35...59P
Altcode:
  Measured positions of sunspot groups that differ in format, precision
  and observing procedure are collected from various data sets:
  GPR (Greenwich Photoheliographic Results), SOON/USAF/NOAA (Solar
  Optical Observing Network/United States Air Force/National Oceanic and
  Atmospheric Administration), as well as from the Kodaikanal and Debrecen
  observatories. Kanzelh&amp;{uml;o}he and Kandilli Observatory currently
  provide the digitized sunspot drawings, from which the positions
  of selected sunspot groups are determined with a special software
  Sungrabber. The rotation velocities are calculated from the position
  data. The aim of this work is to compare and to check the precision
  of the mentioned data sets using the Kanzelh&amp;{uml;o}he Observatory
  data set as the reference basis of sunspot position measurements. The
  selected groups (about 40% consist of single sunspots Z&amp;{uml;u}rich
  types H and J) are from the years 1972 and 1993 belonging to similar
  declining phases of two solar activity cycles. The occurrence of some
  systematic differences of the sunspot group positions and rotation
  velocities suggests the need for a more detailed analysis of the data
  accumulation procedures.

Title: Heating of the quiet solar corona from measurements of the
    FET/TESIS instrument on-board the KORONAS-FOTON satellite
Authors: Rybák, J.; Gömöry, P.; Benz, A.; Bogachev, P.; Brajša, R.
Bibcode: 2010nspm.conf..107R
Altcode:
  The paper presents the first results of the observations of time
  evolution of the quiet solar corona brightenings obtained due to
  very rapid photography of the corona with full-disk EUV telescopes
  of the FET/TESIS instrument onboard the KORONA FOTON satellite. The
  measurements were performed simultaneously in the emission of the Fe
  IX / X 17.1 and Fe VIII 13.1 spectral lines with 10 second temporal
  cadence and spatial scale of 1.7 arc seconds within one hour. This
  test observation, carried out on 15 July 2009, was analyzed in order
  to determine whether this type of observation can be used to identify
  individual microevents in the solar corona heating that are above the
  tresholds of spatial and temporal resolutions of the observations
  of non-active regions in the solar atmosphere. For this purpose,
  a simple method was used involving cross-correlation of the plasma
  emission time evolution at different temperatures, each time from
  observations of identical elements. The results obtained are confronted
  with the expected observable manifestations of the corona heating
  via nanoflares. TESIS is a set of instruments for the Sun photography
  developed in the Lebedev Physics Institute of the Russian Academy of
  Sciences that was launched into orbit in January 2009.

Title: A Comparison of Sunspot Position Measurments from Different
    Data Sets
Authors: Poljancic, I.; Brajsa, R.; Ruzdjak, D.; Hrzina, D.;
   Jurdana-Sepic, R.; Wohl, H.; Otruba, W.
Bibcode: 2010SunGe...5...52P
Altcode:
  There are several data sets containing information about the positions
  of sunspots and sunspot groups that differ in format and precision,
  e.g. GPR (Greenwich Photoheliographic Results) and SOON/USAF/NOAA
  (Solar Optical Observing Network/United States Air Force/National
  Oceanic and Atmosferic Administration). The aim of this paper is to
  check the precision of the SOON/USAF/NOAA data set and compare it with
  the GPR data set. For this purpose, we have used a third data set,
  the Kanzelhöhe Observatory data set, as a basis of sunspot position
  measurments comparison. The positions of selected sunspot groups in the
  digitized Solar Observatory Kanzelhöhe drawings were determined with
  a special software Sungrabber. The selected groups consisted mostly of
  single sunspots (Zürich types H and J) from the years 1972 and 1993
  belonging to the similar phases of the solar activity cycles. The
  determined Kanzelhöhe sunspot group coordinates were compared with
  those from GPR for the year 1972 and SOON/USAF/NOAA for the year
  1993. The rotation velocities calculated for sunspot groups observed
  at Kanzelhöhe were compared with the ones obtained from the two data
  sets mentioned above in the same observing periods. With the assumption
  of constant precision of Kanzelhöhe drawings, it was established that
  SOON/USAF/NOAA data are somewhat less precise than the GPR ones.

Title: A precise measurement of the solar differential rotation by
    tracing small bright coronal structures in SOHO-EIT images. Results
    and comparisons for the period 1998-2006
Authors: Wöhl, H.; Brajša, R.; Hanslmeier, A.; Gissot, S. F.
Bibcode: 2010A&A...520A..29W
Altcode:
  <BR /> Aims: We precisely determine the solar rotation velocity during
  most of the 23rd solar cycle, in the years 1998-2006. We measure the
  solar differential rotation by tracing small bright coronal structures
  (SBCS) in SOHO-EIT images. <BR /> Methods: The 28.4 nm EIT channel was
  used and positions of more than 55 000 structures were measured applying
  an interactive and improved automatic method of data reduction. <BR />
  Results: We achieve the closest representation of the observational
  data when all three solar differential rotation parameters are used
  and obtain the formula ω (b) = 14.499 (±0.006) - 2.54 (±0.06)
  sin<SUP>2</SUP> b - 0.77 (±0.09) sin<SUP>4</SUP>b. This result
  represents the sidereal rotation velocity in deg day<SUP>-1</SUP>
  and is produced by the automatic method applied in 1998-2006. A
  north-south rotational asymmetry and a rigid component of the solar
  rotation at high latitudes were found. <BR /> Conclusions: A more
  differential rotation profile of SBCS than of sunspots and sunspot
  groups was found. The rotation velocity of SBCS is very similar
  to those obtained by small photospheric magnetic features. The
  north-south rotational asymmetry of SBCS was interpreted with a model
  of the relationship between solar rotation and activity. The rigid
  component of the solar rotation at high latitudes, identifiable only
  from the results of the automatic method, was related to larger
  structures mostly identified by that method, in contrast to the
  interactive method, which detected smaller structures. <P />Tables
  3-11 and Figs. 4, 5 are only available in electronic form at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: The chaotic solar cycle. I. Analysis of cosmogenic
    <SUP>14</SUP>C-data
Authors: Hanslmeier, A.; Brajša, R.
Bibcode: 2010A&A...509A...5H
Altcode:
  Context. The study of solar activity over long time intervals using
  proxies. <BR /> Aims: The periodicity of the solar activity cycle
  is studied. The solar activity cycle is governed by a complex dynamo
  mechanism. Methods of nonlinear dynamics enable us to learn more about
  the regular and chaotic behavior of solar activity. <BR /> Methods:
  By applying methods of nonlinear dynamics, the solar activity cycle is
  studied by using solar activity proxies that have been reaching into the
  past for over 10 000 years. The complexity of the system is expressed by
  several parameters of nonlinear dynamics, such as embedding dimension or
  false nearest neighbors, and the method of delay coordinates is applied
  to the time series. <BR /> Results: The solar activity cycle is found
  to be on the edge of chaotic behavior. This can explain the observed
  intermittent period of longer lasting solar activity minima. Filtering
  the data by eliminating variations below a certain period (the periods
  380 yr and 57 yr were used) yields a far more regular behavior of
  solar activity. <BR /> Conclusions: The solar time series of solar
  activity proxies used here clearly shows that solar activity behaves
  differently from random data. The unfiltered data exhibit a complex
  dynamics requiring an embedding dimension &gt;15. The variations become
  more regular when filtering the data. The results also indicate that
  solar activity proxies are influenced by other than solar variations
  and reflect solar activity only on longer time scales.

Title: Solar activity proxies - geomagnetic variations
Authors: Hanslmeier, A.; Brajša, R.
Bibcode: 2010CEAB...34..109H
Altcode:
  Solar activity proxies are needed for studies of the long term
  behaviour of the solar activity cycles. Cosmogenic isotopes like
  ^{14}C are influenced also by geomagnetic field variations. We study
  the influence of such variations on the global behaviour of solar
  activity measured by methods of non linear dynamics.

Title: Comparison of the sidereal angular velocity of subphotospheric
    layers and small bright coronal structures during the declining
    phase of solar cycle 23
Authors: Zaatri, A.; Wöhl, H.; Roth, M.; Corbard, T.; Brajša, R.
Bibcode: 2009A&A...504..589Z
Altcode: 2009arXiv0907.4099Z
  Context: We compare solar differential rotation of subphotospheric
  layers derived from local helioseismology analysis of GONG++
  dopplergrams and the one derived from tracing small bright coronal
  structures (SBCS) using EIT/SOHO images for the period August
  2001-December 2006, which correspond to the declining phase of solar
  cycle 23. <BR />Aims: The study aims to find a relationship between
  the rotation of the SBCS and the subphotospheric angular velocity. The
  north-south asymmetries of both rotation velocity measurements are also
  investigated. <BR />Methods: Subphotospheric differential rotation was
  derived using ring-diagram analysis of GONG++ full-disk dopplergrams of
  1 min cadence. The coronal rotation was derived by using an automatic
  method to identify and track the small bright coronal structures in
  EIT full-disk images of 6 h cadence. <BR />Results: We find that the
  SBCS rotate faster than the considered upper subphotospheric layer
  (3 Mm) by about 0.5 deg/day at the equator. This result joins the
  results of several other magnetic features (sunspots, plages, faculae,
  etc.) with a higher rotation than the solar plasma. The rotation rate
  latitudinal gradients of the SBCS and the subphotospheric layers
  are very similar. The SBCS motion shows an acceleration of about
  0.005°day<SUP>-1</SUP>/month during the declining phase of solar cycle
  23, whereas the angular velocity of subsurface layers does not display
  any evident variation with time, except for the well known torsional
  oscillation pattern. Finally, both subphotospheric and coronal rotations
  of the southern hemisphere are predominantly larger than those of the
  northern hemisphere. At latitudes where the north-south asymmetry of
  the angular velocity increases (decreases) with activity for the SBCS,
  it decreases (increases) for subphotospheric layers.

Title: On solar cycle predictions and reconstructions
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
   Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
Bibcode: 2009A&A...496..855B
Altcode:
  Context: Generally, there are two procedures for solar cycle
  predictions: the empirical methods - statistical methods based on
  extrapolations and precursor methods - and methods based on dynamo
  models. <BR />Aims: The goal of the present analysis is to forecast
  the strength and epochs of the next solar cycle, to investigate proxies
  for grand solar minima and to reconstruct the relative sunspot number
  in the Maunder minimum. <BR />Methods: We calculate the asymmetry of
  the ascending and descending solar cycle phases (Method 1) and use this
  parameter as a proxy for solar activity on longer time scales. Further,
  we correlate the relative sunspot numbers in the epochs of solar
  activity minima and maxima (Method 2) and estimate the parameters of
  an autoregressive moving average model (ARMA, Method 3). Finally,
  the power spectrum of data obtained with the Method 1 is analysed
  and the Methods 1 and 3 are combined. <BR />Results: Signatures of
  the Maunder, Dalton and Gleissberg minima were found with Method 1. A
  period of about 70 years, somewhat shorter than the Gleissberg period
  was identified in the asymmetry data. The maximal smoothed monthly
  sunspot number during the Maunder minimum was reconstructed and found
  to be in the range 0-35 (Method 1). The estimated Wolf number (also
  called the relative sunspot number) of the next solar maximum is in
  the range 88-102 (Method 2). Method 3 predicts the next solar maximum
  between 2011 and 2012 and the next solar minimum for 2017. Also, it
  forecasts the relative sunspot number in the next maximum to be 90
  ± 27. A combination of the Methods 1 and 3 gives for the next solar
  maximum relative sunspot numbers between 78 and 99. <BR />Conclusions:
  The asymmetry parameter provided by Method 1 is a good proxy for solar
  activity in the past, also in the periods for which no relative sunspot
  numbers are available. Our prediction for the next solar cycle No. 24
  is that it will be weaker than the last cycle, No. 23. This prediction
  is based on various independent methods.

Title: Solar Differential Rotation Determined by Tracing Low and
    High Brightness Temperature Regions at 8 mm
Authors: Romštajn, I.; Brajša, R.; Wöhl, H.; Benz, A. O.; Temmer,
   M.; Roša, D.; Ruždjak, V.
Bibcode: 2009CEAB...33...79R
Altcode:
  At the wavelength of 8 mm absorption features (Low brightness
  Temperature Regions, LTRs) and emission features (High brightness
  Temperature Regions, HTRs) can be traced for determination of solar
  rotation. From earlier studies it is known that about two thirds of LTRs
  are associated with Hα filaments. The goal of the present analysis is
  to determine the heights of these solar structures and their rotational
  velocities. We used the method for the simultaneous determination of
  the solar synodic rotation velocity and the height of tracers. The
  rotation velocities were determined by the linear least-square fit of
  their central meridian distances as a function of time. The mean value
  of the low brightness temperature regions' heights is about 45 600
  km. The results of solar rotation determined by tracing LTRs and HTRs
  are mutually compared and also compared with the results using other
  tracers and methods. The method for the simultaneous determination
  of the solar synodic rotation velocity and the height of the tracers
  could be applied properly only on LTRs, since a wide distribution
  over latitudes and central meridian distances of a large data set is
  necessary, which was not available for HTRs. Observational findings that
  HTRs rotate systematically faster than LTRs and the possibility that
  they can be observed at and outside the solar limb are consistent with
  relatively high altitudes of HTRs. It was concluded that the radiation
  mechanism of HTRs is thermal bremsstrahlung, probably associated with
  flaring active regions.

Title: Measurements of the He I 1083 nm Line on the Sun During
Different Solar Activity Phases: in the Years 1993 and 1995
Authors: Jurdana-Šepić, R.; Brajša, R.; Šaina, B.; Wöhl, H.
Bibcode: 2009CEAB...33..337J
Altcode:
  Latitudinal variations and North--South asymmetry of the He I 1083 nm
  line across the solar disc are investigated, based on 69 solar scans
  obtained during two observational campaigns in 1993 and 1995. In both
  time intervals the He I 1083 nm line was observed in absorption. The
  ratio of average intensity in the line and the average intensity of
  the nearby quasi-continuum was calculated <P />and cautiously used
  as a measure of the line absorption and represented as a function of
  position on the solar disc. Results indicate a distinct dependence of
  the He I 1083 nm average relative line intensity on the solar latitude,
  its North--South asymmetry and well pronounced differences for the two
  campaigns belonging to different solar cycle phases. The latitudinal
  dependence is analysed with and without discriminating quiet Sun and
  active regions. The observed behaviour (the latitudinal dependence
  and a North--South asymmetry) is to a large extent a consequence
  of the presence/absence of active regions. The differences found
  for the two observing campaigns are not only due to decreased solar
  activity in 1995 as compared to 1993, but also due to different and
  much more pronounced telluric water-vapour contamination during the
  second observing interval. Finally, in the Appendix we describe all
  He scans used here in more detail and compare the numbers of solar
  features identified in other spectral regions along the scans for the
  two observational campaigns.

Title: A Prediction for the 24<SUP>th</SUP> Solar Cycle
Authors: Brajša, R.; Wöhl, H.; Hanslmeier, A.; Verbanac, G.;
   Ruždjak, D.; Cliver, E.; Svalgaard, L.; Roth, M.
Bibcode: 2009CEAB...33...95B
Altcode:
  The aim of the present analysis is to forecast the strength of the
  next solar maximum of the 24<SUP>th</SUP> cycle. We correlate the
  relative sunspot numbers in the epochs of solar activity minima and
  maxima. Using this method, the estimated relative sunspot number (also
  called the Wolf number) of the next solar maximum is in the range 67-81,
  i.e., about 40 % below the peak sunspot number of 121 for cycle No. 23.

Title: Heights of solar tracers observed at 8 mm and an interpretation
    of their radiation
Authors: Brajša, R.; Romštajn, I.; Wöhl, H.; Benz, A. O.; Temmer,
   M.; Roša, D.
Bibcode: 2009A&A...493..613B
Altcode:
  Context: At the wavelength of 8 mm, emissive features (high
  brightness-temperatrue regions, HTRs) and absorptive features
  (low brightness-temperature regions, LTRs) can be traced for the
  determining the solar rotation. From earlier studies it is known
  that about two thirds of LTRs are associated with Hα filaments. <BR
  />Aims: Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation
  mechanism can be important for explaining the observed phenomena,
  so we determine the heights of solar structures and interpret their
  radiation mechanism(s). <BR />Methods: We use the method of simultaneous
  determination of the solar synodic rotation velocity and the height
  of tracers. The rotation velocities were determined by the linear
  least-square fit of their central meridian distance as a function of
  time. We used a procedure for calculating the brightness temperature for
  a given wavelength and model atmosphere, which integrates the radiative
  transfer equation for the thermal bremsstrahlung. <BR />Results:
  The mean value of the low brightness-temperature regions' heights
  is about 45 600 km. This height was used as input for constructing
  prominence and coronal condensation models, which, when assuming thermal
  bremsstrahlung as the radiation mechanism, yield a decrease in the
  brightness temperature of 2-14%, in agreement with observations. If the
  same radiation mechanism is considered, the models of the solar corona
  above active regions give an increase in the brightness temperature of
  5-19%, also in agreement with observations. In this case an indirect
  indication (from the rotational analysis) that the HTRs are located
  higher in the solar atmosphere than the LTRs was taken into account. <BR
  />Conclusions: The method for simultaneously determining the solar
  synodic rotation velocity and the height of tracers could have only
  been properly applied on LTRs, since a homogeneous distribution over
  latitudes and central meridian distances of a large enough data set is
  necessary. Thermal bremsstrahlung can explain both the LTR (prominences
  and coronal condensations) and HTR (ordinary active regions) phenomena
  observed at 8 mm. At this wavelength, thermal gyromagnetic emission
  is almost surely excluded as a possible radiation mechanism.

Title: On the Solar Rotation and Activity in the Years 1998 - 2003
Authors: Brajsa, R.; Woehl, H.; Hanslmeier, A.; Gissot, S. F.
Bibcode: 2008ESPM...122.114B
Altcode:
  Full-disc full-resolution solar images obtained by the Extreme
  Ultraviolet Imaging Telescope on board the Solar and Heliospheric
  Observatory are used to analyse solar differential rotation by tracing
  coronal bright points. We applied an interactive and an improved
  automatic method of data reduction to process data obtained during
  the period 1998 - 2003 with the Fe XV filter (28.4 nm). Using the
  interactive method, the data obtained during 8 months of observation
  were reduced, while the automatic method was applied to analyse the
  whole 57-month period of observations, since the interactive method is
  much more time consuming than the automatic one. In the present work we
  especially focus on a possible relationship between the solar rotation
  (57 monthly values of the solar rotation parameters determined with
  the automatic method) and activity (relative sunspot numbers for the
  same months) during the maximum phase of the solar cycle 23.

Title: Proper Motions of Coronal Bright Points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.; Verbanac, G.; Skokić, I.; Hanslmeier, A.
Bibcode: 2008CEAB...32..165B
Altcode:
  Full-field full-resolution solar images obtained by the Extreme
  Ultraviolet Imaging Telescope on board the Solar and Heliospheric
  Observatory are used to analyse proper motions, velocity distributions,
  lifetimes, and diffusion coefficient of coronal bright points. The
  results obtained by the interactive method for three tracer subtypes
  (point-like structures, small loops, and small active regions)
  of coronal bright points for the period 4 June 1998 to 22 May 1999
  are presented and compared. Distributions of meridional velocities,
  residual azimuthal velocities and velocities of proper motions are
  presented for the three tracer subtypes. Lifetimes up to 54 hours
  are found for 98% of all observed coronal bright points. Small active
  regions last on the average longer than point-like structures and small
  loops. The correlation between the absolute velocity of proper motion
  and lifetime is investigated and the mean free path (in the range from
  3000 km to 15000 km) and the diffusion coefficient (approximately 200
  km<SUP>2</SUP>/s) of coronal bright points are estimated. Finally,
  characteristics of the random walk process associated to the motions
  of coronal bright points are discussed in the Appendix.

Title: Coronal Bright Points as Tracers for Solar Rotation in
    October-November 1999
Authors: Brajša, R.; Mulec, M.; Hanslmeier, A.; Wöhl, H.; Ruždjak,
   V.; Hochedez, J. -F.
Bibcode: 2008CEAB...32..117B
Altcode:
  Whole-disc full-resolution solar images taken in the extreme ultraviolet
  part of the spectrum (Fe XV line at 28.4 nm) with the EIT instrument
  on board the SOHO spacecraft were used to visually identify coronal
  bright points appropriate for solar rotation determination. From the
  time differences in successive tracer positions amounting to six hours
  the solar rotation velocity was determined tracing coronal bright
  points in images obtained in October and November 1999. The resulting
  parameters and profiles of the solar rotation are presented.

Title: On the solar rotation and activity
Authors: Brajša, R.; Wöhl, H.; Ruždjak, D.; Vršnak, B.; Verbanac,
   G.; Svalgaard, L.; Hochedez, J. -F.
Bibcode: 2007AN....328.1013B
Altcode:
  The interaction between differential rotation and magnetic fields in
  the solar convection zone was recently modelled by Brun (2004). One
  consequence of that model is that the Maxwell stresses can oppose the
  Reynolds stresses, and thus contribute to the transport of the angular
  momentum towards the solar poles, leading to a reduced differential
  rotation. So, when magnetic fields are weaker, a more pronounced
  differential rotation can be expected, yielding a higher rotation
  velocity at low latitudes taken on the average. This hypothesis
  is consistent with the behaviour of the solar rotation during the
  Maunder minimum. In this work we search for similar signatures of
  the relationship between the solar activity and rotation determined
  tracing sunspot groups and coronal bright points. We use the extended
  Greenwich data set (1878-1981) and a series of full-disc solar images
  taken at 28.4 nm with the EIT instrument on the SOHO spacecraft
  (1998-2000). We investigate the dependence of the solar rotation on
  the solar activity (described by the relative sunspot number) and
  the interplanetary magnetic field (calculated from the interdiurnal
  variability index). Possible rotational signatures of two weak solar
  activity cycles at the beginning of the 20th century (Gleissberg
  minimum) are discussed.

Title: An Interpretation of the Coronal Holes' Visibility in the
    Millimeter Wavelength Range
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
   Šaina, B.; Wöhl, H.
Bibcode: 2007SoPh..245..167B
Altcode:
  Various observations indicate that coronal holes generally appear as low
  brightness temperature regions (LTRs) in the centimeter and millimeter
  wavelength ranges. However, within their borders local enhancements of
  radiation, that is, high brightness temperature regions (HTRs), often
  occur. The theory behind the described behavior is not fully understood
  and therefore we analyze full-disk solar images obtained at a wavelength
  of 8 mm at Metsähovi Radio Observatory and compare them with data
  simultaneously taken in other wavelength ranges. The observational
  finding that the average brightness temperature of coronal holes is
  not much different from the quiet-Sun level (with localized deviations
  toward higher and lower intensities on the order of a few percent)
  is compared with theoretical models of the thermal bremsstrahlung
  radiation originating in the solar chromosphere, transition region,
  and corona. Special attention is devoted to the interpretation of the
  localized enhancements of radiation observed inside coronal holes at
  millimeter wavelengths. The main conclusion is that the most important
  contribution to the brightness temperature comes from an increased
  density in the transition region and low corona (i.e., at the heights
  where the temperature is below 10<SUP>6</SUP> K). This can explain
  both the LTRs and HTRs associated with coronal holes.

Title: Are There Radio-quiet Solar Flares?
Authors: Benz, Arnold O.; Brajša, Roman; Magdalenić, Jasmina
Bibcode: 2007SoPh..240..263B
Altcode: 2007astro.ph..1570B
  Some 15% of solar flares having a soft X-ray flux above GOES class C5
  are reported to lack coherent radio emission in the 100 - 4000 MHz
  range (type I - V and decimetric emissions). A detailed study of 29
  such events reveals that 22 (76%) of them occurred at a radial distance
  of more than 800″ from the disk center, indicating that radio waves
  from the limb may be completely absorbed in some flares. The remaining
  seven events have statistically significant trends to be weak in GOES
  class and to have a softer non-thermal X-ray spectrum. All of the
  non-limb flares that were radio-quiet above 100 MHz were accompanied by
  metric type III emission below 100 MHz. Out of 201 hard X-ray flares,
  there was no flare except near the limb (R&gt;800″) without coherent
  radio emission in the entire meter and decimeter range. We suggest
  that flares above GOES class C5 generally emit coherent radio waves
  when observed radially above the source.

Title: Solar Rotation Velocity Determined by Coronal Bright Points -
    New Data and Analysis
Authors: Mulec, M.; Brajša, R.; Wöhl, H.; Hanslmeier, A.; Vršnak,
   B.; Ruždjak, V.; Hochedez, J. -F.; Engler, J.
Bibcode: 2007CEAB...31....1M
Altcode:
  Full-disc solar images obtained with the Extreme Ultraviolet Imaging
  Telescope on board the Solar and Heliospheric Observatory were used
  to analyse solar differential rotation determined by tracing coronal
  bright points. Rotation velocity residuals, meridional motions and
  their relationship are investigated for a new data set from October
  1, 1999 to March 31, 2000. Further we take care for the evolution
  of the single structures, dividing them into Point-Like-Structures,
  Small Loops and Small Active Regions and analysing their variation in
  intensity and size.

Title: Sungrabber - Software for Measurements on Solar Synoptic Images
Authors: Hržina, D.; Roša, D.; Hanslmeier, A.; Ruždjak, V.;
   Brajša, R.
Bibcode: 2007CEAB...31..273H
Altcode:
  Measurement of positions of the tracers on synoptic solar images and
  conversion to heliographic coordinates is a time-consuming procedure
  with different sources of errors. To make measurements faster and
  easier, the application "Sungrabber" was developed. The data of the
  measured heliographic coordinates are stored in text files which are
  linked to the related solar images, which allows also a fast and simple
  comparison of the measurements from different sources. Extension of
  the software is possible and therefore Sungrabber can be used for
  different purposes (e.g. determining the solar rotation rate, proper
  motions of the tracers on the Sun, etc.).

Title: On the Visibility of Coronal Holes in Microwaves
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
   Šaina, B.; Wöhl, H.; Ruždjak, V.
Bibcode: 2007CEAB...31..219B
Altcode:
  Previous observations indicate that coronal holes generally appear as
  low brightness temperature regions in microwaves. However, within their
  borders local enhancements of radiation often occur. This is confirmed
  by comparing a full-disc solar image obtained at 37 GHz on 27 May 1993
  with full-disc solar images obtained at various wavelengths. Microwave
  brightness temperatures of three coronal holes are determined and
  interpreted.

Title: Are there Radio-quiet Solar Flares?
Authors: Benz, Arnold O.; Brajsa, Roman; Magdalenic, Jasmina
Bibcode: 2007astro.ph..1566B
Altcode:
  This submission has been withdrawn by arXiv administrators because it
  is a duplicate of astro-ph/0701570.

Title: Temporal Variations of the Solar Rotation Determined by
    Sunspot Groups
Authors: Brajša, R.; Ruždjak, D.; Wöhl, H.
Bibcode: 2006SoPh..237..365B
Altcode: 2006SoPh..tmp...37B
  The extended Greenwich data set consisting of positions of sunspot
  groups is used for the investigation of cycle-related variations of the
  solar rotation in the years 1874-1981. Applying the residual method,
  which yields a single number for each year describing the average
  deviation from the mean value of the solar rotation, the dependence
  of the rotation velocity residual on the phase of the solar cycle is
  investigated. A secular deceleration of the solar rotation was found:
  the slope being statistically significant at the 3σ level. Periods
  of 33, 22, 11, 5.2, and 3.5 years can be identified in the power
  spectra. The rotation velocity residuals were averaged for all years
  with the same solar cycle phase relative to the nearest preceding
  sunspot minimum. The variation pattern reveals a higher than average
  rotation velocity in the minimum of activity and, to a lesser extent,
  also around the maximum of activity. The analysis was repeated with
  several changes in the reduction method, such as elimination of the
  secular trend, application of statistical weights, different cutoffs of
  the central meridian distance, division of the latitude into subregions
  and treating data from the years of activity minima separately. The
  results obtained are compared with those from the literature, and an
  interpretation of the observed phenomena is proposed.

Title: Periodical patterns in major flare occurrence and their
    relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
Bibcode: 2006AdSpR..38..886T
Altcode:
  A periodical occurrence rate of major solar flares (observed in hard
  X-rays) of ∼24 days (synodic) was first reported by Bai (1987)
  [Bai, T. Distribution of flares on the sun superactive regions and
  active zones of 1980 1985. ApJ 314, 795 807, 1987] for the years 1980
  1985. Here, we report a significant relation between the appearance of
  the 24-day period in major Hα flares and magnetically complex sunspot
  groups (i.e., including a γ and/or δ configuration). From synoptic
  maps of magnetograms (NSO/KP) patterns in the magnetic flux evolution
  are traced which might be the cause of the 24-day period observed in
  flare activity.

Title: Spatial Distribution and North-South Asymmetry of Coronal
    Bright Points from Mid-1998 to Mid-1999
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Rušdjak, V.; Clette,
   F.; Hochedez, J. -F.; Verbanac, G.; Temmer, M.
Bibcode: 2005SoPh..231...29B
Altcode:
  Full-disc full-resolution (FDFR) solar images obtained with the Extreme
  Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric
  Observatory (SOHO) were used to analyse the centre-to-limb function and
  latitudinal distribution of coronal bright points. The results obtained
  with the interactive and the automatic method, as well as for three
  subtypes of coronal bright points for the time period 4 June 1998 to 22
  May 1999 are presented and compared. An indication of a two-component
  latitudinal distribution of coronal bright points was found. The
  central latitude of coronal bright points traced with the interactive
  method lies between 10<SUP>∘</SUP> and 20<SUP>∘</SUP>. This is
  closer to the equator than the average latitude of sunspots in the
  same period. Possible implications for the interpretation of the
  solar differential rotation are discussed. In the appendix, possible
  differences between the two solar hemispheres are analysed. More coronal
  bright points were present in the southern solar hemisphere than in
  the northern one. This asymmetry is statistically significant for the
  interactive method and not for the automatic method. The visibility
  function is symmetrical around the central meridian.

Title: The Influence of the Evolution of Sunspot Groups on the
    Determination of the Solar Velocity Field
Authors: Ruždjak, D.; Brajša, R.; Sudar, D.; Wöhl, H.
Bibcode: 2005SoPh..229...35R
Altcode:
  Meridional motions and differential rotation of stable recurrent
  sunspot groups from the Greenwich data set are investigated. Simple
  and complex, as well as younger and older sunspot groups are treated
  separately. There is no difference in behavior of the meridional
  motions for the simple and complex sunspot groups, while complex groups
  rotate faster than the simple ones. If we attribute the differences of
  rotational velocities to the errors in position determination, it can be
  concluded that the rotational velocities determined by using sunspot
  groups as tracers are slightly overestimated. Both the meridional
  motions and differential rotation show the same dependence on the age,
  when simple and complex recurrent sunspot groups are considered.

Title: The Two Complexes of Activity Observed in the Northern
    Hemisphere during 1982 and the 24-Day Periodicity of Flare Occurrence
Authors: Ruždjak, V.; Ruždjak, D.; Brajša, R.; Temmer, M.;
   Hanslmeier, A.
Bibcode: 2005HvaOB..29..117R
Altcode:
  Daily numbers of solar Hα flares of importance classes ≥ 1 for
  the northern solar hemisphere in 1982 are studied applying wavelet
  power spectra (WPS). Special attention is paid to the occurrence of a
  24-day period in the WPS. The wavelet power spectra method is combined
  with synoptic maps of the magnetic fields. Separately, flare indices
  of two activity complexes mainly contributing to flare occrrence in
  this period are examined. It is found that the detected 24-day signal
  in the WPS is mainly a consequence of the presence of the two flare
  activity complexes separated by about 45° in longitude during several
  succesive Carrington rotations.

Title: On the 24-day period observed in solar flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
Bibcode: 2004SoPh..221..325T
Altcode:
  Time series of daily numbers of solar Hα flares from 1955 to
  1997 are studied by means of wavelet power spectra with regard to
  predominant periods in the range of ∼ 24 days (synodic). A 24-day
  period was first reported by Bai (1987) for the occurrence rate of
  hard X-ray flares during 1980-1985. Considering the northern and
  southern hemisphere separately, we find that the 24-day period is not
  an isolated phenomenon but occurs in each of the four solar cycles
  investigated (No. 19-22). The 24-day period can be established also
  in the occurrence rate of subflares but occurs more prominently in
  major flares (importance classes ≥ 1). A comparative analysis of
  magnetically classified active regions subdivided into magnetically
  complex (i.e., including a γ and/or δ configuration) and non-complex
  (α, β) reveals a significant relation between the appearance of
  the 24-day period in Hα flares and magnetically complex sunspot
  groups, whereas it cannot be established for non-complex groups. It is
  suggested that the 24-day period in solar flare occurrence is related
  to a periodic emergence of new magnetic flux rather than to the surface
  rotation of sunspots.

Title: Deceleration of the rotational velocities of sunspot groups
    during their evolution
Authors: Ruždjak, D.; Ruždjak, V.; Brajša, R.; Wöhl, H.
Bibcode: 2004SoPh..221..225R
Altcode:
  Using the Greenwich Photoheliographic Results for the years
  1874-1976 the daily rotational velocities for 955 recurrent and 13169
  non-recurrent sunspot groups from the first day of their appearance and
  during their evolution have been determined. The rotational velocities
  were divided in six latitude strips with a width of five degrees and
  grouped according to the age of the groups. It was established that
  the rotational velocities of recurrent and non-recurrent sunspot
  groups decrease with time in all studied latitude strips. At their
  birth the recurrent spot groups rotate faster by about 0.15°
  day<SUP>−1</SUP> than the non-recurrent ones and settle, within
  the errors of measurements, to an about 0.5° day<SUP>−1</SUP>
  slower velocity value during the second disc passage. A comparison
  of our results with helioseismology measurements indicates that in
  the frame of the anchoring hypothesis, the recurrent sunspot groups
  at their birth could be coupled to the fast rotating layer at about
  r=0.93 R<SUB>⊙</SUB>.

Title: Height correction in the measurement of solar differential
    rotation determined by coronal bright points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.; Roša, D.
Bibcode: 2004A&A...414..707B
Altcode:
  Full-disc solar images obtained with the Extreme Ultraviolet Imaging
  Telescope (EIT) on board the Solar and Heliospheric Observatory
  (SOHO) are used to analyse solar differential rotation by tracing
  coronal bright points for the period June 4, 1998 to May 22, 1999. A
  method for the simultaneous determination of the true solar synodic
  rotation velocity and the height of the tracers is applied to data
  sets analysed with interactive and automatic methods. The calculated
  height of coronal bright points is on average 8000-12000 km above
  the photosphere. Corrected rotation velocities are transformed
  into sidereal ones and compared with results from the literature,
  obtained with various methods and tracers. The differential rotation
  profile determined by coronal bright points with the interactive method
  corresponds roughly to the profile obtained by correlating photospheric
  magnetic fields and the profile obtained from the automatic method
  corresponds roughly to the rotation of sunspot groups. This result is
  interpreted in terms of the differences obtained in the latitudinal
  distribution of coronal bright points using the two methods.

Title: Importance of magnetically complex active regions on solar
    flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
Bibcode: 2004HvaOB..28...95T
Altcode:
  Daily numbers of solar Hα flares from 1955 to 1997 and daily numbers
  of magnetically classified active regions for the time span 1964--1997
  are studied applying wavelet power spectra. The occurrence of dominant
  periods in the range of ∼24 days (synodic) is investigated considering
  the northern and southern hemisphere separately. From the flare events
  it is revealed that the 24-day period occurs in each of the four solar
  cycles investigated (no. 19--22). The 24-day period can be established
  also in the occurrence rate of subflares but occurs more prominently
  in major flares (importance classes ≥1). Magnetically complex active
  regions, i.e. including a γ and/or δ configuration, show the 24-day
  period closely related to those found for major Hα flares, whereas
  it cannot be established for non-complex α, β groups.

Title: Variation of the solar rotation during the activity cycle
    applying the residual method to Greenwich data
Authors: Brajša, R.; Wöhl, H.; Ruždjak, D.; Schawinski-Guiton, K.
Bibcode: 2004HvaOB..28...55B
Altcode:
  The Greenwich data set consisting of positions of sunspot groups was
  used for the investigation of possible cycle-related variations of the
  solar rotation in the years from 1874 to 1976. The measurements were
  extended with the USAF/SOON and NOAA data for the years 1977--1981. The
  residual method providing yearly deviations from the mean rotation
  velocity (averaged over all years) for each 5-deg latitude band was
  applied. These deviations were averaged over latitudes and yearly
  residuals were calculated. A dependence of the rotation velocity
  residual on the phase of the solar cycle was found and compared with
  results from the literature.

Title: Proper motions of sunspots - new data and further results
Authors: Wöhl, H.; Brajša, R.; Kučera, A.; Ruždjak, V.; Rybák, J.
Bibcode: 2004HvaOB..28...47W
Altcode:
  The attempts to investigate patterns of motions of main spot components
  and small pores in complex sunspot groups were continued. The data
  discussed stem mainly from observations at Hvar/HR and Tatranská
  Lomnica/SK. Two historic collections of photographic plates are
  included: The plate archives of the former Fraunhofer Institute and
  that of photographic plates taken at Skalnate Pleso/SK.

Title: Periodical patterns in major flare occurrence and their
    relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybak, J.; Brajsa, R.; Hanslmeier, A.
Bibcode: 2004cosp...35.1395T
Altcode: 2004cosp.meet.1395T
  A periodical occurrence rate of solar major flares (observed in
  hard X-rays) of about 24 days (synodic) was first reported by Bai
  (1987) for the years 1980--1985. Its origin is still far from being
  understood. Applying wavelet analyses for daily numbers of Hα flare
  events covering almost four entire solar cycles (no. 19--22) reveals a
  24-day period in each of the cycles studied. This can be established
  primarily in the occurrence rate of major flares but is also seen
  in subflares. Since large flares occur preferentially in association
  with active regions of complex magnetic configuration a comparative
  study of magnetically classified active regions, subdivided into
  magnetically complex (i.e. including a γ and/or δ configuration)
  and non-complex (α, β) was performed. A significant relation
  between the appearance of the 24-day period in major Hα flares and
  magnetically complex sunspot groups is found, whereas it cannot be
  established for non-complex groups. From solar rotation studies based
  on tracing sunspots practically no siderial rotation velocities as high
  as 16 deg/day (which corresponds to a synodic period of ∼24 days)
  are reported. Thus the cause of the 24-day period is very likely not
  related to solar surface rotation. Alternatively it might be due to
  periodical patterns in magnetic flux emergence which is an important
  driver of flare eruptions. We test this hypothesis by investigating
  synoptic maps of magnetograms (National Solar Observatory/Kitt Peak)
  for selected time ranges in which the 24-day period is revealed for
  both flares and magnetically complex active regions.

Title: Extracting the apparent motion from two successive EIT images
Authors: Gissot, Samuel F.; Hochedez, J. -F.; Dibos, F.; Brajša,
   R.; Jacques, L.; Berghmans, D.; Zhukov, A.; Clette, F.; Wöhl, H.;
   Antoine, J. -P.
Bibcode: 2003ESASP.535..853G
Altcode: 2003iscs.symp..853G
  The EIT observations cover more than seven years of the 23rd solar
  cycle. The main synoptic dataset, usually refered to as the "CME
  Watch", is a nearly uninterrupted sequence of images taken in the Fe
  XII bandpass at a cadence of four images per hour. In this work we
  study motion tracking methods in order to estimate displacements from
  frame to frame. We have implemented a novel optical flow algorithm,
  and tested it on a couple of successive images. We have linked the
  apparent motion occurring between two frames to the expected rotation
  rate. On this short time scale (20 minutes), we are able to retrieve
  the global parameters of the solar differential rotation. A strategy
  for the extraction of region with reliable motion will be discussed.

Title: Properties of the solar velocity field indicated by motions
    of coronal bright points
Authors: Vršnak, B.; Brajša, R.; Wöhl, H.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.
Bibcode: 2003A&A...404.1117V
Altcode:
  Full-disc solar images obtained with the Extreme Ultraviolet Imaging
  Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
  are used to analyse properties of the solar velocity field by tracing
  coronal bright points from June 4, 1998 to May 22, 1999. Rotation
  velocity residuals, meridional motions and their relationship are
  investigated. Zones of slow and fast rotation found in motions of
  coronal bright points are consistent with the pattern of torsional
  oscillations, indicating that the statistical velocity pattern
  of bright point motions reflects the large-scale plasma flows. A
  complex pattern of meridional motion is deduced: The equatorward
  flows are found to dominate at low (B&lt;10<SUP>deg</SUP>) and high
  (B&gt;40<SUP>deg</SUP>) latitudes, whereas at mid-latitudes (B~
  10<SUP>deg</SUP>-40<SUP>deg</SUP>) a poleward flow is inferred. The
  complete data set shows no significant correlation between rotation
  residuals and meridional motions. However, when a subsample of
  coronal bright points including only the ``point-like structures''
  (predominantly young bright points) is considered, a statistically
  significant correlation is found. On average, faster tracers show
  equatorward motion and the slower ones show poleward motion. Such
  a segregation is reflected in a statistically significant
  covariance of the rotation residuals and meridional velocities
  in the order of -1000 m<SUP>2</SUP> s<SUP>-2</SUP>, revealing an
  equatorward transport of angular momentum. The negative value of the
  covariance is provided by the high velocity tail in the velocity
  distribution of point-like structures, representing less than 15%
  of the population. The latitude dependence of the covariance can be
  expressed as Q=-62 B + 200 m<SUP>2</SUP> s<SUP>-2</SUP> covering the
  range B=0<SUP>deg</SUP>-60<SUP>deg</SUP>.

Title: Solar rotation velocity determined by coronal bright points
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. F.; Roša, D.; Hržina, D.
Bibcode: 2003HvaOB..27...13B
Altcode:
  Full-disc solar images in the extreme ultraviolet part of the spectrum
  from the SOHO spacecraft (instrument EIT, data in the spectral line of
  Fe XV at a wavelength of 28.4 nm) are used to identify and trace coronal
  bright points with the interactive and automatic method. The Solar
  rotation was determined for the period June 4, 1998 to May 22, 1999
  and a two-step velocity filter was applied. Histograms of latitudinal
  and central meridian distance distributions of coronal bright points,
  for both solar hemispheres treated together (north and south, east and
  west), are presented and compared for different reduction procedures.

Title: Proper motions of sunspot groups
Authors: Wöhl, H.; Brajša, R.; Kučera, A.; Ruždjak, V.; Rybák, J.
Bibcode: 2003HvaOB..27....1W
Altcode:
  Attempts to investigate typical patterns of motions of main spot
  components and small pores in complex sunspot groups are described. The
  data used up to now stem from observations at Hvar/HR, Tatranská
  Lomnica/SK, Izaña/E, Debrecen/H and from the MDI instrument on
  SoHO. Preliminary results are presented.

Title: Flare waves observed in Helium I 10 830 Å. A link between
    Hα Moreton and EIT waves
Authors: Vršnak, B.; Warmuth, A.; Brajša, R.; Hanslmeier, A.
Bibcode: 2002A&A...394..299V
Altcode:
  Three traveling disturbances recorded in the absorption line of
  Helium I at 10 830 Å, (He I), analogous to Hα Moreton waves,
  are analyzed. The morphology and kinematics of the wavefronts are
  described in detail. The He I wave appears as an expanding arc of
  increased absorption roughly corresponding to the Hα disturbance,
  although not as sharply defined. He I perturbations consist of a
  relatively uniform diffuse component and a patchy one that appears as
  enhanced absorption in He I mottles. It leads the Hα front by some
  20 Mm and can be followed to considerably larger distances than in
  Hα observations. Behind the front stationary areas of reduced He I
  absorption develop, resembling EUV coronal dimming. The observed He I
  as well as the Hα disturbances show a deceleration of the order of
  100-1000 m s<SUP>-2</SUP>. Moreover, in the event where Hα , He I,
  and EUV wavefronts are observed, all of them follow closely related
  kinematical curves, indicating that they are a consequence of a common
  disturbance. The analysis of spatial perturbation profiles indicates
  that He I disturbances consist of a forerunner and a main dip, the
  latter being cospatial with the Hα disturbance. The properties and
  behavior of the wavefronts can be comprehended as a consequence of a
  fast-mode MHD coronal shock whose front is weakly inclined to the solar
  surface. The Hα disturbance and the main He I dip are a consequence
  of the pressure jump in the corona behind the shock front. The He I
  forerunner might be caused by thermal conduction from the oblique shock
  segments ahead of the shock-chromosphere intersection, or by electron
  beams accelerated in the quasi-perpendicular section of the shock.

Title: Solar differential rotation determined by tracing coronal
    bright points in SOHO-EIT images. II. Results for 1998/99 obtained
    with interactive and automatic methods
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.
Bibcode: 2002A&A...392..329B
Altcode:
  Full-disc solar images obtained with the Extreme Ultraviolet Imaging
  Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
  were used to analyse solar differential rotation by tracing coronal
  bright points. The results obtained with the interactive and the
  automatic method for the time period June 4, 1998 to May 22, 1999 are
  presented and compared. A possible north-south rotational asymmetry
  and differences in the rotation velocity curves for various subtypes
  of tracers are investigated.

Title: Differential Rotation of Stable Recurrent Sunspot Groups
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, D.; Sudar,
   D.; Roša, D.; Hržina, D.
Bibcode: 2002SoPh..206..229B
Altcode:
  Stable recurrent sunspot groups from the Greenwich data set which
  were identified in at least two subsequent solar rotations were
  traced. The solar rotation was determined by the period method from
  the time difference of the two central meridian passages of each of
  the 327 identified groups. Sidereal rotation periods were calculated
  from the synodic ones by a seasonal-dependent procedure taking into
  account the details of the Earth's motion around the Sun. Growing
  recurrent sunspot groups rotate on the average faster than decaying
  recurrent sunspot groups, while sunspot groups of all types taken
  together rotate faster than both growing and decaying recurrent sunspot
  groups. A north-south rotational asymmetry and a cycle-dependence of
  rotational velocity of recurrent sunspot groups were analyzed. Positive
  rotation velocity deviations are larger, but less numerous than the
  negative ones. Signatures of torsional oscillations were not found
  analyzing the rotation velocity residual of recurrent sunspot groups
  as a function of the distance from the average latitude of activity.

Title: Solar differential rotation determined by tracing coronal
    bright points in SOHO-EIT images. I. Interactive and automatic
    methods of data reduction
Authors: Brajša, R.; Wöhl, H.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.
Bibcode: 2001A&A...374..309B
Altcode:
  Full-disc solar images obtained with the Extreme Ultraviolet Imaging
  Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO)
  were used to analyse solar differential rotation determined by tracing
  coronal bright points. Two different procedures were developed and
  compared: an interactive and an automatic method. The interactive method
  is based on the visual tracing of coronal bright points in consecutive
  images using computer programs written in the Interactive Data Language
  (IDL). The automatic method relies on the IDL procedure ``Regions Of
  Interest (ROI) segmentation'' which is used to detect and follow bright
  points in triplets of consecutive images. The test-results obtained
  applying both methods by different persons who performed tracing are
  presented and compared. The advantages and disadvantages of the two
  methods are discussed.

Title: On the Rigid Component in the Solar Rotation
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
   Pohjolainen, S.; Urpo, S.
Bibcode: 2001ASSL..259..263B
Altcode: 2001dysu.conf..263B
  A rigid component in the rotation velocity determined by tracing low
  brightness temperature regions in the microwave regime was found and
  interpreted in terms of their association rate (39%) with rigidly
  rotating ``pivot-points".

Title: Meridional Motions of Stable Recurrent Sunspot Groups
Authors: Wöhl, H.; Brajša, R.
Bibcode: 2001SoPh..198...57W
Altcode:
  Stable recurrent sunspot groups from the Greenwich data set which
  were identified in at least two subsequent solar rotations were traced
  and meridional motions were determined from the two central meridian
  passages. In total, 327 meridional velocities were calculated and
  the results for the northern and the southern solar hemisphere were
  compared. A dependence of the solar meridional velocity vectors on the
  development status, latitude and position respectively to the activity
  belt of sunspots is investigated. The results indicate that sunspot
  groups are moving on the average away from the center of activity. This
  was found for sunspot groups growing and decreasing in area.

Title: Determination of the Solar Rotation Tracing EUV Bright Points
    with the Automatic Method
Authors: Wöhl, H.; Brajša, R.; Vršnak, B.; Ruždjak, V.; Clette,
   F.; Hochedez, J. -F.
Bibcode: 2001HvaOB..25...27W
Altcode:
  Full-disc solar images in the extreme ultraviolet part of the spectrum
  from the SOHO spacecraft (instrument EIT, data in the spectral
  line of Fe XV at the wavelength of 28.4 nm) are used for the solar
  rotation determination tracing coronal bright points. From the time
  differences in tracer positions, approximately six hours, the solar
  rotation velocity is determined automatically for image sequences in
  several time intervals from June 4, 1998 to May 22, 1999. The resulting
  rotational profiles are mutually compared.

Title: Determination of the Solar Rotation Tracing EUV Bright Points
    with the Interactive Method
Authors: Brajša, R.; Wöhl, H.; Schuck, T. J.; Schawinski-Guiton,
   K.; Wegner, A.; Vršnak, B.; Ruždjak, V.; Clette, F.; Hochedez, J. -F.
Bibcode: 2001HvaOB..25...13B
Altcode:
  Full-disc solar images in the extreme ultraviolet part of the spectrum
  from the SOHO spacecraft (instrument EIT, data in the spectral line of
  Fe XV at a wavelength of 28.4 nm) are used to visually identify coronal
  bright points appropriate for the solar rotation determination. From the
  time differences in successive tracer positions, about six hours, the
  solar rotation velocity is determined tracing coronal bright points in
  several time intervals from June 4, 1998 to May 22, 1999. The resulting
  rotational profiles obtained by five observers are mutually compared.

Title: An Analysis of the Solar Rotation Velocity by Tracing Coronal
    Features
Authors: Brajsa, R.; Vrsnak, B.; Ruzdjak, V.; Rosa, D.; Hrzina, D.;
   Wöhl, H.; Clette, F.; Hochedez, J. -F.
Bibcode: 2001IAUS..203..377B
Altcode:
  Full-disc solar images in the extreme ultraviolet part of the spectrum
  from the SOHO spacecraft (EIT) are used to identify various coronal
  structures appropriate for the solar rotation determination (e.g. bright
  points and coronal holes). From the time differences in tracer positions
  (more than 1 image per day) solar rotation velocities are measured,
  primarily by well-defined tracers, such as coronal bright points, whose
  large number and broad coverage of latitudes may provide an unique
  opportunity for a solar rotation analysis. The analysis started using
  the SOHO data from 1997-1999 and preliminary experiences obtained
  measuring solar rotation from the full-disc images in soft X-rays
  from the YOHKOH (SXT) satellite were taken into account. This work is
  connected to the SOHO EIT Proposal Brajsas.

Title: Statistical Weights and Selective Height Corrections in the
    Determination of the Solar Rotation Velocity
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
   Pohjolainen, S.; Upro, S.
Bibcode: 2000SoPh..196..279B
Altcode:
  Observations of the Sun performed at 37 GHz with the 14-m radio
  telescope of the Metsähovi Radio Observatory were analyzed. Rotation
  velocities were determined, tracing Low Temperature Regions (LTRs) in
  the years 1979-1980, 1981-1982, 1987-1988, and 1989-1991. Statistical
  weights were ascribed to the determined rotation velocities of LTRs,
  according to the number of tracing days. Measured changes of the
  rotation velocity during the solar activity cycle, as well as a
  north-south rotation asymmetry, are discussed. The results obtained
  with and without the statistical weights procedure are compared, and it
  was found that the statistical significance of the solar differential
  rotation parameters' changes is higher when the statistical weights
  procedure is applied. A selective application of the height correction
  on LTR's positions has not removed the cycle-related changes nor the
  north-south asymmetry of the solar rotation measured tracing LTRs. So,
  projection effects cannot explain these changes. The differential
  rotation of LTRs is more rigid than the differential rotation obtained
  tracing magnetic features and measuring Doppler shifts, which can be
  explained by the association rate of the LTRs' positions with rigidly
  rotating `pivot points'. The observed cycle-related changes and the
  north-south asymmetry of the rotation velocity of LTRs are consistent
  with the cycle-related changes and the north-south asymmetry of the
  association rate between LTRs and pivot points.

Title: Characteristics of Flares with Hα Emission Protruding over
    Major Sunspot Umbrae
Authors: Vršnak, B.; Ruždjak, V.; Brajša, R.; Zlobec, P.; Altaş,
   L.; Özgüç, A.; Aurass, H.; Schroll, A.
Bibcode: 2000SoPh..194..285V
Altcode:
  A sample of 47 importance ≥ 1 flares whose Hα emission occurred
  or protruded over umbrae of major sunspots (so called Z-flares) was
  studied to investigate characteristics of the associated dm - m radio,
  microwave and soft X-ray emission as the energy release site permeats
  into regions of strong magnetic fields. A close time association was
  found between the microwave burst peak and the `contact' of the Hα
  emission with the sunspot umbra. The Hα emission attained maximum
  close to or a few minutes after the contact. The soft X-ray bursts
  were delayed more, attaining maximum 0-10 min after the contact. The
  onset of bursts in the dm - m wavelength range was associated with the
  period of growth or the peak of the microwave burst. Two categories
  of type III and IV bursts could be recognized: the ones starting some
  ten minutes before the microwave peak, and those that begin close to
  the microwave burst peak. Type III bursts occur preferably when the
  microwave burst peaks simultaneously with or after the contact. The
  results are explained presuming that the contact reveals a permeation
  of the energy release process into a region of strong magnetic fields,
  where the process intensifies, and where the accelerated particles
  have access to magnetic field lines extending to large coronal
  heights. Different manifestations of the energy release process in
  various magnetic field topologies are considered to account for the
  various time sequences observed.

Title: Position Measurements on Synoptic Solar Images
Authors: Rosa, D.; Hrzina, D.; Vrsnak, B.; Brajsa, R.
Bibcode: 2000HvaOB..24..145R
Altcode:
  Procedures for finding the solar sidereal rotation rate, which are
  taking into account the height of tracers are described. The related
  algorithms for data reduction, including detailed corrections for the
  Earth's motion, are presented.

Title: Measurements of Solar Rotation Using EUV Bright Points -
    Preliminary Results
Authors: Brajsa, R.; Woehl, H.; Kasabasic, M.; Rodmann, J.; Vrsnak,
   B.; Ruzdjak, V.; Rosa, D.; Hrzina, D.; Clette, F.; Hochedez, J. -F.
Bibcode: 2000HvaOB..24..153B
Altcode:
  Full-disc solar images in the extreme ultraviolet part of the spectrum
  from the SOHO spacecraft (instrument EIT, data in the spectral line
  of Fe XV at the wavelength of 28.4 nm) are used to identify visually
  various small-scale coronal structures appropriate for the determination
  of the solar rotation. From the time differences in tracer positions,
  approximately six hours, the solar rotation velocity is determined
  tracing coronal bright points in the period June 4-14, 1998 by four
  observers. The resulting rotational profiles are mutually compared
  and the reduction methods are discussed.

Title: On the Meridional Motions of Recurrent Stable Sunspot Groups
Authors: Brajsa, R.; Woehl, H.
Bibcode: 2000HvaOB..24..125B
Altcode:
  Meridional motions of recurrent stable sunspot groups are analysed as
  a function of the distance from the average latitude of activity in
  each solar hemisphere. Results were obtained for two data subsets,
  consisting of recurrent sunspot groups decreasing and growing in
  area respectively, and are compared with the ones published in the
  literature. An interpretation of the results in the frame of the model
  of magnetic flux-transport on the Sun is discussed.

Title: Correlated Radio Bursts Observed at Metric and Millimetric
    Wavelengths
Authors: Zlobec, P.; Urpo, S.; Vrsnak, B.; Brajsa, R.; Ruzdjak, V.
Bibcode: 2000HvaOB..24...41Z
Altcode:
  Characteristics of the bursts that occur almost contemporaneously at
  metric and millimetric wavelengths are presented. It is found that
  such events are rather rare. The correlated impulsive bursts observed
  at 237 MHz and at 37 GHz start in average almost simultaneously (time
  difference 0.3 - 2.8 s). The first peaks at 37 GHz are delayed few
  seconds (3.1 - 3.0 s) in respect to the 237 MHz peaks, whereas for the
  bursts maxima the delay is about 1s in average (1.0 - 2.7 s). A weak
  correlation between peak fluxes at 37 GHz and 237 MHz is found. Spectral
  characteristics of these events indicate electron beams of extremely
  high energies. The association of the gradual bursts observed at 37
  GHz and the phenomena at 237 MHz is not so clear, however in some
  cases a relationship was established.

Title: Height of Tracers and the Correction of the Measured Solar
Synodic Rotation Rate: Demonstration of the Method
Authors: Vršnak, B.; Roša, D.; Božić, H.; Brajša, R.; Ruždjak,
   V.; Schroll, A.; Wöhl, H.
Bibcode: 1999SoPh..185..207V
Altcode:
  Two large stable solar filaments were used as test tracers to determine
  the apparent synodic rotation rate as a function of the central meridian
  distance for several filaments' segments at different heights. An
  analytic fitting procedure was applied to determine simultaneously
  the real synodic rotation rate and the height of the traced filament
  segments. The determined heights were compared with the values obtained
  from the widths of filament contours on the solar disk and with the
  values obtained by direct measurements at the solar limb. Furthermore,
  the obtained rotation rates and heights of the filaments' segments close
  to the filaments' pivot points were compared with the values obtained
  using two successive central meridian passages. Finally, sources and
  scales of errors were investigated and possible implications on the
  previous studies of the solar differential rotation were considered.

Title: An Estimate of Microwave low-Brightness-Temperature Regions'
    Heights Obtained Measuring Their Rotation Velocity
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
   Pohjolainen, S.; Urpo, S.
Bibcode: 1999SoPh..184..281B
Altcode:
  Daily full-disk solar maps obtained at 37 GHz in the years 1979,
  1980, 1981, 1982, 1987, 1988, 1989, 1990, and 1991 are analysed
  and compared with full-disk solar maps in Hα. A search for a
  difference in the measured angular rotation velocity for two classes
  of microwave low-brightness-temperature regions (LTRs), associated and
  not associated with Hα filaments, is performed. Procedures with and
  without statistical weights, assigned to angular rotation velocities
  according to the tracing time, are applied and the statistical
  significance of the results is discussed. A higher angular rotation
  velocity is measured for LTRs associated with Hα filaments than for
  the not-associated ones. This angular velocity difference is interpreted
  as a consequence of a height difference between these two types of LTR
  tracers. Changes of the solar differential rotation velocity during
  the activity cycle measured using LTRs as tracers are explained by
  the measured cycle-dependence of the association rate between LTRs
  and Hα filaments. Similarly, the north-south asymmetry in the solar
  rotation velocity measured tracing LTRs is explained by the measured
  north-south asymmetry in the association rate between LTRs and Hα
  filaments. The rotation velocity of LTRs and Hα filaments is on the
  average more rigid in comparison with sunspots.

Title: An analysis of the solar rotation velocity determined tracing
    microwave features and an estimate of their heights.
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Wöhl, H.;
   Pohjolainen, S.; Urpo, S.
Bibcode: 1999joso.proc..156B
Altcode:
  Measurements of the Sun performed at 37 GHz (8 mm) with the 14 m
  radio telescope of the Metsähovi Radio Observatory were analysed
  and rotation velocities tracing microwave Low brightness Temperature
  Regions in the years 1979 - 1980, 1981 - 1982, 1987 - 1988, and 1989 -
  1991 were determined. The statistical weights method was applied and
  possible changes of the measured rotation velocity values are discussed.

Title: A Method to Determine the Solar Synodic Rotation Rate and
    the Height of Tracers
Authors: Roša, D.; Vršnak, B.; Božić, H.; Brajša, R.; Ruždjak,
   V.; Schroll, A.; Wöhl, H.
Bibcode: 1998SoPh..179..237R
Altcode:
  The dependence of the measured apparent synodic solar rotation rate
  on the height of the chosen tracer is studied. A significant error
  occurs if the rotation rate is determined by tracing the apparent
  position of an object above the photospheric level projected on the
  solar disc. The centre-to-limb variation of this error can be used to
  determine simultaneously the height of the object and the true synodic
  rotation rate. The apparent (projected) heliographic coordinates
  are presented as a function of the height of the traced object and
  the coordinates of its `footpoint'. The relations obtained provide
  an explicit expression for the apparent rotation rate as a function
  of the observed heliographic coordinates of the tracer, enabling an
  analytic least-squares fit expression to determine simultaneously the
  real synodic rotation rate and the height of the tracer.

Title: On the Possible Changes of the Solar Differential Rotation
    during the Activity Cycle Determined Using Microwave Low-Brightness
    Regions and Hα Filaments as Tracers
Authors: Brajša, R.; Ruždjak, V.; Vršnak, B.; Pohjolainen, S.;
   Urpo, S.; Schroll, A.; Wöhl, H.
Bibcode: 1997SoPh..171....1B
Altcode:
  The solar rotation rate obtained using the microwave
  Low-brightness-Temperature Regions (LTRs) as tracers in the heliographic
  range ± 55° from the years 1979-1980, 1981-1982, 1987-1988, and
  1989-1991 varied from 3% to 4% in medium latitudes, and below 1%
  at the equator. Using Hα filaments as tracers at higher latitudes
  from the years 1979, 1980, 1982, 1984, and 1987, the solar rotation
  rate variation was between 2% and 8%. This represents an upper limit
  on the rotation rate variation during the solar activity cycle. Such
  changes could be caused by short-lived, large-scale velocity patterns
  on the solar surface. The Sun revealed a higher rotation rate on the
  average during the maxima of the solar activity cycles 21 and 22,
  i.e., in the periods 1979-1980 and 1989-1991, respectively, which
  differs from the rotation rates (lower on the average) in some years,
  1981-1982 and 1987-1988, between the activity maximum and minimum
  (LTR data). Simultaneous comparison of rotation rates from LTRs and
  Hα filament tracings was possible in very limited time intervals
  and latitude bands only, and no systematic relationship was found,
  although the rotation rates determined by LTRs were mostly smaller than
  the rotation rates determined by Hα filaments. The errors obtained by
  applying different fitting procedures of the LTR data were analyzed, as
  well as the influence of the height correction. Finally, the north-south
  asymmetry in the rotation rate investigated by LTRs indicates that
  the southern solar hemisphere rotated slower in the periods under
  consideration, the difference being about 1%. The reliability of all
  obtained results is discussed and a comparison with other related
  studies was performed.

Title: Soft X-ray, Microwave and He I Measurements of Coronal Holes
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
   S.; Sakurai, T.; Wohl, H.
Bibcode: 1997IAUJD..19E..15B
Altcode:
  The Poster presents and describes microwave signatures of three
  coronal holes that were recorded on May 27, 1993. Differences in the
  brightness temperatures between an equatorial and two polar coronal
  holes were found. The measurements in the He I 10830 AA absorption
  line for that day were also analyzed and compared with the microwave
  and soft X-ray data.

Title: On the Determination of the Height of Microwave Low Temperature
    Regions from Solar Rotation Measurements
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
   S.; Woehl, H.
Bibcode: 1997HvaOB..21...67B
Altcode:
  A larger angular rotation velocity was measured for microwave LTRs
  associated with H-alpha filaments than for the not associated ones. This
  implies that LTRs not associated with H-alpha filaments are located
  at lower heights above the solar photosphere than LTRs associated with
  H-alpha filaments. Data from three intervals were analysed (1979-1980,
  1981-1982 and 1987-1988) with different percentages of association
  between LTRs and H-alpha filaments.

Title: A New Method for Numerical Data Reduction of Solar Microwave
    Measurements
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Woehl, H.; Pohjolainen,
   S.; Urpo, S.
Bibcode: 1996HvaOB..20...15B
Altcode:
  Numerical data reduction of full-disk solar measurement taken in
  the microwave part of the spectrum (37 GHz) at the Metsahovi Radio
  Research Station is described. The basic parameter distinguishing
  between various features on the microwave solar maps is the brightness
  temperature. Regions on the Sun with a lower brightness temperature
  than the quiet Sun level are called Low Temperature Regions (LTRs),
  and in the present paper mainly LTRs are considered. On the other
  hand, High Temperature Regions (HTRs) have a brightness temperature
  higher than the quiet Sun level. The data reduction includes: to
  obtain a circular solar picture, to construct twelve radial vectors
  from the preliminary solar disk center in order to determinate the
  coordinates of the solar limb, to remove "erroneous" limb points,
  to determine a circle trough the limb points by the least-squares
  method, to obtain corrected coordinates of the solar disk center and
  the radius and to repeat the procedures using the obtained results
  as input parameters. The quiet Sun level was determined as the mean
  value of all data points on the disk for every map separately. Several
  numerical criteria were tested, and the minima of relative intensities
  for all data points were determined. Taking these minima as centers,
  circles of different radii were drawn with criterion that the mean value
  inside the circle is less than the quiet Sun level. The latitudinal
  distribution of LTRs, as well as the solar rotation rate as determined
  by the LTRs, were investigated using automatic numerical procedures. It
  was established how the parameters which describe the solar rotation
  rate and corresponding errors depend upon various numerical criteria
  including: definition of LTR's size, allowing different deviations
  of LTR's positions and rotation rate, confining the set of obtained
  rotation rates according to each error of the rotation rate and
  confining the set of obtained rotation rates according to allowance
  of a specific rotation rate at a specific latitude.

Title: Helium 10830 Å measurements of the Sun
Authors: Brajša, R.; Pohjolainen, S.; Ruždjak, V.; Sakurai, T.;
   Urpo, S.; Vršnak, B.; Wöhl, H.
Bibcode: 1996SoPh..163...79B
Altcode:
  Measurements of the Sun in the near-infrared He I 10830 Å absorption
  line were performed using the echelle spectrograph with a dispersion
  of 6.71 mÅ per pixel at the Vacuum Tower Telescope (German Solar
  Telescopes, Teide Observatory, Izaña, Tenerife, Spain) on May 26,
  1993. These measurements were compared with full-disc soft X-ray images
  of the Sun (Japanese solar satellite Yohkoh), full-disc solar images
  in Hα (Big Bear Solar Observatory), full-disc solar images in the
  He I 10830 Å line (National Solar Observatory, Kitt Peak) and with
  full-disc microwave solar maps at 37 GHz (Metsähovi Radio Research
  Station). In the He 10830 Å line the Sun displays a limb darkening
  similar to that in the visible part of the spectrum. Active regions
  and Hα filaments show a strong absorption in the He 10830 Å line,
  whereas the absorption is weak in coronal holes.

Title: The Relation between the Synodic and Sidereal Rotation Period
    of the Sun
Authors: Roša, D.; Brajša, R.; Vršnak, B.; Wöhl, H.
Bibcode: 1995SoPh..159..393R
Altcode:
  The relation between the synodic and sidereal rotation period of
  the Sun for an arbitrary date of observation is derived taking into
  account details of the Earth's motion. The transformation procedure
  between the synodic (apparent) and sidereal rotation period presented
  here can be performed without using the annual ephemerides.

Title: An Investigation of Cycle-Related Changes of the Solar Rotation
    by Tracing Microwave Low Brightness Temperature Regions
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
   S.; Woehl, H.
Bibcode: 1995HvaOB..19....1B
Altcode:
  Indications of possible changes of the solar rotation rate during
  several phases of the solar activity cycle (the years analyzed were
  1979, 1980, 1981, 1982, 1987, 1988, 1989, 1990 and 1991) were found. The
  solar rotation rates were determined by tracing microwave Low brightness
  Temperature Regions in the latitude range 55 deg. These changes of the
  rotation rate, although of low statistical significance, indicate that
  the Sun has nearly equal rotation rates during successive cycle maxima,
  which are different from the measured rotation rates in the periods
  between the maxima.

Title: Solar Centre-to-Limb Functions in Optical and Radio Wavelength
    Ranges
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Pohjolainen, S.; Urpo,
   S.; Woehl, H.
Bibcode: 1994HvaOB..18....9B
Altcode:
  No abstract at ADS

Title: A comparison of large-scale patterns outlined by low brightness
    temperature microwave regions and magnetic fields on the Sun
Authors: Brajša, R.; Pohjolainen, S.; Ruždjak, V.; Teräsranta,
   H.; Urpo, S.; Vršnak, B.; Wöhl, H.
Bibcode: 1994smf..conf...62B
Altcode:
  No abstract at ADS

Title: A Comparison of H<SUB>α</SUB> and Microwave Full-Disc
    Solar Maps
Authors: Brajša, R.; Ruždjak, V.; Wöhl, H.
Bibcode: 1994emsp.conf..125B
Altcode:
  No abstract at ADS

Title: On the Possible Physical Conditions which Result in Appearance
    of Low Brightness Temperature Microwave Regions on the Sun
Authors: Brajsa, R.
Bibcode: 1993SoPh..144..199B
Altcode:
  The physical conditions causing the appearance of the low brightness
  temperature regions at 37 and 22 GHz are discussed. The source radiation
  stems from free-free processes (bremsstrahlung), and passes through the
  transparent chromosphere and corona. The absorption occurs either in
  the prominences or in coronal condensations with physical parameters
  between those of prominences and corona. A deficit in emission of the
  chromosphere-corona transition region in the vicinity of the inversion
  lines of the longitudinal component of the photospheric magnetic field
  could also result in the appearance of low temperature region.

Title: Erratum: "Variations of solar global rotation during the
    polarity reversal" [Hvar Obs. Bull., Vol. 16, No. 1, p. 13 - 22
    (1992)].
Authors: Brajša, R.; Vršnak, B.; Ruždjak, V.; Božić, H.;
   Pohjolainen, S.; Teräsranta, H.; Urpo, S.
Bibcode: 1993HvaOB..17...65B
Altcode:
  No abstract at ADS

Title: Variations of Solar Global Rotation During the Polarity
    Reversal
Authors: Brajsa, R.; Vrsnak, B.; Ruzdjak, V.; Bozic, H.; Pohjolainen,
   S.; Urpo, S.; Terasranta, H.
Bibcode: 1992HvaOB..16...13B
Altcode:
  No abstract at ADS

Title: Cycle Dependent Rotation of Solar Large Scale Patterns as
    Determined from Millimeter-Range Observations
Authors: Brajsa, R.; Ruzdjak, V.; Vrsnak, B.; Jurac, S.; Pohjolainen,
   S.; Terasranta, H.; Urpo, S.
Bibcode: 1992ASPC...27..274B
Altcode: 1992socy.work..274B
  No abstract at ADS

Title: Giant Cells on the Sun Revealed by Low Temperature Microwave
    Regions?
Authors: Brajsa, R.; Vrsnak, B.; Ruzdjak, V.; Jurac, S.; Pohjolainen,
   S.; Urpo, S.; Terasranta, H.
Bibcode: 1992HvaOB..16....1B
Altcode:
  No abstract at ADS

Title: Large-scale patterns on the Sun observed in the millimetric
    wavelength range
Authors: Vrsnak, B.; Pohjolainen, S.; Urpo, S.; Terasranta, H.;
   Brajsa, R.; Ruzdjak, V.; Mouradian, Z.; Jurac, S.
Bibcode: 1992SoPh..137...67V
Altcode:
  The nature and behaviour of large-scale patterns on the solar surface,
  indicated by the areas of brightness-temperature depressions in
  the millimetric wavelength range, is studied. A large sample of 346
  individual, low-temperature regions (LTRs) was employed to provide
  reliable statistical evidence. An association of 99% was found between
  the locations of LTRs and the large-scale magnetic field inversion
  lines, and 60% of the LTRs were associated with the inversion
  line filaments. A tentative physical association with filaments is
  reconsidered, and one particularly well-observed case is presented. The
  heights of the perturbers causing brightness-temperature depressions are
  discussed. The long-term evolution of the latitudinal distribution of
  LTRs is presented in a butterfly diagram. Two belts of low-temperature
  regions outline the active region belts, shifting with them towards the
  equator during the solar activity cycle. The low-temperature region
  belts of the forthcoming cycle appear already at the maximum of the
  actual cycle at latitudes of about 55 °. The superpositions of the
  temperature minima distributions in the synoptic maps show patterns
  appearing as `giant cells' and compatible with indications inferred
  from magnetographic data. The reliability of the inferred cells is
  considered, and a statistical analysis reveals a negligible probability
  for an accidental distribution appearing in the form of giant cells.

Title: Solar Differential Rotation Determined by Polar Crown Filaments
Authors: Brajša, R.; Vršnak, B.; Ruždjak, V.; Schroll, A.;
   Pohjolainen, S.; Urpo, S.; Teräsranta, H.
Bibcode: 1991SoPh..133..195B
Altcode:
  The rotation rates obtained by tracing 124 polar crown filaments are
  presented in comparison with previous results. Higher filament rotation
  rate in polar regions was detected and discussed in terms of the various
  phenomena such as: the projection effect due to the height of measured
  tracers, the connection of polar filaments with the magnetic field
  patterns which show an increase of the rotation rate at high latitudes,
  rigid rotation of polar filaments which form pivot points, and eventual
  change of the differential rotation law during the cycle. However, when
  the height correction for an average height of 1% of the solar radius is
  applied, the filament rotation rate in polar regions decreases. Then
  the rotation law becomes: Ω(φ) = 14.45 − 0.11 sin<SUP>2</SUP>
  φ − 3.69 sin<SUP>4</SUP> φ (° day<SUP>−1</SUP>, sidereal).

Title: Intensity Variations and Short Time Evolution of Solar
    Microwave Low Temperature Regions
Authors: Pohjolainen, S.; Urpo, S.; Terasranta, H.; Vrsnak, B.;
   Brajsa, R.; Ruzdjak, V.; Jurac, S.
Bibcode: 1991HvaOB..15...21P
Altcode:
  No abstract at ADS

Title: Rotation of large scale patterns on the solar surface as
    determined from filament and millimeter data
Authors: Pohjolainen, S.; Vršnak, B.; Teräsranta, H.; Urpol, S.;
   Brajša, R.; Ruždjak, V.; Jurač, S.; Schroll, A.
Bibcode: 1991LNP...380..279P
Altcode: 1991IAUCo.130..279P; 1991sacs.coll..279P
  The rotation of large scale solar magnetic field patterns was studied
  using quiescent filaments and low temperature regions observed at 37
  GHz as tracers.

Title: Large scale patterns on the solar surface indicated by
    microwave observations
Authors: Vršnak, B.; Pohjolainen, S.; Teräsranta, H.; Urpol, S.;
   Brajša, R.; Ruždjak, V.; Schroll, A.; Jurač, S.
Bibcode: 1991LNP...380..282V
Altcode: 1991IAUCo.130..282V; 1991sacs.coll..282V
  A large set of observations of the Sun at 37 GHz is analysed. An
  association of 99% is found between the regions of brightness
  temperature depression and the magnetic field inversion
  lines. Observations indicate a possible existence of giant cells with
  duration of 1-2 years and a longitudinal extension up to 90°.

Title: Oscillatory Motions in an Active Prominence
Authors: Vrsnak, B.; Ruzdjak, V.; Brajsa, R.; Zloch, F.
Bibcode: 1990SoPh..127..119V
Altcode:
  Different types of oscillatory motions were detected in the late
  phases of eruption of a prominence. We found oscillations of
  the prominence axis and diameter with periods of 4.3 and 9.1 min,
  corresponding to the eigenmodes m = 4 and m = 8 with a damping factor
  4.6 × 10<SUP>−3</SUP> s<SUP>−1</SUP>. A period about 4.5 min was
  found for oscillations of the pitch angle of the helically twisted
  filaments. The m = 2 and m = 3 eigenmodes could be also identified
  and they led to the final relaxation of the prominence axis. The
  observations are compared with a model in which we consider forces
  acting in a curved, cylindrical magnetic tube anchored at both ends
  in the photosphere and carrying an electric current. The stability of
  the prominence is discussed.

Title: Polar Crown Filaments and Solar Differential Rotation at
    High Latitudes
Authors: Brajša, R.; Vršnak, B.; Rundjak, V.; Schroll, A.
Bibcode: 1990LNP...363..293B
Altcode: 1990doqp.coll..293B; 1990IAUCo.117..293B
  No abstract at ADS

Title: Motion of High Latitude Solar Microwave Sources and Comparison
    with Polar Prominences
Authors: Urpo, S.; Pohjolainen, S.; Teräsranta, H.; Vrsnak, B.;
   Ruzdjak, V.; Brajsa, R.; Schroll, A.
Bibcode: 1990LNP...363..292U
Altcode: 1990doqp.coll..292U; 1990IAUCo.117..292U
  Solar microwave sources at high solar latitudes have been observed
  with a 14 m radio telescope at the Metsahovi Radio Research Station in
  Finland. Several periods for observations were organized in 1986-1989
  in order to detect sources close to the north and south pole of
  the Sun. Measurements at 22 and 37 GHz (wavelengths 14 and 8 mm
  respectively) have revealed the existence of high temperature and low
  temperature regions (relative to the quiet Sun level) at latitudes 50-80
  degrees. The motions of these regions have been studied and compared
  with optical measurements of polar prominences. The temperature
  enhancement at 37 GHz is typically 100-400 K above the quiet Sun
  level (7800 K) at that frequency. Although in most cases temperature
  depression in a low temperature area amounts 50-300 K, at 37 GHz,
  the temperature drop in the low temperature area which was observed in
  July 1982 was as low as 900 K. The results of the radio measurements
  of the Sun at 22 and 37 GHz on high solar latitudes imply that high
  temperature areas correspond to polar faculae while low temperature
  areas correspond to polar prominences. The principal cause of the
  observed lower temperature area is the absorbtion by the filament.

Title: On the Appearances, Intensities and Motions of Solar Microwave
    Low Temperature Areas
Authors: Pohjolainen, S.; Brajša, R.; Urpo, S.; Teräsranta, H.;
   Vršnak, B.; Ruždjak, V.; Jurač, S.
Bibcode: 1990PDHO....7...56P
Altcode: 1990ESPM....6...56P; 1990dysu.conf...56P
  Solar microwave sources at 37 GHz have been observed at Metsähovi since
  1978. The solar maps have revealed the existence of low temperature
  regions, i.e. areas where the brightness temperature is typically 100 -
  400K lower than the quiet Sun level, throughout the solar cycle. The
  authors have investigated the appearances, intensities and motions
  of these temperature depressions and compared them with the activity
  features in the optical part of the spectrum.

Title: Oscillatory Relaxation of an Eruptive Prominence
Authors: Vršnak, B.; Ruždjak, V.; Brajša, R.; Zloch, F.
Bibcode: 1990LNP...363..256V
Altcode: 1990IAUCo.117..256V; 1990doqp.coll..256V
  Different types of oscillatory motions were detected in the late phases
  of eruption of a prominence. We found oscillations of the prominence
  axis and diameter with periods of 4.3 and 9.1 minutes corresponding
  to the eigenmodes m=4 and m=8 with a damping factor 4.6 10-3 s{-1}. A
  period of about 4.5 minutes was found for oscillations of the pitch
  angle of the helically twisted filaments. The m=2 and m=3 eigenmodes
  could be also identified and they led to the final relaxation of the
  prominence axis. The observations are interpreted in analogy with
  damped oscillations of an elastic string. The lowest eigenmode was
  not excited due to &gt;hile the m=2 and m=3 eigenmodes were highly
  damped. The frequency of free oscillations due to restoring forces
  and the decay constant were inferred using the dispersion relation for
  oscillation of the elastic string and the observed frequentes in the
  m=4 and m=8 modes to =3.1x10-3-1, corresponding to a period of T=34
  min. and S =4.6x10-3s-1.

Title: A Comparison of Hα and Soft X-Ray Characteristics of Spotless
    and SPOT Group Flares
Authors: Ruždjak, V.; Vršnak, B.; Schroll, A.; Brajša, R.
Bibcode: 1989SoPh..123..309R
Altcode:
  A comparative analysis of spotless and spot group flares recorded
  at Hvar and Kanzelhöhe Observatories during the 21st cycle of solar
  activity is presented. The rate of occurrence of two-ribbon flares was
  found to be significantly higher for the spotless flares. In comparison
  with spot group flares of corresponding Hα importance, the soft X-ray
  peak values have been systematically lower for the spotless flares. The
  highest peak values and the energy released in soft X-rays was found
  for flares with a Hα ribbon protruding over a major spot umbra. It
  was found that the effective plasma temperatures in spotless flares
  have been considerably lower than the temperatures in spot group flares.

Title: Motion of High Latitude Solar Microwave Sources and Comparison
    with Solar Prominences
Authors: Urpo, S.; Pohjolainen, S.; Terasranta, H.; Vrsnak, B.;
   Ruzdjak, V.; Brajsa, R.; Schroll, A.
Bibcode: 1989HvaOB..13..437U
Altcode:
  No abstract at ADS

Title: Oscillatory Relaxation of an Eruptive Prominence
Authors: Vrsnak, B.; Ruzdjak, V.; Brajsa, R.; Zloch, F.
Bibcode: 1989HvaOB..13..137V
Altcode:
  No abstract at ADS

Title: Polar Crown Filaments and Solar Differential Rotation at
    High Latitudes
Authors: Brajsa, R.; Vrsnak, B.; Ruzdjak, V.; Schroll, A.
Bibcode: 1989HvaOB..13..449B
Altcode:
  No abstract at ADS

Title: Structure and Stability of Prominences with Helical Structure
Authors: Vrsnak, B.; Ruzdjak, V.; Brajsa, R.; Dzubur, A.
Bibcode: 1988SoPh..116...45V
Altcode:
  Observations of internal structure and development of four helical
  prominences are presented. We assume that the helically twisted fine
  structure threads are outlining magnetic field lines and we found
  that it is possible to describe the magnetic fields by the uniform
  twist configuration, with the twists ranging between 2π and 7π. The
  estimated lower limits for the magnetic fields were about 20 G which
  give lower limits for the currents flowing along the prominences in
  the range between 2 × 10<SUP>10</SUP> A and 2 × 10<SUP>11</SUP> A and
  current densities at the axis of the prominences about 10<SUP>-4</SUP>
  A m<SUP>-2</SUP>. The upper limit of electron drift velocity could
  be estimated as 1 m s<SUP>-1</SUP>, which is far below the critical
  velocities for the onset of plasma microinstabilities.

Title: Analysis of errors in visual brightness estimates of variable
    stars.
Authors: Brajša, R.; Baćani, K.
Bibcode: 1983Vasio..31...17B
Altcode:
  No abstract at ADS

