Author name code: alissandrakis
ADS astronomy entries on 2022-09-14
author:"Alissandrakis, Costas E." 
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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: The solar atmosphere and kappa distributions
Authors: Alissandrakis, Costas
Bibcode: 2022cosp...44.1220A
Altcode:
  The sun and its environment is an immense plasma physics laboratory,
  where the magnetic field plays a crucial role. The magnetic field
  is responsible for a large variety of energy release phenomena, in
  all observable temporal an spatial scales, from tiny bright points
  to huge flares and coronal mass ejections. In the most energetic
  phenomena, electrons are accelerated to energies of hundreds of keV,
  giving observational signatures in hard X-rays and in the microwave
  range, whereas electron beams traveling at 1/3 of the speed of light
  in the corona and the solar wind produce plasma emission in metric
  and longer wavelengths. In latter case a bump-in-tail distribution is
  invoked, while in the first case a power-law distribution on top of
  a Maxwellian is usually employed. However, there have been efforts
  to describe suprathermal electrons in terms of kappa-distributions,
  both in energetic phenomena an in the quiet Sun. In this review I
  will give an overview of the solar atmosphere and of phenomena where
  kappa-distributions may play a role.

Title: Where is the base of the Transition Region? Evidence from
    TRACE, SDO, IRIS and ALMA observations
Authors: Alissandrakis, C. E.
Bibcode: 2022arXiv220703159A
Altcode:
  Classic solar models put the Chromosphere-Corona Transition Region
  (CCTR} at $\sim2$Mm above the $\tau_{5000} = 1$ level, whereas rMHD
  models place it in a wider range of heights. Observational verification
  is scarce. We review and discuss recent results from various instruments
  and spectral domains. In SDO and TRACE images spicules appear in
  emission in the 1600, 1700 and 304 A bands and in absorption in the
  EUV bands; the latter is due to photo-ionization of H and He I. At the
  shortest available AIA wavelength and taking into account that the
  photospheric limb is $\sim0.34$Mm above the $\tau_{5000}=1$ level,
  we found that CCTR emission starts at $\sim3.7$Mm; extrapolating
  to $\lambda=0$, where there is no chromospheric absorption, we
  deduced a height of $3.0\pm 0.5$Mm, above the value of 2.14Mm of
  the Avrett &amp; Loeser model. Another indicator of the extent of
  the chromosphere is the height of the network structures. Height
  differences produce a limbward shift of features with respect to
  their counterparts in magnetograms. Using this approach, we measured
  heights of $0.14\pm0.04$Mm (at 1700 A), $0.31\pm0.09$Mm (at 1600 A)
  and $3.31\pm 0.18$Mm (at 304 A) for the center of the solar disk. A
  previously reported possible solar cycle variation is not confirmed. A
  third indicator is the position of the limb in the UV, where IRIS
  observations of the Mg II triplet lines show that they extend up to
  $\sim2.1$Mm above the 2832 A limb, while AIA/SDO images give a limb
  height of $1.4 \pm 0.2$Mm (1600 A) and $5.7\pm 0.2$Mm (304 A). Finally,
  ALMA mm-$\lambda$ full-disk images provide useful diagnostics, though
  not very accurate; values of $2.4\pm0.7$Mm at 1.26mm and $4.2\pm2.5$Mm
  at 3mm were obtained. Putting everything together, we conclude that the
  average chromosphere extends higher than homogeneous models predict,
  but within the range of rMHD models.

Title: First detection of metric emission from a solar surge
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bouratzis,
   C.; Hillaris, A.
Bibcode: 2022A&A...662A..14A
Altcode: 2022arXiv220301043A
  We report the first detection of metric radio emission from a surge,
  observed with the Nançay Radioheliograph (NRH), STEREO, and other
  instruments. The emission was observed during the late phase of the
  M9 complex event SOL2010-02-012T11:25:00, described in a previous
  publication. It was associated with a secondary energy release,
  also observed in STEREO 304 Å images, and there was no detectable
  soft X-ray emission. The triangulation of the STEREO images allowed
  for the identification of the surge with NRH sources near the central
  meridian. The radio emission of the surge occurred in two phases and
  consisted of two sources, one located near the base of the surge,
  apparently at or near the site of energy release, and another in the
  upper part of the surge; these were best visible in the frequency
  range of 445.0 to about 300 MHz, whereas a spectral component of
  a different nature was observed at lower frequencies. Sub-second
  time variations were detected in both sources during both phases,
  with a 0.2-0.3 s delay of the upper source with respect to the lower,
  suggesting superluminal velocities. This effect can be explained if
  the emission of the upper source was due to scattering of radiation
  from the source at the base of the surge. In addition, the radio
  emission showed signs of pulsations and spikes. We discuss possible
  emission mechanisms for the slow time variability component of
  the lower radio source. Gyrosynchrotron emission reproduced the
  characteristics of the observed total intensity spectrum at the
  start of the second phase of the event fairly well, but failed to
  reproduce the high degree of the observed circular polarization or the
  spectra at other instances. On the other hand, type IV-like plasma
  emission from the fundamental could explain the high polarization
  and the fine structure in the dynamic spectrum; moreover, it gives
  projected radio source positions on the plane of the sky, as seen from
  STEREO-A, near the base of the surge. Taking all the properties into
  consideration, we suggest that type IV-like plasma emission with
  a low-intensity gyrosynchrotron component is the most plausible
  mechanism. <P />Movie associated to Fig. A.2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202243169/olm">https://www.aanda.org</A>

Title: A first look at the submillimeter Sun with ALMA
Authors: Alissandrakis, C. E.; Bastian, T. S.; Nindos, A.
Bibcode: 2022A&A...661L...4A
Altcode: 2022arXiv220501008A
  We present the first full-disk solar images obtained with the Atacama
  Large Millimeter/submillimeter Array (ALMA) in Band 7 (0.86 mm;
  347 GHz). In spite of the low spatial resolution (21″), several
  interesting results were obtained. During our observation, the sun
  was practically devoid of active regions. Quiet Sun structures on
  the disk are similar to those in Atmospheric Imaging Assembly images
  at 1600 Å and 304 Å, after the latter are smoothed to the ALMA
  resolution, as noted previously for Band 6 (1.26 mm) and Band 3 (3 mm)
  images; they are also similar to negative Hα images of equivalent
  resolution. Polar coronal holes, which are clearly seen in the 304
  Å band and small Hα filaments, are not detectable at 0.86 mm. We
  computed the center-to-limb variation of the brightness temperature,
  T<SUB>b</SUB>, in Band 7, as well as in Bands 6 and 3, which were
  obtained during the same campaign, and we combined them to a unique
  curve of T<SUB>b</SUB>(log μ<SUB>100</SUB>), where μ<SUB>100</SUB>
  is the cosine of the heliocentric angle reduced to 100 GHz. Assuming
  that the absolute calibration of the Band 3 commissioning observations
  is accurate, we deduced a brightness temperature at the center of the
  disk of 6085 K for Band 7, instead of the value of 5500 K, extrapolated
  from the recommended values for Bands 3 and 6. More importantly, the
  T<SUB>b</SUB>(log μ<SUB>100</SUB>) curve flattens at large values
  of μ<SUB>100</SUB>, and so does the corresponding T<SUB>e</SUB>(log
  τ<SUB>100</SUB>) at large τ<SUB>100</SUB>. This is probably an
  indication that we are approaching the temperature minimum.

Title: High-resolution observations with ARTEMIS/JLS and the
    NRH. IV. Imaging spectroscopy of spike-like structures near the
    front of type-II bursts
Authors: Armatas, S.; Bouratzis, C.; Hillaris, A.; Alissandrakis,
   C. E.; Preka-Papadema, P.; Kontogeorgos, A.; Tsitsipis, P.; Moussas, X.
Bibcode: 2022A&A...659A.198A
Altcode: 2022arXiv220107832A
  Context. Narrowband bursts (spikes) are very small duration and
  bandwidth bursts which appear on dynamic spectra from microwave to
  decametric frequencies. They are believed to be manifestations of
  small-scale energy release through magnetic reconnection. <BR /> Aims:
  We study the position of the spike-like structures relative to the front
  of type-II bursts and their role in the burst emission. <BR /> Methods:
  We used high-sensitivity, low-noise dynamic spectra obtained with the
  acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph,
  in conjunction with high-time-resolution images from the Nançay
  Radioheliograph (NRH) in order to study spike-like bursts near the front
  of a type-II radio burst recorded at the west limb during the November
  3, 2003 extreme solar event. The spike-like emission in the dynamic
  spectrum was enhanced by means of high-pass-time filtering. <BR />
  Results: We identified a number of spikes in the NRH images. Due to
  the lower temporal resolution of the NRH, multiple spikes detected in
  the dynamic spectrum appeared as single structures in the images. These
  spikes had an average size of ≈200″ and their observed brightness
  temperature was 1.4 to 5.6 × 10<SUP>9</SUP> K, providing a significant
  contribution to the emission of the type-II burst front. At variance
  with a previous study on the type-IV associated spikes, we found no
  systematic displacement between the spike emission and the emission
  between spikes. At 327.0 MHz, the type II emission was located about
  0.3 R<SUB>⊙</SUB> above the pre-existing continuum emission, which,
  in turn, was located 0.1 R<SUB>⊙</SUB> above the western limb. <BR
  /> Conclusions: This study, combined with our previous results,
  indicates that the spike-like chains aligned along the type II burst
  MHD shock front are not a perturbation of the type II emission, as
  in the case of type IV spikes, but a manifestation of the type II
  emission itself. The preponderance of these chains, together with the
  lack of isolated structures or irregular clusters, points towards some
  form of small-scale magnetic reconnection, organized along the type-II
  propagating front. <P />This work is dedicated to the memory of Costas
  Caroubalos (1928-2021), founder of the ARTEMIS radiospectrograh.

Title: Multiwavelength observations of a metric type-II event
Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.; Hillaris,
   A.
Bibcode: 2021A&A...654A.112A
Altcode: 2021arXiv210802855A
  We have studied a complex metric radio event that originated in a
  compact flare, observed with the ARTEMIS-JLS radiospectrograph on
  February 12, 2010. The event was associated with a surge observed at 195
  and 304 Å and with a coronal mass ejection observed by instruments on
  board STEREO A and B near the eastern and western limbs respectively. On
  the disk the event was observed at ten frequencies by the Nançay
  Radioheliograph (NRH), in Hα by the Catania observatory, in soft
  X-rays by GOES SXI and Hinode XRT, and in hard X-rays by RHESSI. We
  combined these data, together with MDI longitudinal magnetograms,
  to get as complete a picture of the event as possible. Our emphasis
  is on two type-II bursts that occurred near respective maxima in
  the GOES light curves. The first, associated with the main peak
  of the event, showed an impressive fundamental-harmonic structure,
  while the emission of the second consisted of three well-separated
  bands with superposed pulsations. Using positional information for the
  type-IIs from the NRH and triangulation from STEREO A and B, we found
  that the type-IIs were associated neither with the surge nor with the
  disruption of a nearby streamer, but rather with an extreme ultraviolet
  (EUV) wave probably initiated by the surge. The fundamental-harmonic
  structure of the first type-II showed a band split corresponding to
  a magnetic field strength of 18 G, a frequency ratio of 1.95 and a
  delay of 0.23−0.65 s of the fundamental with respect to the harmonic;
  moreover it became stationary shortly after its start and then drifted
  again. The pulsations superposed on the second type-II were broadband
  and had started before the burst. In addition, we detected another
  pulsating source, also before the second type-II, polarized in the
  opposite sense; the pulsations in the two sources were out of phase
  and hence hardly detectable in the dynamic spectrum. The pulsations
  had a measurable reverse frequency drift of about 2 s<SUP>−1</SUP>.

Title: ALMA observations of the variability of the quiet Sun at
    millimeter wavelengths
Authors: Nindos, A.; Patsourakos, S.; Alissandrakis, C. E.; Bastian,
   T. S.
Bibcode: 2021A&A...652A..92N
Altcode: 2021arXiv210604220N
  <BR /> Aims: We address the variability of the quiet solar chromosphere
  at 1.26 mm and 3 mm with a focus on the study of spatially resolved
  oscillations and transient brightenings, which are small, weak
  events of energy release. Both phenomena may have a bearing on the
  heating of the chromosphere. <BR /> Methods: We used Atacama Large
  Millimeter/submillimeter Array (ALMA) observations of the quiet Sun
  at 1.26 mm and 3 mm. The spatial and temporal resolution of the data
  were 1 − 2″ and 1 s, respectively. The concatenation of light
  curves from different scans yielded a frequency resolution in spectral
  power of 0.5−0.6 mHz. At 1.26 mm, in addition to power spectra of
  the original data, we degraded the images to the spatial resolution
  of the 3 mm images and used fields of view that were equal in area
  for both data sets. The detection of transient brightenings was made
  after the effect of oscillations was removed. <BR /> Results: At both
  frequencies, we detected p-mode oscillations in the range 3.6−4.4
  mHz. The corrections for spatial resolution and field of view at 1.26 mm
  decreased the root mean square (rms) of the oscillations by a factor of
  1.6 and 1.1, respectively. In the corrected data sets, the oscillations
  at 1.26 mm and 3 mm showed brightness temperature fluctuations of
  ∼1.7 − 1.8% with respect to the average quiet Sun, corresponding to
  137 and 107 K, respectively. We detected 77 transient brightenings at
  1.26 mm and 115 at 3 mm. Although their majority occurred in the cell
  interior, the occurrence rate per unit area of the 1.26 mm events was
  higher than that of the 3 mm events; this conclusion does not change
  if we take into account differences in spatial resolution and noise
  levels. The energy associated with the transient brightenings ranged
  from 1.8 × 10<SUP>23</SUP> to 1.1 × 10<SUP>26</SUP> erg and from 7.2
  × 10<SUP>23</SUP> to 1.7 × 10<SUP>26</SUP> erg for the 1.26 mm and
  3 mm events, respectively. The corresponding power-law indices of the
  energy distribution were 1.64 and 1.73. We also found that ALMA bright
  network structures corresponded to dark mottles or spicules that can be
  seen in broadband Hα images from the GONG network. <BR /> Conclusions:
  The fluctuations associated with the p-mode oscillations represent
  a fraction of 0.55−0.68 of the full power spectrum. Their energy
  density at 1.26 mm is 3 × 10<SUP>−2</SUP> erg cm<SUP>−3</SUP>. The
  computed low-end energy of the 1.26 mm transient brightenings is among
  the smallest ever reported, irrespective of the wavelength of the
  observation. Although the occurrence rate per unit area of the 1.26
  mm transient brightenings was higher than that of the 3 mm events,
  their power per unit area is smaller likely due to the detection of
  many weak 1.26 mm events.

Title: Radio Measurements of the Magnetic field in the Solar
    Chromosphere and the Corona
Authors: Alissandrakis, Costas E.; Gary, Dale E.
Bibcode: 2021FrASS...7...77A
Altcode:
  The structure of the upper solar atmosphere, on all observable scales,
  is intimately governed by the magnetic field. The same holds for a
  variety of solar phenomena that constitute solar activity, from tiny
  transient brightening to huge Coronal Mass Ejections. Due to inherent
  difficulties in measuring magnetic field effects on atoms (Zeeman and
  Hanle effects) in the corona, radio methods sensitive to electrons
  are of primary importance in obtaining quantitative information about
  its magnetic field. In this review we explore these methods and point
  out their advantages and limitations. After a brief presentation of
  the magneto-ionic theory of wave propagation in cold, collisionless
  plasmas, we discuss how the magnetic field affects the radio emission
  produced by incoherent emission mechanisms (free-free, gyroresonance
  and gyrosynchrotron processes) and give examples of measurements of
  magnetic filed parameters in the quiet sun, active regions and radio
  CMEs. We proceed by discussing how the inversion of the sense of
  circular polarization can be used to measure the field above active
  regions. Subsequently we pass to coherent emission mechanisms and
  present results of measurements from fiber bursts, zebra patterns
  and type II burst emission. We close this review with a discussion
  of the variation of the magnetic field, deduced by radio measurement,
  from the low corona up to 10 solar radii and with some thoughts about
  future work.

Title: Observations of Solar Spicules at Millimeter and Ultraviolet
    Wavelengths
Authors: Bastian, T.; De Pontieu, B.; Shimojo, M.; Iwai, K.;
   Alissandrakis, C.; Nindos, A.; Vial, J. C.; White, S. M.
Bibcode: 2020AGUFMSH004..08B
Altcode:
  Solar spicules are a ubiquitous chromospheric phenomenon in which
  multitudes of dynamic jets with temperatures of order 10<SUP>4</SUP>
  K extend thousands of kilometers into the solar atmosphere. Recent
  progress has been made refining the observational characteristics
  of spicules using the Hinode Solar Optical Telescope (SOT) and the
  Interface Region Imaging Spectrograph (IRIS) observations at optical
  and ultraviolet wavelengths, respectively. Two types of spicule
  have been identified. Type I spicules, prevalent in solar active
  regions, have upward speeds of order 25 km/s and lifetimes of 3-7
  min. They may be the limb counterpart to shock-wave-driven fibrils
  commonly seen against the solar disk in active regions. In contrast,
  type II spicules, more common in quiet regions and coronal holes,
  display upward speeds of 50-150 km/s, lifetimes of 30-110 s, and
  appear to be partially heated to temperatures of 10<SUP>5 </SUP>K and
  higher. These observations have provoked intense interest in spicules
  and have led to proposals that type II spicules play a central role
  as a source of hot plasma in the corona. Nevertheless, their role in
  mass and energy transport between the lower and upper layers of the
  solar atmosphere remains an outstanding problem. <P />Here, we report
  imaging observations of solar spicules at millimeter wavelengths using
  the Atacama Large Millimeter-submillimeter Array (ALMA) with arcsecond
  angular resolution. Continuum millimeter wavelength radiation forms
  under conditions of local thermodynamic equilibrium, thereby providing a
  complementary tool to UV lines, which form under non-LTE conditions. The
  observations were made on 2018 December 24-25 at λ=1.25 mm and λ=3
  mm. The ALMA observations pose special challenges, particularly at
  1.25 mm, where the limited field of view of the instrument motivated
  us to use a novel mosaic imaging technique: multiple pointings were
  assembled to form a single map with an angular resolution of 1" x 0.7"
  on a cadence of roughly 2 min. In contrast, we were able to image at 3
  mm continuously, with a map cadence of 2 s and an angular resolution of
  2.3" x 1.3". <P />We compare and contrast the morphology and dynamics
  of mm-λ observations of spicules with those obtained by IRIS at UV
  wavelengths and place constraints on spicule temperatures and masses
  using the joint millimeter-wavelength observations.

Title: Structure of the solar atmosphere: a radio perspective
Authors: Alissandrakis, Costas E.
Bibcode: 2020FrASS...7...74A
Altcode:
  Solar radio emission has been providing information about the Sun for
  over half a century. In order to fully exploit this information, one
  needs to have a broader view of the solar atmosphere, which cannot be
  provided by radio observations alone. The purpose of this review is to
  present this background information, which is necessary to understand
  the physical processes that determine the solar radio emission
  and to link the radio domain with the rest of the electromagnetic
  spectrum. <P />Both classic and modern results are presented in a
  concise manner. After a brief discussion of the solar interior, the
  basic physics of the solar atmosphere and some elements of radiative
  transfer are presented. Subsequently the atmospheric structure as
  a function of height is examined and one -dimensional models of the
  photosphere, the chromosphere, the transition region and the corona are
  presented and discussed. An introduction to basic magnetohydrodynamics
  precedes the discussion of the rich fine structure of the solar
  atmosphere as a 3D object. Active regions are briefly discussed in a
  separate section, and this is followed by a section on the problem of
  heating of the chromosphere and the corona. I finish with some thoughts
  on what to expect from the new instruments currently under development.

Title: Modeling the quiet Sun cell and network emission with ALMA
Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T. S.; Patsourakos,
   S.
Bibcode: 2020A&A...640A..57A
Altcode: 2020arXiv200609886A
  Observations of the Sun at millimeter wavelengths with the Atacama
  Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity
  to investigate the temperature structure of the solar chromosphere. In
  this article we expand our previous work on modeling the chromospheric
  temperature of the quiet Sun, by including measurements of the
  brightness temperature in the network and cell interiors, from
  high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We
  also examine the absolute calibration of ALMA full-disk images. We
  suggest that the brightness temperature at the center of the solar disk
  in Band 6 is ∼440 K above the value recommended by White et al. (2017,
  Sol. Phys., 292, 88). In addition, we give improved results for the
  electron temperature variation of the average quiet Sun with optical
  depth and the derived spectrum at the center of the disk. We found
  that the electron temperature in the network is considerably lower
  than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319)
  and that of the cell interior considerably higher than predicted by
  model A. Depending on the network/cell segregation scheme, the electron
  temperature difference between network and cell at τ = 1 (100 GHz)
  ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted
  by the models; similarly, the electron temperature, T<SUB>e</SUB>
  ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model
  prediction. We also found that the network/cell T<SUB>e</SUB>(τ)
  curves diverge as τ decreases, indicating an increase of contrast
  with height and possibly a steeper temperature rise in the network
  than in the cell interior.

Title: Transient brightenings in the quiet Sun detected by ALMA at
    3 mm
Authors: Nindos, A.; Alissandrakis, C. E.; Patsourakos, S.; Bastian,
   T. S.
Bibcode: 2020A&A...638A..62N
Altcode: 2020arXiv200407591N
  <BR /> Aims: We investigate transient brightenings, that is, weak,
  small-scale episodes of energy release, in the quiet solar chromosphere;
  these episodes can provide insights into the heating mechanism of the
  outer layers of the solar atmosphere. <BR /> Methods: Using Atacama
  Large Millimeter/submillimeter Array (ALMA) observations, we performed
  the first systematic survey for quiet Sun transient brightenings at 3
  mm. Our dataset included images of six 87″ × 87″ fields of view
  of the quiet Sun obtained with angular resolution of a few arcsec at
  a cadence of 2 s. The transient brightenings were detected as weak
  enhancements above the average intensity after we removed the effect
  of the p-mode oscillations. A similar analysis, over the same fields
  of view, was performed for simultaneous 304 and 1600 Å data obtained
  with the Atmospheric Imaging Assembly. <BR /> Results: We detected 184
  3 mm transient brightening events with brightness temperatures from
  70 K to more than 500 K above backgrounds of ∼7200 - 7450 K. All
  events showed light curves with a gradual rise and fall, strongly
  suggesting a thermal origin. Their mean duration and maximum area were
  51.1 s and 12.3 Mm<SUP>2</SUP>, respectively, with a weak preference
  of appearing at network boundaries rather than in cell interiors. Both
  parameters exhibited power-law behavior with indices of 2.35 and 2.71,
  respectively. Only a small fraction of ALMA events had either 304
  or 1600 Å counterparts but the properties of these events were not
  significantly different from those of the general population except
  that they lacked their low-end energy values. The total thermal
  energies of the ALMA transient brightenings were between 1.5 ×
  10<SUP>24</SUP> and 9.9 × 10<SUP>25</SUP> erg and their frequency
  distribution versus energy was a power law with an index of 1.67 ±
  0.05. We found that the power per unit area provided by the ALMA events
  could account for only 1% of the chromospheric radiative losses (10%
  of the coronal ones). <BR /> Conclusions: We were able to detect, for
  the first time, a significant number of weak 3 mm quiet Sun transient
  brightenings. However, their energy budget falls short of meeting the
  requirements for the heating of the upper layers of the solar atmosphere
  and this conclusion does not change even if we use the least restrictive
  criteria possible for the detection of transient brightenings.

Title: Modeling of the Brightness of the Chromospheric Network Based
    on ALMA High Resolution Observations of the Quiet Sun
Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T.; Patsourakos, S.
Bibcode: 2020AAS...23610607A
Altcode:
  ALMA observations of the Sun at mm-λ offer a unique opportunity
  to investigate the temperature/density structure of the solar
  chromosphere. In a previous work (Alissandrakis et al 2017, A&amp;A
  605, A78) we measured the center-to-limb variation of the brightness
  temperature, T<SUB>b</SUB>, using low resolution ALMA full-disk
  observations in Band 3 (3mm) and Band 6 (1.26 mm), together with data
  at 0.85 mm from Bastian et al. 1993 (ApJ, 415, 364). Combining all
  data and inverting the solution of the transfer equation we found
  that the electron temperature, T<SUB>e</SUB>, in the range of 0.34
  &lt; τ<SUB>100</SUB> &lt; 12, where τ<SUB>100</SUB> is the optical
  depth at 100 GHz, was ~5% (~300 K) below the one predicted by model C
  (average quiet sun) of FAL93 (Fontenla, Avrett, &amp; Loeser, 1993,
  ApJ, 406, 319). Here we expand that work by including measurements
  of the brightness temperature in the network and cell interiors,
  from high resolution ALMA images in Bands 3 and 6. We found that
  the observed T<SUB>b</SUB> in the network is considerably lower
  than predicted by the FAL93 model F and that of the cell interior
  considerably higher than predicted by the FAL93 model A. The observed
  network/cell difference of brightness temperature at the center of the
  disk, at 100 GHz is about 920 K, compared to ~3250 K predicted by the
  FAL93 models; similarly, the T<SUB>b</SUB>, ratio is ~1.14, against
  ~1.51 of the model prediction. After inversion of the observed data,
  the electron temperature of cell interior at τ<SUB>100</SUB>=1 is
  ~390 K below the average (~600 K above model A) and of the network
  ~400 K above the average (~1800 K below model A). The implications of
  these results will be discussed. We will also discuss the question of
  the normalization of brightness temperature observed by ALMA.

Title: Observations of solar chromospheric oscillations at 3 mm
    with ALMA
Authors: Patsourakos, S.; Alissandrakis, C. E.; Nindos, A.; Bastian,
   T. S.
Bibcode: 2020A&A...634A..86P
Altcode: 2019arXiv191203480P
  <BR /> Aims: We aim to study spatially resolved chromospheric
  oscillations of the quiet Sun (QS) in the mm-domain at a resolution
  of a few arcsec, typically 2.4″ × 4.5″. <BR /> Methods: We used
  Atacama Large millimeter and submillimeter Array (ALMA) time series
  of interferometric observations of the QS obtained at 3 mm with a 2-s
  cadence and a spatial resolution of a few arcsec. The observations were
  performed on March 16, 2017 and seven 80″ × 80″ fields of view
  (FoV) going from disk center to limb were covered, each one observed for
  10 min, therefore limiting the frequency resolution of the power spectra
  to 1.7 mHz. For each FoV, masks for cell and network were derived,
  and the averaged power spectral densities (PSDs) for the entire FoV,
  cell, and network were computed. The resulting power spectra were
  fit with an analytical function in order to derive the frequency
  and the root-mean-square (rms) power associated with the peaks. The
  same analysis, over the same FoVs and for the same intervals, was
  performed for simultaneous Atmospheric Imaging Assembly (AIA) image
  sequences in 1600 Å. <BR /> Results: Spatially resolved chromospheric
  oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed
  in the QS, in both cell and network. The coherence length-scale of
  the oscillations is commensurate with the spatial resolution of our
  ALMA observations. Brightness-temperature fluctuations in individual
  pixels could reach up to a few hundred K, while the spatially averaged
  PSDs yield rms in the range ≈55-75 K, i.e., up to ≈1% of the
  averaged brightness temperatures and exhibit a moderate increase
  towards the limb. For AIA 1600 Å, the oscillation frequency is 3.7
  ± 1.7 mHz. The relative rms is up to 6% of the background intensity,
  with a weak increase towards the disk center (cell, average). ALMA
  3 mm time-series lag AIA 1600 Å by ≈100 s, which corresponds to
  a formation-height difference of ≈1200 km, representing a novel
  determination of this important parameter. <BR /> Conclusions: The
  ALMA oscillations that we detected exhibit higher amplitudes than those
  derived from previous lower (≈10″) resolution observations at 3.5 mm
  by the Berkeley-Illinois-Maryland Array. Chromospheric oscillations are,
  therefore, not fully resolved at the length-scale of the chromospheric
  network, and possibly not even at the spatial resolution of our ALMA
  observations. Any study of transient brightenings in the mm-domain
  should take into account the oscillations.

Title: Measurement of the Height of the Chromospheric Network Emission
    from Solar Dynamics Observatory Images
Authors: Alissandrakis, C. E.
Bibcode: 2019SoPh..294..161A
Altcode: 2019arXiv191100758A
  We measured the height of the chromospheric network in the 1700,
  1600, and 304 Å wavelength bands of the Atmospheric Imaging Assembly
  (AIA) onboard the Solar Dynamics Observatory (SDO) from the shift
  of features on the disk with respect to corresponding features in
  SDO/Helioseismic and Magnetic Imager (HMI) images of the absolute
  value of the longitudinal magnetic field. We found that near the limb
  the 304 Å network emission forms 3.60 ±0.24 Mm above the 1600 Å
  emission, which, in turn, forms 0.48 ±0.10 Mm above the HMI (6173 Å)
  level. At the center of the disk the corresponding height differences
  are 2.90 ±0.02 Mm and 0.39 ±0.06 Mm respectively. We also found that
  the 1600 Å network emission forms 0.25 ±0.02 Mm above the 1700 Å
  emission near the limb and 0.20 ±0.02 Mm at the disk center. Finally,
  we examined possible variations with the solar cycle. Our results can
  help to check and refine atmospheric models.

Title: Erratum: Correction to: Structure of the Transition Region
    and the Low Corona from TRACE and SDO Observations Near the Limb
Authors: Alissandrakis, C. E.; Valentino, A.
Bibcode: 2019SoPh..294..146A
Altcode:
  In computing the height with respect to the tau = 1 level, the height
  difference between the white light limb and that level was subtracted
  rather than added to the values in Table 4. This affects Sections 3.3
  and 3.4, Figures 14 and 15, as well as Table 5. The correct versions
  are given below.

Title: Structure of the Transition Region and the Low Corona from
    TRACE and SDO Observations Near the Limb
Authors: Alissandrakis, C. E.; Valentino, A.
Bibcode: 2019SoPh..294...96A
Altcode: 2019arXiv190609497A
  We examined the structure near the solar limb in TRACE images of the
  continuum and in the 1600 and 171 Å bands as well as in SDO images in
  the continuum (from HMI) and all AIA bands. The images in different
  wavelength bands were carefully coaligned by using the position of
  Mercury for TRACE and Venus for SDO during their transit in front of
  the solar disk in 1999 and 2012, respectively. Chromospheric absorbing
  structures in the TRACE 171-Å band are best visible 7<SUP>''</SUP>
  above the white-light limb, very close to the inner limb, defined as
  the inflection point of the rising part of the center-to-limb intensity
  variation. They are correlated with, but are not identical to, spicules
  in emission, seen in the 1600-Å band. Similar results were obtained
  from AIA and SOT images. Tall spicules in 304 Å are not associated
  with any absorption in the higher temperature bands. Performing
  azimuthal averaging of the intensity over 15<SUP>∘</SUP> sectors
  near the N, S, E and W limbs, we measured the height of the limb and
  of the peak intensity in all AIA bands. We found that the inner limb
  height in the transition region AIA bands increases with wavelength,
  consistent with a bound-free origin of the absorption from neutral
  H and He. From that we computed the column density and the density
  of neutral hydrogen as a function of height. We estimated a height
  of (2300 ±500 )km for the base of the transition region. Finally,
  we measured the scale height of the AIA emission of the corona and
  associated it with the temperature; we deduced a value of (1.24 ±0.25
  )×10<SUP>6</SUP>K for the polar corona

Title: High-resolution observations with ARTEMIS-JLS and the
    NRH. III. Spectroscopy and imaging of fiber bursts
Authors: Alissandrakis, C. E.; Bouratzis, C.; Hillaris, A.
Bibcode: 2019A&A...627A.133A
Altcode: 2019arXiv190603434A
  <BR /> Aims: We study the characteristics of intermediate drift
  bursts (fibers) embedded in a large type-IV event. <BR /> Methods:
  We used high-sensitivity, low-noise dynamic spectra obtained with the
  acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph,
  in conjunction with high time-resolution images from the Nançay
  radioheliograph (NRH) and extreme ultraviolet (EUV) images from the
  Transition Region and Coronal Explorer (TRACE) to study fiber bursts
  during the large solar event of July 14, 2000. We computed both 2D and
  1D images and applied high pass time filtering to the images and the
  dynamic spectrum in order to enhance the fiber-associated emission. For
  the study of the background continuum emission we used images averaged
  over several seconds. <BR /> Results: Practically all fibers visible in
  the SAO dynamic spectra are identifiable in the NRH images. Fibers were
  first detected after the primary energy release in a moving type-IV
  event, probably associated with the rapid eastward expansion of the
  flare and the post-flare loop arcade. We found that fibers appeared as
  a modulation of the continuum intensity with a root mean square value
  of the order of 10%. Both the fibers and the continuum were strongly
  circularly polarized in the ordinary mode sense, indicating plasma
  emission at the fundamental. We detected a number of discrete fiber
  emission sources along two parallel stripes of ∼300 Mm in length,
  apparently segments of large-scale loops encompassing both the EUV loops
  and the CME-associated flux rope. We found cases of multiple fiber
  emissions appearing at slightly different positions and times; their
  consecutive appearance can give the impression of apparent motion with
  supra-luminal velocities. Images of individual fibers were very similar
  at 432.0 and 327.0 MHz. From the position shift of the sources and the
  time delays at low and high frequencies, we estimated the exciter speed
  and the frequency scale length along the loops for a well-observed group
  of fibers; we obtained consistent values from imaging and spectral
  data, supporting the whistler origin of the fiber emission. Finally
  we found that fibers in emission and fibers in absorption are very
  similar, confirming that they are manifestations of the same wave
  train. <P />Movies associated to Figs. 2, 7, and 10 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201935627/olm">https://www.aanda.org</A>

Title: High resolution observations with Artemis-JLS. II. Type IV
    associated intermediate drift bursts
Authors: Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.;
   Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2019A&A...625A..58B
Altcode: 2019arXiv190402262B
  <BR /> Aims: We examined the characteristics of isolated intermediate
  drift bursts and their morphologies on dynamic spectra, in particular
  the positioning of emission and absorption ridges. Furthermore we
  studied the repetition rate of fiber groups. These were compared with a
  model in order to determine the conditions under which the intermediate
  drift bursts appear and exhibit the above characteristics. <BR />
  Methods: We analyzed sixteen metric type IV events with embedded
  intermediate drift bursts, observed with the Artemis-JLS radio
  spectrograph from July 1999 to July 2005 plus an event on 1st
  August 2010. The events were recorded with the SAO high resolution
  (10 ms cadence) receiver in the 270-450 MHz range with a frequency
  resolution of 1.4 MHz. We developed cross- and autocorrelation
  techniques to measure the duration, spectral width, and frequency
  drift of fiber bursts in 47 intermediate drift bursts (IMD) groups
  embedded within the continuum of the sixteen events mentioned above. We
  also developed a semi-automatic algorithm to track fibers on dynamic
  spectra. <BR /> Results: The mean duration of individual fiber bursts
  at fixed frequency was δt ≈ 300 ms, while the instantaneous relative
  bandwidth was f<SUB>w</SUB>/f ≈ 0.90% and the total frequency extent
  was Δf<SUB>tot</SUB> ≈ 35 MHz. The recorded intermediate drift bursts
  had frequency drift, positive or negative, with average values of df/fdt
  equal to -0.027 and 0.024 s<SUP>-1</SUP> respectively. Quite often
  the fibers appeared in groups; the burst repetition rate within groups
  was, on average, ∼0.98 s. We distinguish six morphological groups of
  fibers, based on the relative position of the emission and absorption
  ridges. These included fibers with emission or absorption ridges
  only, fibers with the absorption ridge at lower or higher frequency
  than the emission, or with two absorption ridges above and below the
  emission. There were also some fibers for which two emission ridges
  were separated by an absorption ridge. Some additional complex groups
  within our data set were not easy to classify. A number of borderline
  cases of fibers with very high drift rate (∼0.30 s<SUP>-1</SUP>)
  or very narrow total bandwidth (∼8 MHz) were recorded; among them
  there was a group of rope-like fibers characterized by fast repetition
  rate and relatively narrow total frequency extent. We found that
  the whistler hypothesis leads to reasonable magnetic field values
  (∼4.6 G), while the Alfven-wave hypothesis requires much higher
  field. From the variation of the drift rate with time we estimated
  the ratio of the whistler to the cyclotron frequency, x, to be in
  the range of 0.3-0.6, varying by ∼0.05-0.1 in individual fibers;
  the same analysis gives an average value of the frequency scale along
  the loop of ∼220 Mm. Finally, we present empirical relations between
  fiber burst parameters and discuss their possible origin.

Title: Detection of spike-like structures near the front of type-II
    bursts
Authors: Armatas, S.; Bouratzis, C.; Hillaris, A.; Alissandrakis,
   C. E.; Preka-Papadema, P.; Moussas, X.; Mitsakou, E.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2019A&A...624A..76A
Altcode: 2019arXiv190210617A
  <BR /> Aims: We examine high time resolution dynamic spectra for fine
  structures in type II solar radio bursts <BR /> Methods: We used data
  obtained with the acousto-optic spectrograph receiver of the Artemis-JLS
  (ARTEMIS-IV) solar radio spectrograph in the 450-270 MHz range at 10 ms
  cadence and identified more than 600 short, narrowband features. Their
  characteristics, such as instantaneous relative bandwidth and total
  duration were measured and compared with those of spikes embedded
  in type IV emissions. <BR /> Results: Type II associated spikes
  occur mostly in chains inside or close to the slowly drifting type
  II emission. These spikes coexist with herringbone and pulsating
  structures. Their average duration is 96 ms and their average relative
  bandwidth 1.7%. These properties are not different from those of type
  IV embedded spikes. It is therefore possible that they are signatures
  of small-scale reconnection along the type II shock front.

Title: Modeling of the Sunspot-Associated Microwave Emission Using
    a New Method of DEM Inversion
Authors: Alissandrakis, C. E.; Bogod, V. M.; Kaltman, T. I.;
   Patsourakos, S.; Peterova, N. G.
Bibcode: 2019SoPh..294...23A
Altcode: 2018arXiv181205751A
  We develope a method to compute the temperature and density structure
  along the line of sight by inversion of the differential emission
  measure (DEM), under the assumptions of stratification and hydrostatic
  equilibrium. We apply this method to the DEM obtained from the
  Atmospheric Imaging Assembly (AIA) observations and use the results,
  together with potential extrapolations of the photospheric magnetic
  field, to compute the microwave emission of three sunspots, which we
  compare with observations from the Academy of Sciences Radio Telescope
  - 600 (RATAN-600) radio telescope and the Nobeyama Radioheliograph
  (NoRH). Our DEM-based models reproduce very well the observations of
  the moderate-size spot on October 2011 and within 25% the data of a
  similar sized spot on March 2016, but predict too low values for the
  big spot of 14 April 2016. The latter is better fitted by a constant
  conductive flux atmospheric model which, however, cannot reproduce the
  peak brightness temperature of 4.7 ×10<SUP>6</SUP>K and the shape of
  the source at the NoRH frequency. We propose that these deviations are
  due to the low intensity non-thermal emission associated to a moving
  pore and to an opposite polarity light bridge. We also find that the
  double structure of the big spot at high RATAN-600 frequencies can be
  interpreted in terms of the variation of the angle between the magnetic
  field and the line of sight along the sunspot.

Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
   S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
   T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
Bibcode: 2018A&A...619L...6N
Altcode: 2018arXiv181005223N
  We present an overview of high-resolution quiet Sun observations,
  from disk center to the limb, obtained with the Atacama Large
  millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
  regions were observed at a resolution of up to 2.5″ by 4.5″. We
  produced both average and snapshot images by self-calibrating the ALMA
  visibilities and combining the interferometric images with full-disk
  solar images. The images show well the chromospheric network, which,
  based on the unique segregation method we used, is brighter than the
  average over the fields of view of the observed regions by ∼305
  K while the intranetwork is less bright by ∼280 K, with a slight
  decrease of the network/intranetwork contrast toward the limb. At 3
  mm the network is very similar to the 1600 Å images, with somewhat
  larger size. We detect, for the first time, spicular structures,
  rising up to 15″ above the limb with a width down to the image
  resolution and brightness temperature of ∼1800 K above the local
  background. No trace of spicules, either in emission or absorption,
  is found on the disk. Our results highlight the potential of ALMA for
  the study of the quiet chromosphere.

Title: IRIS Observations of Spicules and Structures Near the
    Solar Limb
Authors: Alissandrakis, C. E.; Vial, J. -C.; Koukras, A.; Buchlin,
   E.; Chane-Yook, M.
Bibcode: 2018SoPh..293...20A
Altcode: 2018arXiv180102082A
  We have analyzed Interface Region Imaging Spectrograph (IRIS)
  spectral and slit-jaw observations of a quiet region near the South
  Pole. In this article we present an overview of the observations, the
  corrections, and the absolute calibration of the intensity. We focus
  on the average profiles of strong (Mg II h and k, C II and Si IV),
  as well as of weak spectral lines in the near ultraviolet (NUV) and
  the far ultraviolet (FUV), including the Mg II triplet, thus probing
  the solar atmosphere from the low chromosphere to the transition
  region. We give the radial variation of bulk spectral parameters as
  well as line ratios and turbulent velocities. We present measurements
  of the formation height in lines and in the NUV continuum from which
  we find a linear relationship between the position of the limb and
  the intensity scale height. We also find that low forming lines,
  such as the Mg II triplet, show no temporal variations above the limb
  associated with spicules, suggesting that such lines are formed in a
  homogeneous atmospheric layer and, possibly, that spicules are formed
  above the height of 2<SUP>″</SUP>. We discuss the spatio-temporal
  structure of the atmosphere near the limb from images of intensity as
  a function of position and time. In these images, we identify p-mode
  oscillations in the cores of lines formed at low heights above the
  photosphere, slow-moving bright features in O I and fast-moving bright
  features in C II. Finally, we compare the Mg II k and h line profiles,
  together with intensity values of the Balmer lines from the literature,
  with computations from the PROM57Mg non-LTE model, developed at the
  Institut d' Astrophysique Spatiale, and estimated values of the physical
  parameters. We obtain electron temperatures in the range of ∼8000 K
  at small heights to ∼20 000 K at large heights, electron densities
  from 1.1 ×10<SUP>11</SUP> to 4 ×10<SUP>10</SUP>cm−<SUP>3</SUP>
  and a turbulent velocity of ∼24 kms−<SUP>1</SUP>.

Title: Center-to-limb observations of the Sun with ALMA . Implications
    for solar atmospheric models
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian,
   T. S.
Bibcode: 2017A&A...605A..78A
Altcode:
  <BR /> Aims: We seek to derive information on the temperature structure
  of the solar chromosphere and compare these results with existing
  models. <BR /> Methods: We measured the center-to-limb variation of
  the brightness temperature, T<SUB>b</SUB>, from ALMA full-disk images
  at two frequencies and inverted the solution of the transfer equation
  to obtain the electron temperature, T<SUB>e</SUB> as a function of
  optical depth, τ. <BR /> Results: The ALMA images are very similar
  to AIA images at 1600 Å. The brightness temperature at the center
  of the disk is 6180 and 7250 K at 239 and 100 GHz, respectively,
  with dispersions of 100 and 170 K. Plage regions stand out clearly in
  the 239/100 GHz intensity ratio, while faculae and filament lanes do
  not. The solar disk radius, reduced to 1 AU, is 961.1 ± 2.5'' and 964.1
  ± 4.5'' at 239 and 100 GHz, respectively. A slight but statistically
  significant limb brightening is observed at both frequencies. <BR />
  Conclusions: The inversion of the center-to-limb curves shows that
  T<SUB>e</SUB> varies linearly with the logarithm of optical depth for
  0.34 &lt;τ<SUB>100 GHz</SUB>&lt; 12, with a slope dT<SUB>e</SUB>/
  dlnτ = -608 K. Our results are 5% lower than predicted by the average
  quiet Sun model C of Fontenla et al. (1993, ApJ. 406, 319), but do
  not confirm previous reports that the mm-λ solar spectrum is better
  fitted with models of the cell interior.

Title: Evidence for two-loop interaction from IRIS and SDO
    observations of penumbral brightenings
Authors: Alissandrakis, C. E.; Koukras, A.; Patsourakos, S.; Nindos, A.
Bibcode: 2017A&A...603A..95A
Altcode: 2017arXiv170407344A
  <BR /> Aims: We investigate small scale energy release events which
  can provide clues on the heating mechanism of the solar corona. <BR />
  Methods: We analyzed spectral and imaging data from the Interface
  Region Imaging Spectrograph (IRIS), images from the Atmospheric
  Imaging Assembly (AIA) aboard the Solar Dynamics Observatoty (SDO),
  and magnetograms from the Helioseismic and Magnetic Imager (HMI)
  aboard SDO. <BR /> Results: We report observations of small flaring
  loops in the penumbra of a large sunspot on July 19, 2013. Our main
  event consisted of a loop spanning 15'', from the umbral-penumbral
  boundary to an opposite polarity region outside the penumbra. It lasted
  approximately 10 min with a two minute impulsive peak and was observed
  in all AIA/SDO channels, while the IRIS slit was located near its
  penumbral footpoint. Mass motions with an apparent velocity of 100 km
  s<SUP>-1</SUP> were detected beyond the brightening, starting in the
  rise phase of the impulsive peak; these were apparently associated
  with a higher-lying loop. We interpret these motions in terms of
  two-loop interaction. IRIS spectra in both the C II and Si iv lines
  showed very extended wings, up to about 400 km s<SUP>-1</SUP>, first
  in the blue (upflows) and subsequently in the red wing. In addition
  to the strong lines, emission was detected in the weak lines of Cl
  I, O I and C I, as well as in the Mg II triplet lines. Absorption
  features in the profiles of the C II doublet, the Si iv doublet and
  the Mg II h and k lines indicate the existence of material with a
  lower source function between the brightening and the observer. We
  attribute this absorption to the higher loop and this adds further
  credibility to the two-loop interaction hypothesis. Tilts were
  detected in the absorption spectra, as well as in the spectra of Cl I,
  O I, and C I lines, possibly indicating rotational motions from the
  untwisting of magnetic flux tubes. <BR /> Conclusions: We conclude
  that the absorption features in the C II, Si iv and Mg II profiles
  originate in a higher-lying, descending loop; as this approached
  the already activated lower-lying loop, their interaction gave rise
  to the impulsive peak, the very broad line profiles and the mass
  motions. <P />Movies associated to Figs. A.1-A.3 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201730643/olm">http://www.aanda.org</A>

Title: Center-to-limb observations of the Sun with ALMA
Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian,
   T. S.
Bibcode: 2017arXiv170509008A
Altcode:
  We measured the center-to-limb variation of the brightness temperature,
  $T_b$, from ALMA full-disk images at two frequencies and inverted the
  solution of the transfer equation to obtain the electron temperature,
  $T_e$ as a function of optical depth, $\tau$. The ALMA images are very
  similar to AIA images at 1600Å. The brightness temperature at the
  center of the disk is 6180 and 7250 K at 239 and 100 GHz respectively,
  with dispersions of 100 and 170 K. Plage regions stand out clearly
  in the 239/100 GHz intensity ratio, while faculae and filament lanes
  do not. The solar disk radius, reduced to 1 AU, is $961.1\pm2.5$
  arcsec and $964.1\pm4.5$ arcsec at 239 and 100 GHz respectively. A
  slight but statistically significant limb brightening is observed at
  both frequencies. The inversion of the center-to-limb curves shows
  that $T_e$ varies linearly with the logarithm of optical depth for
  $0.34&lt;\tau_{100\,GHz}&lt;12$, with a slope $d\ln T_e/d\tau=-608$
  K. Our results are 5% lower than predicted by the average quiet sun
  model C of Fontenla et al. (1993), but do not confirm previous reports
  that the mm-$\lambda$ solar spectrum is better fitted with models of
  the cell interior.

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: High resolution observations with Artemis-IV and the
    NRH. I. Type IV associated narrow-band bursts
Authors: Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.;
   Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2016A&A...586A..29B
Altcode: 2015arXiv151202481B
  Context. Narrow-band bursts appear on dynamic spectra from microwave
  to decametric frequencies as fine structures with very small duration
  and bandwidth. They are believed to be manifestations of small
  scale energy release through magnetic reconnection. <BR /> Aims: We
  analyzed 27 metric type IV events with embedded narrow-band bursts,
  which were observed by the ARTEMIS-IV radio spectrograph from 30 June
  1999 to 1 August 2010. We examined the morphological characteristics of
  isolated narrow-band structures (mostly spikes) and groups or chains of
  structures. <BR /> Methods: The events were recorded with the SAO high
  resolution (10 ms cadence) receiver of ARTEMIS-IV in the 270-450 MHz
  range. We measured the duration, spectral width, and frequency drift of
  ~12 000 individual narrow-band bursts, groups, and chains. Spike sources
  were imaged with the Nançay radioheliograph (NRH) for the event of 21
  April 2003. <BR /> Results: The mean duration of individual bursts at
  fixed frequency was ~100 ms, while the instantaneous relative bandwidth
  was ~2%. Some bursts had measurable frequency drift, either positive
  or negative. Quite often spikes appeared in chains, which were closely
  spaced in time (column chains) or in frequency (row chains). Column
  chains had frequency drifts similar to type-IIId bursts, while most
  of the row chains exhibited negative frequently drifts with a rate
  close to that of fiber bursts. From the analysis of NRH data, we found
  that spikes were superimposed on a larger, slowly varying, background
  component. They were polarized in the same sense as the background
  source, with a slightly higher degree of polarization of ~65%, and
  their size was about 60% of their size in total intensity. <BR />
  Conclusions: The duration and bandwidth distributions did not show any
  clear separation in groups. Some chains tended to assume the form of
  zebra, lace stripes, fiber bursts, or bursts of the type-III family,
  suggesting that such bursts might be resolved in spikes when viewed
  with high resolution. The NRH data indicate that the spikes are not
  fluctuations of the background, but represent additional emission such
  as what would be expected from small-scale reconnection.

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: A tiny event producing an interplanetary type III burst
Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.;
   Kontogeorgos, A.; Tsitsipis, P.
Bibcode: 2015A&A...582A..52A
Altcode: 2015arXiv150708423A
  <BR /> Aims: We investigate the conditions under which small-scale
  energy release events in the low corona gave rise to strong
  interplanetary (IP) type III bursts. <BR /> Methods: We analyzed
  observations of three tiny events, detected by the Nançay Radio
  Heliograph (NRH), two of which produced IP type III bursts. We
  took advantage of the NRH positioning information and of the high
  cadence of AIA/SDO data to identify the associated extreme-UV (EUV)
  emissions. We measured positions and time profiles of the metric and
  EUV sources. <BR /> Results: We found that the EUV events that produced
  IP type III bursts were located near a coronal hole boundary, while the
  one that did not was located in a closed magnetic field region. In all
  three cases tiny flaring loops were involved, without any associated
  mass eruption. In the best observed case, the radio emission at the
  highest frequency (435 MHz) was displaced by ~55'' with respect to
  the small flaring loop. The metric type III emission shows a complex
  structure in space and in time, indicative of multiple electron
  beams, despite the low intensity of the events. From the combined
  analysis of dynamic spectra and NRH images, we derived the electron
  beam velocity as well as the height, ambient plasma temperature, and
  density at the level of formation of the 160 MHz emission. From the
  analysis of the differential emission measure derived from the AIA
  images, we found that the first evidence of energy release was at the
  footpoints, and this was followed by the development of flaring loops
  and subsequent cooling. <BR /> Conclusions: Even small energy release
  events can accelerate enough electrons to give rise to powerful IP
  type III bursts. The proximity of the electron acceleration site to
  open magnetic field lines facilitates the escape of the electrons
  into the interplanetary space. The offset between the site of
  energy release and the metric type III location warrants further
  investigation. <P />The movie is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201526265/olm">http://www.aanda.org</A>

Title: Properties of solar energetic particle events inferred from
    their associated radio emission
Authors: Kouloumvakos, A.; Nindos, A.; Valtonen, E.; Alissandrakis,
   C. E.; Malandraki, O.; Tsitsipis, P.; Kontogeorgos, A.; Moussas, X.;
   Hillaris, A.
Bibcode: 2015A&A...580A..80K
Altcode: 2015arXiv150703776K
  <BR /> Aims: We study selected properties of solar energetic particle
  (SEP) events as inferred from their associated radio emissions. <BR
  /> Methods: We used a catalogue of 115 SEP events, which consists
  of entries of proton intensity enhancements at one AU, with complete
  coverage over solar cycle 23 based on high-energy (~68 MeV) protons from
  SOHO/ERNE. We also calculated the proton release time at the Sun using
  velocity dispersion analysis (VDA). After an initial rejection of cases
  with unrealistic VDA path lengths, we assembled composite radio spectra
  for the remaining events using data from ground-based and space-borne
  radio spectrographs. We registered the associated radio emissions for
  every event, and we divided the events in groups according to their
  associated radio emissions. In cases of type III-associated events, we
  extended our study to the timings between the type III radio emission,
  the proton release, and the electron release as inferred from VDA
  based on Wind/3DP 20-646 keV data. <BR /> Results: The proton release
  was found to be most often accompanied by both type III and II radio
  bursts, but a good association percentage was also registered in cases
  accompanied by type IIIs only. The worst association was found for the
  cases only associated with type II. In the type III-associated cases,
  we usually found systematic delays of both the proton and electron
  release times as inferred by the particles' VDAs, with respect to the
  start of the associated type III burst. The comparison of the proton
  and electron release times revealed that, in more than half of the
  cases, the protons and electrons were simultaneously released within
  the statistical uncertainty of our analysis. For the cases with type
  II radio association, we found that the distribution of the proton
  release heights had a maximum at ~2.5 R<SUB>⊙</SUB>. Most (69%) of
  the flares associated with our SEP events were located in the western
  hemisphere, with a peak within the well-connected region of 50°-60°
  western longitude. <BR /> Conclusions: Both flare- and shock-related
  particle release processes are observed in major proton events at
  &gt;50 MeV. Typically, the protons are released after the start of the
  associated type III bursts and simultaneously or before the release of
  energetic electrons. Our study indicates that a clear-cut distinction
  between flare-related and CME-related SEP events is difficult to
  establish. <P />Appendices are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201424397/olm">http://www.aanda.org</A>

Title: RATAN-600 Observations of Small-Scale Structures with High
    Spectral Resolution
Authors: Bogod, V. M.; Alissandrakis, C. E.; Kaltman, T. I.;
   Tokhchukova, S. K.
Bibcode: 2015SoPh..290....7B
Altcode: 2014arXiv1403.7658B; 2014SoPh..tmp...65B
  We present observations of quiet-Sun small-scale structures (SSS)
  in the microwave range with the Radio Astronomical Telescope of the
  Academy of Sciences 600 (RATAN-600) spectral-polarization facility
  in a wide range of frequencies. The SSS are regularly recorded in
  routine observations of the large reflector-type radio telescope and
  represent manifestations in the radio range of various structures of
  the quiet Sun: supergranulation network, bright points, plage patches,
  and so on. A comparison with images from the Solar Dynamics Observatory
  (SDO) showed that the microwave emission comes from a region extending
  from the chromosphere to the low transition region. We measured the
  properties of the SSS as well as the degree of circular polarization
  averaged over the beam of the radio telescope, and from this we
  estimated the magnetic field at the formation level of the radiation.

Title: Fine Structure of Metric Type IV Radio Bursts Observed with
the ARTEMIS-IV Radio-Spectrograph: Association with Flares and
    Coronal Mass Ejections
Authors: Bouratzis, C.; Hillaris, A.; Alissandrakis, C. E.;
   Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2015SoPh..290..219B
Altcode: 2014arXiv1406.1202B; 2014SoPh..tmp..101B
  Fine structures embedded in type IV burst continua may be used as
  diagnostics of the magnetic-field restructuring and the corresponding
  energy release associated with the low-corona development of
  flare or coronal mass ejection (CME) events. A catalog of 36 type
  IV bursts observed with the SAO receiver of the ARTEMIS-IV solar
  radio-spectrograph in the 450 - 270 MHz range at high cadence (0.01
  sec) was compiled; the fine structures were classified into five basic
  classes with two or more subclasses each. The time of fine-structure
  emission was compared with the injection of energetic electrons as
  recorded by hard X-ray and microwave emission, the soft X-ray (SXR)
  light curves and the CME onset time. Our results indicate a very tight
  temporal association between energy release episodes and pulsations,
  spikes, narrow-band bursts of the type III family, and zebra bursts. Of
  the remaining categories, the featureless broadband continuum starts
  near the time of the first energy release, between the CME onset
  and the SXR peak, but extends for several tens of minutes after that,
  covering almost the full extent of the flare-CME event. The intermediate
  drift bursts, fibers in their majority, mostly follow the first energy
  release, but have a wider distribution than other fine structures.

Title: Microwave and EUV Observations of an Erupting Filament and
    Associated Flare and Coronal Mass Ejections
Authors: Alissandrakis, Costas E.; Kochanov, Alexey A.; Patsourakos,
   Spiros; Altyntsev, Alexander T.; Lesovoi, Sergey V.; Lesovoya, Nadya N.
Bibcode: 2013PASJ...65S...8A
Altcode: 2013arXiv1309.1703A
  A filament eruption was observed with the Siberian Solar Radio Telescope
  (SSRT) on 2012 June 23, starting at around 06:40 UT, beyond the west
  limb. The filament could be followed in SSRT images to heights above 1
  R<SUB>⊙</SUB>, and coincided with the core of the CME, seen in LASCO
  C2 images. We briefly discuss the dynamics of the eruption: the top of
  the filament showed a smooth acceleration up to an apparent velocity
  of ∼ 1100 km s<SUP>-1</SUP>. Images behind the limb from STEREO-A
  show a two-ribbon flare and the interaction of the main filament,
  located along the primary neutral line, with an arch-like structure,
  oriented in the perpendicular direction. The interaction was accompanied
  by strong emission and twisting motions. The microwave images show
  a low-temperature component, a high-temperature component associated
  with the interaction of the two filaments and another high-temperature
  component apparently associated with the top of flare loops. We
  computed the differential emission measure from the high-temperature
  AIA bands and from this the expected microwave brightness temperature;
  for emission associated with the top of the flare loops, the computed
  brightness was 35% lower than the observed value.

Title: Hot coronal loops associated with umbral brightenings
Authors: Alissandrakis, C. E.; Patsourakos, S.
Bibcode: 2013A&A...556A..79A
Altcode: 2013arXiv1307.3392A
  <BR /> Aims: We aim to investigate the association of umbral
  brightenings with coronal structures. <BR /> Methods: We analyzed
  AIA/SDO high-cadence images in all bands, HMI/SDO data, soft X-ray
  images from SXI/GOES-15, and Hα images from the GONG network. <BR
  /> Results: We detected umbral brightenings that were visible
  in all AIA bands as well as in Hα. Moreover, we identified
  hot coronal loops that connected the brightenings with nearby
  regions of opposite magnetic polarity. These loops were initially
  visible in the 94 Å band, subsequently in the 335 Å band, and
  in one case in the 211 Å band. A differential emission measure
  analysis revealed plasma with an average temperature of about 6.5
  × 10<SUP>6</SUP> K. This behavior suggests cooling of impulsively
  heated loops. <P />Two movies are available in electronic from at <A
  href="http://www.aanda.org">http://www.aanda.org</A>

Title: Study of the Three-Dimensional Shape and Dynamics of Coronal
    Loops Observed by Hinode/EIS
Authors: Syntelis, P.; Gontikakis, C.; Georgoulis, M. K.;
   Alissandrakis, C. E.; Tsinganos, K.
Bibcode: 2012SoPh..280..475S
Altcode: 2012SoPh..tmp..119S; 2012arXiv1206.0126S
  We study plasma flows along selected coronal loops in NOAA Active
  Region 10926, observed on 3 December 2006 with Hinode'sEUVImaging
  Spectrograph (EIS). From the shape of the loops traced on intensity
  images and the Doppler shifts measured along their length we compute
  their three-dimensional (3D) shape and plasma flow velocity using a
  simple geometrical model. This calculation was performed for loops
  visible in the Fe VIII 185 Å, Fe X 184 Å, Fe XII 195 Å, Fe XIII
  202 Å, and Fe XV 284 Å spectral lines. In most cases the flow is
  unidirectional from one footpoint to the other but there are also cases
  of draining motions from the top of the loops to their footpoints. Our
  results indicate that the same loop may show different flow patterns
  when observed in different spectral lines, suggesting a dynamically
  complex rather than a monolithic structure. We have also carried out
  magnetic extrapolations in the linear force-free field approximation
  using SOHO/MDI magnetograms, aiming toward a first-order identification
  of extrapolated magnetic field lines corresponding to the reconstructed
  loops. In all cases, the best-fit extrapolated lines exhibit left-handed
  twist (α&lt;0), in agreement with the dominant twist of the region.

Title: On the shape of active region coronal loops observed by
    Hinode/EIS.
Authors: Syntelis, P.; Gontikakis, C.; Alissandrakis, C.; Georgoulis,
   M.; Tsinganos, K.
Bibcode: 2012hell.confQ..14S
Altcode:
  We study plasma flows in NOAA Active Region (AR) 10926, observed on
  December 3, 2006 with Hinode's EUV Imaging Spectrograph (EIS). We
  measured the line-of-sight velocity along coronal loops in the Fe
  VIII 185A, Fe X 184A , Fe XII 195A, Fe XIII 202A, and Fe XV 284A
  spectral lines and reconstructed the three dimensional (3D) shape
  and velocity of plasma flow using a simple geometrical model. In
  most cases the flow is unidirectional from one footpoint to the other,
  resembling siphon flow. However there are also cases of draining motions
  from the top of the loops to their footpoints. The multi-wavelength
  observations of the AR indicate that similar loops may show different
  flow patterns if observed in different spectral lines. We have also
  carried out magnetic field extrapolations using an SOHO/MDI and an
  SOT/Spectropolarimeter (SP) magnetogram, in order to identify magnetic
  field lines corresponding to the reconstructed 3D loops.

Title: Radio Emission Associated with Solar Energetic Particle Events
Authors: Kouloumvakos, A.; Nindos, A.; Preka-Papadema, P.; Hillaris,
   A.; Caroubalos, C.; Moussas, X.; Alissandrakis, C.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2012hell.confR..12K
Altcode:
  The corona probed at meter and decimeter wavelengths is a crucial region
  for the acceleration and propagation of solar energetic particles
  (SEPs), and radio diagnostics in this plasma plays a major role in
  assessing the origin of SEP events. Using data from the ARTEMIS IV solar
  radio spectro-graph, we report the properties of the radio emission
  associated with several major SEP events. The association of the radio
  emission with the related flares and CMEs is also investigated.

Title: Multi-wavelength Observations of a Metric Type-II Event
Authors: Alissandrakis, C.; Nindos, A.; Patsourakos, S.; Hillaris,
   Al.; Artemis Group
Bibcode: 2012hell.conf....6A
Altcode:
  We have studied a complex metric radio event,observed with the ARTEMIS
  radiospectrogarph on February 12, 2010. The event was associated with
  a surge observed at 195 and 304 A and with a coronal mass ejection
  observed by STEREO A and B instruments near the East wnd West limbs
  respectively. On the disk the event was observed at 10 frequencies by
  the Nancay Radioheliograph (NRH), in H-alpha by the Catania observatory
  and in soft x-rays by GOES SXI. We combined these data, together with
  MDI longitudinal magnetic field, to get as complete a picture of the
  event as possible. Our emphasis is on two type-II bursts that occured
  near respective maxima in the GOES light curves. The first, associated
  with the main peak of the event, showed a clear foundamental-harmonic
  structure, while the emission of the second consisted of three
  well-separated bands. Using positional infornation for the type-IIs
  from the NRH we explore their possible association with the surge,
  the coronal front and the CME. We also studied fine structured and
  foundamental harmonic structure in the metric dynamic spectrum.

Title: Radio Emission of the Quiet Sun and Active Regions (Invited
    Review)
Authors: Shibasaki, K.; Alissandrakis, C. E.; Pohjolainen, S.
Bibcode: 2012esrs.book....3S
Altcode:
  Solar radio emission provides valuable information on the structure
  and dynamics of the solar atmosphere above the temperature minimum. We
  review the background and most recent observational and theoretical
  results on the quiet Sun and active region studies, covering the entire
  radio range from millimeter to decameter wavelengths. We examine
  small- and large-scale structures, at short and long time scales,
  as well as synoptic aspects. Open questions and challenges for the
  future are also identified.

Title: Radio Emission of the Quiet Sun and Active Regions (Invited
    Review)
Authors: Shibasaki, K.; Alissandrakis, C. E.; Pohjolainen, S.
Bibcode: 2011SoPh..273..309S
Altcode: 2011SoPh..tmp..313S; 2011SoPh..tmp..246S; 2011SoPh..tmp..122S;
   2011SoPh..tmp..288S; 2011SoPh..tmp..177S
  Solar radio emission provides valuable information on the structure
  and dynamics of the solar atmosphere above the temperature minimum. We
  review the background and most recent observational and theoretical
  results on the quiet Sun and active region studies, covering the entire
  radio range from millimeter to decameter wavelengths. We examine
  small- and large-scale structures, at short and long time scales,
  as well as synoptic aspects. Open questions and challenges for the
  future are also identified.

Title: On the relationship of shock waves to flares and coronal
    mass ejections
Authors: Nindos, A.; Alissandrakis, C. E.; Hillaris, A.;
   Preka-Papadema, P.
Bibcode: 2011A&A...531A..31N
Altcode: 2011arXiv1105.1268N
  Context. Metric type II bursts are the most direct diagnostic
  of shock waves in the solar corona. <BR /> Aims: There are two
  main competing views about the origin of coronal shocks: that they
  originate in either blast waves ignited by the pressure pulse of a
  flare or piston-driven shocks due to coronal mass ejections (CMEs). We
  studied three well-observed type II bursts in an attempt to place
  tighter constraints on their origins. <BR /> Methods: The type II
  bursts were observed by the ARTEMIS radio spectrograph and imaged by
  the Nançay Radioheliograph (NRH) at least at two frequencies. To take
  advantage of projection effects, we selected events that occurred away
  from disk center. <BR /> Results: In all events, both flares and CMEs
  were observed. In the first event, the speed of the shock was about
  4200 km s<SUP>-1</SUP>, while the speed of the CME was about 850 km
  s<SUP>-1</SUP>. This discrepancy ruled out the CME as the primary shock
  driver. The CME may have played a role in the ignition of another shock
  that occurred just after the high speed one. A CME driver was excluded
  from the second event as well because the CMEs that appeared in the
  coronagraph data were not synchronized with the type II burst. In
  the third event, the kinematics of the CME which was determined by
  combining EUV and white light data was broadly consistent with the
  kinematics of the type II burst, and, therefore, the shock was probably
  CME-driven. <BR /> Conclusions: Our study demonstrates the diversity
  of conditions that may lead to the generation of coronal shocks.

Title: CME on CME Interaction on January 17, 2005
Authors: Bouratzis, C.; Preka-Papadima, P.; Moussas, X.; Hillaris,
   A. E.; Caroubalos, C.; Alissandrakis, C. E.; Tsitsipis, P.;
   Kontogeorgos, A.
Bibcode: 2010ASPC..424...39B
Altcode: 2010arXiv1009.3025B
  On January 17, 2005 a complex radio event associated with an X3.8 SXR
  flare and two fast Halo CMEs (CME<SUB>1</SUB> &amp; CME<SUB>2</SUB>
  henceforward) in close succession was observed. We present combined
  ARTEMIS-IV &amp; WIND WAVES dynamic spectra which provide a complete
  view of the radio emission induced by shock waves and electron beams
  from the low corona to about 1 A.U. These are supplemented with data,
  from the Nançay Radioheliograph (NRH), GOES, EIT and LASCO for the
  study of the associated flare and CME activity.

Title: On the Origin of Coronal Shocks
Authors: Nindos, Alexander; Alissandrakis, C. E.; Hillaris, A.;
   Caroubalos, C.
Bibcode: 2009SPD....40.1924N
Altcode:
  Type II bursts represent the passage of a shock wave through the
  tenuous plasma of the solar corona. Their exact origin has not been
  unambiguously determined, although they are associated with eruptive
  phenomena and are identified either with a flare blast wave or with
  a CME forward shock or with a shock driven by the flanks of a CME. We
  investigate the location of the shock formation and its association with
  flares and/or CMEs by studying the properties of three Type II radio
  bursts associated with eruptions that occurred relatively close to the
  limb where the influence of projection effects is rather small. The
  Type II bursts were identified in 110-687 MHz range observations of
  the ARTEMIS-IV Solar Radio spectrograph and observed simultaneously
  with the Nancay Radioheliograph (NRH). The NRH makes images of the
  Sun at several fixed frequencies between 150 and 432 MHz, and our
  events could be mapped at two or three of its frequencies, allowing
  us to determine the propagation of the shocks in the low corona. The
  information provided by the radio data combined with observations of
  the associated flares and CMEs by space-borne instruments has been
  used to constrain the shock wave kinematics and discuss whether they
  were flare-ignited or CME-driven.

Title: New Developments in ARTEMIS IV Solar Radio Spectrograph
Authors: Alissandrakis, C. E.; Kontogeorgos, A.; Tsitsipis, P.;
   Caroubalos, C.; Moussas, X.; Preka-Papadema, P.; Hilaris, A.; Bougeret,
   J. -L.; Dumas, G.
Bibcode: 2009EM&P..104...93A
Altcode:
  We present recent developments of the ARTEMIS IV solar radio
  spectrograph operating at Thermopylae, central Greece. Observations
  are obtained daily in total intensity and in the frequency range from
  20 to 650 MHz, using two antennas and two receivers. We are now in
  the process of developing a new system that will record consecutively
  the intensity of right-hand and left-hand polarized waves using one
  of the antennas and the same receivers.

Title: Metric radio bursts and fine structures observed on 17
    January, 2005
Authors: Bouratzis, C.; Preka-Papadema, P.; Moussas, X.; Alissandrakis,
   C.; Hillaris, A.
Bibcode: 2009AdSpR..43..605B
Altcode: 2010arXiv1009.3577B
  A complex radio event was observed on January 17, 2005 with the
  radio-spectrograph ARTEMIS-IV, operating at Thermopylae, Greece;
  it was associated with an X3.8 SXR flare and two fast Halo CMEs in
  close succession. We present dynamic spectra of this event; the high
  time resolution (1/100 s) of the data in the 450-270 MHz range, makes
  possible the detection and analysis of the fine structure which this
  major radio event exhibits. The fine structure was found to match,
  almost, the comprehensive Ondrejov Catalogue which it refers to the
  spectral range 0.8-2 GHz, yet seems to produce similar fine structure
  with the metric range.

Title: A Statistical Study of Microwave Flare Morphologies
Authors: Tzatzakis, V.; Nindos, A.; Alissandrakis, C. E.
Bibcode: 2008SoPh..253...79T
Altcode: 2008SoPh..tmp..166T
  This study has been motivated by the detection of a small number of
  optically thin microwave bursts with maximum emission near the loop
  top, which is contrary to the prediction of isotropic gyrosynchrotron
  models. Using Nobeyama Radioheliograph (NoRH) high-spatial-resolution
  images at 17 and 34 GHz, we study the morphology at the radio peak of
  104 flares that occurred relatively close to the limb. Using data from
  the Nobeyama Polarimeter we were able to determine whether the 17-
  and 34-GHz emissions came from optically thin or thick sources. We
  identified single-loop events, taking into account supplementary
  information from EUV and soft X-ray (SXR) images. We found optically
  thin emission from the top of the loop in 36% of single-loop events. In
  agreement with standard models, in this sample 46% and 18% of the events
  showed optically thin emission from the footpoints and optically thick
  emission from the entire loop, respectively. The derived percentage
  of events with gyrosynchrotron emission from isotropic populations
  of energetic electrons is possibly an upper limit. This point is
  illustrated by the analysis of an optically thin event that shows
  footpoint emission during the rise phase and loop-top emission during
  the decay phase. A model that takes into account both anisotropies in
  the distribution function of nonthermal electrons and time evolution
  can reproduce the observed transition from footpoint to loop-top
  morphology, if electrons with pitch-angle anisotropy are injected near
  one of the footpoints.

Title: Determination of the True Shape of Coronal Loops
Authors: Alissandrakis, C. E.; Gontikakis, C.; Dara, H. C.
Bibcode: 2008SoPh..252...73A
Altcode: 2008SoPh..tmp..143A
  Using line of sight velocity measurements from the SUMER and CDS
  instruments aboard SOHO, in conjunction with a simple geometrical
  model, we reconstructed the true, 3D shape and the velocity of plasma
  flow along coronal loops. The projection of the loop on the sky and
  the position of the footpoints define a family of curves. Assuming
  that the loop is located on a plane, the line of sight velocity
  can be used to select the most plausible solution. For two loops,
  observed in the Ne VIII 770 Å and O V 630 Å spectral lines,
  we find asymmetric, subsonic uni-directional flows, with velocity
  maxima of ≈ 80 km s<SUP>−1</SUP> near the footpoints. The loops
  are highly inclined with respect to the vertical, by 55<SUP>°</SUP>
  and 70<SUP>°</SUP>, respectively; thus the true height of the loop
  tops from the photospheric level is ≈ 20<SUP>''</SUP>, comparable
  to the isothermal scale height.

Title: ARTEMIS, a Solar Radiospectrograph
Authors: Caroubalos, C.; Moussas, X.; Preka-Papadema, P.; Hillaris,
   A.; Mitsakou, E.; Pothitakis, G.; Bouratzis, C.; Tsitsipis, P.;
   Kontageorgos, A.; Alissandrakis, C. E.; Bourgeret, J. -L.; Dumas, G.
Bibcode: 2008RoAJ...18S.215C
Altcode:
  No abstract at ADS

Title: M otions Near The Solar Limb From TRACE Ly-α O bservations
Authors: Zachariadis, G.; Alissandrakis, C. E.
Bibcode: 2007ESASP.641E..53Z
Altcode:
  We presenty preliminary results of a study of flows near the limb. The
  observations were obtained with TRACE in a quiest region near the
  limb in the Ly-α, (1216 Å) band, and cover two periods of about 19
  and 16 min respectively with a cadence of ~ 10 sec. The high temporal
  resolution of the images allows one to follow the evolution of small
  bright features of the solar disk and the activity of the spicules
  beyond the solar limb. The analysis of the images shows that many bright
  feature, with lifetime of a few minutes, shift toward the solar limb,
  with a velocity of about 14 km/sec. Spicules show motions both in the
  radial direction and parallel to the solar limb.

Title: M odeling The 3-D Geometry of Coronal Loops
Authors: Alissandrakis, C. E.; Gontikakis, C.; Dara, H. C.
Bibcode: 2007ESASP.641E..52A
Altcode:
  Loops are the basic structural elements of the solar atmosphere in
  low beta regions, particularly in the corona. Important progress
  has been made in recent years thanks to the SOHO and TRACE space
  missions, which provided opportunities for better studies of the loop
  morphology and their physical properties. In this work we use line of
  sight velocity measurements from the SUMER and CDS instruments aboard
  SOHO, in conjunction with a simple geometrical model, to reconstruct
  the velocity of plasma flow along loops. The flow appears to be
  uni-directional, with velocity maxima near the footpoints.

Title: Type II and IV radio bursts in the active period
    October-November 2003
Authors: Petoussis, V.; Tsitsipis, P.; Kontogeorgos, A.; Moussas,
   X.; Preka-Papadema, P.; Hillaris, A.; Caroubalos, C.; Alissandrakis,
   C. E.; Bougeret, J. -L.; Dumas, G.
Bibcode: 2006AIPC..848..199P
Altcode: 2010arXiv1009.4485P
  In this report we present the Type II and IV radio bursts observed
  and analyzed by the radio spectrograph ARTEMIS IV<SUP>1</SUP>, in the
  650-20MHz frequency range, during the active period October-November
  2003. These bursts exhibit very rich fine structures such fibers,
  pulsations and zebra patterns which is associated with certain
  characteristics of the associated solar flares and CMEs.

Title: A Statistical Study of Microwave Flare Morphologies
Authors: Tzatzakis, V.; Nindos, A.; Alissandrakis, C. E.; Shibasaki, K.
Bibcode: 2006AIPC..848..248T
Altcode:
  Using Nobeyama Radioheliograph (NoRH) high spatial resolution images
  at 17 and 34 GHz, we study the morphology of several flare events that
  occured relatively close to the limb. Our study has been motivated by
  the recent detection of a small number of optically thin flares whose
  maximum emission peaks close to the loop top. These events may show
  significant anisotropy of the density and pitch angle distribution
  of the nonthermal electrons. However, we do not know how often they
  occur. Our sample consists of 104 flare events. Using data from the
  Nobeyama Polarimeter we were able to determine whether the 17 and 34
  GHz emissions are optically thin or thick. Almost half of our events
  appear unresolved in the NoRH images. Among the resolved events,
  special attention is paid to those with circular polarization (V)
  showing two distinct sources. Such V sources are considered proxies to
  the flaring loop footpoints if the total intensity (I) morphology is
  consistent with a single flaring loop configuration. A small number of
  events, as expected at such high frequencies, are optically thick with
  I maximum between the loop footpoints. The number of optically thin
  events showing I maxima co-spatial with the V sources is approximately
  the same as the number of those optically thin resolved events showing
  emission peak between the V sources. Our future plans concerning the
  study of our database are also outlined.

Title: Ten Years of the Solar Radiospectrograph ARTEMIS-IV
Authors: Caroubalos, C.; Alissandrakis, C. E.; Hillaris, A.;
   Preka-Papadema, P.; Polygiannakis, J.; Moussas, X.; Tsitsipis, P.;
   Kontogeorgos, A.; Petoussis, V.; Bouratzis, C.; Bougeret, J. -L.;
   Dumas, G.; Nindos, A.
Bibcode: 2006AIPC..848..864C
Altcode: 2010arXiv1009.4150C
  The Solar Radiospectrograph of the University of Athens (ARTEMIS-IV)
  is in operation at the Thermopylae Satellite Communication Station
  since 1996. The observations extend from the base of the Solar Corona
  (650 MHz) to about 2 Solar Radii (20 MHz) with time resolution
  1/10-1/100 sec. The instruments recordings, being in the form of
  dynamic spectra, measure radio flux as a function of height in the
  corona; our observations are combined with spatial data from the
  Nancay Radioheliograph whenever the need for 3D positional information
  arises. The ARTEMIS-IV contribution in the study of solar radio bursts
  is two fold- Firstly, in investigating new spectral characteristics
  since its high sampling rate facilitates the study of fine structures in
  radio events. On the other hand it is used in studying the association
  of solar bursts with interplanetary phenomena because of its extended
  frequency range which is, furthermore, complementary to the range of the
  WIND/WAVES receivers and the observations may be readily combined. This
  reports serves as a brief account of this operation. Joint observations
  with STEREO/WAVES and LOFAR low frequency receivers are envisaged in
  the future.

Title: Type II Shocks Characteristics: Comparison with associated
    CMEs and Flares
Authors: Pothitakis, G.; Mitsakou, E.; Preka-Papadema, P.; Moussas,
   X.; Caroubalos, C.; Alissandrakis, C. E.; Hillaris, A.; Tsitsipis,
   P.; Kontogeorgos, A.; Bougeret, J. -L.; Dumas, G.
Bibcode: 2006AIPC..848..238P
Altcode: 2010arXiv1009.4294P
  A number of metric (100-650 MHz) typeII bursts was recorded by
  the ARTEMIS-IV radiospectrograph in the 1998-2000 period; the
  sample includes both CME driven shocks and shocks originating from
  flare blasts. We study their characteristics in comparison with
  characteristics of associated CMEs and flares.

Title: Type III events, flares and CMEs, in the extremely active
    period October-November 2003
Authors: Mitsakou, E.; Thanasa, M.; Preka-Papadema, P.; Moussas, X.;
   Hillaris, A.; Caroubalos, C.; Alissandrakis, C. E.; Tsitsipis, P.;
   Kontogeorgos, A.; Bougeret, J. -L.; Dumas, G.
Bibcode: 2006AIPC..848..234M
Altcode: 2010arXiv1009.3592M
  The type III observations trace the propagation of energetic electron
  populations through the Solar Corona which, more often than not,
  precede or are associated with energy release on the Sun. A sample
  of Type III bursts in the range 20-650 MHz during the period of
  extraordinary solar activity (20 October to 4 November 2003) recorded
  by the ARTEMIS-IV<SUP>1</SUP> radio spectrograph is analysed; its
  parameters are compared with characteristics of associated flares
  (Ha and GOES SXR) and CMEs, observed in the same period and reported
  in the SGR and the LASCO archives respectively. In this report we
  attempt to establish a correlation between energetic particles and
  major manifestations of solar activity such as flares and CMEs.

Title: Periodicities in Fine Structure of Type IV Radio Solar Bursts
Authors: Tsitsipis, P.; Kontogeorgos, A.; Moussas, X.; Preka-Papadema,
   P.; Hillaris, A.; Petoussis, V.; Caroubalos, C.; Alissandrakis, C. E.;
   Bougeret, J. -L.; Dumas, G.
Bibcode: 2006AIPC..848..243T
Altcode:
  A study of periodicities appearing in the type-IV bursts fine structure
  (fibers and pulsations in particular) is presented. Our data set
  includes recordings by ARTEMIS IV with high time resolution; this
  facilitates the detection of lower than 1 sec periodicities. We
  introduce a method which employs directional filtering for the
  separation of intertwined fibers and pulsations for independent analysis
  of different events within complex radio bursts. For further analysis
  we use Short Time Fourier and Wavelet transforms which enable the study
  of the evolution of periodicities with time over specified periods
  of solar radio activity. Since, according to existing theoretical
  models, periodicities depend on basic parameters of active regions,
  this methodology provides the appropriate diagnostic tools.

Title: Detection of slopes of linear and quasi-linear structures in
    noisy background, using 2D-FFT
Authors: Tsitsipis, P.; Kontogeorgos, A.; Moussas, X.; Preka-Papadema,
   P.; Hillaris, A.; Petoussis, V.; Caroubalos, C.; Alissandrakis, C. E.;
   Bougeret, J. -L.; Dumas, G.
Bibcode: 2006AIPC..848..874T
Altcode:
  We present a fast algorithm for slope detection on grey scale images,
  based on 2D-FFT, which may be used for line or edge detection. Our
  approach is based on the calculation of ``energy'' per direction of the
  image, thus obtaining the Energy Spectrum on Slope (α). This exhibits
  local maxima at the points where α equals the slopes of linear or
  quasi-linear segments within the image, yet it is not affected by their
  position within it. The process thus outlined was motivated by the study
  of astrophysical images (Solar Dynamic Radio Spectra) which necessitated
  the introduction of a method for fast extraction of drifting structures,
  since they appear as linear or quasi linear segments on these spectra.

Title: The improved ARTEMIS IV multichannel solar radio spectrograph
    of the University of Athens
Authors: Kontogeorgos, A.; Tsitsipis, P.; Caroubalos, C.; Moussas,
   X.; Preka-Papadema, P.; Hilaris, A.; Petoussis, V.; Bouratzis, C.;
   Bougeret, J. -L.; Alissandrakis, C. E.; Dumas, G.
Bibcode: 2006ExA....21...41K
Altcode: 2006ExA...tmp...16K; 2010arXiv1009.3628K
  We present the improved solar radio spectrograph of the University
  of Athens operating at the Thermopylae Satellite Telecommunication
  Station. Observations now cover the frequency range from 20 to
  650 MHz. The spectrograph has a 7-meter moving parabola fed by a
  log-periodic antenna for 100 650 MHz and a stationary inverted V fat
  dipole antenna for the 20 100 MHz range. Two receivers are operating in
  parallel, one swept frequency for the whole range (10 spectrums/sec,
  630 channels/spectrum) and one acousto-optical receiver for the range
  270 to 450 MHz (100 spectrums/sec, 128 channels/spectrum). The data
  acquisition system consists of two PCs (equipped with 12 bit, 225
  ksamples/sec ADC, one for each receiver). Sensitivity is about 3 SFU
  and 30 SFU in the 20 100 MHz and 100 650 MHz range respectively. The
  daily operation is fully automated: receiving universal time from a
  GPS, pointing the antenna to the sun, system calibration, starting
  and stopping the observations at preset times, data acquisition,
  and archiving on DVD. We can also control the whole system through
  modem or Internet. The instrument can be used either by itself or in
  conjunction with other instruments to study the onset and evolution
  of solar radio bursts and associated interplanetary phenomena.

Title: Observing the Sun at 20 650 MHz at Thermopylae with Artemis
Authors: Kontogeorgos, A.; Tsitsipis, P.; Moussas, X.; Preka-Papadema,
   G.; Hillaris, A.; Caroubalos, C.; Alissandrakis, C.; Bougeret, J. -L.;
   Dumas, G.
Bibcode: 2006SSRv..122..169K
Altcode:
  Fine structure of type IV radio solar bursts with a great variety and
  complexity often give much information in different ways and enable
  estimation of various coronal characteristics. In this work, we expose
  our new method for fine structure revealing and separation of two
  basic kinds of type IV fine structure, as fibers and pulsations. We
  also estimate frequency drift of fibers from dynamic spectra, clean
  from continuous background, with a prototype method using 2-D Fourier
  transform and we estimate periodicities of fibers as well as pulsations
  with continuous wavelet transform. Working with the last method we
  found periodicities close to 3 min umbral oscillations and 5 min global
  solar oscillations.

Title: Solar flares with and without SOHO/LASCO coronal mass ejections
    and type II shocks
Authors: Hillaris, A.; Petousis, V.; Mitsakou, E.; Vassiliou, C.;
   Moussas, X.; Polygiannakis, J.; Preka-Papadema, P.; Caroubalos, C.;
   Alissandrakis, C.; Tsitsipis, P.; Kontogeorgos, A.; Bougeret, J. -L.;
   Dumas, G.
Bibcode: 2006AdSpR..38.1007H
Altcode: 2010arXiv1009.3636H
  We analyse of a set of radio rich (accompanied by type IV or II
  bursts) solar flares and their association with SOHO/LASCO Coronal
  Mass Ejections in the period 1998 2000. The intensity, impulsiveness
  and energetics of these events are investigated. We find that,
  on the average, flares associated both with type IIs and CMEs are
  more impulsive and more energetic than flares associated with type
  IIs only (without CME reported), as well as flares accompanied by
  type IV continua but not type II shocks. From the last two classes,
  flares with type II bursts (without CMEs reported) are the shortest
  in duration and the most impulsive.

Title: Multiwavelength Analysis of an Active Region
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th. G.;
   Alissandrakis, C. E.; Nindos, A.; Vial, J. -C.; Tsiropoula, G.
Bibcode: 2006SoPh..233...57G
Altcode:
  We study active region NOAA 8541, observed with instruments on board
  SOHO, as well as with TRACE. The data set mainly covers the transition
  region and the low corona. In selected loops studied with SUMER on SOHO,
  the VIII 770 Å line is systematically redshifted. In order to estimate
  the plasma velocity, we combine the Doppler shifts with proper motions
  (TRACE) along these loops. In the case of an ejection, apparently
  caused by the emergence of a parasitic polarity, proper motions and
  Doppler shifts give consistent results for the velocity. A cooler loop,
  observed in the same active region with CDS, shows a unidirectional
  motion reminiscent of a siphon flow. The derived electron temperature
  and density along a large steady loop confirm that it cannot be
  described by hydrostatic models.

Title: Trace Observations of Solar Spicules Beyond the Limb in -
    and CIV
Authors: Alissandrakis, C. E.; Zachariadis, Th.; Gontikakis, C.
Bibcode: 2005ESASP.600E..54A
Altcode: 2005ESPM...11...54A; 2005dysu.confE..54A
  No abstract at ADS

Title: Complex Solar Events Observed with the Artemis-Iv
    Radio-Spectrograph in October/november 2003
Authors: Alissandrakis, C. E.; Nindos, A.; Hilaris, A.; Caroubalos,
   C.; Artemis Team
Bibcode: 2005ESASP.600E.106A
Altcode: 2005dysu.confE.106A; 2005ESPM...11..106A
  No abstract at ADS

Title: RATAN-600 Observations of Unusual Inversion of Polarization
    in Sunspot Associated Microwave Sources
Authors: Gizani, Nectaria A. B.; Alissandrakis, C.; Bogod, V.;
   Garaimov, V.; Zheleznyakov, V.; Zlotnik, E.
Bibcode: 2005HiA....13..137G
Altcode:
  We present multi-wavelength observations of an active region in the
  range of 1.7 to 30 cm obtained with the RATAN-600 radio telescope with
  high polarization accuracy (up to 0.5%). The active region was observed
  on six consecutive days in May 96. At short wavelengths the circular
  polarization scans show a bipolar structure in conformity with the
  bipolar magnetic field. However at 14.5 cm the circular polarization
  drops practically to zero and at longer wavelengths the sense of the
  polarization is reversed in {both components}. This was consistently
  observed through all our six days of observation while the region
  was moving from the center of the disk to the west limb. This unusual
  polarization inversion cannot be interpreted in terms of the well-known
  propagation effects under conditions of weak and strong coupling.

Title: Solar type II and type IV radio bursts observed during
    1998-2000 with the ARTEMIS-IV radiospectrograph
Authors: Caroubalos, C.; Hillaris, A.; Bouratzis, C.; Alissandrakis,
   C. E.; Preka-Papadema, P.; Polygiannakis, J.; Tsitsipis, P.;
   Kontogeorgos, A.; Moussas, X.; Bougeret, J. -L.; Dumas, G.; Perche, C.
Bibcode: 2004A&A...413.1125C
Altcode:
  A catalogue of the type II and type IV solar radio bursts in the 110-687
  MHz range, observed with the radio spectrograph ARTEMIS-IV operated
  by the University of Athens at Thermopylae, Greece from 1998-2000 is
  presented. These observations are compared with the LASCO archives
  of Coronal Mass Ejections and the Solar Geophysical Reports of solar
  flares (Hα &amp; SXR) and examined for possible associations. The
  main results are: <P />68% of the catalogue events were associated
  with CMEs. <P />67% of the type II events were associated with CMEs,
  in accordance with previous results. This percentage rises to 79%
  in the case of composite type II/IV events. <P />77% of the type IV
  continua were associated with CMEs, which is higher that the CME-type
  II association probability. <P />The type II associated CMEs had an
  average velocity of (835 ± 380) km s<SUP>-1</SUP>, while the CMEs
  not associated with type IIs had an average velocity of (500 ± 150)
  km s<SUP>-1</SUP>. <P />All events, but one, were well associated with
  H\alpha and/or SXR flares. <P />Most of the CME launch times precede
  by 5-60 min (30 min on average) the associated SXR flare peak; an
  important fraction (72%) precede the flare onset as well. <P />Appendix
  A is only available in electronic form at http://www.edpsciences.org

Title: The Improved Multichannel Solar Radiospectrograph ARTEMIS IV
    (Abstract)
Authors: Kontogeorgos, P.; Tsitsipis, P.; Caroubalos, C.; Moussas, X.;
   Alissandrakis, C. E.; Hillaris, A.; Preka-Papadema, P.; Polygiannakis,
   J.; Bougeret, J. -L.; Dumas, G.; Perche, C.
Bibcode: 2004hell.conf..338K
Altcode:
  No abstract at ADS

Title: Solar Flares with and without Coronal Mass Ejections and Type
    II shocks
Authors: Mitsakou, E.; Petousis, V.; Vassiliou, C.; Moussas, X.;
   Polygiannakis, J.; Hillaris, A.; Preka-Papadema, P.; Caroubalos, C.;
   Alissandrakis, C.; Tsitsipis, P.; Artemis Team
Bibcode: 2004cosp...35.2293M
Altcode: 2004cosp.meet.2293M
  An analysis is presented of a set of ``radio rich'' solar SXR flares,
  i.e. accompanied by type IV or II metric radio bursts, associated with
  Coronal Mass Ejections and MHD shocks, recorded as type II events, in
  the period 1998-2000. The relative size, impulsiveness and energetics
  of these events are investigated. We find that, on the average, the
  flares with type II bursts and CME's are larger, more impulsive and
  energetic from the flares with type II but without CME's. The latter are
  more energetic than flares associated with relatively ``slow CME's''
  accompanied by type IV continua but not type II shocks. Although a
  simple classification may not be readily determined the results imply
  that associated energetic events originate, more often than not,
  from sources with characteristics fairly well correlated.

Title: Study of 40 Solar Energetic Events Based on GOES, LASCO and
    ARTEMIS IV Data (1998-2000)
Authors: Mitsakou, E.; Vassiliou, C.; Moussas, X.; Polygiannakis,
   J.; Hillaris, A.; Preka-Papadema, P.; Caroubalos, C.; Alissandrakis,
   C. E.; Tsitsipis, P.; Kontogeorgos, A.; Bougeret, J. -L.; Dumas, G.;
   Perche, C.
Bibcode: 2004hell.confR..77M
Altcode:
  No abstract at ADS

Title: Fine Structure in Type IV Solar Radio Bursts during three
    major Solar Events of October-November 2003 observed by Artemis IV.
Authors: Tsitsipis, P.; Kontogeorgos, A.; Caroubalos, C.; Moussas,
   X.; Hillaris, A.; Preka-Papadema, P.; Bougeret, J. -L.; Alissandrakis,
   C.; Dumas, G.; Polygiannakis, J.
Bibcode: 2004cosp...35.2705T
Altcode: 2004cosp.meet.2705T
  The fine structure in three solar type IV radio bursts was studied
  using the French-Greek ARTEMIS-IV multichannel radio spectrograph. The
  bursts were recorded during three major solar events, on the 26 and 28
  October.and 3 Nov. 2003; these we associated with intense flares and
  CMEs. The observed fine structure includes intermediate drift bursts
  (fibers) and pulsations. The complexity and overlapping of the various
  spectral characteristics necessitated the utilization of certain, 2D-FFT
  based, filtering processes, aiming firstly at structure detection in
  the frequency-time plane (ie the dynamic spectrum) and secondly in the
  separation of fibers and pulsations and the suppression of the type
  IV continuum. This methodology results also to the fibers frequency
  drift rate distributions and their evolution in time. These fiber
  frequency drift distributions may be interpreted as the exciter velocity
  distributions, using a Newkirk coronal density model; the latter may
  be used as diagnostics of the magnetic field restructuring and energy
  release during a solar energetic event (flare and/or CME). Artemis IV
  will provide complementary data to the STEREO/WAVES experiment.

Title: Fine Radio Structures During a Major Solar Event Observed
    with Artemis IV (Abstract)
Authors: Tsitsipis, P.; Kontogeorgos, A.; Caroubalos, C.; Moussas, X.;
   Alissandrakis, C. E.; Hillaris, A.; Preka-Papadema, P.; Polygiannakis,
   J.; Bougeret, J. -L.; Dumas, G.; Perche, C.
Bibcode: 2004hell.confQ..64T
Altcode:
  No abstract at ADS

Title: Unusual Inversion of Polarization in Sunspot Sources
Authors: Gizani, Nectaria A.; Alissandrakis, C. E.; Bogod, V.;
   Garaimov, V.; Gelfreikh, G.; Zheleznyakov, V.; Zlotnik, E.
Bibcode: 2003IAUJD...3E...2G
Altcode:
  We present multi-wavelength observations of an active region in the
  range of 1.7 to 30 cm obtained with the RATAN-600 radio telescope with
  high polarization accuracy (up to 0.5%). The active region was observed
  on six consecutive days in May 96. At short wavelengths the circular
  polarization scans show a bipolar structure in conformity with the
  bipolar magnetic field. However at 14.5 cm the circular polarization
  drops practically to zero and at longer wavelengths the sense of the
  polarization is reversed in {both components}. This was consistently
  observed through all our six days of observation while the region
  was moving from the center of the disk to the west limb. This unusual
  polarization inversion cannot be interpreted in terms of the well-known
  propagation effects under conditions of weak and strong coupling.

Title: Radio signatures of magnetic restructuring during the 2000
    July 14 major solar event
Authors: Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A.; Moussas, X.;
   Alissandrakis, C. E.; Hillaris, A.; Preka-Papadema, P.; Polygiannakis,
   J.; Bougeret, J. -L.; Dumas, G.; Kurt, V.; Vassiliou, C.; Perche,
   C.; Gazeas, K.; Kolovos, G.
Bibcode: 2002ESASP.505..377C
Altcode: 2002IAUCo.188..377C; 2002solm.conf..377C
  We analyse the fine structure of the type IV radio burst, during
  the main phase of the 14th July 2000 major event recorded by the
  radiospectrograph ARTEMIS-IV, in the 110-650 MHz (10 Hz sampling
  rate) and the 270-450 MHz (100 Hz rate) range. In this report we
  focus on variations in frequency drift rate and repetition rate of
  fibers bursts. A pronounced asymmetry between the number of bursts
  with positive and negative frequency drift is noted at certain time
  periods. These variations follow closely the evolution of the magnetic
  structure associated with the major solar event and the onset of the
  corresponding CME.

Title: Oscillations and waves near the limb from TRACE UV observations
Authors: Alissandrakis, C. E.; Zachariadis, Th. G.; Gontikakis, C.
Bibcode: 2002ESASP.505..329A
Altcode: 2002solm.conf..329A; 2002IAUCo.188..329A
  We analyze TRACE observations near the limb in the 1550, 1600 and 1700
  Å UV bands. Intensity-time images were computed at various distances
  from the limb. Two dimensional Fourier analysis on the ω-k plane
  shows very well the well-known p-mode ridges which persist up to the
  limb in all three bands. Their power decreases almost proportionally
  to the cosine of the heliocentric angle at 1600 and 1700 Å, being
  more flat in the C IV 1550 Å band.

Title: Study of coronal loops using TRACE and SOHO
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th.; Nindos, A.;
   Alissandrakis, C.; Tsiropoula, G.; Vial, J. -C.
Bibcode: 2002ESASP.505..417G
Altcode: 2002solm.conf..417G; 2002IAUCo.188..417G
  We analysed coronal loops observed in many spectral lines from TRACE and
  SUMER, at the active region NOAA 8541, on May 15, 1999. For the loops,
  which are identified in a number of wavelengths, we try to combine
  the good temporal and spatial resolution of TRACE with the spectral
  information obtained by the SUMER rasters, in order to determine some
  physical parameters such as temperature, flow velocity and electron
  density. The morphology of the magnetic field of the loops is also
  approximated by a force-free extrapolation of the photospheric magnetic
  field, measured with MDI, and is compared to the loop morphology.

Title: Spatially resolved microwave oscillations above a sunspot
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Bogod,
   V. M.; Gontikakis, C.
Bibcode: 2002A&A...386..658N
Altcode:
  Using high quality VLA observations, we detected for the first time
  spatially resolved oscillations in the microwave total intensity
  (I) and circular polarization (V) emission of a sunspot-associated
  gyroresonance (g-r) source. Oscillations were detected at 8.5 and 5
  GHz during several time intervals of our 10-hour-long dataset. The
  oscillations are intermittent: they start suddenly and are damped
  somehow more gradually. Despite their transient nature when they
  are observed they show significant positional, amplitude and phase
  stability. The spatial distribution of intensity variations is
  patchy and the location of the patches of strong oscillatory power
  is not the same at both frequencies. The strongest oscillations are
  associated with a small region where the 8.5 GHz emission comes from
  the second harmonic of the gyrofrequency while distinct peaks of weaker
  oscillatory power appear close to the outer boundaries of the 8.5 and 5
  GHz g-r sources, where the emissions come from the third harmonic of the
  gyrofrequency. Overall, the 5 GHz oscillations are weaker than the 8.5
  GHz oscillations (the rms amplitudes of the I oscillations are 1.3-2.5 x
  10<SUP>4</SUP> K and 0.2-1.5 x 10<SUP>5</SUP> K, respectively). At both
  frequencies the oscillations have periods in the three-minute range: the
  power spectra show two prominent peaks at 6.25-6.45 mHz and 4.49-5.47
  mHz. Our models show that the microwave oscillations are caused by
  variations of the location of the third and/or second harmonic surfaces
  with respect to the base of the chromosphere-corona transition region
  (TR), i.e. either the magnetic field strength or/and the height of the
  base of the TR oscillates. The best-fit model to the observed microwave
  oscillations can be derived from photospheric magnetic field strength
  oscillations with an rms amplitude of 40 G or oscillations of the height
  of the base of the TR with an rms amplitude of 25 km. Furthermore,
  small variations of the orientation of the magnetic field vector yield
  radio oscillations consistent with the observed oscillations. Tables
  1-3 are only available in electronic form at http://www.edpsciences.org

Title: Multiwavelength analysis of an active region observed with
    SOHO and TRACE
Authors: Dara, H. C.; Gontikakis, C.; Zachariadis, Th.; Tsiropoula,
   G.; Alissandrakis, C. E.; Vial, J. -C.
Bibcode: 2002ESASP.477...95D
Altcode: 2002scsw.conf...95D
  We study the solar active region NOAA 8541, observed on May 15, 1999,
  from 13:00 to 15:00 UT, with the instruments aboard SOHO (SUMER,
  CDS, MDI) and TRACE. The SOHO observations produced a set of raster
  scans of the region with a field of view of 159"×120" for SUMER and
  of 244"×240" for CDS. TRACE gave a sequence of high time resolution
  images for a much larger (510"×510") field of view, in several spectral
  passbands, while MDI gave the photospheric full disk longitudinal
  magnetic field. The data set mainly covers the transition region and
  the low corona. We have used the data to construct intensity, velocity
  and magnetic field maps of the region. The comparison of the intensity
  images in various wavelengths with the velocity images, as well as
  with the magnetic field, gives us information about the dynamical
  characteristics of the observed features and their relationship to
  the photospheric magnetic field.

Title: Relation between intensity and Dopplershifts in the quiet
    Sun transition region
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th.; Alissandrakis,
   C. E.; Vial, J. -C.
Bibcode: 2002ESASP.477..107G
Altcode: 2002scsw.conf..107G
  In this work we used CDS and SUMER (SOHO) observations of a quiet
  region (41°W 41°N) on the 28th of July 1996. The study of the
  histograms of the velocities corresponding to the network and the
  internetwork regions, shows that the network plasma is redshifted
  with respect to the internetwork one. The shifts in the histograms
  are small, but they are systematic for all lines. It should be
  mentioned that the internetwork is also statistically redshifted,
  with the exception of the He I line. In the low transition region the
  morphology in the intensity images is different from the morphology
  in the Dopplergrams. It seems that the network intensity structures
  correspond to more than one in the Dopplergrams, since the latter
  are quite smaller than the intensity structures. This was verified by
  calculating the average autocorrelation function for intensity images
  and Dopplergrams of spectral lines from SUMER and CDS. On the average,
  the FWHM of the autocorrelation function of the intensity images is
  two times larger than that of the corresponding Dopplergram ones.

Title: Cooling and evacuation of an active region loop complex
    observed with TRACE
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
   Th.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2002ESASP.477..179T
Altcode: 2002scsw.conf..179T
  We analyse the temporal variation of temperature and emission measure
  at the top of a coronal loop system observed with the Transition
  Region and Coronal Explorer (TRACE). Loops delineate regions of highly
  localized heating and are thus typically the focus of coronal heating
  theories. The analyzed data consist of observations in the 171 Å and
  195 Å passbands taken at a cadence of ~10 min obtained on May 15,
  1999 during an observing campaign. The temperature and emission measure
  diagnostic is based in the 171 Å / 195 Å filter-ratio technique. The
  loop system evacuates after the plasma at the top of the loops has
  cooled. Estimates of the timescales of energy losses by radiation
  and by conduction clearly suggest that the cooling is mainly due to
  radiation losses.

Title: ARTEMIS IV Radio Observations of the 14 July 2000 Large
    Solar Event
Authors: Caroubalos, C.; Alissandrakis, C. E.; Hillaris, A.; Nindos,
   A.; Tsitsipis, P.; Moussas, X.; Bougeret, J. -L.; Bouratzis, K.;
   Dumas, G.; Kanellakis, G.; Kontogeorgos, A.; Maroulis, D.; Patavalis,
   N.; Perche, C.; Polygiannakis, J.; Preka-Papadema, P.
Bibcode: 2001SoPh..204..165C
Altcode: 2010arXiv1009.3654C
  In this report we present a complex metric burst, associated with
  the 14 July 2000 major solar event, recorded by the ARTEMIS-IV radio
  spectrograph at Thermopylae. Additional space-borne and Earth-bound
  observational data are used, in order to identify and analyze the
  diverse, yet associated, processes during this event. The emission at
  metric wavelengths consisted of broad-band continua including a moving
  and a stationary type IV, impulsive bursts and pulsating structures. The
  principal release of energetic electrons in the corona was 15-20 min
  after the start of the flare, in a period when the flare emission spread
  rapidly eastwards and a hard X-ray peak occurred. Backward extrapolation
  of the CME also puts its origin in the same time interval, however,
  the uncertainty of the extrapolation does not allow us to associate
  the CME with any particular radio or X-ray signature. Finally, we
  present high time and spectral resolution observations of pulsations
  and fiber bursts, together with a preliminary statistical analysis.

Title: Dopplershifts in the solar transition region
Authors: Gontikakis, C.; Dara, H. C.; Alissandrakis, C. E.;
   Zachariadis, Th. G.; Vial, J. -C.
Bibcode: 2001A&A...378..257G
Altcode:
  We study the dynamics of the quiet sun transition region, using
  observations obtained with the SOHO CDS/NIS and SUMER spectrographs. We
  examine the morphology of the network as a function of temperature and
  we compare the intensity features with those of the dopplergrams. The
  velocity distributions have a different behaviour for the bright
  features which outline the network and the dark ones, located in
  the internetwork. A redshift and a smaller standard deviation are
  observed for the bright feature distributions relative to the dark
  ones. It should be mentioned that the internetwork is also statistically
  redshifted, with the exception of the He I line. Velocity distributions
  from different lines are compared.

Title: Ratan-600 observations of unusual inversion of polarization
Authors: Gizani, N. A. B.; Alissandrakis, C. E.; Bogod, V.; Garaimov,
   V.; Gelfreikh, G.; Zheleznyakov, V.; Zlotnik, E.
Bibcode: 2001A&AT...20..543G
Altcode:
  No abstract at ADS

Title: Multi-wavelength analysis of a solar active region loop system
    with SOHO, TRACE and ground-based telescopes
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
   Th. G.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2001hell.confE..40T
Altcode:
  No abstract at ADS

Title: Statistical analysis of type IV radio bursts fine structure
    observed during the 14th July 2000 large solar event.
Authors: Tsitsipis, P.; Kontogeorgos, A.; Hillaris, A.; Polygiannakis,
   J.; Moussas, X.; Preka-Papadema, P.; Bouratzis, C.; Caroubalos, C.;
   Alissandrakis, C.; Maroulis, D.; Patavalis, N.; Bougeret, J. L.;
   Dumas, G.; Perche, C.
Bibcode: 2001hell.confE..37T
Altcode:
  No abstract at ADS

Title: Statistics on the occurence of CMEs related radio bursts
    observed by ARTEMIS IV radio spectrograph during the maximum of the
    solar cycle 23.
Authors: Bouratzis, C.; Desilas, C.; Hillaris, A.; Preka-Papadema,
   P.; Moussas, X.; Caroubalos, C.; Alissandrakis, C.; Maroulis, D.;
   Patavalis, N.; Polygiannakis, J.; Bougeret, J. -L.; Dumas, G.; Perche,
   C.; Kontogeorgos, A.; Tsitsipis, P.
Bibcode: 2001hell.confE..36B
Altcode:
  No abstract at ADS

Title: Joint observations of solar radio bursts and cosmic ray events
    recorded by the ARTEMIS IV radio spectrograph and Athens Cosmic Ray
    Station (Super 6NM-64) of the University of Athens
Authors: Caroubalos, C.; Hillaris, A.; Bouratzis, C.; Mavromichalaki,
   H.; Souvatzoglou, G.; Sarlanis, C.; Tatsis, S.; Maroulis, D.;
   Patavalis, N.; Polygiannakis, J.; Moussas, X.; Preka-Papadema,
   P.; Alissandrakis, C.; Bougeret, J. -L.; Dumas, G.; Perche, C.;
   Kontogeorgos, A.; Tsitsipis, P.
Bibcode: 2001hell.confE..35C
Altcode:
  No abstract at ADS

Title: Fine Structure of the Quiet Solar Chromosphere: Limb-Crossing
    Features
Authors: Zachariadis, Th. G.; Dara, H. C.; Alissandrakis, C. E.;
   Koutchmy, S.; Gontikakis, C.
Bibcode: 2001SoPh..202...41Z
Altcode:
  In this article we study chromospheric structures (spicules) crossing
  the solar limb in Hα images corrected for limb darkening. This
  correction enabled us to view structures both on the disk and beyond the
  limb in the same image. The observations were obtained at the Sacramento
  Peak Observatory at Hα±0.75 Å. The processed images reveal both
  bright and dark (relative to the local background) features crossing
  the limb. We also observed bushes (rosettes) crossing the limb, as well
  as structures indicating probably arch-shaped mottles beyond the limb.

Title: On-the-Disk Development of the Halo Coronal Mass Ejection on
    1998 May 2
Authors: Pohjolainen, S.; Maia, D.; Pick, M.; Vilmer, N.; Khan, J. I.;
   Otruba, W.; Warmuth, A.; Benz, A.; Alissandrakis, C.; Thompson, B. J.
Bibcode: 2001ApJ...556..421P
Altcode:
  A halo coronal mass ejection (CME) was observed at 15:03 UT on 1998 May
  2 by the Solar and Heliospheric Observatory Large-Angle Spectrometric
  Coronagraph. The observation of the CME was preceded by a major soft
  X-ray flare in NOAA Active Region 8210, characterized by a delta spot
  magnetic configuration and some activity in region 8214. A large
  transequatorial interconnecting loop (TIL) seen in the soft X-rays
  connected AR 8210 to a faint magnetic field region in the periphery
  of region 8214. Smaller loop systems were also connecting AR 8210 to
  other fainter bipolar magnetic structures, the interconnecting loop
  (IL) east of AR 8210 being one of the most visible. We present here
  a multiwavelength analysis of the large- and small-scale coronal
  structures associated with the development of the flare and of the
  CME, with emphasis placed on radio-imaging data. In the early phases
  of the flare, the radio emission sources traced the propagation paths
  of electrons along the TIL and the IL, which are accelerated in the
  vicinity of AR 8210. Furthermore, jetlike flows were observed in soft
  X-rays and in Hα in these directions. Significantly, the TIL and
  IL loop systems disappeared at least partially after the CME. An EUV
  Imaging Telescope (EIT) dimming region of similar size and shape to the
  soft X-ray TIL, but noticeably offset from it, was also observed. During
  the ``flash'' phase of the flare, new radio sources appeared, presenting
  signatures of destabilization and reconnection at discrete locations of
  the connecting loops. We interpret these as possible signatures of the
  CME liftoff on the disk. An Hα Moreton wave (blast wave) and an ``EIT
  wave'' were also observed, originating from the flaring AR 8210. The
  signatures in radio, after the wave propagated high into the corona,
  include type II-like emissions in the spectra. The radio images link
  these emissions to fast-moving sources, presumably formed at locations
  where the blast wave encounters magnetic structures. The opening of
  the CME magnetic field is revealed by the radio observations, which
  show large and expanding moving sources overlying the later-seen EIT
  dimming region.

Title: Radio observations of filaments at metric and decimetric
    wavelengths
Authors: Marqué, Ch.; Lantos, P.; Delouis, J. M.; Alissandrakis, C. E.
Bibcode: 2001Ap&SS.277..329M
Altcode:
  A filament eruption at decimetric wavelength is illustrated here,
  involving a quiescent filament seen in absorption. A CME occurs in
  the vicinity of the event.

Title: Joint EUV/Radio Observations of a Solar Filament
Authors: Chiuderi Drago, F.; Alissandrakis, C. E.; Bastian, T.;
   Bocchialini, K.; Harrison, R. A.
Bibcode: 2001SoPh..199..115C
Altcode:
  In this paper we compare simultaneous extreme ultraviolet (EUV) line
  intensity and microwave observations of a filament on the disk. The
  EUV line intensities were observed by the CDS and SUMER instruments on
  board SOHO and the radio data by the Very Large Array and the Nobeyama
  radioheliograph. The main results of this study are the following: (1)
  The Lyman continuum absorption is responsible for the lower intensity
  observed above the filament in the EUV lines formed in the transition
  region (TR) at short wavelengths. In the TR lines at long wavelengths
  the filament is not visible. This indicates that the proper emission of
  the TR at the filament top is negligible. (2) The lower intensity of
  coronal lines and at radio wave lengths is due to the lack of coronal
  emission: the radio data supply the height of the prominence, while EUV
  coronal lines supply the missing hot matter emission measure (EM). (3)
  Our observations support a prominence model of cool threads embedded
  in the hot coronal plasma, with a sheath-like TR around them. From the
  missing EM we deduce the TR thickness and from the neutral hydrogen
  column density, derived from the Lyman continuum and He i absorption,
  we estimate the hydrogen density in the cool threads.

Title: The New Multichannel Radiospectrograph ARTEMIS-IV/HECATE,
    of the University of Athens
Authors: Caroubalos, C.; Maroulis, D.; Patavalis, N.; Bougeret, J. -L.;
   Dumas, G.; Perche, C.; Alissandrakis, C.; Hillaris, A.; Moussas, X.;
   Preka-Papadema, P.; Kontogeorgos, A.; Tsitsipis, P.; Kanelakis, G.
Bibcode: 2001ExA....11...23C
Altcode:
  We present the new solar radiospectrograph of the University of Athens
  operating at the Thermopylae Station since 1996. Observations cover the
  frequency range from 110 to 688 MHz. The radiospectrograph has a 7-meter
  parabolic antenna and two receivers operating in parallel. One is a
  sweep frequency receiver and the other a multichannel acousto-optical
  receiver. The data acquisition system consists of a front-end VME based
  subsystem and a Sun Sparc-5 workstation connected through Ethernet. The
  two subsystems are operated using the VxWorks real-time package. The
  daily operation is fully automated: pointing of the antenna to the
  sun, starting and stopping the observations at pre-set times, data
  acquisition, data compression by `silence suppression', and archiving
  on DAT tapes. The instrument can be used either by itself to study
  the onset and evolution of solar radio bursts or in conjunction with
  other instruments including the Nançay Decametric Array and the
  WIND/WAVES RAD1 and RAD2 low frequency receivers to study associated
  interplanetary phenomena.

Title: Brightness Variations of mg ib Bright Features
Authors: Dara, H. C.; Koutchmy, S.; Zachariadis, Th. G.; Alissandrakis,
   C. E.
Bibcode: 2001SoPh..198..313D
Altcode:
  We study the temporal intensity variations of Mgib bright features and
  investigate the corresponding Hα velocity pattern. The network bright
  features are well visible in the continuum, in images averaged over the
  duration of the observations (130 min). We detected `flashing' bright
  features, which appear and disappear within two to five minutes, while
  the rest of the bright features undergo small variations of either their
  shape and/or their intensity. A power spectrum analysis reveals a 10-min
  oscillation for approximately half of the stable bright features. The
  5-min oscillations are detected mainly at the network boundaries,
  where stable bright features are located, while 3-min oscillations
  coincide with few bright features, but are also quite intense inside
  the network cells. The majority of bright features are associated
  with Hα downflows. The downflow is very intense at the location of
  `flashing' bright features.

Title: DEM Study of Selected Quiet Sun Regions
Authors: Gontikakis, C.; Landi, E.; Dara, H. C.; Alissandrakis, C. E.;
   Vial, J. -C.
Bibcode: 2001IAUS..203..390G
Altcode:
  In the present work EUV spectra of quiet Sun regions, observed with
  the Coronal Diagnostic Spectometer (CDS), are analysed in order to
  determine the Differential Emission Measure (DEM) of selected areas
  of the field of view. In particular, we study the differences between
  the DEM curves of the quiet Sun cell center areas, network areas and
  cell-network boundaries. The results are discussed in the light of
  theoretical models for the solar upper atmospheres.

Title: Association of chromospheric sunspot umbral oscillations and
    running penumbral waves. I. Morphological study
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Mein, P.
Bibcode: 2000A&A...355..375T
Altcode:
  Observations of a sunspot region located near the center of the solar
  disk were obtained on October 3, 1994, with the Multichannel Subtractive
  Double Pass Spectrograph (MSDP). This instrument, operating in Hα ,
  was installed at the focus of the VTT at Tenerife (Canary Islands)
  and provided Hα intensity profiles at every pixel of the field of
  view. Reconstruction of the Hα profile allowed the computation of
  two dimensional intensity and Doppler velocity images at different
  wavelengths within the line. We analyse a time series of 1 hour and
  8 min, obtained with a cadence of 36 sec and investigate the relation
  between umbral oscillations and running penumbral waves. The Doppler
  velocity as a function of time, along radial cuts through the center of
  the spot, shows several clear cases where waves that originate inside
  the umbra continue to propagate in the penumbra. In one case we were
  able to follow the evolution of an oscillating element for 216 sec,
  from the inner part of the umbra to the penumbra and we describe the
  propagation characteristics. We confirm the close association between
  sunspot oscillations and running penumbral waves and suggest that they
  are probably due to the same resonator.

Title: RATAN-600 Observations of Unusual Inversion of Polarization
    in Microwave Sources
Authors: Alissandrakis, C.; Gizani, N.; Bogod, V.; Garaimov, V.;
   Gelfreikh, G.; Zheleznyakov, V.; Zlotnik, E.
Bibcode: 1999ESASP.448.1225A
Altcode: 1999mfsp.conf.1225A; 1999ESPM....9.1225A
  No abstract at ADS

Title: The Expedition of the University of Ioannina and the Academy
    of Athens to Shabla, Bulgaria
Authors: Alissandrakis, C. E.; Zachariadis, Th.; Nakas, Ch.;
   Ladoyanni, G.
Bibcode: 1999ESASP.448.1287A
Altcode: 1999mfsp.conf.1287A; 1999ESPM....9.1287A
  No abstract at ADS

Title: Association between Umbral Oscillations and Running Penumbral
    Waves
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1999ESASP.448..217A
Altcode: 1999ESPM....9..217A; 1999mfsp.conf..217A
  No abstract at ADS

Title: Structure and Dynamics in the Transition Region
Authors: Gontikakis, C. P.; Dara, H. C.; Alissandrakis, C. E.;
   Zachariadis, Th. G.; Vial, J. -C.; Bastian, T.; Chiuderi Drago, F.
Bibcode: 1999ESASP.448..297G
Altcode: 1999mfsp.conf..297G; 1999ESPM....9..297G
  No abstract at ADS

Title: Magnetic Field Diagnostics in the Low Corona from Microwave
    Circular Polarization Inversion
Authors: Alissandrakis, C. E.
Bibcode: 1999spro.proc...53A
Altcode:
  The characteristics of the observed polarization of radio waves
  are determined by the emission mechanism and by the propagation
  conditions in the corona. In the case of weak coupling between
  the two electromagnetic wave modes, the polarization changes
  along the ray path, reflecting the local physical conditions; this
  results in inversion of the sense of circular polarization when a
  transverse field region (TFR) is crossed. On the contrary, if the wave
  coupling is strong, the polarization is fixed and its sense does not
  change when a TFR is crossed. As a result, Stokes V maps of active
  regions do not always correspond to the magnetic polarities shown in
  photospheric magnetograms. The differences depend on the wavelength,
  the heliographic position of the region, as well as on the density
  and the magnetic field of the corona, at about 0.1 R<SUB>solar</SUB>
  above the photosphere. In this short review I present older and recent
  observation of polarization inversion and will discuss the diagnostics
  they provide on the magnetic field.

Title: Analysis of coronal emissions observed at meter wavelengths
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1999A&A...351..373L
Altcode:
  We present an extensive analysis of large and medium scale radio
  sources observed with the Nançay Radioheliograph at 169 MHz, over
  more than four solar rotations in 1984 (during the declining phase of
  the solar cycle). The large scale emission is dominated by the coronal
  plateau, the radio counterpart of the coronal plasma sheet, which had
  an oscillatory structure around the equator. Medium scale local sources
  include both faint noise storm continua and thermal sources. Noise storm
  continua have greater brightness (8 10<SUP>5</SUP> to 3.8 10<SUP>6</SUP>
  K) and smaller diameter than thermal sources. We present distributions
  of brightness temperatures, sizes as well as longitude and latitude
  of the thermal sources and we study their location with respect to
  faculae and neutral lines. Based on their rotation rate, we estimate
  their altitude at 70 000 km. We find that most thermal sources at 169
  MHz are located between faculae and neutral lines and we present a
  geometrical model to account for this observation, according to which
  these sources are located in the upper leg of large scale loops. A
  small number of thermal sources is closer to neutral lines; these
  might be loops at the base of isolated coronal streamers.

Title: Metric and Decimetric Observations of the Quiet Solar Corona
Authors: Marqué, Ch.; Lantos, P.; Delouis, J. M.; Alissandrakis, C. E.
Bibcode: 1999ESASP.446..483M
Altcode: 1999soho....8..483M
  We describe a multi-wavelength analysis of the solar corona in the
  metric and decimetric range for a period in May 1992. The four radio
  wavelengths, available with the Nancay Radioheliograph provide
  a 3-dimensional view of the corona from about 1.05 to 1.2 solar
  radius. Some of the radio features are relative to the large scale
  structure of the corona (coronal plateau, coronal holes) and to medium
  scale structures (streamers) we can follow during their transit on the
  disk. We also observe thermal emission associated to active regions
  and we compare locations of radio emissions with structures of the
  X-ray loops.

Title: Magnetic Field Diagnostics from Microwave Circular Polarization
    Inversion
Authors: Alissandrakis, C. E.
Bibcode: 1999ASPC..184...23A
Altcode:
  The characteristics of the observed polarization of radio waves
  are determined by the emission mechanism and by the propagation
  conditions in the corona. In the case of weak coupling between the two
  electromagnetic wave modes, the polarization changes along the ray path,
  reflecting the local physical conditions; this results in inversion
  of the sense of circular polarization when a transverse field region
  (TFR) is crossed. On the contrary, if the wave coupling is strong,
  the polarization is fixed and its sense does not change when a TFR
  is crossed. In this article I present older and recent observation
  of polarization inversion and discuss the diagnostics they provide on
  the magnetic field.

Title: Erratum: "Fine structure of the solar chromosphere: arch-shaped
    mottles" [Sol. Phys., Vol. 184, No. 1, p. 77 - 86 (Jan 1999)].
Authors: Zachariadis, T. G.; Georgakilas, A. A.; Koutchmy, S.; Dara,
   H. C.; Alissandrakis, C. E.
Bibcode: 1999SoPh..187..227Z
Altcode:
  No abstract at ADS

Title: Coronal Magnetography of an Active Region From Microwave
    Polarization Inversion
Authors: Ryabov, B. I.; Pilyeva, N. A.; Alissandrakis, C. E.;
   Shibasaki, K.; Bogod, V. M.; Garaimov, V. I.; Gelfreikh, G. B.
Bibcode: 1999SoPh..185..157R
Altcode:
  The microwave circular polarization of the active region (AR) NOAA 7260
  on 21-23 August 1992 is analyzed. Two-dimensional images at 1.76 cm
  with spatial resolution of θ=10'' from the Nobeyama radioheliograph
  and one-dimensional scans at 9 wavelengths in the range of 1.81-3.43
  cm and θ=16.3''-31.1'' from the radio telescope RATAN-600 were
  used. An inversion of the sense of circular polarization through
  the wavelength range was recorded on 22 August. It is shown that
  both the wavelength and the time dependence of the inversion are
  consistent with quasi-transverse (QT) propagation of the radiation
  in the solar corona. From this, the strength of the coronal magnetic
  field in the active region was found to be H=20-65 G at a height of h=
  (5.7-8.7)×109 cm above the photosphere on 22 and 30 August and 125
  G at the lower height of (3.7-6.4)×109 cm on 23 August. We present a
  new technique, based on the radio mapping (in both Stokes I and V) of
  an AR undergoing circular polarization inversion; applying this method
  to the Nobeyama data we obtained, for the first time, a magnetogram of
  the coronal magnetic field. For AR 7260 we found values in the range of
  70-100 G at heights of (4-6)×109 cm on 23 August, adopting a constant
  value of N Lα (where N is the electron density and Lα is the scale
  of the coronal field divergence) of 2.5×1018 cm−2. We compare our
  results with force-free extrapolations of the photospheric magnetic
  field from a MSFC magnetogram obtained on 20 August.

Title: Dynamics of subrelativistic electron beams in the solar
    corona. Type III group analysis
Authors: Hillaris, A.; Alissandrakis, C. E.; Bougeret, J. -L.;
   Caroubalos, C.
Bibcode: 1999A&A...342..271H
Altcode:
  A number of type III groups is studied. Wave particle interactions
  are neglected and the so called drift approximation is used to model
  the electron beam evolution. We extrapolated the observed Flux-Time
  profiles towards higher frequencies and estimated the injection time
  for the individual beams responsible for the excitation of the type
  III's. A simple clustering algorithm, based on the temporal separation
  of nearest neighbour injections as a proximity criterion, was used to
  identify patterns of burst subgroups within the type III groups. The
  question of whether the acceleration and injection of component bursts
  exciters is coherently modulated in a single source, or this process
  is driven by a statistical flare in a spatially fragmented energy
  release site, is addressed.

Title: Polar surges and macrospicules: simultaneous Hα and He BT
    II 304 Angstroms observations
Authors: Georgakilas, A. A.; Koutchmy, S.; Alissandrakis, C. E.
Bibcode: 1999A&A...341..610G
Altcode:
  We compare simultaneous sequences of Hα and He ii 304 Angstroms images
  near the solar limb. We propose to distinguish polar surges and giant
  spicules (macrospicules), among the He ii structures observed beyond
  the solar limb. Polar surges have a complex structure when observed
  in Hα and an eruptive nature, reminiscent of normal surges in small
  scale. Giant spicules are simple spikes, very narrow compared to
  surges. They don't go as high as polar surges and apparently have
  shorter lifetimes. We found that most polar surges and giant spicules
  observed in He ii are associated with Hα spikes; however there were
  cases without any corresponding Hα structure. Furthermore we observed
  Hα spikes that did not have He ii counterparts. We analyze an example
  of a polar surge that appeared in He ii well before its appearance in
  Hα and remained visible for a longer time. Most polar surges that we
  observed showed a similar behavior.

Title: Gradient of the line-of-sight velocities in the dark
    superpenumbral fibrils.
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Mein, P.; Mein, N.
Bibcode: 1999joso.proc..116T
Altcode:
  An isolated sunspot located near the centre of the solar disk was
  observed on October 3, 1994. The present high resolution observations
  were obtained with the Multichannel Subtractive Double Pass Spectrograph
  (MSDP) operating in Hα. Two dimensional intensity and Doppler velocity
  maps at several depths in the Hα line were computed. The monochromatic
  intensities at two wavelengths on either side of the line are used in
  terms of the photographic subtraction method expressing the "Doppler
  signal" to give, under some assumptions, the velocities at different
  depths in the Hα line. The values of the velocities obtained by
  this method are compared to those given by the bisector method while
  comparison of the velocities at different depths can give a picture
  of the gradient of the velocity in the dark superpenumbral fibrils.

Title: Mg bright points and the corresponding velocity pattern.
Authors: Dara, H. C.; Zachariadis, T.; Alissandrakis, C.; Koutchmy, S.
Bibcode: 1999joso.proc..135D
Altcode:
  The authors study the temporal intensity variations of the Mg b1
  bright points, in an effort to detect oscillations and investigate
  the corresponding Hα velocity pattern. Apart from the "flashing
  bright points", bright points which appear and disappear within two to
  three minutes, the rest of the bright points undergo small intensity
  variations. Power spectrum analysis revealed a 10-min oscillation
  for half of the stable bright points. The 5-min oscillations are
  detected mainly at sites where there are no bright points, while 3-min
  oscillations coincide with some of the bright points. The majority of
  the bright points are associated with Hα downflows. The downflow is
  very intense at the "flashing bright points".

Title: Fine structure of the Solar Chromosphere: Arch-Shaped Mottles
Authors: Zachariadis, Th. G.; Georgakilas, A. A.; Koutchmy, S.;
   Alissandrakis, C. E.; Dara, H. C.
Bibcode: 1999SoPh..184...77Z
Altcode:
  We analyze a time series of high resolution observations near the solar
  limb, obtained in Hα and the Mg b1 line. We identified arch-shaped dark
  mottles, which are thin, faint Hα structures observable under very
  good seeing conditions, best seen in Hα +0.75 Å. Their mean length
  is about 15'', their mean height about 6'' and indicative lifetimes
  is of the order of 5 min. They show negative (away from the observer)
  line-of-sight velocities. A possible interpretation is that material
  flows from the apex towards the feet of the arches.

Title: Correction [to “A shock associated (SA) radio event and
    related phenomena observed from the base of the solar corona to
    1 AU”]
Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.;
   Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis,
   C. E.; Dumas, G.; Perche, C.
Bibcode: 1998GeoRL..25.4103B
Altcode:
  No abstract at ADS

Title: Microwave, Soft and Hard X-Ray Observations of Solar Flares -
    a Self-Consistent Model of the Flare Site
Authors: Chiuderi Drago, F.; Alissandrakis, C. E.; Bentley, R. D.;
   Philips, A. T.
Bibcode: 1998SoPh..182..459C
Altcode:
  High-resolution microwave observations of several flares performed
  with the Westerbork Synthesis Radio Telescope (WRST) on 3 and 4 July
  1993 are compared with Yohkoh observations in the soft and hard X-ray
  domain. Only for one flare, among the six analyzed, was the hard
  X-ray spectrum between 20 and 200 keV available from the Wide Bragg
  Spectrometer, supplying the energy spectrum of non-thermal particles
  responsible for this radiation and for the radio emission. A complete
  model of this flare is derived which accounts for all available
  observations in the X-ray and radio wavelengths.

Title: A shock associated (SA) radio event and related phenomena
    observed from the base of the solar corona to 1 AU
Authors: Bougeret, J. -L.; Zarka, P.; Caroubalos, C.; Karlický, M.;
   Leblanc, Y.; Maroulis, D.; Hillaris, A.; Moussas, X.; Alissandrakis,
   C. E.; Dumas, G.; Perche, C.
Bibcode: 1998GeoRL..25.2513B
Altcode:
  We present for the first time an almost complete frequency coverage of a
  Shock Associated (SA) radio event and related phenomena observed on May
  6, 1996 at 9:27 UT. It is observed from the base of the solar corona
  up to almost 1 Astronomical Unit (AU) from the Sun by the following
  radio astronomical instruments: the Ondřejov spectrometer operating
  between 4.5 GHz and 1 GHz (radiation produced near the chromosphere);
  the Thermopyles Artemis-IV spectrograph operating between 600 MHz
  and 110 MHz (distance range about 1.1-1.4 R<SUB>⊙</SUB> from sun
  center); the Nançay Decameter Array operating between 75 and 25 MHz
  (distance range about 1.4-2 R<SUB>⊙</SUB>) and the RAD2 and RAD1
  radio receivers on the WIND spacecraft covering the range from 14
  MHz to about 20 kHz (distance range between 3 R<SUB>⊙</SUB> and
  about 1 AU). Observations at the Nançay Decameter Array clearly show
  that the SA event starts from a coronal type II radio burst which
  traces the progression of a shock wave through the corona above 1.8
  R<SUB>⊙</SUB>-2 R<SUB>⊙</SUB> from the sun center. This SA event
  has no associated radio emission in the decimetric-metric range, thus
  there is no evidence for electron injection in the low/middle corona.

Title: Umbral and Penumbral Waves in a Chromospheric Sunspot
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1998ASPC..155...49A
Altcode: 1998sasp.conf...49A
  No abstract at ADS

Title: Second Advances in Solar Physics Euroconference:
    Three-Dimensional Structure of Solar Active Regions
Authors: Alissandrakis, Costas E.; Schmieder, Brigitte
Bibcode: 1998ASPC..155.....A
Altcode: 1998sasp.conf.....A
  No abstract at ADS

Title: EUV and Microwave Observations of a Filament
Authors: Chiuderi-Drago, F.; Bocchialini, K.; Lamartinie, S.;
   Vial, J. -C.; Bastian, T.; Alissandrakis, C. E.; Harrison, R.;
   Delaboudiniere, J. -P.; Lemaire, P.
Bibcode: 1998ASPC..150...55C
Altcode: 1998IAUCo.167...55C; 1998npsp.conf...55C
  No abstract at ADS

Title: Quiescent filament diagnostic.
Authors: Lamartinie, S.; Bocchialini, K.; Vial, J. -C.; Chiuderi-Drago,
   F.; Harrison, R.; Alissandrakis, C. E.
Bibcode: 1998joso.proc..139L
Altcode:
  UV observations of a quiescent filament were performed on July 28,
  1996 by SUMER and CDS, two spectrometers onboard SOHO.

Title: Spicules and Macrospicules: Simultaneous Hα and He II (304
    Å) Observations
Authors: Georgakilas, A. A.; Dara, H.; Zachariadis, Th.; Alissandrakis,
   C. E.; Koutchmy, S.; Delannée, C.; Delaboudinière, J. -P.; Hochedez,
   J. -F.
Bibcode: 1998ASPC..155..376G
Altcode: 1998sasp.conf..376G
  No abstract at ADS

Title: Sunspot-associated Sources, a Peculiar Source and a Halo-like
    Source as Basic Components of the 3D Structure of a Large Active
    Region from RATAN-600 and SSRT Observations
Authors: Kaltman, T. I.; Korzhavin, A. N.; Peterova, N. G.; Lubyshev,
   B. I.; Maksimov, V. P.; Alissandrakis, C. E.; Fu, Q.
Bibcode: 1998ASPC..155..140K
Altcode: 1998sasp.conf..140K
  No abstract at ADS

Title: Unusual inversion of polarization in sunspot associated
microwave sources: RATAN-600 observations and their interpretation
Authors: Alissandrakis, C.; Gizani, Nectaria A. B.; Bogod, V.;
   Garaimov, V.; Zheleznyakov, V.; Zlotnik, E.
Bibcode: 1998cee..workE..72A
Altcode:
  Results of RATAN-600 observations of unusual sunspot-associated
  microwave sources on May 12-16, 1996 and their interpretation are
  given. The intensity and circular polarization of radio emission were
  recorded at 39 frequencies in the wave band 1.74 cm - 30 cm. The
  peculiarity of polarizational pattern is that the microwave source
  was bipolar one, and at the wavelength about 15 cm the sense of
  circular polarization reversed for both sunspots. The most important
  and unexpected feature is that the frequency of reversal is the
  same for preceding and following spots, and the picture as a whole
  was invariable during 5 days of observations. It is easy to see that
  the picture can't be explained by standard effect of linear coupling
  of electromagnetic modes in transverse magnetic field originating
  from bipolar group, because the reversal of polarization occurred
  at both parts of bipolar source and the picture was invariable for
  several days. It also can't be due to coupling in a neutral current
  sheet, since transformation coefficient in zero magnetic field is
  independent on frequency. Moreover, it can't be due to linear coupling
  in transverse magnetic field in current sheet (in a case when magnetic
  field in current sheet has small transverse component which makes
  waves to couple not in zero, but transverse magnetic field), because
  the angle in which reversal can take place is extremely small, and the
  picture must vary with solar rotation. So, the only conceivable way
  to explain observed polarization by linear coupling is to consider
  magnetic field perpendicular to the plane connecting the spots of
  the group, that is parallel to a solar meridian. It is obviously that
  only such a field can provide independence of polarizational pattern
  on solar rotation and reversal at the same frequency for both parts
  of the group. We cannot say where this field originates from: it may
  be a general magnetic field of the Sun (the form of magnetic field
  created by vertical dipole in the center of the Sun suits observational
  pattern) or some large-scale structure in the upper corona. Numerical
  estimations are quite appropriate for reversal at 15 cm. This work
  is supported by INTAS Grant No.94-4625 and partially by RFBR Grants
  No.98-02-16238 and No.96-02-16598.

Title: Three-dimensional structure of solar active regions. 2nd
    Euroconference ASPE97 (Advances in Solar Physics Euroconference 1997),
    Preveza (Greece), 7 - 11 Oct 1997. Poster contributions.
Authors: Schmieder, B.; Alissandrakis, C.
Bibcode: 1998joso.proc...78S
Altcode:
  All of the oral presentations of ASPE97 will be published in a separate
  volume of the ASP Conference Series, while this volume contains the
  poster presentations.

Title: Kinematics of Hα spicules from near-limb observations.
Authors: Zachariadis, T. G.; Georgakilas, A. A.; Dara, H. C.;
   Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1998joso.proc..126Z
Altcode:
  The authors have studied the behavior of dark mottles near the solar
  limb. After the corrections for flat field and limb darkening the
  authors can identify spicules crossing the solar limb. Most of the
  mottles initially show an ascending velocity which gradually turns
  to descending. Moreover, the authors observe a group of dark mottles
  which have the shape of arches. One of the footpoints of the arch is
  in a chromospheric network cell, while the other in a nearby rosette.

Title: Flashing Mgb1 bright points.
Authors: Dara, H. C.; Georgakilas, A.; Zachariadis, T.; Alissandrakis,
   C.; Koutchmy, S.
Bibcode: 1998joso.proc..124D
Altcode:
  High resolution observations, obtained at the Sacramento Peak
  Observatory near the solar limb, are analysed for the study of
  the evolution of Mgb1 (5183.22 Å) bright points, as well as their
  association to bright features in the continuum (5256.40 Å) and Hα
  wings (±0.75 Å). The authors have detected stable bright points from
  the beginning to the end of the time series which hardly move and
  whose shape undergoes small changes, bright points whose brightness
  increases and decreases periodically, and bright points which suddenly
  appear and disappear within one or two minutes.

Title: Unusual inversion of polarization in microwave sources
associated with sunspot group: RATAN-600 observations and their
    interpretation.
Authors: Alissandrakis, C. E.; Bogod, V. M.; Garaimov, V.; Gelfreikh,
   G. B.; Zheleznyakov, V. V.; Zlotnik, E.
Bibcode: 1998joso.proc..101A
Altcode:
  The data of multi-wavelength observations (in the range from 1.7 cm to
  32 cm) on the reflector type radiotelescope RATAN-600 were obtained with
  high polarization accuracy up to 0.5%. They detect a new polarization
  phenomenon in radio emission of active region on the Sun. The signs
  of polarization of the leading and following spot associated sources
  are changed simultaneously for both sources at decimeter part of
  the spectrum. One of the interpretation versions of the phenomenon
  is proposed.

Title: Magnetic and velocity field in association with Ellerman bombs.
Authors: Dara, H. C.; Alissandrakis, C. E.; Zachariadis, T. G.;
   Georgakilas, A. A.
Bibcode: 1997A&A...322..653D
Altcode:
  We present two dimensional maps of the longitudinal magnetic field,
  obtained in the CaI 6103Å line, as well as line of sight velocity maps
  in Hα for an active region. The observations were obtained with the
  Tower telescope of the Sacramento Peak Observatory and the Universal
  Birefrigent Filter, with circular polarization measurements. The
  comparison of the photographs in the wing of Hα, where the Ellerman
  bombs (EBs) are best observed, with the corresponding magnetic maps
  shows that very few EBs are associated with small scale magnetic
  elements, while the great majority, especially the brighter ones,
  appear at the boundaries of magnetic features. The comparison of
  EBs with the velocity maps in the wings of Hα shows that most of
  them coincide with blue wing intensity excess; near the brightest EBs
  ascending motions are observed. We also found a very good coincidence
  of EBs with photospheric facular granules.

Title: Modeling of a Microwave Burst Emission
Authors: Preka-Papadema, P.; Alissandrakis, C. E.; Dennis, B. R.;
   Kundu, M. R.
Bibcode: 1997SoPh..172..233P
Altcode: 1997ESPM....8..233P
  We applied model computations on a microwave burst observed with
  the Westerbork Synthesis Radio Telescope (WSRT) at 6 cm. We used
  additional data from Hα, soft and hard X-rays in order to reproduce
  the flaring loop and to compute the microwave total intensity and
  circular polarization. We examined both cases of thin and thick
  target. The computations show a large emission source in an optically
  thick loop. We compare our results with the observation.

Title: Artemis Mark-IV, the New Greek-French Digital Radio
    Spectrograph at Thermopyles, Greece
Authors: Maroulis, D.; Dumas, G.; Caroubalos, C.; Bougeret, J. L.;
   Moussas, X.; Alissandrakis, C.; Patavalis, N.
Bibcode: 1997SoPh..172..353M
Altcode: 1997ESPM....8..353M
  We present the new digital solar radio spectrograph located at
  the Thermopyles station, Greece, operated by the University of
  Athens. Observations cover the range from 110 to 600 MHz, using a
  7-m parabolic antenna. The reception system uses two techniques in
  parallel: sweep frequency and multi-channel, the latter being based
  on the Acousto-Optical technique. The data acquisition system is based
  on two subsystems, a Sun Sparc-5 workstation and a front end based on
  a VME Motorola system. The two subsystems are connected through the
  Ethernet and are operated using the VxWorks real-time package. The
  daily operation is completely automated: pointing of the antenna to
  the sun, starting and stopping the observations at pre-set times,
  acquiring data, compressing data by silence suppression in real time,
  and archiving the data on a routine manner on DAT tapes. Apart from
  its usual function, this instrument will be used in conjunction with
  other instruments, including the Nançay decameter array and the low
  frequency radio receivers on the Wind spacecraft.

Title: Fine Structure of the solar atmosphere from near-limb
    observations in three wavelengths
Authors: Georgakilas, A. A.; Dara, H.; Zachariadis, Th.; Alissandrakis,
   C. E.; Koutchmy, S.
Bibcode: 1997SoPh..172..133G
Altcode: 1997ESPM....8..133G
  We analyze a time series of high-resolution observations near the
  limb, in the continuum, in the Mg b<SUB>1</SUB> line (-0.4 Å off
  line center), and in the wings of Hα (+0.75 Å). The observations
  were obtained with a CCD camera at the Vacuum Tower telescope of
  the Sacramento Peak Observatory. We study the association of facular
  points, as they appear at different heights of the solar atmosphere
  (continuum, b<SUB>1</SUB> - 0.4 Å, Hα + 0.75 Å) with the feet of
  fine dark mottles.

Title: Evolution in Space and Time of Superpenumbral Chromospheric
    Fibrils
Authors: Tsiropoula, G.; Dialetis, D.; Alissandrakis, C. E.; Mein,
   P.; Mein, N.
Bibcode: 1997SoPh..172..139T
Altcode: 1997ESPM....8..139T
  We have studied the spatial structure and temporal evolution of the
  intensity and Doppler velocity of dark fibrils forming the superpenumbra
  of an isolated regular sunspot. The observations were obtained with the
  Multichannel Subtractive Double Pass (MSDP) spectrograph which operates
  in Hα and is installed at the focus of the Vacuum Tower Telescope (VTT)
  at Tenerife (Canary Islands). The fibril pattern shows a remarkable
  stability during the period of our observations (64 min). Moreover,
  almost all individual fibrils are identifiable in all frames, but they
  undergo continual changes in contrast, shape and size. Investigating the
  temporal evolution of intensity and velocity of individual fibrils,
  fluctuations were found which have a quasi periodic behavior. As
  mechanisms for these changes we may suggest (a) change of the Doppler
  shift due to a wave, (b) periodic changes of the density of the Hα
  absorbing material, (c) disappearance and reappearance of fibrils,
  in more or less the same magnetic flux tube, at regular intervals.

Title: Radio Observations of the Quiet Sun and Their Implications
    on Coronal Heating
Authors: Alissandrakis, Costas E.; Einaudi, Giorgio
Bibcode: 1997LNP...483...53A
Altcode: 1997cprs.conf...53A
  We discuss the actual and potential contribution of radio techniques
  in the study of the structure and the dynamics of the corona as well as
  in the problem of coronal heating. Radio observations provide powerful
  diagnostics of the physical conditions in the transition region and the
  corona. Recent observational and theoretical results are presented and
  their implications are discussed. The prospects of further observations,
  in conjunction with other wavelength ranges are given.

Title: Testing the Extrapolated Coronal Magnetic Fields by Using
    Propagation Effects at Microwaves
Authors: Chiuderi Drago, F.; Alissandrakis, C. E.; Borgioli, F.
Bibcode: 1997ESASP.404..275C
Altcode: 1997cswn.conf..275C
  No abstract at ADS

Title: Radio Observations of Sunspots
Authors: Alissandrakis, C. E.
Bibcode: 1997ASPC..118..150A
Altcode: 1997fasp.conf..150A
  High spatial resolution observations of sunspots have been made
  with aperture synthesis instruments for over two decades. Sunspots
  appear as bright features at short cm wavelengths, due to thermal
  gyroresonance (g-r) emission from layers where the local gyrofrequency
  is a sub-harmonic of the observing frequency, providing a powerful
  diagnostic of the sunspot magnetic field above the photosphere.

Title: Medium and large scale structures of the low corona from
    decimeter and meter wavelength observations.
Authors: Lantos, P.; Coulais, A.; Alissandrakis, C. E.
Bibcode: 1997ASIC..494..121L
Altcode: 1997topr.conf..121L
  Since 1991, the Nançay Radioheliograph provides daily observations of
  the Sun at wavelengths from 69 cm (435 MHz) to 1.83 m (164 MHz). Older
  observations were available mostly at 169 or 164 MHz. Two-dimensional
  maps could be computed with an aperture synthesis method when the
  brightness distribution remains constant during the day (i.e. in absence
  of strong noise storms). At meter wavelengths, detected large scale
  structures are coronal holes, the quiet sun and a new component called
  "coronal plateau" which is a signature at low altitude of the coronal
  streamer belt and of the heliospheric current sheet. Medium scale
  structures observed at meter and decimeter wavelengths are explained
  as emissions in loop systems. They may be either faint noise storm
  continua or thermal emissions.

Title: Microwave and UV observations of filaments with SOHO and
    the VLA
Authors: Alissandrakis, C. E.; Drago, F.; Bastian, T.; Bocchialini,
   K.; Delaboudiniere, J. -P.; Lemaire, P.; Vial, J. -C.; Harrison,
   R. A.; Thompson, B.
Bibcode: 1997ASPC..118..289A
Altcode: 1997fasp.conf..289A
  Observations performed in coordination between SOHO instruments and
  ground-based observatories offer the unique possibility to derive
  information simultaneously in several wavelengths formed at different
  altitudes and/or temperatures in the solar atmosphere. The SUMER and
  CDS spectrometers, the imaging telescope EIT aboard SOHO, and the VLA
  provide complementary information in the UV and the radio ranges. We
  illustrate such a coordination with observations of filaments in the
  transition region, performed in July 1996. The observations in the UV
  between 10(4) and 10(6) K provide the differential emission measure
  as a function of temperature; this can be used to compute the expected
  brightness temperature in the microwave range and check models of the
  filament-corona transition region.

Title: Coronal Magnetic Fields from Microwave Polarization
    Observations
Authors: Alissandrakis, C. E.; Borgioli, F.; Chiuderi Drago, F.;
   Hagyard, M.; Shibasaki, K.
Bibcode: 1996SoPh..167..167A
Altcode:
  The solar active region (AR) 7530 was observed at 6 cm on July 3
  and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a
  multi-channel receiver with very narrow bandwidth. We compare the
  radio data with Yohkoh SXT observations and with the magnetic field
  extrapolated from the Marshall vector magnetograms in the force-free
  and current-free approximations. The comparison with soft X-rays shows
  that, although a general agreement exists between the shape of the
  radio intensity map and the X-ray loops, the brightness temperature,
  T<SUB>b</SUB>, obtained using the parameters derived from the SXT is
  much lower than that observed. The comparison with the extrapolated
  photospheric fields shows instead that they account very well for
  the observed T<SUB>b</SUB> above the main sunspots, if gyroresonance
  emission is assumed. In the observation of July 4 an inversion and
  strong suppression of the circular polarization was clearly present
  above different portions of the AR, which indicates that particular
  relationships exist between the electron density and the magnetic
  field in the region where the corresponding lines of sight cross the
  field quasi-perpendicularly. The extrapolated magnetic field at a
  much higher level (∼ 10<SUP>10</SUP> cm), satisfies the constraints
  required by the wave propagation theory all over the AR. However,
  a rather low electron density is derived.

Title: Periodic and Non-Periodic Phenomena in a Sunspot Region
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Dialetis, D.; Mein, P.
Bibcode: 1996SoPh..167...79T
Altcode:
  We have studied running penumbral waves, the homogeneous Evershed
  effect, and the spatial relation between intensity and Doppler velocity
  penumbral features of a chromospheric sunspot. The observations were
  obtained with the multichannel subtractive double-pass spectrograph
  (MSDP) operating in Hα at the Vacuum Tower Telescope (VTT) installed
  at Tenerife (Canary Islands). We derived intensity and Doppler velocity
  maps at Hα ± 0.3 Å over a two-dimensional field of view. We have
  computed the components of the velocity vector (radial, azimuthal,
  vertical) as a function of distance from the center of the spot under
  the assumption of axial symmetry. The results show the well-known,
  from previous observations, general large-scale characteristics of the
  chromospheric Evershed flow. Our measurements show that the axes along
  the discrete structures, where the Evershed flow is confined, are not
  spatially related to the axes along Hα ± 0.3 Å intensity features,
  and we suggest that either the flow is confined in flow channels or that
  it takes place along sheared magnetic field lines. We also detected,
  for the first time in velocity images, running penumbral waves, which
  started in the outer 0.3 of the umbral radius and propagated through
  the penumbra with propagation velocities 13-24 km s<SUP>−1</SUP>. The
  propagation velocity, as well as the velocity amplitude, is greater
  for the waves closer to the center of the spot and diminishes as one
  moves outward.

Title: A Model for Active Region Emission at Centimeter Wavelengths
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Kundu,
   M. R.; Dere, K. P.; Korzhavin, A. N.; Bogod, V. M.
Bibcode: 1996SoPh..166...55N
Altcode:
  We present multi-frequency observations and model computations of the
  microwave emission of a solar active region. The radio observations
  were obtained with the RATAN-600 at several wavelengths between 0.8
  and 31.6 cm and with the VLA at 6 and 20 cm. The active region was
  also observed in the EUV O Iv lines by the HRTS instrument aboard
  the Space Shuttle Spacelab-2 mission. These lines are formed in the
  chromosphere-corona transition region and their intensity ratio is
  sensitive to pressure. Photospheric magnetograms provided both the
  longitudinal and the transverse component of the magnetic field. The
  microwave observations were checked against model computations
  taking into account both the free-free and the gyro-resonance emission
  mechanisms and using the pressure data from the O IV lines. The magnetic
  field was computed through constant-α force-free extrapolations of
  the longitudinal photospheric field. We computed both the flux from
  2 to 20 cm and the spatial structure of the microwave emission at 6
  and 20 cm. The comparison of the computed and observed flux spectra
  allowed us to estimate the magnetic field strength at the base of the
  transition region and in the low corona, as well as the values of the
  conductive flux and the height of the base of the transition region. The
  model maps at 6 cm and 20 cm showed that α was not constant above the
  active region; the same conclusion was reached on the basis of the
  photospheric observations. The use of pressure measurements allowed
  us to identify microwave structures which were determined by pressure
  enhancements. At 6 cm the computations confirmed the fact that the
  magnetic field is the principal factor that determines the structure
  of sunspot-associated sources and showed that the effect of pressure
  variations was small. Pressure variations were more important at 20 cm,
  where the peak of the emission was associated with the sunspot and a
  diffuse component was associated with the plage which had an average
  pressure higher by a factor of 1.54 than the sunspot.

Title: Synoptic Study of Coronal Structures Observed at Meter
    Wavelengths during the Declining Phase of the Solar Cycle
Authors: Alissandrakis, C. E.; Lantos, P.
Bibcode: 1996SoPh..165...61A
Altcode:
  We have produced synoptic maps from daily images of the solar corona
  on the disk obtained with the Nançay Radioheliograph at 169 MHz during
  June-August 1984. We discuss briefly the structures seen on the synoptic
  maps and we compare the location of radio sources with photospheric
  neutral lines and Ha filaments derived from synoptic charts from Meudon,
  Boulder, and Stanford. We measured the distance of radio sources from
  these optical features and compared their distribution with computed
  random distributions. A criterion of confidence is proposed which,
  when applied to our data, shows that the metric radio sources of
  thermal origin are best associated with the large-scale neutral lines
  shown on the low resolution Stanford magnetograms. This association
  indicates that the emission comes from arcades of moderately dense
  loops spanning the neutral line. However, the radio sources are not
  usually located directly above or very close to neutral lines, but
  their distribution peaks at distances between 4 and 6°. Our results
  show no statistically significant association with Meudon filaments.

Title: Coronal Sources at Meter and Optical Wavelengths during the
    Declining Phase of the Solar Cycle
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1996SoPh..165...83L
Altcode:
  We present observations of the corona at 169 MHz with the Nançay
  Radioheliograph during the summer of 1984. We compare synoptic maps
  of the metric radio emission on the solar disk with synoptic charts of
  the K-corona as well as of the green and the red lines. Local sources
  of radio emission are not located near regions of enhanced green or
  red line emission which, in turn, are in general above chromospheric
  faculae. Thus the radio emissions located in the surroundings of
  faculae are apparently related to different loop systems, with lower
  density. The comparison of the radio data with the K-corona showed one
  radio source associated with enhanced emission both at 1.3 and at 1.7
  R<SUB>⊙</SUB>, apparently a streamer. Other radio sources did not
  show any clear associations, but were nevertheless located within
  the coronal plasma sheet, delineated by the large-scale K-corona
  emission. Moreover the large-scale structure of the corona at 169
  MHz was quite similar to the coronal plasma sheet observed at 1.3
  R<SUB>⊙</SUB> above the limb. The extent of the radio emission in
  latitude is very similar to that of the K-corona, while the coronal
  line emission is more concentrated near the solar equator.

Title: Two-Dimensional Mapping of the Sun with the RATAN-600
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.; Borovik,
   V. N.; Korzhavin, A. N.; Bogod, V. M.
Bibcode: 1996SoPh..165...41N
Altcode:
  We present two-dimensional solar maps at 2.7, 3.2, 4, and 8.2 cm
  computed from one-dimensional observations with the RATAN-600, using
  Earth rotation aperture synthesis techniques. Before the calculation
  of maps, the position of each scan was corrected with respect to the
  center of the solar disk and the scans were calibrated. The circular
  polarization scans were corrected for polarization cross-talk between
  the I and V channels. Subsequently, the quiet-Sun background emission
  was subtracted. After all corrections, a dirty map was computed by
  combining the scans at different position angles. The last step of
  the processing was an attempt to free the dirty map of the sidelobes,
  using the standard CLEAN procedure. The resolution of the clean maps
  at 2.7 cm was 0.5' by 6'. Both active regions which were present on
  the solar disk were mapped. We studied the flux spectra of different
  types of sources: one was associated with a sunspot, the second was
  located over the neutral line of an active region, and the other was
  associated with the plage. The emission mechanism of the former was
  attributed to the gyroresonance process, while the short wavelength
  emission of the others was attributed to the free-free process. For
  the sunspot-associated source we estimated the magnetic field strengths
  at the base of the transition region and in the low corona.

Title: Large scale structure of the solar corona observed at meter
    and decimeter wavelengths and in X-rays
Authors: Lantos, P.; Alissandrakis, C. E.; YOHKOH Team
Bibcode: 1996AdSpR..17d.261L
Altcode: 1996AdSpR..17..261L
  Maps of the quiet solar corona, obtained at meter and decimeter
  wavelengths with the Nancay (France) Radioheliograph, are compared
  to Yohkoh soft X-ray images in order to study large scale density
  structures of the corona. Of particular interest is a global
  restructuring of the corona, observed on 19 May 1992 in X-rays, in
  conjunction with a coronal mass ejection. The radio observations show
  the CME moving continuum, while the Yohkoh images show the slower
  motion of the X-ray loops. After this event the appearance of a new
  noise storm, with a duration of several days, was observed.

Title: Running Penumbral Waves in a chromospheric Sunspot
Authors: Tsiropoula, G.; Dialetis, D.; Alissandrakis, C. E.; Mein, P.
Bibcode: 1996hell.conf...37T
Altcode:
  No abstract at ADS

Title: Coronal Magnetic Fields from Polarization Observations at
    Microwaves
Authors: Chiuderi Drago, F.; Borgioli, F.; Alissandrakis, C. E.;
   Hagyard, M.; Shibasaki, K.
Bibcode: 1996mpsa.conf..443C
Altcode: 1996IAUCo.153..443C
  No abstract at ADS

Title: The fine scale Structure of the velocity Field in the
    chromospheric Penumbra of a solar Sunspot
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Dialetis, D.; Mein, P.
Bibcode: 1996hell.conf...32T
Altcode:
  No abstract at ADS

Title: Evolution of the coronal plasma sheet from cycle maximum to
    cycle minimum observed at meter wavelengths
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1995AdSpR..16i.185L
Altcode: 1995AdSpR..16..185L
  The Nancay Radioheliograph provides maps of the quiet solar corona
  around 160 MHz. In addition to coronal holes, localized emission
  sources and quiet sun, an unresolved component can be detected on the
  disk. The so-called ``coronal plateau'' corresponds to the K-corona
  dense regions observed on the limb and is thus located at the base of
  the interplanetary plasma sheet. Its evolution is studied from 1980
  to 1986, during the declining phase of the cycle 21.

Title: Large Scale Structure of the Solar Corona in the Declining
    Phase of the Solar Cycle
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1995SSRv...72...45L
Altcode:
  Maps of the corona, obtained at meter wavelengths with the Nançay
  Radioheliograph (France), are used to study, on the disk, the radio
  counterpart of the coronal plasma sheet observed in K-corona on the
  limb. We study here the evolution of the coronal plasma sheet from
  the maximum of the activity cycle in 1980 to the minimum in 1986 and
  identify some of its large scale structures.

Title: Large Scale Structure of the Solar Corona in the Declining
    Phase of the Solar Cycle
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1995hlh..conf...45L
Altcode:
  No abstract at ADS

Title: Dynamical fine structures of the chromosphere
Authors: Tsiropoula, G.; Schmieder, B.; Alissandrakis, C. E.
Bibcode: 1994SSRv...70...65T
Altcode:
  We have studied the spatial structure and temporal evolution of a
  chromospheric region with chains of mottles at the junction of three
  supergranules. The observations were obtained with the Multichannel
  Subtractive Double Pass spectrograph operating in Hα at the Pic du
  Midi Observatory. From a statistical point of view the fine structures
  were stable in intensity over the observation period (15 min), while the
  line of sight velocity showed remarkable changes within a few minutes. A
  detailed analysis shows that the predominant pattern of bulk motion in
  the dark mottles is that of downflow at their footpoints and upflow at
  their tops, which is followed by downflows along the whole structure and
  that this process repeats itself several times during their lifetime.

Title: Time evolution of fine structures in the solar chromosphere.
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1994A&A...290..285T
Altcode:
  We have studied the temporal evolution of two quiet chromospheric
  regions, one with a typical rosette and another with chains of
  mottles at the junction of three supergranules. The observations
  were obtained during 15 minutes with the Multichannel Subtractive
  Double Pass spectrograph (MSDP) operating in Hα at the Pic du Midi
  Observatory. We derived intensity maps and Doppler shift velocities at
  different wavelengths along the Hα profile over a two dimensional
  field of view. The observed contrast profiles were matched with
  theoretical contrast profiles using Beckers' cloud model for a more
  accurate determination of the line of sight velocity. A statistical
  analysis with cross correlation functions showed that the fine
  structures were stable in intensity over the observation period (15
  min), but the line of sight velocity showed important changes within
  a few minutes. A detailed analysis of the velocities along the axes
  of dark mottles showed that the predominant pattern of bulk motion is
  that of downflow at their footpoints and alternating phases of upflow
  and downflow at their tops. This motion is consistent with Pikel'ner's
  model for spicules, which attributes this pattern to the reconnection of
  opposite magnetic filed lines. This picture is also consistent with the
  velocity reversals with time observed in spicules and may be associated
  to the systematic downflows observed in the transition region. Doppler
  shift velocities in dark mottles are too low compared to those derived
  with the cloud model; the latter are comparable to those reported for
  spicules, strengthening the view that these structures are identical.

Title: Detection of Linear Polarization in the Microwave Emission
    of Solar Active Regions
Authors: Alissandrakis, C. E.; Chiuderi-Drago, F.
Bibcode: 1994ApJ...428L..73A
Altcode:
  We report the detection for the first time of linear polarization in the
  microwave emission above a Solar Active Region. The observations were
  made with the Westerbork Synthesis Radio Telescope, taking advantage of
  the very small bandwidth of a multichannel spectral line receiver. The
  intensity of the Stokes parameter U, measured at several points close
  to the line of zero circular polarization, shows a clear sinusoidal
  trend as a function of lambda<SUP>2</SUP>, in accordance to what is
  expected from Faraday rotation. From the measured period, reasonable
  values of integral NB<SUB>L</SUB>dr were derived. Such observations
  could present in the future a unique way to measure coronal magnetic
  fields above Active Regions.

Title: Meter wavelength observations of the quiet sun and the slowly
    varying component during declining phase of the solar cycle
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1994AdSpR..14d..97L
Altcode: 1994AdSpR..14...97L
  Two dimensional maps of the Sun at 164 MHz, obtained with the Nançay
  Radioheliograph from April to August 1984 are presented. The quiet
  sun emission and the slowly varying component far from sunspots are
  studied. The association of local emissions with the chromospheric
  calcium plages is pointed out and interpreted. The altitude of the radio
  sources is estimated. The comparison of the location of the sources
  with K-corona observations confirms previous results obtained for the
  minimum of the cycle. The brightness temperature of the coronal plateau,
  which is the radio counterpart of the coronal plasma sheet, is given.

Title: Radio observations of the quiet solar corona
Authors: Alissandrakis, C. E.
Bibcode: 1994AdSpR..14d..81A
Altcode: 1994AdSpR..14...81A
  Observations of radio emission from the quiet solar atmosphere and
  the associated emission mechanisms are discussed. Long wavelength
  observations, with a spatial resolution of ~1 arc min are ideal
  for the study of the large scale structure of the corona, including
  coronal holes, arches, streamers and the base of the heliospheric
  current sheet. These structures are observed both beyond the limb
  and on the solar disk, with little line of sight integration. We also
  discuss diagnostics of electron temperature and density, as well as
  the interpretation problems arising from the inhomogeneity of the
  corona and refraction effects.

Title: The magnetic field of the solar corona.
Authors: Alissandrakis, C. E.
Bibcode: 1994LNP...432..109A
Altcode: 1994LNPM...11..109A
  The structure of the solar corona, on all observable scales,
  is intimately controlled by the magnetic field. Although direct
  measurements of the magnetic field are from difficult to impossible,
  its presence is evident in all spectral ranges where the corona is
  observable. This review discusses the measurement of coronal magnetic
  fields and the indirect information provided by radio, white light
  and soft X-ray observations.

Title: Time Evolution of Chromospheric Fine Structures
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1994emsp.conf..111T
Altcode:
  No abstract at ADS

Title: The Magnetic Field of a Bipolar Sunspot Region in the
    Photosphere and the Chromosphere
Authors: Dara, H. C.; Koutchmy, S.; Alissandrakis, C. E.
Bibcode: 1994emsp.conf...61D
Altcode:
  No abstract at ADS

Title: Evidence for Ordinary Mode Emission from Microwave Bursts
Authors: Alissandrakis, C. E.; Nindos, A.; Kundu, M. R.
Bibcode: 1993SoPh..147..343A
Altcode:
  We analyze high-resolution, one-dimensional observations of simple
  microwave bursts, obtained at 4.9 GHz with the Westerbork Synthesis
  Radio Telescope in 1980, together with Hα photographs of the associated
  flares from the Observatories of Athens and Meudon. In most cases the
  polarization structure can be interpreted in terms of extraordinary mode
  emission, taking into account the polarity of the underlying magnetic
  field and propagation effects, which may lead to inversion of the sense
  of polarization in the limbward part of the flaring loop. We found
  evidence for ordinary mode emission in two classes of events. In one
  class theo-mode comes from regions overlying strong magnetic field,
  which we interpret in terms of thermal gyroresonance absorption of
  the extraordinary mode at the third harmonic of the gyrofrequency. In
  the other class the entire burst emits in theo-mode, which may be
  attributed to high gyrosynchrotron optical depth.

Title: Photospheric and chromospheric magnetic field structure of
    a bipolar sunspot region
Authors: Dara, H. C.; Koutchmy, S.; Alissandrakis, C. E.
Bibcode: 1993A&A...277..648D
Altcode:
  We present high resolution magnetograms of a large split spot and an
  opposite polarity pore in the 6102.7 Å Ca I photospheric line and in
  Hα and we discuss their fine structure. We found important differences
  between the photospheric and chromospheric magnetic field. Although
  the large spot was apparently unipolar at the photospheric level, we
  detected an opposite polarity region at the chromospheric level. We
  also found that there was hardly any trace of the pore magnetic field
  in the Hα magnetogram. These results cannot be interpreted in terms
  of constant-α magnetic fields. Finally we confirm the occurrence
  of filamentary magnetic structures in Hα at the location of the
  superpenumbra of the large spot.

Title: VizieR Online Data Catalog: Asymmetry of FeI lines in solar
    spectrum (Stathopoulou+ 1993)
Authors: Stathopoulou, M.; Alissandrakis, C. E.
Bibcode: 1993yCat..32740555S
Altcode:
  75 FeI lines were studied from wide slit FTS spectra obtained at Kitt
  Peak at the center of the disk, near the limb (μ=0.2) (1 data file).

Title: Evolution of an Active Region and Associated Hα Arch
    Structures
Authors: Georgakilas, A. A.; Zachariadis, Th. G.; Alissandrakis, C. E.
Bibcode: 1993SoPh..146..241G
Altcode:
  We have studied the early stages of development of two adjacent active
  regions observed at the center and the wings of Hα for six days. From
  the growth of spots and arch structures we found that periods of slow
  flux emergence were followed by periods of vigorous flux emergence. We
  observed arch filaments covering an appreciable range of sizes (from a
  length of about 27 000 km and a height of 2000-3000 km to a length of
  45 000 km and a height of about 15 000 km). Individual arch filaments
  within the same arcade sometimes have different inclinations of their
  planes with respect to the vertical. We observed isolated cases of
  arches crossing each other at an angle of ∼45°. During their early
  stages arch filament systems are short and they expand at a rate of
  about 0.8 km s<SUP>−1</SUP>. The rate of growth of arch filament
  systems is faster when the orientation of the flux tubes is nearly
  parallel to the equator. Our observations suggest that the early part
  of the evolution of individual arch filaments in a grown system is not
  visible; however, in a few cases we observed arch filaments appearing
  as dark features near one footpoint and expanding towards the other,
  with a mean velocity of about 30 km s<SUP>−1</SUP>.

Title: A study of the asymmetry of Fe I lines in the solar spectrum
Authors: Stathopoulou, M.; Alissandrakis, C. E.
Bibcode: 1993A&A...274..555S
Altcode:
  We have studied 75 Fe I lines from wide slit FTS spectra obtained
  at Kitt Peak at the center of the disk, near the limb (μ=O.2) and
  in total flux. We present measurements of the intensity at the line
  center, the equivalent width and the asymmetry. We have done a detailed
  analysis of bisectors and studied the dependence of the asymmetry on
  the optical depth. Plots of the asymmetry versus the effective depth
  of formation are similar for all lines, with a small dependence on the
  excitation potential. The combined curve from all lines at the center
  of the disk shows that the asymmetry decreases with optical depth
  with a minimum at log τ = -O.33, which corresponds to the turning
  point of the C-shaped bisectors; no such minimum is observed at μ =
  O.2, where the measurements go up to log τ ∼ -0.8. We infer that
  the asymmetry is a measure of the average line of sight velocity of
  the material and we discuss the results in terms of characteristic
  heights derived by other observers.

Title: A new determination of the mean lifetime of bright and dark
    chromospheric mottles
Authors: Bratsolis, E.; Dialetis, D.; Alissandrakis, C. E.
Bibcode: 1993A&A...274..940B
Altcode:
  We determined the lifetime of dark and bright mottles of the solar
  chromosphere using a more accurate method proposed by Alissandrakis et
  al. (1987). Our study is based on an excellent sequence of photographs
  taken at the Pic-du-Midi Observatory. We found that the mean lifetime
  of both bright and dark mottles is 13-14 min. We discuss this result
  and we compare it with previous investigations.

Title: Correction: Two-dimensional solar mapping at 5.2 CM with the
    Siberian Solar Radio Telescope
Authors: Alissandrakis, C. E.; Lubyshev, B. I.; Smol'Kov, G. Ia.;
   Krissinel', B. B.; Treskov, T. A.; Miller, V. G.; Kardapolova, N. N.
Bibcode: 1993SoPh..145..418A
Altcode:
  No abstract at ADS

Title: The fine structure of a chromospheric rosette
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1993A&A...271..574T
Altcode:
  We have studied the spatial behaviour of the physical properties
  of dark mottles forming a well-defined rosette. The observations
  were obtained with the Multichannel Subtractive Double Pass (MSDP)
  spectrograph, operating in Hα at the Pic du Midi Observatory. From
  these observations, intensity fluctuations and Doppler shift velocities
  at different wavelengths were derived over a two dimensional field of
  view. The observed contrast profiles were matched with theoretical
  contrast profiles using Beckers' cloud model and 4 parameters were
  derived for the dark mottles: the source function, the line-of-sight
  velocity, the Doppler width and the optical depth. From these parameters
  a range for the temperature and electron density can be derived using
  Vernazza's et al. (1981) model D. We detected strong downflows at
  the roots of the mottles, while their upper part is ascending with
  velocities sometimes greater than 10 km s<SUP>-1</SUP>. The values of
  the cloud parameters are consistent with values given by other authors
  for this kind of features. Consistency was also found between cloud
  parameters and the values given for spicules, leading to the conclusion
  for the identity of these structures.

Title: Spectral observations of active region sources with RATAN-600
    and WSRT
Authors: Alissandrakis, C. E.; Gel'Frejkh, G. B.; Borovik, V. N.;
   Korzhavin, A. N.; Bogod, V. M.; Nindos, A.; Kundu, M. R.
Bibcode: 1993A&A...270..509A
Altcode:
  We present spectral observations of neutral line and sunspot associated
  sources obtained with the RATAN-600 radio telescope and the WSRT
  in the wavelength range of 2 to 6 cm. Sources associated with large
  sunspots have flat spectra, while neutral line sources have very steep
  spectra. In the case of a large spot we estimated the magnetic field
  to be at least 2700 G at the base of the transition region and 1800 G
  in the low corona. We consider possible interpretations of the radio
  emission above the neutral lines. Gyroresonance emission at the fourth
  harmonic is inadequate, whereas emission from a small population of
  nonthermal electrons (total number 10 exp 30 to 10 exp 31) with a
  delta = 3 power law distribution seems to be sufficient.

Title: Two-Dimensional Solar Mapping at 5.2-CM with the Siberian
    Solar Radio Telescope
Authors: Alissandrakis, C. E.; Lubyshev, B. I.; Smol'Kov, G. Ia.;
   Krissinel', B. B.; Treskov, T. A.; Miller, V. G.; Kardapolova, N. N.
Bibcode: 1992SoPh..142..341A
Altcode:
  We present two-dimensional solar maps at 5.2 cm computed from
  one-dimensinal observations with the Siberian Solar Radio Telescope
  (SSRT), using Earth rotation aperture synthesis techniques. The
  resolution attained with the E-W branch of the instrument is 15 by
  45″ for a solar declination of about 23°. Maps during the period of
  June 8 to 13, 1988 clearly show the quiet-Sun background, sunspot and
  plage associated emission as well as compact sources above the neutral
  line in some active regions. We found that the latter disappear as the
  gradient of the longitudinal magnetic field decreases. We also detected
  emission associated with active regions behind the limb, apparently
  from unresolved loops, extending up to ∼40″. The prospects of the
  SSRT, as a dedicated solar instrument, are discussed.

Title: Observation of a coronal streamer at meter and decimeter
    wavelengths.
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1992ESASP.348..141L
Altcode: 1992cscl.work..141L
  Maps obtained at meter and decimeter wavelengths with the Nançay
  Radioheliograph on October 24 and 25, 1987 are presented. One of the
  meter wavelength emission sources is located above a chromospheric
  magnetic field neutral line and a small Hα prominence. The source
  has decimeter wavelength counterparts on both sides of the neutral
  line. The decimeter sources are close to regions of enhanced large
  scale photospheric magnetic field, while the meter wavelength source
  is located in between. This suggests emissions at different altitudes
  in a loop system straddling the neutral line. The region corresponds
  to a Fe XIV coronal streamer seen during the eastern limb passage. The
  distance between the footpoints is of the order of 370000 km and the
  angle between the loops and the neutral line is about 50°, projected
  on a synoptic chart.

Title: Time evolution of arch filaments
Authors: Tsiropoula, G.; Georgakilas, A. A.; Alissandrakis, C. E.;
   Mein, P.
Bibcode: 1992A&A...262..587T
Altcode:
  We have studied the spatial structure and the temporal evolution of the
  velocity in active region arch filaments. The observations were obtained
  with the Multichannel Double Pass Spectrograph operating in H-alpha
  at the Pic du Midi Observatory. Line profiles were reconstructed and
  monochromatic images and Doppler shift velocities were derived over a 2D
  FOV. Using Beckers' (1964) cloud model we derived physical parameters,
  in particular the line of sight velocity. The arches showed the
  'classical' type of motion, with material moving towards the observer
  near the apex and away from the observer near the footpoints. Assuming
  a symmetric loop, we reconstructed the velocity vector along the arch
  filaments. The results are consistent with the picture where material is
  draining out of the filament, while the whole structure is ascending. In
  one case we observed changes in the geometry and the velocity vector;
  however, other arch filaments did not change appreciably in a time
  period of about 13.5 min.

Title: Two-dimensional model maps of flaring loops at cm-wavelengths
Authors: Preka-Papadema, P.; Alissandrakis, C. E.
Bibcode: 1992A&A...257..307P
Altcode:
  We present a complete set of model computations of the microwave
  emission from a flaring loop. Two-dimensional maps in total intensity
  and circular polarization are given, as a function of wavelength,
  heliocentric distance and the orientation of the loop with respect
  to the direction of the limb. In agreement with our previous
  one-dimensional computations, the emission in the optically thin
  case comes from the one or both feet of the loop, with the primary
  maximum usually at the diskward side; in the optically thick case the
  emission comes from the entire loop, with one or two maxima near the
  top. We discuss in detail the effects of the orientation of the loop,
  as well as the polarization structure produced by self-absorption and
  gyroresonance absorption. The latter produce a patchy structure in the
  V map, with regions polarized both in the extraordinary sense (in the
  upper part of the loop) and in the ordinary sense (in the lower part
  of the loop). Finally we compare our computations with high spatial
  resolution observations of simple bursts.

Title: Dynamic Phenomena in the Chromospheric Layer of a Sunspot
Authors: Alissandrakis, C. E.; Georgakilas, A. A.; Dialetis, D.
Bibcode: 1992SoPh..138...93A
Altcode:
  We have studied running penumbral waves, umbral oscillations, umbral
  flashes and their interrelations from Hα observations of a large
  isolated sunspot. Using a subtraction image processing technique
  we removed the sharp intensity gradient between the umbra and the
  penumbra and enhanced the low contrast, fine features. We observed
  running penumbral waves which started in umbral elements with a size
  of a few arcseconds, covered the umbra and subsequently propagated
  through the penumbra. The period of the waves was 190 s and the mean
  propagation velocity was about 15 km s<SUP>−1</SUP>. We detected
  intense brightenings, located between umbral elements from where waves
  started, which had the characteristics of umbral flashes. There are
  indications that umbral flashes are related to the propagation of the
  waves through the umbra and their coupling. The subtraction images
  also show considerable fine structure in the chromospheric umbra,
  with size between 0.3″ and 0.8″.

Title: Quiet-Sun Emission and Local Sources at Meter and Decimeter
    Wavelengths and Their Relationship with the Coronal Neutral Sheet
Authors: Lantos, P.; Alissandrakis, C. E.; Rigaud, D.
Bibcode: 1992SoPh..137..225L
Altcode:
  We analysed multifrequency 2-dimensional maps of the solar corona
  obtained with the Nançay radioheliograph during two solar rotations
  in 1986. We discuss the emission of the quiet Sun, coronal holes
  and local sources and its association with chromospheric and coronal
  features as well as with large-scale magnetic fields. The brightness
  temperature of the quiet Sun was 5 to 5.5 × 10<SUP>5</SUP> K at
  164 MHz and 4.5 to 5 × 10<SUP>5</SUP> K at 408 MHz. A coronal hole,
  also detected in the 10830 Å He I line, had a brightness temperature
  of 4.5 × 10<SUP>5</SUP> at 164 and 2.5 × 10<SUP>5</SUP> at 408
  MHz. We give statistics of source brightness temperatures (on the
  average 8% above the background at 164 MHz and 14% at 408 MHz), as
  well as distributions in longitude and latitude. Although we found no
  significant center-to-limb effect in the brightness temperature, the
  sources were not visible far from the central meridian (apparently a
  refraction effect). The brightest sources at 164 MHz were near, but not
  directly above active regions and had characteristics of faint type I
  continua. At 408 MHz some sources were observed directly above active
  regions and one was unambiguously a type I continuum. The majority
  of the fainter sources showed no association with chromospheric
  features seen on Hα synoptic charts, including filaments. Most
  of them were detected at one frequency only. Sources identified at
  three frequencies (164, 327, and 408 MHz) were located in regions of
  enhanced large-scale magnetic field, some of them at the same location
  as decayed active regions visible one rotation before on synoptic
  Hα charts. Multifrequency sources are associated with maxima of the
  green line corona. The comparison with K-corona synoptic charts shows a
  striking association of the radio sources with dense coronal regions,
  associated with the coronal neutral sheet. Furthermore, we detected
  an enhanced brightness region which surrounds the local sources and
  is stable over at least one solar rotation. We call this feature a
  coronal plateau and we identify it with the radio counterpart of the
  coronal neutral sheet.

Title: Detection of the coronal plasma sheet on the solar disk
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1992sws..coll..213L
Altcode:
  The large scale coronal neutral sheet, which is considered to be the
  source of low speed solar wind, is the low altitude counterpart of the
  interplanetary heliosheet. It is routinely detected with white light
  corona observations at the limb. Maps of the sun at meter wavelengths,
  obtained with the Nancay Radioheliograph, lead to the first detection
  of this density structure on the disk, in the form of a 'plateau' in
  brightness temperature. The radio observations also show the denser
  parts of the coronal neutral sheet as discrete emission sources. Some
  of them may be identified as coronal streamers.

Title: VLA observations of solar active regions at 6 and 20 CM
Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, K. R.
Bibcode: 1991A&A...251..276A
Altcode:
  High-resolution observations are presented of two active regions
  at 6 and 20 cm over a period of 5 days, together with H-alpha and
  photospheric magnetic fields. The large-scale emission at 20 cm is
  associated with the H-alpha plage. In one region the strongest source
  was over the neutral line, near the tip of an active-region filament,
  which indicates that the emission probably originated in small-scale
  coronal loops. In the second region the peak of the emission was near
  a well-developed sunspot. Neither region showed evidence of large-scale
  loops joining their preceding and following parts. Several other sources
  were observed at 20 cm; a source associated with an H-alpha plage
  region crossed by a filament and one associated with a small bipolar
  region are briefly discussed. The 6-cm emission from a well-developed
  spot showed clearly the characteristics expected from gyroresonance
  model computations.

Title: Study of small scale magnetic flux and the corresponding
    velocity pattern
Authors: Alissandrakis, C. E.; Dara, H. C.; Koutchmy, S.
Bibcode: 1991A&A...249..533A
Altcode:
  Two-dimensional maps of the longitudinal magnetic field and the
  line of sight velocity of two small-scale magnetic regions in
  the quiet sun, using a one-hour time sequence of filtergrams in
  the magnetically sensitive lambda 6103 A CaI line (with circular
  polarization measurements) obtained with the Sacramento Peak Vacuum
  Tower Telescope and the universal filter, are calculated. After the
  elimination of the effect of the 5-minute photospheric oscillations,
  downflows smaller than 300 m/s are found in both magnetic regions. The
  magnetic field intensity and the velocity are weakly correlated:
  high values of the magnetic field tend to occur in regions of small
  negative velocities. The magnetic field intensity increased during
  the observations, while some magnetic peaks moved with respect to
  others. The difference of the magnetic field intensity measured in
  the blue and the red wing indicates a line asymmetry; this asymmetry
  was found to be independent of the line of sight velocity.

Title: Small scale magnetic field mapping with high temporal
    resolution.
Authors: Dara, H. C.; Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1991sopo.work..257D
Altcode:
  Two dimensional maps of the longitudinal magnetic field can be readily
  calculated for small-scale magnetic regions. Here the authors use
  an one-hour time sequence of high spatial resolution (0.75 arc sec)
  filtergrams, obtained at the Sacramento Peak Vacuum Tower Telescope with
  the universal filter (UBF) in the wings of the magnetically sensitive
  λ 6103 Ca I line. The time difference between two magnetic maps is
  32 sec. The measurements of the magnetic field in the blue wing are
  about 40% higher than in the red wing.

Title: Multifrequency radio observations of the solar corona during
    cycle minimum
Authors: Rigaud, D.; Lantos, P.; Alissandrakis, C. E.
Bibcode: 1991AdSpR..11a..65R
Altcode: 1991AdSpR..11...65R
  Observations obtained at meter and decimeter wavelengths during a
  period of very low solar activity (from May to July 1986) are studied
  to analyse the relationship between the corona and the underlying
  levels. The location of radio sources observed on the disk is compared
  with active regions and with H<SUB>α</SUB> filaments. The radio
  emission is found to trace on the disk the large scale structure of
  the corona as observed with K-coronameter: the so-called coronal sheet
  (belt of equatorial streamers) is observed and individual streamers
  could be located, for the first time, on the disk.

Title: Mass Motions Associated with Hα Active Region Arch Structures
Authors: Georgakilas, A. A.; Alissandrakis, C. E.; Zachariadis, Th. G.
Bibcode: 1990SoPh..129..277G
Altcode:
  We have studied mass motions associated with active region arch
  structures from observations of a developing active region near the
  center of the solar disk. We present a method for the computation of
  the line-of-sight velocity from photographs at Hα ± 0.5 under the
  assumption of Beckers' cloud model and reasonable assumptions about the
  Doppler width and optical depth of the arches. Some arches show motions
  typical to arch filaments (the material moves towards the observer near
  the apex of the arch and away from the observer near the footpoints),
  while in others the velocity field is more complex. Assuming a symmetric
  loop, we reconstructed the velocity vector along an arch filament. The
  results are consistent with the picture where material is draining out
  of the filament while the whole structure is ascending with a velocity
  near that of the apex, which does not exceed 10 km s<SUP>−1</SUP>. The
  motion is systematically slower than expected from a free-fall model.

Title: Flow patterns in a sunspot region observed in the photosphere,
    chromosphere and transition region
Authors: Dere, K. P.; Schmieder, B.; Alissandrakis, C. E.
Bibcode: 1990A&A...233..207D
Altcode:
  The flow patterns around a sunspot at photospheric, chromospheric, and
  transition zone temperatures is examined. The spiral fibril pattern
  observed in H-alpha is consistent with a constant alpha force-free
  field extrapolation of the photospheric magnetic field. Evidence
  is found for the first time that C IV fibrils near spots follow the
  field lines parallel to the chromospheric H-alpha fibrils. The observed
  large-scale pattern of redshifts and blueshifts in the vicinity of the
  sunspot is stable and conforms to the typical Evershed flow patterns
  of radial outflow at the photospheric levels and radial inflows at
  the chromospheric and transition region levels. The three-dimensional
  velocity vectors associated with this flow are derived assuming an
  axially symmetric Evershed flow.

Title: Erratum: Velocity Pattern of Small Scale Magnetic Fields
Authors: Dara, H. C.; Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1990SoPh..128..431D
Altcode:
  No abstract at ADS

Title: Physical parameters of solar H-alpha absorption features
    derived with the cloud model
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1990A&A...230..200A
Altcode:
  Observations of a fibril region and of an arch filament region
  obtained by the Multichannel Subtractive Double Pass Spectrograph
  (MSDP) operating in H-alpha at the Pic du Midi Observatory are
  presented. Intensity fluctuations and Doppler shift velocities were
  derived over two dimensional fields of view. The observed contrast
  profiles have been matched with theoretical contrast profiles based on
  the cloud model which has four parameters: the line-of-sight velocity,
  the source function, the optical depth, and the Doppler width. Contour
  maps and histograms of the 4 parameters were made for these regions,
  and a comparison of the velocities given by 3 different methods (cloud
  model, Doppler shift, and the '3-optical depths' method of Mein and
  Mein, 1988) is made.

Title: Velocity pattern of small scale magnetic fields
Authors: Dara, H. C.; Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1990SoPh..126..403D
Altcode:
  High resolution observations of horizontal proper motions, as well
  as vertical Doppler velocities measured over two selected regions
  of small scale magnetic elements show a coherent behaviour. In a
  region with two opposite polarities, approching with a velocity of
  0.4 km s<SUP>-1</SUP>, the material in between moves downwards with
  a velocity of 0.10 to 0.45 km s<SUP>-1</SUP>; while in a region with
  two peaks of the same polarity, moving apart with a velocity of 0.3 km
  s<SUP>-1</SUP>, the material in between moves predominantly upwards,
  with a velocity of up to 0.3 km s<SUP>-1</SUP>.

Title: VLA Observations of Solar Active Regions at 6 and 20 cm During
    the Spacelab 2 Mission
Authors: Alissandrakis, C. E.; Kundu, M. R.; Shevgaonkar, R. K.
Bibcode: 1990BAAS...22..795A
Altcode:
  No abstract at ADS

Title: Computation of electron beam parameters for solar type III
    and J bursts
Authors: Hillaris, A.; Alissandrakis, C. E.; Caroubalos, C.; Bougeret,
   J. -L.
Bibcode: 1990A&A...229..216H
Altcode:
  The dynamic evolution of mildly relativistic electrons (10-100 keV)
  propagating outward in the solar corona following open or closed
  magnetic lines is studied using the drift approximation. Wave-particle
  interactions are neglected, since the beam-plasma system is considered
  as almost decoupled in the range of parameters used in this model. The
  results of this simulation are used for the computation of observable
  quantities and the analysis of dynamic spectra of isolated type III or
  J bursts, obtained with the Digital Multichannel Radio Spectrograph of
  the Space Research Laboratory of Paris, Meudon. The initial velocity
  dispersion of the exciter and the coronal scale height are thus
  determined. The implications of the results on the emission processes
  are discussed.

Title: Small Scale Motions Over Concentrated Magnetic Field Regions
    of the Quiet Sun
Authors: Dara, H. C.; Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1990IAUS..138..153D
Altcode:
  No abstract at ADS

Title: Relationship between a spot and a filament observed during
    spacelab 2 mission
Authors: Schmieder, B.; Dere, K. P.; Raadu, M. A.; Démoulin, P.;
   Alissandrakis, C. E.
Bibcode: 1990AdSpR..10i.195S
Altcode: 1990AdSpR..10..195S
  During the Spacelab 2 Mission, an active region including a sunspot,
  plages, fibrils and a filament which disappears during the observation
  period, was observed in Hα and in the C IV lines. The analysis of the
  observations leads to several conclusions. Shear in the active region
  filament is observed before its disappearance. Hα and C IV upflows
  in the filament are well correlated spatially, but the transition
  zone (C IV) velocities are an order of magnitude larger than the Hα
  chromospheric ones. Over the sunspot, the reverse-Evershed effect is
  observed in Hα and in C IV Dopplershift images while strong downflows
  are also detected in the C IV profiles. <P />Magnetograph data for
  the whole region are used to calculate the linear force-free magnetic
  field. A single value of the force-free parameter α is found to give a
  good fit to both the sheared filament structure and the sunspot spiral
  structures, indicating a causal relationship. <P />We propose a model
  based on the inductive coupling between current systems associated with
  the filament and the sunspot. Relaxation phenomena due to resistive
  effects in the filament could lead to irreversible conversion of
  magnetic energy into kinetic energy and heating.

Title: Formation of a Filament around a Magnetic Region
Authors: Schmieder, B.; Démoulin, P.; Ferreira, J.; Alissandrakis,
   C. E.
Bibcode: 1990LNP...363..232S
Altcode: 1990doqp.coll..232S; 1990IAUCo.117..232S
  The evolution of the active region AR4682 observed in 1985 during six
  rotations was dominated by three different phenomena: . the large
  scale pattern activity: relationship between two active regions,
  formation of a quiescent filament during the decay phase of the
  active region, . the presence of two pivot points along the filament
  surrounding the sunspot-with the long term one is associated the
  existence of the filament, with the short term one the activity with
  partial disappearance, . the magnetic shear during one rotation. The
  magnetic field lines have been extrapolated from photospheric data
  using Alissandrakis code (1981). The magnetic configuration with the
  existence of a dip favors the formation of a filament. We note that
  the shearing of the sunspot region and of the filament are both well
  described by force-free magnetic fields with the same constant α. This
  suggests that they are both a consequent of the same shear process.

Title: Coronal meter wavelength observations during solar minimum:
    location of dense streamers.
Authors: Rigaud, D.; Lantos, P.; Alissandrakis, C. E.
Bibcode: 1990PDHO....7..270R
Altcode:
  No abstract at ADS

Title: Observation of the heliosheet at meter wavelengths
Authors: Lantos, P.; Rigaut, D.; Alissandrakis, C. E.
Bibcode: 1989AdSpR...9d..37L
Altcode: 1989AdSpR...9...37L
  The Nancay Radioheliograph provides detailed radio maps at 169 MHz
  of the solar corona. The meter wavelength maps are used in particular
  to map the heliosheet on the limb in a way similar to the HAO K-corona
  synoptic maps. In absence of X-ray observations, the radio data provides
  presently the unique possibility to compare directly the heliosheet
  structure with the solar chromospheric features because the radio
  emissions are also observed on the disk and may be followed during
  their transit on the sun.

Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
   Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
   Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
   Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
   H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
   Trottet, G.; Tsuneta, S.; van Hoven, G.
Bibcode: 1989epos.conf..127V
Altcode:
  Contents: 1. Introduction. 2. Phenomena associated with
  mildly-relativistic electrons. 3. Phenomena associated with ions and
  relativistic electrons in solar flares. 4. Theoretical studies of
  particle acceleration. 5. Achievements - outstanding questions.

Title: Formation of a Filament around a Magnetic Region
Authors: Schmieder, B.; Demoulin, P.; Ferreira, J.; Alissandrakis,
   C. E.
Bibcode: 1989HvaOB..13....1S
Altcode:
  No abstract at ADS

Title: The Evershed flow in the solar photosphere, chromosphere and
    chromosphere-corona transition region
Authors: Alissandrakis, C. E.; Dialetis, D.; Mein, P.; Schmieder,
   B.; Simon, G.
Bibcode: 1988A&A...201..339A
Altcode:
  The authors have studied the height dependence of the characteristics
  of the Evershed flow in the photosphere, chromosphere and
  chromosphere-corona transition region. The Multichannel Subtractive
  Double Pass Spectrograph was used to obtain line of sight velocity maps
  in Hα, the Meudon magnetograph for mapping the photospheric velocity
  and magnetic field and the Ultraviolet Spectrometer and Polarimeter on
  the Solar Maximum Mission spacecraft for line-of-sight velocities in C
  IV, in sunspot regions. The observations are practically simultaneous in
  the three atmospheric levels and cover three consecutive days (Sep 28,
  29 and 30, 1980). The emphasis was on the large scale, quasi-stationary
  characteristics of the flow.

Title: Dynamics of sub-relativistic electron beams in magnetic traps -
    A model for solar N-bursts
Authors: Hillaris, A.; Alissandrakis, C. E.; Vlahos, L.
Bibcode: 1988A&A...195..301H
Altcode:
  The dynamic evolution of mildly relativistic electrons (10 - 100 keV)
  injected into a model magnetic trap is studied numerically, using
  the drift approximation. Wave-particle interactions are neglected,
  since the beam plasma system is shown to be non-linearly decoupled
  in the range of parameters used in this study. The results from the
  simulation are used to interpret certain observational characteristics
  of the N-bursts observed by the Nançay radio spectrograph. N-bursts
  are believed to be the first direct radio evidence for mirror effects
  in solar magnetic loops.

Title: High resolution microwave and X-ray observations of solar
    flares
Authors: Alissandrakis, C. E.; Schadee, A.; Kundu, M. R.
Bibcode: 1988A&A...195..290A
Altcode:
  This paper presents an analysis of high spatial resolution observations
  of 18 weak flares, carried out during the Solar Maximum Year in the
  microwave range, H-alpha, and soft X-rays, together with observations
  of the associated hard X-ray emission and the photospheric magnetic
  field. This combination of observations made it possible to obtain a
  picture of the flare geometry and the relative position of the various
  emissions, to study the change of the geometry during the flare, to
  estimate the electron temperature and emission measure of the thermal
  plasma, and to compute the contribution of the free-free process in
  the microwave emission. Results are interpreted as evidence for the
  presence of energetic electrons even in the post-burst phase of some
  flares. There was also found a clear case of homologous radio and X-ray
  bursts, one case of foot-point expansion with a relative velocity of
  20 km/s at 6.16 cm, as well as some evidence of triggering of flares
  by disturbances moving with a velocity of 5000-13,000 km/s.

Title: Spatial and spectral structure of a solar flaring loop at
    centimeter wavelengths
Authors: Preka-Papadema, P.; Alissandrakis, C. E.
Bibcode: 1988A&A...191..365P
Altcode:
  The authors have studied the behaviour of the gyrosynchrotron emission
  coefficient and source function as a function of the strength and
  direction of the magnetic field. The results are applied in the
  qualitative description of the spatial and spectral structure of
  solar microwave bursts. In addition the authors present a complete set
  of model computations of microwave emission from a loop filled with
  energetic electrons. Their model predicts footpoint emission at short
  wavelengths and emission from the entire loop at long wavelengths. The
  computed spectra of the emission show considerable variation along
  the flaring loop.

Title: Quiet Sun and Slowly Varying Component at Meter and Decameter
    Wavelengths
Authors: Lantos, P.; Alissandrakis, C. E.; Gergely, T.; Kundu, M. R.
Bibcode: 1987SoPh..112..325L
Altcode:
  Comparison of maps of the Sun obtained over the period June 29 to July
  8, 1982 at 169 MHz with the Nançay Radioheliograph and at 73.8, 50,
  and 30.9 MHz with the Clark Lake Radioheliograph shows that the slowly
  varying component at meter and decameter wavelengths is not always
  thermal emission. During the period under study weak noise storm
  continua were the most frequent sources of slowly varying component
  at 169 and 73.8 MHz. Most filaments show no radio counterpart on the
  disk. A streamer has been detected on the disk from 169 to 30.9 MHz with
  an optimum observability at 50 MHz. The brightest source of the slowly
  varying component from 73.8 to 30.9 MHz for most of the period was
  located above an extended coronal hole in a region where a depression
  was observed at 169 MHz. In favorable cases, electron densities can
  be derived from the positions of noise storms and radio streamers;
  these are in agreement with previous K-corona eclipse observations.

Title: Observations of Ellerman bombs in H α
Authors: Zachariadis, Th. G.; Alissandrakis, C. E.; Banos, G.
Bibcode: 1987SoPh..108..227Z
Altcode:
  A developing active region near the center of the solar disk was
  observed for 80 min at the center and the wings of Hα. Ellerman
  bombs lying both below an Arch Filament System and near sunspots were
  studied at Hα - 1.0 Å and Hα - 0.75 Å. We determined their average
  contrast, lifetime, size and we studied their flux as a function of
  time. We found evidence that the size of Ellerman bombs increases with
  height. The time curves of flux provide evidence for both impulsive
  and gradual energy release. Under the AFS the Ellerman bombs form a
  cellular pattern with a characteristic size of 3.1 × 10<SUP>3</SUP>
  km. Fifty percent of the bombs appear and disappear in pairs, possibly
  associated with bipolar emerging magnetic flux tubes.

Title: Microwave Emission above Steady and Moving Sunspots
Authors: Chiuderi Drago, F.; Alissandrakis, C.; Hagyard, M.
Bibcode: 1987SoPh..112...89C
Altcode:
  Two-dimensional maps of radio brightness temperature and polarization,
  computed assuming thermal emission with free-free and gyroresonance
  absorption, are compared with observations of active region 2502,
  performed at Westerbork at λ = 6.16 cm during a period of 3 days in
  June 1980. The computation is done assuming a homogeneous model in
  the whole field of view (5' × 5') and a force-free extrapolation of
  the photospheric magnetic field observed at MSFC with a resolution of
  2″.34. The mean results are the following: A very good agreement is
  found above the large leading sunspot of the group, assuming a potential
  extrapolation of the magnetic field and a constant conductive flux in
  the transition region ranging from 2 × 10<SUP>6</SUP> to 10<SUP>7</SUP>
  erg cm<SUP>−2</SUP>s<SUP>−1</SUP>.

Title: Determination of the mean lifetime of solar features from
    photographic observations
Authors: Alissandrakis, C. E.; Dialetis, D.; Tsiropoula, G.
Bibcode: 1987A&A...174..275A
Altcode:
  Two approaches, one based on a lifetime distribution and the second
  based on survival functions, are combined in order to determine the
  mean lifetimes of solar features. The relations between the lifetime
  distributions and the survival and probability density functions
  are derived. This method is applied to the determination of the mean
  lifetimes of solar granules. The accuracy of the method is evaluated by
  comparing the calculated lifetimes with data obtained using different
  methods. It is determined that the proposed method provides accurate
  lifetime data, and a mean lifetime value of 16 min with a standard
  deviation of about 5 min was obtained for the solar granules.

Title: Small-scale motions over concentrated magnetic regions of
    the quiet Sun
Authors: Dara, H. C.; Alissandrakis, C. E.; Koutchmy, S.
Bibcode: 1987SoPh..109...19D
Altcode:
  We have used a 5.5 min time-sequence of spectra in the Fe I lines
  λ5576 (magnetically insensitive), λ6301.5 and λ6302.5 (magnetically
  sensitive) to study the association of concentrated magnetic regions
  and velocity in the quiet Sun. After the elimination of photospheric
  oscillations we found downflows of 100-300 m s <SUP>−1</SUP>,
  displaced by about 2″ from the peaks of the magnetic field; this
  velocity is comparable to downflow velocity associated with the
  granulation and of the same order or smaller than the oscillation
  amplitude. Quasi-periodic time variations of the vertical component
  of the magnetic field up to ± 40% were also found with a period near
  250 s, close to the values found for the velocity field. Finally we
  report a possible association of intensity maxima at the line center
  with peaks of the oscillation amplitude.

Title: The Evershed flow in the solar photosphere, chromosphere and
    chromosphere-corona transition region.
Authors: Alissandrakis, C. E.; Dialetis, D.; Mein, P.; Schmieder,
   B.; Simon, G.
Bibcode: 1987PAICz..66..147A
Altcode:
  The authors have studied the height dependent characteristics of the
  Evershed flow in the photosphere, chromosphere and chromosphere-corona
  transition region.

Title: Microwave emission from steady and moving sunspots.
Authors: Alissandrakis, C. E.; Chiuderi Drago, F.; Hagyard, M. J.
Bibcode: 1987PAICz..66..267A
Altcode: 1987eram....1..267A
  The authors have used force-free extrapolations of photospheric magnetic
  field observations from Marshall Space Flight Center to compute the
  total intensity and circular polarisation of sunspot associated emission
  from active region 2502 in the period June 13 to 15, 1980.

Title: Synoptic study of the corona at meter wavelength.
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1986NASCP2442..257L
Altcode: 1986copp.nasa..257L
  The Mark III Nancay Radioheliograph is used to observe the Sun at 169
  MHz with a time resolution of 25 East-West and North-South images
  per second. When the brightness distribution of the Sun is stable
  during the eight hours of daily observation, a two dimensional map
  can be produced using the technique of earth rotation synthesis. The
  best images are obtained during the period April to August, when the
  declination of the Sun is high to give a good coverage in the uv plane
  and a reasonable North-South resolution. The spatial resolution is 1.5'
  East-West and in summer, 3.5' North-South. The maps are calibrated using
  Cygnus A as a reference. Examples of the maps are given and discussed.

Title: Emission of Lyman-α radiation by solar coronal
    loops. II. Filtergram analysis.
Authors: Tsiropoula, G.; Alissandrakis, C.; Bonnet, R. M.; Gouttebroze,
   P.
Bibcode: 1986A&A...167..351T
Altcode:
  The authors study active region loops, observed on Lα high resolution
  filtergrams obtained with a rocket borne instrument. Some formulae or
  diagrams are given for the computations of Lα and Hα intensities
  emitted by homogeneous loop models. The dimensions and emitted
  intensities of the observed loops being known, the authors determine
  the variations of temperature, pressure and density inside these
  objects under the assumption of constant temperature and hydrostatic
  equilibrium. The influence of temperature gradient and mass flow
  on the results is discussed, and an alternative model with radial
  temperature increase is envisaged. The case of an isolated loop with
  a larger diameter is also discussed.

Title: Gyrosynchrotron Emission of Solar Flares
Authors: Alissandrakis, C. E.
Bibcode: 1986SoPh..104..207A
Altcode:
  The current status of our knowledge on the theory of radio emission from
  mildly relativistic electrons and its application in the interpretation
  of solar radio bursts are reviewed. The recent high spatial resolution
  microwave observations have given important information about the
  geometry of the emitting region and have helped in the computation
  of better inhomogeneous models that reproduce qualitatively several
  observational characteristics of the emission. The limitations of the
  observations and the theory (particularly the effect of mode coupling
  on the observed polarisation) are pointed out and the potential of the
  gyrosynchrotron process as a diagnostic of the physical conditions is
  discussed. This will help us to obtain quantitative information about
  the changes of the magnetic field and the acceleration of particles
  in solar flares.

Title: Coronal structures observed at meter wavelengths.
Authors: Lantos, P.; Alissandrakis, C. E.
Bibcode: 1986HiA.....7..761L
Altcode:
  Two dimensional maps obtained with the Nançay Radioheliograph at 169
  MHz from 1980 are used to describe and identify the features of the
  quiet sun at meter wavelengths.

Title: The Evershed flow as a steady-state homogeneous phenomenon
Authors: Dialetis, D.; Mein, P.; Alissandrakis, C. E.
Bibcode: 1985A&A...147...93D
Altcode:
  The present observations of photospheric and chromospheric line-of-sight
  velocity, as well as the photospheric magnetic field, facilitate the
  comprehensive study of the Evershed (1909) flow, with emphasis on large
  scale, quasi-stationary characteristics of the flow and its association
  with the topology of the magnetic field. A multichannel subtractive
  double pass spectrograph was used to obtain line-of-sight velocity
  maps in H-alpha, together with the Meudon magnetograph. Computations
  are made for the components of the velocity vector as a function of
  distance from the center of the spot, under the assumption of axial
  symmetry. The radial component is the dominant one in both chromosphere
  and magnetosphere. The present analysis of the magnetograms, using
  current-free and force-free models, indicates that the velocity maximum
  occurs in regions where the magnetic field is almost horizontal in both
  layers; the results are judged to appear consistent with subsonic flow
  in magnetic flux tubes.

Title: Coronal structures observed at metric wavelengths with the
    Nançay radioheliograph
Authors: Alissandrakis, C. E.; Lantos, P.; Nicolaidis, E.
Bibcode: 1985SoPh...97..267A
Altcode:
  We present and discuss two-dimensional maps of the Sun at 169 MHz,
  obtained with the Nançay radioheliograph used as an Earth rotation
  aperture synthesis instrument. The maps have been computed on the basis
  of about 6 hr of one-dimensional observations by the east-west and
  the north-south arrays of the radioheliograph and have a resolution of
  1.5' by 4.2' for a solar declination near 23°. In addition to a broad
  background component, the maps show several features both brighter and
  darker than the background. Some of the bright features are sources
  of noise storm continua, as evidenced by their positions relative to
  active regions and by the occurrence of type I bursts. Weaker emission
  regions are apparently associated with neutral lines of the photospheric
  magnetic field. We found no sources associated with extended quiescent
  filaments. Some of the depressions on the maps correspond to coronal
  holes both in the equatorial region and near the poles, while the
  more shallow ones may be arch regions with low electron temperature
  and/or emission measure. The distribution of brightness temperature at
  a height of 0.15 solar radii above the photospheric limb shows a gross
  similarity with coronal green line observations. The present results
  indicate that the notion of the slowly varying component at metric
  wavelengths may have to be reexamined, since sources of different
  nature may have been grouped in this component in the past.

Title: Observations of Ellerman Bombs in H&amp;alpha
Authors: Zachariadis, Th.; Alissandrakis, C. E.; Banos, G.
Bibcode: 1985LNP...233..304Z
Altcode: 1985hrsp.proc..304Z
  A developing active region near the center of the solar disk was
  observed for 80 min at the center and the wings of H-alpha. Ellerman
  bombs lying below an arch filament system (AFS) and near sunspots were
  studied at H -1 A and H -0.75 A. It was found that 50 percent of the
  bombs appear and disappear in pairs, the axis of each pair forming a
  small angle with the magnetic field lines of force as evidenced by the
  AFS. In addition, the members of each pair show proper motions with an
  average relative velocity of 600 m/sec. This behavior suggests their
  association with bipolar emerging magnetic flux tubes. The average
  contrast (1.29), lifetime (19 minutes), size (0.96 in. x 0.58 in.) and
  flux of some 70 bombs was also determined. Evidence was found for an
  increase in size with height and a fluctuation in flux with time.

Title: Solar Coronal Holes Observed with Nancay Meter Radioheliograph
Authors: Lantos, P.; Alissandrakis, C.
Bibcode: 1985ESASP.229..367L
Altcode: 1985erbp.symp..367L
  Observations of the sun at meter wavelengths, with the Nançay
  radioheliograph, provide maps of the structures of the middle
  corona. In particular, coronal holes with low temperature and density
  are well observed both in equatorial regions and near the poles as
  deep depressions in brightness temperature. This provides a new set
  of data to study solar wind and geomagnetic activity origin.

Title: Dynamic Phenomena in the Chromospheric Umbra and Penumbra of
    a Sunspot
Authors: Alissandrakis, C. E.; Dialetis, D.; Macris, C. J.
Bibcode: 1985LNP...233..294A
Altcode: 1985hrsp.proc..294A
  A prominent, short lived (70 sec) umbral flash in H-alpha is observed
  with the 50 cm 'Tourelle' refractor at Pic du Midi. The main component
  of the flash was small (1 arcsec by 0.5 arcsec) with a maximum intensity
  25 percent above the background. It occurred in a region which showed
  irregular intensity variations. Umbral oscillations were observed
  in an adjacent region and running penumbral waves around part of the
  superpenumbra.

Title: A siphon flow model for Evershed motion.
Authors: Dialetis, D.; Alissandrakis, C. E.
Bibcode: 1984ESASP.220..245D
Altcode: 1984ESPM....4..245D
  The authors have studied the motion of an inviscid isothermal
  plasma under the influence of gravity along the lines of force of an
  axisymmetric magnetic field. The general behaviour of the solutions
  is in good agreement with the observations.

Title: Coronal structures observed at metric wavelengths with the
    Nançayradioheliograph.
Authors: Alissandrakis, C. E.; Lantos, P.; Nicolaidis, E.
Bibcode: 1984ESASP.220..263A
Altcode: 1984ESPM....4..263A
  The authors present two-dimensional maps of the Sun at 169 MHz,
  obtained with the Nançay radioheliograph, with resolution of 1.5arcmin
  by 4.2arcmin.

Title: Microwave emission and polarization of a flaring loop
Authors: Alissandrakis, C. E.; Preka-Papadema, P.
Bibcode: 1984A&A...139..507A
Altcode:
  The authors present computations of the microwave emission from a
  loop filled with accelerated electrons. At short wavelengths the loop
  is optically thin and the emission comes predominantly from the feet
  of the loop, while at long wavelengths the emission comes from the
  entire loop with a maximum near the top. If the loop is not located
  at the center of the solar disk the observed polarization is greatly
  affected by propagation effects in the corona which may change the
  sense of the circular polarization (V). For the adopted model and for
  a loop located 30° away from the center of the disk the sense of V
  corresponds to the direction of the magnetic field in the region of
  emission only for wavelengths much shorter than 1.4 cm; for wavelengths
  much longer than 7.5 cm the sense of V corresponds to the polarity of
  the field at the diskward foot of the loop.

Title: Center-to-limb variation of a sunspot-associated microwave
    source
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1984A&A...139..271A
Altcode:
  Observations of the simple bipolar active region McMath 16862,
  obtained with the Westerbork Synthesis Radio Telescope at 6.16 cm
  over six consecutive days, indicate two bright sources associated
  with the region's two main spots, as well as some weaker emission
  that may be associated with loop structures. Application of a novel
  analytical method has allowed the mapping of the vertical as well as
  the horizontal component of the sunspot magnetic field at specific
  locations in the low corona. While the vertical component decreases
  away from the source's center, the horizontal component has both a
  radial and an azimuthal part. These results are interpreted in terms
  of a force-free magnetic field model, as well as in terms of a dipole
  whose axis is inclined to the vertical.

Title: Structure and Polarization of Active Region Microwave Emission
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibcode: 1984SoPh...94..249K
Altcode:
  We present observations of active region radio emission at 6.16 cm
  wavelength, obtained with an angular resolution of 3″ by 10″
  arc using the Westerbork Synthesis Radio Telescope (WSRT) during the
  action interval May 20-27, 1980 of the Solar Maximum Year (SMY). We
  present maps in both total intensity (I) and circular polarization (V)
  of three regions (Hale numbers 16850, 16863, and 16864) and provide a
  detailed comparison of these maps with on- and off-band Hα pictures
  and with magnetograms. The strongest sources were associated with
  neutral lines and soft X-ray arcades. We present evidence that these
  neutral lines were characterized by having their two opposite polarities
  close to each other, implying a high magnetic field gradient, and by
  their association with arch filament systems. The sunspot associated
  radio sources had a relatively simple structure in region 16850;
  however for the large spots of regions 16864 and 16863 the emission
  had a patchy appearance with a tendency of the peaks to lie over the
  penumbra. In the V maps we observed for the first time two `islands',
  polarized in the sense of the ordinary mode, which were located inside
  the sunspot associated sources and were associated with intrusions
  of opposite polarity field into the penumbra. These structures can be
  accounted for if the electron temperature along the line of sight is
  not a monotonically increasing function of height, but has a maximum
  near the second harmonic level. Finally we give a detailed analysis of
  observations of the inversion of the sense of circular polarization in
  region 16863. We find that the large scale structure of the magnetic
  field can be approximated by a dipole with its axis inclined by 11°
  with respect to the photosphere and with a dipole moment of about
  2 × 10<SUP>31</SUP> cgs units; the depolarization line is located
  at a height of 0.16-0.19 R⊙ above the dipole, where the estimated
  intensity of the magnetic field is 10-20 G.

Title: Interpretation of microwave active region structures using
    SMM soft X-ray observations
Authors: Strong, K. T.; Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1984ApJ...277..865S
Altcode:
  The purpose of this paper is to investigate the roles played
  by the geometrical effect of gyroresonance absorption and by the
  low-temperature (&lt;10<SUP>6</SUP>K) flux tubes above sunspot regions
  with microwave ring structures, by combining WSRT 6 cm observations
  with the X-ray observations made with the X-ray Polychromator on the
  SMM satellite. Some features associated with Hale regions 16863 and
  16864 are analyzed from observations on 1980 May 25 and 26 combined
  with model computations of the radio emission. The nature of a cool and
  compact coronal feature seen in soft X-rays, which corresponded to some
  interesting microwave and magnetic features, is also examined. Finally,
  the origin of the X-ray and radio emission associated with neutral
  lines of the magnetic field is considered.

Title: Observations of ring structure in a sunspot associated source
    at 6 centimeter wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1982ApJ...253L..49A
Altcode:
  The detection of a new kind of sunspot-associated source in which the
  emission comes predominantly from a ring structure with size between
  that of the umbra and the penumbra is reported. The absence of emission
  from the center of the spot is interpreted in terms of the orientation
  of the magnetic field and the presence of low temperature material
  above the umbra.

Title: Measurements of the granule-intergranular lane contrast at
    5200 Å and 6300 Å
Authors: Alissandrakis, C. E.; Macris, C. J.; Zachariadis, T. G.
Bibcode: 1982SoPh...76..129A
Altcode:
  We present measurements of the granule-intergranular lane intensity
  ratio at 5200 Å and 6300 Å, at the center of the disk. The
  observations were obtained at Pic du Midi and Sacramento Peak
  observatories between 1967 and 1978. The contrast at 5200 Å was
  corrected for the effect of instrumental profile using a two-dimensional
  model. At 6300 Å and in one photograph our measurements gave an
  average contrast of 1.40, while the values at 5200 Å show a variation
  with time, with the highest corrected values in the range of 1.30 to
  1.37. The possible origins of the time variation are discussed.

Title: On the computation of constant alpha force-free magnetic field
Authors: Alissandrakis, C. E.
Bibcode: 1981A&A...100..197A
Altcode:
  Consideration is given to the boundary value problem of the
  determination of the strength and configuration of the magnetic field in
  the half space above the solar photosphere on the basis of photospheric
  observations for the case of a force-free magnetic field with constant
  alpha, a scalar relating the cross product of the currents and the field
  vectors to the field vector. Solutions are derived in terms of Fourier
  transforms and extended to regions far from the center of the disk. It
  is found that the large-scale components of the solutions involve a
  quasi-periodic variation of the field and current with height, carry
  infinite energy, and can be completely specified only with observations
  of a transverse field component at the boundary. The solutions are thus
  unphysical, however solutions are required for the small-scale solution
  to satisfy the boundary condition. It is pointed out that although
  numerical computations based on the fast Fourier transform are about
  100 times faster than those based on the Green's function formulation,
  the use of a rectangular grid may result in important aliasing effects
  unless the observed field is placed in an array somewhat larger than
  the observed region.

Title: A model for sunspot associated emission at 6 CM wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.; Lantos, P.
Bibcode: 1980A&A....82...30A
Altcode:
  Two-dimensional maps of total intensity and circular polarization of
  a sunspot region at 6 cm have been calculated using a simple model
  for the chromosphere-corona transition region and observations of
  the longitudinal component of the photospheric magnetic field. The
  calculations are in good agreement with the high resolution observations
  of the same sunspot region at 6 cm, obtained with the Westerbork
  Synthesis Radio Telescope. It is shown that the 6 cm radiation is
  predominantly due to gyroresonance absorption process at the second
  and third harmonics of the gyrofrequency (H = 900-600 G). Estimates of
  the conductive flux and the electron density in the transition region
  above the sunspot are also given.

Title: Active region magnetic fields and cm-lambda emission
Authors: Alissandrakis, C. E.
Bibcode: 1980IAUS...86..101A
Altcode:
  The influence of the magnetic field on the structure of
  sunspot-associated sources at cm wavelengths has been investigated
  through model calculations. The case of a source observed with the
  Westerbork SRT and the structure of a single sunspot source are
  considered.

Title: 6 centimeter observations of solar bursts with 6" resolution.
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1978ApJ...222..342A
Altcode:
  During May 1974 data were collected on nine 6-cm solar bursts
  originating in two active regions. One-dimensional fan-beam scans
  were obtained every 30 seconds in order to study burst structure
  and evolution. Maximum burst flux was in the 0.34-12.0 sfu range. At
  maximum intensity the estimated brightness temperatures were in the
  10 to the 6th to 2 x 10 to the 7th K range. Angular sizes ranged from
  7-23 arcsec. In most cases an expansion of the burst core after maximum
  intensity was observed along with a drift in the position of the burst
  core. Four bursts were associated important H-alpha flares, and in all
  cases burst maximum occurred before flare maximum. The bursts were
  circularly polarized in the extraordinary mode sense during maximum
  intensity. Since the polarization was the same over the extent of the
  burst source, it is suggested that if the burst is associated with
  loop sources, the emission is associated with one leg of the loop.

Title: 6 centimeter observations of solar active regions with 6"
    resolution.
Authors: Kundu, M. R.; Alissandrakis, C. E.; Bregman, J. D.; Hin, A. C.
Bibcode: 1977ApJ...213..278K
Altcode:
  We have used the Westerbork Synthesis Radio Telescope for observations
  of solar active regions at 6 cm during 1974 May 8-10. The particular
  problems of using a sidereal instrument for solar observations are
  discussed. Maps of total intensity and circular polarization were
  obtained for four active regions with sunspots and a plage region;
  the linear polarization was below the noise limit. The brightest
  components of the 6 cm emission are associated with sunspots, while
  weaker components are associated with the plage magnetic fields, both
  longitudinal and transverse. An inversion of the sense of circular
  polarization was observed in the preceding part of a region with
  bipolar magnetic-field structure, about two days after the region
  passed through the central meridian. Nine bursts were also observed,
  and their one-dimensional positions with respect to the associated
  active regions are given.

Title: .
Authors: Alissandrakis, C. E.
Bibcode: 1977PhDT.........4A
Altcode:
  The Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands
  was used for Solar observations at 6 cm on May 8-10, 1974. The WSRT
  was used for two-dimensional mapping of Solar active regions and for
  one-dimensional mapping of transient burst sources. Synthesis maps of
  four active regions were produced. Compact sources associated both with
  sunspots and with plage regions were detected. The compact plage sources
  were associated with areas of enhanced longitudinal magnetic field
  or with regions near the neutral line of the photospheric field. The
  magnetic field in the transition zone or low corona above the sunspots
  was calculated as 600-900 Gauss. This value is approximately two times
  larger than the predictions of current-free calculation of the magnetic
  field based on the Meudon magnetogram.

Title: A comparison of positions and sizes of sources of centimeter
    and X-ray bursts.
Authors: Kundu, M. R.; Alissandrakis, C. E.; Kahler, S. W.
Bibcode: 1976SoPh...50..429K
Altcode:
  We have made a parallel study of three cm-λ radio bursts, observed
  on 9 August, 1973 with the NRAO 1 three-element interferometer at 3.7
  and 11.1 cm and the associated X-ray flares observed with the S-054
  telescope aboard Skylab. Within the errors of our measurements (±
  5″) the radio and X-ray events are cospatial. We find good agreement
  between the size of the X-ray kernel and that of the core of the cm
  burst, while there is evidence that much of the impulsive radio flux
  was produced in a larger area.

Title: Observations of Solar Bursts at 6 cm Wavelength with Angular
    Resolution of 6" arc.
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1976BAAS....8Q.555A
Altcode:
  No abstract at ADS

Title: A search for periodic variations of solar radio emission at
    3.7- and 11.1-cm wavelengths.
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibcode: 1975MNRAS.173...65K
Altcode:
  Periodic time variations in the emission of quiet solar regions were
  sought with the NRAO three-element interferometer at 3.7 and 11.1
  cm. The visibility function of a source as obtained with a tracking
  interferometer is an implicit function of time, because of projected
  baseline changes, and therefore only observations taken when the
  baseline changes vary slowly with time were used. The visibility
  function shows significant time variations, but a power-spectrum
  analysis of the data revealed no unique periodicity.

Title: Observations at 6 CM of the solar active region
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibcode: 1975Natur.257..465K
Altcode:
  Preliminary results are reported for the synthesis of a solar active
  region from observations with a synthesis radio telescope at a
  wavelength of 6 cm. Several individual sources are observed in the
  total-intensity and circular-polarization maps. These are shown to
  correspond to two large sunspots, two groups of small sunspots, and a
  plage. A magnetogram indicates that this active region had a bipolar
  structure with positive polarity concentrated on the main sunspots
  and negative polarity scattered over the plage and some of the small
  sunspots. It is noted that several radio bursts were recorded during
  the observation period and that one corresponded to a H-alpha flare
  near one of the sunspot groups.

Title: High Resolution Polarization Observations of a Solar Active
    Region at 6 cm.
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1975BAAS....7..473A
Altcode:
  No abstract at ADS

Title: 6 cm Observations of A Solar Active Region with the Westerbork
    Synthesis Radio Telescope.
Authors: Kundu, M. R.; Alissandrakis, C. E.; van Someren Greve, H. W.
Bibcode: 1975BAAS....7..235K
Altcode:
  No abstract at ADS

Title: High Resolution Observations of Solar Bursts at 3.7 and 11.1
    cm Wavelengths
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibcode: 1975SoPh...41..119A
Altcode:
  Four bursts were observed on August 9, 1973 with the NRAO 1 3-element
  interferometer at 3.7 and 11.1 cm. By using a simple source model we
  have calculated the temperature, flux, size and position of the small
  scale components of the bursts as a function of time. We obtained
  peak temperatures around 10<SUP>7</SUP> K for the components with
  size of about 10″ at 11.1 cm and 3″ at 3.7cm. The peak flux
  of these components lies between 4 and 40 % of the total peak flux
  of the bursts. Two of the bursts were found to be right circularly
  polarized. There is evidence that the location of these two bursts does
  not coincide with the location of the brightest point of the associated
  active regions. The existence of burst structures with temperatures
  of the order of 10<SUP>7</SUP>K indicates that at least part of the
  radiation in these bursts is generated by a non-thermal mechanism.

Title: Absence of Periodic Variation in Solar Radiation at 3.7 cm
    and 11.1 cm Wavelengths.
Authors: Alissandrakis, C.; Kundu, M. R.; Becker, R. H.
Bibcode: 1974BAAS....6..348A
Altcode:
  No abstract at ADS

Title: Long Base Line Interferometry of the Sun at 3.7 and 11.1
    cm Wavelengths.
Authors: Kundu, M. R.; Alissandrakis, C.; Becker, R. H.
Bibcode: 1974BAAS....6..219K
Altcode:
  No abstract at ADS

Title: Properties of the Red SPOT of Jupiter in 1971
Authors: Banos, C. J.; Dialetis, D. G.; Alissandrakis, C. E.
Bibcode: 1972A&A....19..381B
Altcode:
  Isodensity tracings of Jupiter and its Red Spot during the year 1971 as
  well as photometric profiles are given. The variation of the relative
  intensity of the Red Spot as the Spot moves from the one edge of the
  planetary disc to the other for 1971 is studied. Key words: planetary
  atmospheres - Jupiter - Red Spot - photometry.

Title: Isophotometry of the Chromospheric Bright and Dark Mottles
    on the Solar Disk
Authors: Alissandrakis, C. E.; Macris, C. J.
Bibcode: 1972ApL....10...59A
Altcode:
  No abstract at ADS

Title: Isodensitometry of Jupiter's Red SPOT and Jupiter
Authors: Banos, C. J.; Alissandrakis, C. E.
Bibcode: 1971A&A....15..424B
Altcode:
  Isodensity tracings for Jupiter in 1968 and for the Red Spot in
  1968-1969-1970 are given. The photometric proffies of both derived
  from the isophotes and for = 5500 A are given in the East-West and
  NorthSouth directions. Key words: planetary atmospheres - Jupiter -
  red spot isophotes.

Title: A Study of the Fine Structure of the Solar Chromosphere at
    the Limb
Authors: Alissandrakis, C. E.; Macris, C. J.
Bibcode: 1971SoPh...20...47A
Altcode:
  We have measured the dimensions, distances from the inner limb and
  the lifetime of bright mottles at the limb. Spicule lifetimes have
  been measured too. The problem of the `dark band', lying just above
  the inner limb, as well as the relations between bright mottles and
  spicules are discussed.

Title: On the relationships between bright mottles and spicules of
    the solar chromosphere.
Authors: Alissandrakis, C. E.; Macris, C. J.
Bibcode: 1971AkAtP..46..107A
Altcode:
  No abstract at ADS

Title: Lifetime of the Dark and Bright Mottles of the Solar
    Chromosphere
Authors: Macris, C. J.; Alissandrakis, C. E.
Bibcode: 1970SoPh...11...59M
Altcode:
  No abstract at ADS

