-
Infrared spectropolarimetry of a C-class solar flare footpoint plasma -- I. Spectral features and forward modelling
Authors:
Z. Vashalomidze,
C. Quintero Noda,
T. V. Zaqarashvili,
M. Benko,
D. Kuridze,
P. Gömöry,
J. Rybák,
S. Lomineishvili,
M. Collados,
C. Denker,
M. Verma,
C. Kuckein,
A. Asensio Ramos
Abstract:
We performed high-spatial resolution spectropolarimetric observations of active region NOAA 13363 during a C-class flare with the Gregor Infrared Spectrograph (GRIS) on 16 July 2023. We examine the coupling between the photosphere and the chromosphere, studying the polarimetric signals during a period that encompasses the decaying phase of a C-class flare and the appearance of a new C-class flare…
▽ More
We performed high-spatial resolution spectropolarimetric observations of active region NOAA 13363 during a C-class flare with the Gregor Infrared Spectrograph (GRIS) on 16 July 2023. We examine the coupling between the photosphere and the chromosphere, studying the polarimetric signals during a period that encompasses the decaying phase of a C-class flare and the appearance of a new C-class flare at the same location. We focus on the analysis of various spectral lines. In particular, we study the Si I 10827 Å, Ca I 10833.4 Å, Na I 10834.9 Å, and Ca I 10838.9 Å photospheric lines, as well as the He I 10830 Å triplet. GRIS data revealed the presence of flare-related red- and blueshifted spectral line components, reaching Doppler velocities up to 90 km/s, and complex Si I profiles where the He i spectral line contribution is blueshifted. In contrast, the photospheric Ca i and Na i transitions remained unchanged, indicating that the flare did not modify the physical conditions of the lower photosphere. We combined that information with simultaneous imaging in the Ca ii H line and TiO band with the improved High-resolution Fast Imager (HiFI+), finding that the flare emission did not affect the inverse granulation or nearby plage, in agreement with the results from GRIS. We also complement the previous studies with a forward modelling computation, concluding that the He I spectral line emission reflects a complex response of the flaring chromosphere. Radiative excitation from coronal EUV irradiation, energy deposition by flare-accelerated electrons, and dynamic field-aligned plasma flows likely act together to produce the observed supersonic downflows and upflows. We plan to expand these findings through inversions of the He I 10830 Å triplet signals in the future.
△ Less
Submitted 24 February, 2026;
originally announced February 2026.
-
Synthesizing Sun-as-a-star flare spectra from high-resolution solar observations
Authors:
M. De Wilde,
A. G. M. Pietrow,
M. K. Druett,
A. Pastor Yabar,
J. Koza,
I. Kontogiannis,
O. Andriienko,
A. Berlicki,
A. R. Brunvoll,
J. de la Cruz Rodríguez,
J. T. Faber,
R. Joshi,
D. Kuridze,
D. Nóbrega-Siverio,
L. H. M. Rouppe van der Voort,
J. Rybák,
E. Scullion,
A. M. Silva,
Z. Vashalomidze,
A. Vicente Arévalo,
A. Wiśniewska,
R. Yadav,
T. V. Zaqarashvili,
J. Zbinden,
E. S. Øyre
Abstract:
Spatially resolved observations of the Sun and the astronomical sample size of stellar bodies are the respective key strengths of solar and stellar observations. However, the large difference in object brightness between the Sun and other stars has led to distinctly different instrumentation and methodologies between the two fields. We produce and analyze synthetic full-disk spectra derived from 1…
▽ More
Spatially resolved observations of the Sun and the astronomical sample size of stellar bodies are the respective key strengths of solar and stellar observations. However, the large difference in object brightness between the Sun and other stars has led to distinctly different instrumentation and methodologies between the two fields. We produce and analyze synthetic full-disk spectra derived from 19 small area field-of-view optical observations of solar flares acquired by the Swedish 1-m Solar Telescope (SST) between 2011 and 2024. These are used to investigate what can and cannot be inferred about physical processes on the Sun from Sun-as-a-star observations. The recently released Numerical Empirical Sun-as-a-Star Integrator (NESSI) code provides synthetic full-disk integrated spectral line emission based on smaller field-of-view input, accounting for center-to-limb variations and differential rotation. We use this code to generate pseudo-Sun-as-a-star spectra from the SST observations. ...
△ Less
Submitted 18 June, 2026; v1 submitted 10 July, 2025;
originally announced July 2025.
-
Measurement of the polytropic index during solar coronal rain using a diagram of the electron density distribution as a function of the electron temperature
Authors:
Z. M. Vashalomidze,
T. V. Zaqarashvili,
V. D. Kukhianidze
Abstract:
A differential emission measure (DEM) method is used to evaluate the relationship of the electron density and temperature before and after a coronal rain event during an active sun over the period from 20:10 UT on October 6 to 02:10 on October 7, 2011. Observational data were obtained from SDO/AIA for six different extreme ultraviolet (EUV) spectral lines. 240 different coronal loops were analyzed…
▽ More
A differential emission measure (DEM) method is used to evaluate the relationship of the electron density and temperature before and after a coronal rain event during an active sun over the period from 20:10 UT on October 6 to 02:10 on October 7, 2011. Observational data were obtained from SDO/AIA for six different extreme ultraviolet (EUV) spectral lines. 240 different coronal loops were analyzed during this time interval, and the average electron density and temperature were obtained using 171 Å (Fe IX) and 193 Å (Fe XII) filters. The relationship between the density and temperature made it possible to estimate the polytropic index in the solar corona before and after the coronal rain. The polytropic index after the termination of the coronal rain was estimated to be γ = 1.3{\pm}0.06, Which shows the usual thermodynamic properties of study-state coronal plasma. The polytropic index at the time of onset of the coronal rain was, however, estimated to be γ = 2.1{\pm}0.11, which indicates an unstable thermodynamic process, i.e., thermal instability. It is suggested that the coronal rain is the result of an unstable process, and the coronal plasma returns its stable state after the rain.
△ Less
Submitted 4 October, 2021;
originally announced October 2021.
-
Eruption of prominence triggered by coronal rain in the solar atmosphere observed by SDO/AIA and Stereo/EUVI
Authors:
Z. M. Vashalomidze,
T. V. Zaqarashvili,
V. D. Kukhianidze,
G. T. Ramishvili
Abstract:
The triggering process for coronal mass ejections (CME) in the solar atmosphere is not fully understood. We use observations from different spacecraft at several wavelengths to detect an instability process for a prominence/filament with a subsequent eruption of CME. Time series of spectral lines at 304, 171, 193, and 211 Å have been obtained with the SDO spacecraft, and at 304, 171, 195, and 284…
▽ More
The triggering process for coronal mass ejections (CME) in the solar atmosphere is not fully understood. We use observations from different spacecraft at several wavelengths to detect an instability process for a prominence/filament with a subsequent eruption of CME. Time series of spectral lines at 304, 171, 193, and 211 Å have been obtained with the SDO spacecraft, and at 304, 171, 195, and 284 Å with the STEREO spacecraft. A prominence/filament system was observed during November 8-23, 2011, at different angles by SDO, STEREO_A, and STEREO_B. The observations show that a giant tornado began to develop near the base of the prominence at 20:00 UT on November 20, which later caused the appearance of droplets of coronal rain (at 16:00 UT, November 21) which fell downward from the main mass of the prominence. The coronal rain continued until 20:20 UT, November 22, and caused instability of the prominence, after which a CME took place at 22:30 UT on November 22. We assume that the loss of mass owing to coronal rain may lead to instability of prominences and their subsequent eruption. Observations of coronal rain falling from the main part of the mass of prominences could be used for predicting space weather.
△ Less
Submitted 4 October, 2021;
originally announced October 2021.
-
Prominence instability and CMEs triggered by massive coronal rain in the solar atmosphere
Authors:
Z. Vashalomidze,
T. V. Zaqarashvili,
V. Kukhianidze,
G. Ramishvili,
A. Hanslmeier,
P. Gomory
Abstract:
Triggering process for prominence instability and consequent CMEs is not fully understood. Prominences are maintained by the Lorentz force against the gravity, therefore reduction of the prominence mass due to the coronal rain may cause the change of the force balance and hence destabilisation of the structures. We aim to study the observational evidence of the influence of coronal rain on the sta…
▽ More
Triggering process for prominence instability and consequent CMEs is not fully understood. Prominences are maintained by the Lorentz force against the gravity, therefore reduction of the prominence mass due to the coronal rain may cause the change of the force balance and hence destabilisation of the structures. We aim to study the observational evidence of the influence of coronal rain on the stability of prominence and subsequent eruption of CMEs. We used the simultaneous observations from AIA/SDO and SECCHI/STEREO spacecrafts from different angles to follow the dynamics of prominence/filaments and to study the role of coronal rain in their destabilisation. Three different prominences/filaments observed during years 2011-2012 were analysed using observations acquired by SDO and STEREO. In all three cases massive coronal rain from the prominence body led to the destabilisation of prominence and subsequently to the eruption of CMEs. The upward rising of prominences consisted in the slow and the fast rise phases. The coronal rain triggered the initial slow rise of prominences, which led to the final instability (the fast rise phase) after 18-28 hours in all cases. The estimated mass flux carried by coronal rain blobs showed that the prominences became unstable after 40 \% of mass loss. We suggest that the initial slow rise phase was triggered by the mass loss of prominence due to massive coronal rain, while the fast rise phase, i.e. the consequent instability of prominences, was caused by the torus instability and/or magnetic reconnection with overlying coronal field. Therefore, the coronal rain triggered the instability of prominences and consequent CMEs. If this is the case, then the coronal rain can be used to predict the CMEs and hence to improve the space weather predictions.
△ Less
Submitted 4 October, 2021;
originally announced October 2021.
-
Formation and evolution of coronal rain observed by SDO/AIA on February 22, 2012
Authors:
Z. Vashalomidze,
V. Kukhianidze,
T. V. Zaqarashvili,
R. Oliver,
B. Shergelashvili,
G. Ramishvili,
S. Poedts,
P. De Causmaecker
Abstract:
The formation and dynamics of coronal rain are currently not fully understood. Coronal rain is the fall of cool and dense blobs formed by thermal instability in the solar corona towards the solar surface with acceleration smaller than gravitational free fall. We aim to study the observational evidence of the formation of coronal rain and to trace the detailed dynamics of individual blobs. We used…
▽ More
The formation and dynamics of coronal rain are currently not fully understood. Coronal rain is the fall of cool and dense blobs formed by thermal instability in the solar corona towards the solar surface with acceleration smaller than gravitational free fall. We aim to study the observational evidence of the formation of coronal rain and to trace the detailed dynamics of individual blobs. We used time series of the 171 Å\, and 304 Å\, spectral lines obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) above active region AR 11420 on February 22, 2012. Observations show that a coronal loop disappeared in the 171 Å channel and appeared in the 304 Å line$\text{}\text{}$ more than one hour later, which indicates a rapid cooling of the coronal loop from 1 MK to 0.05 MK. An energy estimation shows that the radiation is higher than the heat input, which indicates so-called catastrophic cooling. The cooling was accompanied by the formation of coronal rain in the form of falling cold plasma. We studied two different sequences of falling blobs. The first sequence includes three different blobs. The mean velocities of the blobs were estimated to be 50 km s$^{-1}$, 60 km s$^{-1}$ and 40 km s$^{-1}$. A polynomial fit shows the different values of the acceleration for different blobs, which are lower than free-fall in the solar corona. The first and second blob move along the same path, but with and without acceleration, respectively. We performed simple numerical simulations for two consecutive blobs, which show that the second blob moves in a medium that is modified by the passage of the first blob. Therefore, the second blob has a relatively high speed and no acceleration, as is shown by observations. The second sequence includes two different blobs with mean velocities of 100 km s$^{-1}$ and 90 km s$^{-1}$, respectively.
△ Less
Submitted 14 April, 2015;
originally announced April 2015.