kuridze

explanation blue bibcodes open ADS page with paths to full text

Author name code: kuridze
ADS astronomy entries on 2022-09-14
author:Kuridze, David

---------------------------------------------------------
Title: Dark off-limb gap: manifestation of temperature minimum and
dynamic nature of the chromosphere
Authors: Kuridze, D.; Heinzel, P.; Koza, J.; Oliver, R.
2022arXiv220814134K Altcode:
We study off-limb emission of the lower solar atmosphere using
high-resolution imaging spectroscopy in the H$\beta$ and Ca II 8542 Å
lines obtained with the CHROMospheric Imaging Spectrometer (CHROMIS)
and the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m
Solar Telescope. The H$\beta$ line wing images show the dark intensity
gap between the photospheric limb and chromosphere which is absent
in the Ca II images. We calculate synthetic spectra of the off-limb
emissions with the RH code in the one-dimension spherical geometry and
find good agreement with the observations. The analysis of synthetic
line profiles shows that the gap in the H$\beta$ line wing images maps
the temperature minimum region between the photosphere and chromosphere
due to the well known opacity and emissivity gap of Balmer lines in this
layer. However, observed gap is detected farther from the line core
in the outer line wing positions than in the synthetic profiles. We
found that an increased microturbulence in the model chromosphere is
needed to reproduce the dark gap in the outer line wing, suggesting that
observed H$\beta$ gap is the manifestation of the temperature minimum
and the dynamic nature of the solar chromosphere. The temperature
minimum produces a small enhancement in synthetic Ca II line-wing
intensities. Observed off-limb Ca II line-wing emissions show similar
enhancement below temperature minimum layer near the edge of the
photospheric limb.

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

---------------------------------------------------------
Title: The Atmospheric Response to High Nonthermal Electron-beam
Fluxes in Solar Flares. II. Hydrogen-broadening Predictions for
Solar Flare Observations with the Daniel K. Inouye Solar Telescope
Authors: Kowalski, Adam F.; Allred, Joel C.; Carlsson, Mats; Kerr,
Graham S.; Tremblay, Pier-Emmanuel; Namekata, Kosuke; Kuridze, David;
Uitenbroek, Han
2022ApJ...928..190K Altcode: 2022arXiv220113349K
Redshifted components of chromospheric emission lines in the hard X-ray
impulsive phase of solar flares have recently been studied through
their 30 s evolution with the high resolution of the Interface Region
Imaging Spectrograph. Radiative-hydrodynamic flare models show that
these redshifts are generally reproduced by electron-beam-generated
chromospheric condensations. The models produce large ambient electron
densities, and the pressure broadening of the hydrogen Balmer series
should be readily detected in observations. To accurately interpret
the upcoming spectral data of flares with the DKIST, we incorporate
nonideal, nonadiabatic line-broadening profiles of hydrogen into the
RADYN code. These improvements allow time-dependent predictions for
the extreme Balmer line wing enhancements in solar flares. We study two
chromospheric condensation models, which cover a range of electron-beam
fluxes (1 - 5 × 1011 erg s-1 cm-2) and
ambient electron densities (1 - 60 × 1013 cm-3)
in the flare chromosphere. Both models produce broadening and
redshift variations within 10 s of the onset of beam heating. In the
chromospheric condensations, there is enhanced spectral broadening due
to large optical depths at Hα, Hβ, and Hγ, while the much lower
optical depth of the Balmer series H12-H16 provides a translucent
window into the smaller electron densities in the beam-heated layers
below the condensation. The wavelength ranges of typical DKIST/ViSP
spectra of solar flares will be sufficient to test the predictions
of extreme hydrogen wing broadening and accurately constrain large
densities in chromospheric condensations.

---------------------------------------------------------
Title: A Solar-cycle Study of Coronal Rotation: Large Variations,
Rapid Changes, and Implications for Solar-wind Models
Authors: Edwards, Liam; Kuridze, David; Williams, Thomas; Morgan, Huw
2022ApJ...928...42E Altcode: 2022arXiv220303447E
Information on the rotation rate of the corona, and its variation over
latitude and solar cycle, is valuable for making global connections
between the corona and the Sun, for global estimates of reconnection
rates and as a basic parameter for solar-wind modeling. Here,
we use a time series of tomographical maps gained from coronagraph
observations between 2007 and 2020 to directly measure the longitudinal
drift of high-density streamers over time. The method reveals abrupt
changes in rotation rates, revealing a complex relationship between
the coronal rotation and the underlying photosphere. The majority
of rates are between -1.°0 to +0.°5 day-1 relative to
the standard Carrington rate of 14.°18 day-1, although
rates are measured as low as -2.°2 day-1 and as high
as 1.°6 day-1. Equatorial rotation rates during the
2008 solar minimum are slightly faster than the Carrington rate,
with an abrupt switch to slow rotation in 2009, then a return to
faster rates in 2017. Abrupt changes and large variations in rates
are seen at all latitudes. Comparison with a magnetic model suggests
that periods of equatorial fast rotation are associated with times
when a large proportion of the magnetic footpoints of equatorial
streamers are near the equator, and we interpret the abrupt changes
in terms of the latitudinal distribution of the streamer photospheric
footpoints. The coronal rotation rate is a key parameter for solar-wind
models, and variations of up to a degree per day or more can lead to
large systematic errors over forecasting periods of longer than a few
days. The approach described in this paper gives corrected values that
can form a part of future forecasting efforts.

---------------------------------------------------------
Title: Detecting and Characterising Small-Scale Brightenings in
Solar Imaging Data
Authors: Humphries, LlÅ·r. Dafydd; Morgan, Huw; Kuridze, David
2021SoPh..296..140H Altcode:
Observations of small-scale brightenings in the low solar atmosphere
can provide valuable constraints on possible heating and heat
transport mechanisms. We present a method for the detection and
analysis of brightenings, and demonstrate its application to
time-series imagery of the Interface Region Imaging Spectrograph
(IRIS) in the extreme ultraviolet (EUV). The method is based on
spatio-temporal band-pass filtering, adaptive thresholding and
centroid tracking, and records an event's spatial position, duration,
total brightness and maximum brightness. Spatial area, brightness,
and position are also recorded as functions of time throughout the
event's lifetime. Detected brightenings can fragment, or merge,
over time - thus the number of distinct regions constituting a
brightening event is recorded over time, and the maximum number of
regions recorded as Nfrag, which is a simple measure of an
event's coherence or spatial complexity. A test is made on a synthetic
datacube composed of a static background based on IRIS data, Poisson
noise and ≈104 randomly-distributed, moving, small-scale
Gaussian brightenings. Maximum brightness, total brightness, area,
and duration follow power-law distributions, and the results show the
range over which the method can successfully extract information. The
test shows that the recorded maximum brightness of an event is a
reliable measure for the brightest and most accurately detected events,
with an error of 6%. Event area, duration and speed are generally
underestimated by around 15% and have an uncertainty of 20-30%. The
total brightness is underestimated by 30%, and has an uncertainty
of 30%. Applying this detection method to real IRIS quiet-sun data
spanning 19 minutes over a 54.40″×55.23″
field of view (FOV) yields 2997 detections, 1340 of these detections
either remain un-fragmented or fragment to two distinct regions at
least once during their lifetime (Nfrag≤2 ), equating to
an event density of 3.96 ×10−4 arcsec−2
s−1. The method will be used for a future large-scale
statistical analysis of several quiet-sun (QS) data sets from IRIS,
other EUV imagers, and other types of data including Hα and visible
photospheric imagery.

---------------------------------------------------------
Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere (Corrigendum)
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...652C...2C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Flare-induced Photospheric Velocity Diagnostics
Authors: Monson, Aaron J.; Mathioudakis, Mihalis; Reid, Aaron;
Milligan, Ryan; Kuridze, David
2021ApJ...915...16M Altcode: 2021arXiv210502199M
We present radiative-hydrodynamic simulations of solar flares generated
by the RADYN and RH codes to study the perturbations induced in
photospheric Fe I lines by electron beam heating. We investigate how
variations in the beam parameters result in discernible differences
in the induced photospheric velocities. Line synthesis revealed a
significant chromospheric contribution to the line profiles resulting
in an apparent red asymmetry by as much as 40 m s-1 close
to the time of maximum beam heating, which was not reflective of the
upflow velocities that arose from the radiative-hydrodynamic simulations
at those times. The apparent redshift to the overall line profile was
produced by significant chromospheric emission that was blueshifted
by as much as 400 m s-1 and fills in the blue side of
the near-stationary photospheric absorption profile. The velocity
information that can be retrieved from photospheric line profiles during
flares must therefore be treated with care to mitigate the effects of
higher parts of the atmosphere providing an erroneous velocity signal.

---------------------------------------------------------
Title: Detecting and characterising small-scale brightenings in
solar imaging data
Authors: Dafydd Humphries, Llŷr; Morgan, Huw; Kuridze, David
2021arXiv210713635D Altcode:
Observations of small-scale brightenings in the low solar atmosphere
can provide valuable constraints on possible heating/heat-transport
mechanisms. We present a method for the detection and analysis of
brightenings and demonstrate its application to IRIS EUV time-series
imagery. The method uses band-pass filtering, adaptive thresholding
and centroid tracking, and records an event's position, duration,
and total/maximum brightness. Area, brightness, and position are also
recorded as functions of time throughout their lifetime. Detected
brightenings can fragment or merge over time, thus the number of
distinct regions constituting a brightening event is recorded over time
and the maximum number of regions are recorded as a simple measure
of an event's coherence/complexity. A test is made on a synthetic
datacube composed of a static background based on IRIS data, Poisson
noise and $\approx10^4$ randomly-distributed, moving, small-scale
Gaussian brightenings. Maximum brightness, total brightness, area,
and duration follow power-law distributions and the results show the
range over which the method can extract information. The recorded
maximum brightness is a reliable measure for the brightest and most
accurately detected events with an error of 6%. Area, duration,
and speed are generally underestimated by 15% with an uncertainty of
20-30%. Total brightness is underestimated by 30% with an uncertainty
of 30%. Applying this method to real IRIS QS data spanning 19 minutes
over a 54.40"$\times$55.23" FOV yields 2997 detections. 1340 of these
either remain un-fragmented or fragment to two distinct regions at
least once during their lifetime equating to an event density of
$3.96\times10^{-4}$arcsec$^{-2}$s$^{-1}$. The method will be used
for a future large-scale statistical analysis of several QS data
sets from IRIS, other EUV imagers, as well as H-$\alpha$ and visible
photospheric imagery.

---------------------------------------------------------
Title: Magnetic field inference in active region coronal loops using
coronal rain clumps
Authors: Kriginsky, M.; Oliver, R.; Antolin, P.; Kuridze, D.; Freij, N.
2021A&A...650A..71K Altcode: 2021arXiv210403089K
 Aims: We aim to infer information about the magnetic field in
the low solar corona from coronal rain clumps using high-resolution
spectropolarimetric observations in the Ca II 8542 Å line
obtained with the Swedish 1 m Solar Telescope. Methods: The
weak-field approximation (WFA) provides a simple tool to obtain the
line-of-sight component of the magnetic field from spectropolarimetric
observations. We adapted a method developed in a previous paper in
order to assess the different conditions that must be satisfied in
order to properly use the WFA for the data at hand. We also made use
of velocity measurements in order to estimate the plane-of-the-sky
magnetic field component, so that the magnetic field vector could be
inferred. Results: We have inferred the magnetic field vector
from a data set totalling 100 spectral scans in the Ca II 8542 Å line,
containing an off-limb view of the lower portion of catastrophically
cooled coronal loops in an active region. Our results, albeit limited by
the cadence and signal-to-noise ratio of the data, suggest that magnetic
field strengths of hundreds of Gauss, even reaching up to 1000 G, are
omnipresent at coronal heights below 9 Mm from the visible limb. Our
results are also compatible with the presence of larger magnetic
field values such as those reported by previous works. However, for
large magnetic fields, the Doppler width from coronal rain is not
that much larger than the Zeeman width, thwarting the application
of the WFA. Furthermore, we have determined the temperature, T,
and microturbulent velocity, ξ, of coronal rain clumps and off-limb
spicules present in the same data set, and we have found that the former
ones have narrower T and ξ distributions, their average temperature is
similar, and coronal rain has microturbulent velocities smaller than
those of spicules. Movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140611/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.

---------------------------------------------------------
Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...647A.182C Altcode: 2021arXiv210200942C
Context. While the longitudinal field that dominates in photospheric
network regions has been studied extensively, small-scale transverse
fields have recently been found to be ubiquitous in the quiet
internetwork photosphere and this merits further study. Furthermore,
few observations have been able to capture how this field evolves. Aims: We aim to statistically characterize the magnetic vector in
a quiet Sun internetwork region and observe the temporal evolution of
specific small-scale magnetic features. Methods: We present
two high spatio-temporal resolution observations that reveal the
dynamics of two disk-centre internetwork regions taken by the new GREGOR
Infrared Spectrograph Integral Field Unit with the highly magnetically
sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87
Å. We record the full Stokes vector and apply inversions with the
Stokes inversions based on response functions code to retrieve the
parameters characterizing the atmosphere. We consider two inversion
schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in
a field free medium, and scheme 2 (S2), with two magnetic models
and a fixed 30% stray light component. Results: The magnetic
properties produced from S1 inversions returned a median magnetic
field strength of 200 and 240 G for the two datasets, respectively. We
consider the median transverse (horizontal) component, among pixels
with Stokes Q or U, and the median unsigned longitudinal (vertical)
component, among pixels with Stokes V, above a noise threshold. We
determined the former to be 263 G and 267 G, and the latter to be 131
G and 145 G, for the two datasets, respectively. Finally, we present
three regions of interest, tracking the dynamics of small-scale magnetic
features. We apply S1 and S2 inversions to specific profiles of interest
and find that the latter produces better approximations when there is
evidence of mixed polarities. We find patches of linear polarization
with magnetic flux density of the order of 130−150 G and find that
linear polarization appears preferentially at granule-intergranular
lane boundaries. The weak magnetic field appears to be organized in
terms of complex `loop-like' structures, with transverse fields often
flanked by opposite polarity longitudinal fields.

---------------------------------------------------------
Title: Semi-empirical Models of Spicule from Inversion of Ca II 8542
Å Line
Authors: Kuridze, David; Socas-Navarro, Hector; Koza, Július;
Oliver, Ramon
2021ApJ...908..168K Altcode: 2020arXiv201203702K
We study a solar spicule observed off-limb using high-resolution imaging
spectroscopy in the Ca II 8542 Å line obtained with the CRisp Imaging
SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. Using
a new version of the non-LTE code NICOLE specifically developed
for this problem we invert the spicule single- and double-peak line
profiles. This new version considers off-limb geometry and computes
atomic populations by solving the 1D radiative transfer assuming
a vertical stratification. The inversion proceeds by fitting the
observed spectral profiles at 14 different heights with synthetic
profiles computed in the model by solving the radiative transfer
problem along its length. Motivated by the appearance of double-peak
Ca II 8542 Å spicule profiles, which exhibit two distinct emission
features well separated in wavelength, we adopt a double-component
scenario. We start from the ansatz that the spicule parameters are
practically constant along the spicule axis for each component,
except for a density drop. Our results support this ansatz by
attaining very good fits to the entire set of 14 × 4 profiles (14
heights and 4 times). We show that the double-component model with
uniform temperature of 9560 K, exponential decrease of density with a
height scale of 1000-2000 km, and the counter-oriented line-of-sight
velocities of components reproduce the double-peak line profiles at
all spicule segments well. Analyses of the numerical response function
reveals the necessity of the inversions of spectra at multiple height
positions to obtain height-dependent, degeneracy-free reliable models
with a limited number of free parameters.

---------------------------------------------------------
Title: Mapping the Magnetic Field of Flare Coronal Loops
Authors: Kuridze, David; Morgan, Huw; Oliver, Ramon; Mathioudakis,
Mihalis; Koza, Julius
2021cosp...43E1791K Altcode:
The magnetic field is key to the dynamics, evolution, and heating
of the solar atmosphere, yet direct measurements are rare and highly
uncertain. We report on the unique observation of flaring coronal loops
at the solar limb using high-resolution imaging spectropolarimetry from
the Swedish 1-m Solar Telescope. The vantage position, orientation,
and nature of the chromospheric material that filled the flare loops
allowed us to determine their magnetic field with unprecedented accuracy
using the weak-field approximation method. Our analysis reveals coronal
magnetic field strengths as high as 350 G at heights up to 25 Mm above
the solar limb. These measurements are substantially higher than a
number of previous estimates and may have considerable implications
for our current understanding of the extended solar atmosphere.

---------------------------------------------------------
Title: An Introduction to Photospheric Flare Line Diagnostics
Authors: Monson, A.; Mathioudakis, M.; Milligan, R.; Reid, A.;
Kuridze, D.
2020AGUFMSH057..04M Altcode:
In preparation for solar cycle 25, we present radiative hydrodynamic
flare models from the F-CHROMA archive constructed using the RADYN and
RH codes. We simulate potential observable perturbations seen in the
line-of-sight velocity and heating induced in the photosphere during
a flare. Many works have focused on the recreation of chromospheric
spectral line profiles as the atmosphere rapidly heats and expands
due to the injection of energy from magnetic reconnection. This
extreme heating mechanism can permeate through the upper atmosphere
and affect the lowest levels of the solar atmosphere. This results
in an observable brightening and Doppler shifting of spectral lines
formed in the deepest regions, though the extent of this photospheric
reaction is still not fully characterised. We investigate how variations
in the properties of a solar flare-accelerated electron beam result in
discernible asymmetries in the flaring profiles of several deep forming
Fe I spectral lines. Through analysis of the contribution functions
and response functions of these lines during a flare, we have found
an unprecedented level of high velocity chromospheric contribution
which significantly alters the emergent profile of these lines. This
comparatively weak, high velocity surplus contributing region of
the chromosphere can result in false red shifts and/or significantly
adds to the flaring Doppler shifted profile, resulting in a greater
blue shift of the line core, which had previously been assumed as a
purely photospheric velocity diagnostic. Based on this evidence, it
is concluded that any future work using these photospheric lines to
diagnose properties of the photosphere in a flaring atmosphere must
be carefully analysed to mitigate effect of higher forming regions
providing a surplus velocity signal.

---------------------------------------------------------
Title: Ubiquitous hundred-Gauss magnetic fields in solar spicules
Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio
Ramos, A.; Antolin, P.
2020A&A...642A..61K Altcode: 2020arXiv200601809K
 Aims: We aim to study the magnetic field in solar spicules
using high-resolution spectropolarimetric observations in the Ca II
8542 Å line obtained with the Swedish 1-m Solar Telescope. 
Methods: The equations that result from the application of the weak
field approximation (WFA) to the radiative transfer equations were
used to infer the line-of-sight (LOS) component of the magnetic
field (BLOS). Two restrictive conditions were imposed
on the Stokes I and V profiles at each pixel before they could be
used in a Bayesian inversion to compute its BLOS. 
Results: The LOS magnetic field component was inferred in six data sets
totalling 448 spectral scans in the Ca II 8542 Å line and containing
both active region and quiet Sun areas, with values of hundreds of
Gauss being abundantly inferred. There seems to be no difference,
from a statistical point of view, between the magnetic field strength
of spicules in the quiet Sun or near an active region. On the other
hand, the BLOS distributions present smaller values on
the disc than off-limb, a fact that can be explained by the effect of
superposition on the chromosphere of on-disc structures. We show that
on-disc pixels in which the BLOS is determined are possibly
associated with spicular structures because these pixels are co-spatial
with the magnetic field concentrations at the network boundaries and
the sign of their BLOS agrees with that of the underlying
photosphere. We find that spicules in the vicinity of a sunspot have
a magnetic field polarity (i.e. north or south) equal to that of the
sunspot. This paper also contains an analysis of the effect of off-limb
overlapping structures on the observed Stokes I and V parameters and
the BLOS obtained from the WFA. It is found that this value
is equal to or smaller than the largest LOS magnetic field components
of the two structures. In addition, using random BLOS,
Doppler velocities, and line intensities of these two structures
leads in ≃50% of the cases to Stokes I and V parameters that are
unsuitable to be used with the WFA. Conclusions: Our results
present a scarcity of LOS magnetic field components smaller than some
50 G, which must not be taken as evidence against the existence of
these magnetic field strengths in spicules. This fact possibly arises
as the consequence of signal superposition and noise in the data. We
also suggest that the failure of previous works to infer the strong
magnetic fields in spicules detected here is their coarser spatial
and/or temporal resolution.

---------------------------------------------------------
Title: Multiwavelength Imaging and Spectral Analysis of Jet-like
Phenomena in a Solar Active Region Using IRIS and AIA
Authors: Dafydd Humphries, Llŷr; Verwichte, Erwin; Kuridze, David;
Morgan, Huw
2020arXiv201004042D Altcode:
High-resolution observations of dynamic phenomena give insight into
properties and processes that govern the low solar atmosphere. We
present the analysis of jet-like phenomena emanating from a penumbral
foot-point in active region (AR) 12192 using imaging and spectral
observations from the Interface Region Imaging Spectrograph (IRIS)
and the Atmospheric Imaging Assembly (AIA) on board the Solar
Dynamics Observatory. These jets are associated with line-of-sight
(LoS) Doppler speeds of $\pm$ 10-22 km s$^{-1}$ and bright fronts
which seem to move across the Plane-of-Sky (PoS) at speeds of 23-130
km s$^{-1}$. Such speeds are considerably higher than the expected
sound speed in the chromosphere. The jets have signatures which are
visible both in the cool and hot channels of IRIS and AIA. Each jet
lasts on average 15 minutes and occur 5-7 times over a period of 2
hours. Possible mechanisms to explain this phenomenon are suggested,
the most likely of which involve p-mode or Alfv\' en wave shock trains
impinging on the transition region (TR) and corona as a result of
steepening photospheric wavefronts or gravity waves.

---------------------------------------------------------
Title: Multiwavelength Imaging and Spectral Analysis of Jet-like
Phenomena in a Solar Active Region Using IRIS and AIA
Authors: Humphries, Llŷr Dafydd; Verwichte, Erwin; Kuridze, David;
Morgan, Huw
2020ApJ...898...17H Altcode:
High-resolution observations of dynamic phenomena give insights into
the properties and processes that govern the low solar atmosphere. We
present an analysis of jet-like phenomena emanating from a penumbral
footpoint in active region (AR) 12192 using imaging and spectral
observations from the Interface Region Imaging Spectrograph (IRIS)
and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory. These jets are associated with line-of-sight Doppler
speeds of ±10-22 km s-1 and bright fronts that seem to move
across the plane-of-sky at speeds of 23-130 km s-1. Such
speeds are considerably higher than the expected sound speed in the
chromosphere. The jets have signatures that are visible both in the
cool and hot channels of IRIS and AIA. Each jet lasts on average
15 minutes and occurs 5-7 times over a period of 2 hr. Possible
mechanisms to explain this phenomenon are suggested, the most likely
of which involve p-mode or Alfvén wave shock trains impinging on the
transition region and corona as a result of steepening photospheric
wavefronts or gravity waves.

---------------------------------------------------------
Title: Magnetic field inference in the chromosphere and lower corona
Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio
Ramos, A.; Antolin, P.
2020sea..confE.201K Altcode:
The Weak Field Approximation (WFA) is used to infer the line-of-sight
magnetic field of the solar chromosphere and lower corona. Using near
limb spectropolarimetric observations in the Ca II 8542 Å line taken
with the CRISP instrument at the Swedish 1-metre telescope in La Palma,
the presence of an active region near/in the field of view allows
for the presence of chromospheric spicules and coronal rain blobs
to be detected. This work focuses mostly in the inference of magnetic
fields of off-limb spicules, but a successful attempt to obtain Stokes V
signal from the coronal rain blobs allowed for the inference of coronal
magnetic fields. A careful treatment of the data pixels is undertaken in
order to guarantee the correct application of the WFA, and the results
show the presence of ubiquitous hundred-Gauss magnetic fields in the
spicular material and in the coronal rain blobs. A Bayesian approach
is used to infer the results.

---------------------------------------------------------
Title: Spectral Characteristics and Formation Height of Off-limb
Flare Ribbons
Authors: Kuridze, David; Mathioudakis, Mihalis; Heinzel, Petr; Koza,
Július; Morgan, Huw; Oliver, Ramon; Kowalski, Adam F.; Allred, Joel C.
2020ApJ...896..120K Altcode: 2020arXiv200510924K
Flare ribbons are bright manifestations of flare energy dissipation
in the lower solar atmosphere. For the first time, we report on
high-resolution imaging spectroscopy observations of flare ribbons
situated off limb in the Hβ and Ca II 8542 Å lines and make a detailed
comparison with radiative hydrodynamic simulations. Observations of
the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the
Swedish Solar Telescope reveal bright horizontal emission layers
in Hβ line-wing images located near the footpoints of the flare
loops. The apparent separation between the ribbon observed in the Hβ
wing and the nominal photospheric limb is about 300-500 km. The Ca II
8542 Å line-wing images show much fainter ribbon emissions located
right on the edge of the limb, without clear separation from the
limb. RADYN models are used to investigate synthetic spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. The simulations show that, toward the limb,
where the line of sight is substantially oblique with respect to the
vertical direction, the flaring atmosphere model reproduces the high
contrast of the off-limb Hβ ribbons and their significant elevation
above the photosphere. The ribbons in the Ca II 8542 Å line-wing
images are located deeper in the lower solar atmosphere with a lower
contrast. A comparison of the height deposition of electron beam energy
and the intensity contribution function shows that the Hβ line-wing
intensities can be a useful tracer of flare energy deposition in the
lower solar atmosphere.

---------------------------------------------------------
Title: Signatures of Helium Continuum in Cool Flare Loops Observed
by SDO/AIA
Authors: Heinzel, Petr; Schwartz, Pavol; Lörinčík, Juraj; Koza,
Július; Jejčič, Sonja; Kuridze, David
2020ApJ...896L..35H Altcode: 2020arXiv200600574H
We present an analysis of off-limb cool flare loops observed by the
Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA)
during the gradual phase of SOL2017-09-10T16:06 X8.2-class flare. In the
extreme-ultraviolet (EUV) channels starting from the 335 Å one, cool
loops appear as dark structures against the bright loop arcade. These
dark structures were precisely coaligned (spatially and temporally)
with loops observed by Swedish Solar Telescope (SST) in emission lines
of hydrogen and ionized calcium. A recently published semi-empirical
model of cool loops based on SST observations serves to predict the
level of hydrogen and helium recombination continua. The continua were
synthesized using an approximate non-LTE (I.e., departures from local
thermodynamic equilibrium) approach and theoretical spectra were then
transformed to AIA signals. Comparison with signals detected inside
the dark loops shows that only in AIA 211 Å channel the computed
level of recombination continua is consistent with observations for
some models, while in all other channels that are more distant from
the continua edges the synthetic continuum is far too low. In analogy
with on-disk observations of flares we interpret the surplus emission
as due to numerous EUV lines emitted from hot but faint loops in front
of the cool ones. Finally we briefly comment on failure of the standard
absorption model when used for analysis of the dark-loop brightness.

---------------------------------------------------------
Title: Spectral Diagnostics of Cool Flare Loops Observed by the
SST. I. Inversion of the Ca II 8542 Å and Hβ Lines
Authors: Koza, Július; Kuridze, David; Heinzel, Petr; Jejčič,
Sonja; Morgan, Huw; Zapiór, Maciej
2019ApJ...885..154K Altcode: 2019arXiv190907356K
Flare loops form an integral part of eruptive events, being detected in
the range of temperatures from X-rays down to cool chromospheric-like
plasmas. While hot loops are routinely observed by the Solar Dynamics
Observatory’s Atmospheric Imaging Assembly, cool loops seen
off-limb are rare. In this paper we employ unique observations of
the SOL2017-09-10T16:06 X8.2-class flare which produced an extended
arcade of loops. The Swedish 1 m Solar Telescope made a series of
spectral images of the cool off-limb loops in the Ca II 8542 Å and
the hydrogen Hβ lines. Our focus is on the loop apices. Non-local
thermal equilibrium (non-LTE; i.e., departures from LTE) spectral
inversion is achieved through the construction of extended grids of
models covering a realistic range of plasma parameters. The Multilevel
Accelerated Lambda Iterations code solves the non-LTE radiative-transfer
problem in a 1D externally illuminated slab, approximating the studied
loop segment. Inversion of the Ca II 8542 Å and Hβ lines yields two
similar solutions, both indicating high electron densities around 2 ×
1012 cm-3 and relatively large microturbulence
around 25 km s-1. These are in reasonable agreement with
other independent studies of the same or similar events. In particular,
the high electron densities in the range 1012-1013
cm-3 are consistent with those derived from the Solar
Dynamics Observatory’s Helioseismic and Magnetic Imager white-light
observations. The presence of such high densities in solar eruptive
flares supports the loop interpretation of the optical continuum
emission of stars which manifest superflares.

---------------------------------------------------------
Title: Multi-wavelength observations of the 2014 June 11 M3.9 flare:
temporal and spatial characteristics
Authors: Christian, Damian J.; Kuridze, David; Jess, David B.; Yousefi,
Menoa; Mathioudakis, Mihalis
2019RAA....19..101C Altcode: 2018arXiv181107077C
We present multi-wavelength observations of an M-class flare (M3.9)
that occurred on 2014 June 11. Our observations were conducted
with the Dunn Solar Telescope (DST), employing adaptive optics,
the multi-camera system Rapid Oscillations in Solar Atmosphere
(ROSA), the new Hydrogen-Alpha Rapid Dynamics camera (HARDcam) in
various wavelengths, such as Ca II K, Mg I b2 (at 5172.7
Å), and Hα narrow band and G-band continuum filters. Images were
re-constructed using the Kiepenheuer-Institut Speckle Interferometry
Package (KISIP) code, to improve our image resolution. We observed
intensity increases of ≈120%-150% in the Mg, Ca K and Hα narrow band
filters during the flare. Intensity increases for the flare observed
in the SDO EUV channels were several times larger, and the X-rays,
as recorded by GOES, increased over a factor of 30 for the harder
band. Only a modest delay was found between the onset of flare ribbons
of a nearby sympathetic flare and the main flare ribbons observed in
these narrow band filters. The peak flare emission occurred within a
few seconds for the Ca K, Mg and Hα bands. Time-distance techniques
indicate propagation velocities of ≈60 km s-1 for the
main flare ribbon and as high as 300 km s-1 for smaller
regions, which we attribute to filament eruptions. This result and
delays and velocities observed with SDO (≈100 km s-1)
for different coronal heights agree well with the simple model of
energy propagation versus height, although a more detailed model for
the flaring solar atmosphere is needed. Finally, we detected marginal
quasi-periodic pulsations (QPPs) in the 40-60 s range for the Ca K,
Mg and Hα bands, and such measurements are important for disentangling
the detailed flare-physics.

---------------------------------------------------------
Title: Mapping the Magnetic Field of Flare Coronal Loops
Authors: Kuridze, D.; Mathioudakis, M.; Morgan, H.; Oliver, R.; Kleint,
L.; Zaqarashvili, T. V.; Reid, A.; Koza, J.; Löfdahl, M. G.; Hillberg,
T.; Kukhianidze, V.; Hanslmeier, A.
2019ApJ...874..126K Altcode: 2019arXiv190207514K
Here, we report on the unique observation of flaring coronal loops at
the solar limb using high-resolution imaging spectropolarimetry from
the Swedish 1 m Solar Telescope. The vantage position, orientation,
and nature of the chromospheric material that filled the flare loops
allowed us to determine their magnetic field with unprecedented accuracy
using the weak-field approximation method. Our analysis reveals coronal
magnetic field strengths as high as 350 G at heights up to 25 Mm above
the solar limb. These measurements are substantially higher than a
number of previous estimates and may have considerable implications
for our current understanding of the extended solar atmosphere.

---------------------------------------------------------
Title: Association between Tornadoes and Instability of Hosting
Prominences
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz; Kukhianidze,
Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina;
Poedts, Stefaan
2018csc..confE..20M Altcode:
We studied the dynamics of all prominence tornadoes detected by the
Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011
January 01 to December 31. In total, 361 events were identified
during the whole year, but only 166 tornadoes were traced until the
end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs
in hosting prominences, 83 (50%) caused failed coronal mass ejections
(CMEs) or strong internal motion in the prominences, and only 3 (2%)
finished their lifetimes without any observed activity. Therefore,
almost all prominence tornadoes lead to the destabilization of their
hosting prominences and half of them trigger CMEs. Consequently,
prominence tornadoes may be used as precursors for CMEs and hence for
space weather predictions.

---------------------------------------------------------
Title: Association between Tornadoes and Instability of Hosting
Prominences
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz V.; Kukhianidze,
Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina M.;
Poedts, Stefaan
2018ApJ...861..112M Altcode: 2018arXiv180701345M
We studied the dynamics of all prominence tornadoes detected by the
Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011
January 01 to December 31. In total, 361 events were identified
during the whole year, but only 166 tornadoes were traced until the
end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs
in hosting prominences, 83 (50%) caused failed coronal mass ejections
(CMEs) or strong internal motion in the prominences, and only 3 (2%)
finished their lifetimes without any observed activity. Therefore,
almost all prominence tornadoes lead to the destabilization of their
hosting prominences and half of them trigger CMEs. Consequently,
prominence tornadoes may be used as precursors for CMEs and hence for
space weather predictions.

---------------------------------------------------------
Title: Spectropolarimetric Inversions of the Ca II 8542 Å Line in
an M-class Solar Flare
Authors: Kuridze, D.; Henriques, V. M. J.; Mathioudakis, M.; Rouppe
van der Voort, L.; de la Cruz Rodríguez, J.; Carlsson, M.
2018ApJ...860...10K Altcode: 2018arXiv180500487K
We study the M1.9-class solar flare SOL2015-09-27T10:40 UT using
high-resolution full Stokes imaging spectropolarimetry of the Ca II
8542 Å line obtained with the CRISP imaging spectropolarimeter at the
Swedish 1-m Solar Telescope. Spectropolarimetric inversions using the
non-LTE code NICOLE are used to construct semiempirical models of the
flaring atmosphere to investigate the structure and evolution of the
flare temperature and magnetic field. A comparison of the temperature
stratification in flaring and nonflaring areas reveals strong heating
of the flare ribbon during the flare peak. The polarization signals
of the ribbon in the chromosphere during the flare maximum become
stronger when compared to its surroundings and to pre- and post-flare
profiles. Furthermore, a comparison of the response functions to
perturbations in the line-of-sight magnetic field and temperature in
flaring and nonflaring atmospheres shows that during the flare, the
Ca II 8542 Å line is more sensitive to the lower atmosphere where the
magnetic field is expected to be stronger. The chromospheric magnetic
field was also determined with the weak-field approximation, which
led to results similar to those obtained with the NICOLE inversions.

---------------------------------------------------------
Title: Hα and Hβ emission in a C3.3 solar flare: comparison between
observations and simulations
Authors: Zuccarello, F.; Simoes, P. J. D. A.; Capparelli, V.; Fletcher,
L.; Romano, P.; Mathioudakis, M.; Cauzzi, G.; Carlsson, M.; Kuridze,
D.; Keys, P.
2017AGUFMSH41A2742Z Altcode:
This work is based on the analysis of an extremely rare set of
simultaneous observations of a C3.3 solar flare in the Hα and Hβ lines
at high spatial and temporal resolution, which were acquired at the
Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22)
made at various wavelengths along the Hα line profile by the
Interferometric Bidimensional Spectrometer (IBIS) and in the Hβ
with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband
imager are analyzed to obtain the intensity evolution. The analysis
shows that Hα and Hβ intensity excesses in three identified flare
footpoints are well correlated in time. In the stronger footpoints,
the typical value of the the Hα/Hβ intensity ratio observed is ∼
0.4 - 0.5, in broad agreement with values obtained from a RADYN non-LTE
simulation driven by an electron beam with parameters constrained by
observations. The weaker footpoint has a larger Hα/Hβ ratio, again
consistent with a RADYN simulation but with a smaller energy flux.

---------------------------------------------------------
Title: Hα and Hβ Emission in a C3.3 Solar Flare: Comparison between
Observations and Simulations
Authors: Capparelli, Vincenzo; Zuccarello, Francesca; Romano, Paolo;
Simões, Paulo J. A.; Fletcher, Lyndsay; Kuridze, David; Mathioudakis,
Mihalis; Keys, Peter H.; Cauzzi, Gianna; Carlsson, Mats
2017ApJ...850...36C Altcode: 2017arXiv171004067C
The hydrogen Balmer series is a basic radiative loss channel from
the flaring solar chromosphere. We report here on the analysis of an
extremely rare set of simultaneous observations of a solar flare in the
{{H}}α and {{H}}β lines, at high spatial and temporal resolutions,
that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare
(SOL2014-04-22T15:22) made at various wavelengths along the {{H}}α line
profile by the Interferometric Bidimensional Spectrometer (IBIS) and in
the {{H}}β with the Rapid Oscillations in the Solar Atmosphere (ROSA)
broadband imager are analyzed to obtain the intensity evolution. The
{{H}}α and {{H}}β intensity excesses in three identified flare
footpoints are well-correlated in time. We examine the ratio of {{H}}α
to {{H}}β flare excess, which was proposed by previous authors as
a possible diagnostic of the level of electron-beam energy input. In
the stronger footpoints, the typical value of the the {{H}}α /H β
intensity ratio observed is ∼0.4-0.5, in broad agreement with values
obtained from a RADYN non-LTE simulation driven by an electron beam
with parameters constrained (as far as possible) by observation. The
weaker footpoint has a larger {{H}}α /H β ratio, again consistent
with a RADYN simulation, but with a smaller energy flux. The {{H}}α
line profiles observed have a less prominent central reversal than is
predicted by the RADYN results, but can be brought into agreement if
the {{H}}α -emitting material has a filling factor of around 0.2-0.3.

---------------------------------------------------------
Title: Spectroscopic Inversions of the Ca II 8542 Å Line in a
C-class Solar Flare
Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Koza, J.;
Zaqarashvili, T. V.; Rybák, J.; Hanslmeier, A.; Keenan, F. P.
2017ApJ...846....9K Altcode: 2017arXiv170800472K
We study the C8.4-class solar flare SOL2016-05-14T11:34 UT using
high-resolution spectral imaging in the Ca II 8542 Å line obtained
with the CRISP imaging spectropolarimeter on the Swedish 1 m Solar
Telescope. Spectroscopic inversions of the Ca II 8542 Å line using
the non-LTE code NICOLE are used to investigate the evolution of
the temperature and velocity structure in the flaring chromosphere. A
comparison of the temperature stratification in flaring and non-flaring
areas reveals strong footpoint heating during the flare peak in the
lower atmosphere. The temperature of the flaring footpoints between
{log} {τ }500 ≈ -2.5 {and} -3.5, where τ 500
is the continuum optical depth at 500 nm, is ∼ 5{--}6.5 {kK} close
to the flare peak, reducing gradually to ∼ 5 {kK}. The temperature in
the middle and upper chromosphere, between {log} {τ }500≈
-3.5 and -5.5, is estimated to be ∼6.5-20 kK, decreasing to preflare
temperatures, ∼5-10 kK, after approximately 15 minutes. However, the
temperature stratification of the non-flaring areas is unchanged. The
inverted velocity fields show that the flaring chromosphere is dominated
by weak downflowing condensations at the formation height of Ca II
8542 Å.

---------------------------------------------------------
Title: Observations and Simulations of the Na I D1 Line
Profiles in an M-class Solar Flare
Authors: Kuridze, D.; Mathioudakis, M.; Christian, D. J.; Kowalski,
A. F.; Jess, D. B.; Grant, S. D. T.; Kawate, T.; Simões, P. J. A.;
Allred, J. C.; Keenan, F. P.
2016ApJ...832..147K Altcode: 2016arXiv160908120K
We study the temporal evolution of the Na I D1 line profiles
in the M3.9 flare SOL2014-06-11T21:03 UT, using observations at high
spectral resolution obtained with the Interferometric Bidimensional
Spectrometer instrument on the Dunn Solar Telescope combined with
radiative hydrodynamic simulations. Our results show a significant
increase in the intensities of the line core and wings during the
flare. The analysis of the line profiles from the flare ribbons
reveals that the Na I D1 line has a central reversal
with excess emission in the blue wing (blue asymmetry). We combine
RADYN and RH simulations to synthesize Na I D1 line
profiles of the flaring atmosphere and find good agreement with
the observations. Heating with a beam of electrons modifies the
radiation field in the flaring atmosphere and excites electrons
from the ground state 3s 2S to the first excited state 3p
2P, which in turn modifies the relative population of the
two states. The change in temperature and the population density of
the energy states make the sodium line profile revert from absorption
into emission. Furthermore, the rapid changes in temperature break the
pressure balance between the different layers of the lower atmosphere,
generating upflow/downflow patterns. Analysis of the simulated spectra
reveals that the asymmetries of the Na I D1 flare profile
are produced by the velocity gradients in the lower solar atmosphere.

---------------------------------------------------------
Title: Kelvin-Helmholtz Instability in Solar Chromospheric Jets:
Theory and Observation
Authors: Kuridze, D.; Zaqarashvili, T. V.; Henriques, V.; Mathioudakis,
M.; Keenan, F. P.; Hanslmeier, A.
2016ApJ...830..133K Altcode: 2016arXiv160801497K
Using data obtained by the high-resolution CRisp Imaging
SpectroPolarimeter instrument on the Swedish 1 m Solar Telescope,
we investigate the dynamics and stability of quiet-Sun chromospheric
jets observed at the disk center. Small-scale features, such as rapid
redshifted and blueshifted excursions, appearing as high-speed jets
in the wings of the Hα line, are characterized by short lifetimes and
rapid fading without any descending behavior. To study the theoretical
aspects of their stability without considering their formation
mechanism, we model chromospheric jets as twisted magnetic flux tubes
moving along their axis, and use the ideal linear incompressible
magnetohydrodynamic approximation to derive the governing dispersion
equation. Analytical solutions of the dispersion equation indicate
that this type of jet is unstable to Kelvin-Helmholtz instability
(KHI), with a very short (few seconds) instability growth time at
high upflow speeds. The generated vortices and unresolved turbulent
flows associated with the KHI could be observed as a broadening of
chromospheric spectral lines. Analysis of the Hα line profiles shows
that the detected structures have enhanced line widths with respect to
the background. We also investigate the stability of a larger-scale Hα
jet that was ejected along the line of sight. Vortex-like features,
rapidly developing around the jet’s boundary, are considered as
evidence of the KHI. The analysis of the energy equation in the
partially ionized plasma shows that ion-neutral collisions may lead
to fast heating of the KH vortices over timescales comparable to the
lifetime of chromospheric jets.

---------------------------------------------------------
Title: High-cadence observations of spicular-type events on the Sun
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T.
2016A&A...589A...3S Altcode: 2016arXiv160108087S
Context. Chromospheric observations taken at high-cadence and
high-spatial resolution show a range of spicule-like features,
including Type-I, Type-II (as well as rapid blue-shifted excursions
(RBEs) and rapid red-shifted excursions (RREs) which are thought to
be on-disk counterparts of Type-II spicules) and those which seem to
appear within a few seconds, which if interpreted as flows would imply
mass flow velocities in excess of 1000 km s-1. Aims:
This article seeks to quantify and study rapidly appearing spicular-type
events. We also compare the multi-object multi-frame blind deconvolution
(MOMFBD) and speckle reconstruction techniques to understand if
these spicules are more favourably observed using a particular
technique. Methods: We use spectral imaging observations taken
with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m
Solar Telescope. Data was sampled at multiple positions within the Hα
line profile for both an on-disk and limb location. Results: The
data is host to numerous rapidly appearing features which are observed
at different locations within the Hα line profile. The feature's
durations vary between 10-20 s and lengths around 3500 km. Sometimes,
a time delay in their appearance between the blue and red wings of
3-5 s is evident, whereas, sometimes they are near simultaneous. In
some instances, features are observed to fade and then re-emerge at
the same location several tens of seconds later. Conclusions:
We provide the first statistical analysis of these spicules and suggest
that these observations can be interpreted as the line-of-sight (LOS)
movement of highly dynamic spicules moving in and out of the narrow 60
mÅ transmission filter that is used to observe in different parts of
the Hα line profile. The LOS velocity component of the observed fast
chromospheric features, manifested as Doppler shifts, are responsible
for their appearance in the red and blue wings of Hα line. Additional
work involving data at other wavelengths is required to investigate
the nature of their possible wave-like activity.

---------------------------------------------------------
Title: High Cadence Observations and Analysis of Spicular-type Events
Using CRISP Onboard SST
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.
2016ASPC..504..115S Altcode:
We present spectroscopic and imaging observations of apparent ultra-fast
spicule-like features observed with CRisp Imaging SpectroPolarimeter
(CRISP) at the Swedish 1-m Solar Telescope (SST). The data shows
spicules with an apparent velocity above 500 km s-1,
very short lifetimes of up to 20 s and length/height around 3500
km. The spicules are seen as dark absorption structures in the Hα
wings ±516 mÅ, ±774 mÅ and ±1032 mÅ which suddenly appear and
disappear from the FOV. These features show a time delay in their
appearance in the blue and red wings by 3-5 s. We suggest that their
appearance/disappearance is due to their Doppler motion in and out of
the 60 mÅ filter. See Fig. 1 for the evolution of the event at two
line positions.

---------------------------------------------------------
Title: Quiet-Sun Hα Transients and Corresponding Small-scale
Transition Region and Coronal Heating
Authors: Henriques, V. M. J.; Kuridze, D.; Mathioudakis, M.; Keenan,
F. P.
2016ApJ...820..124H Altcode: 2016arXiv160204820H
Rapid blue- and redshifted excursions (RBEs and RREs) are likely to
be the on-disk counterparts of Type II spicules. Recently, heating
signatures from RBEs/RREs have been detected in IRIS slit-jaw
images dominated by transition region (TR) lines around network
patches. Additionally, signatures of Type II spicules have been observed
in Atmospheric Imaging Assembly (AIA) diagnostics. The full-disk,
ever-present nature of the AIA diagnostics should provide us with
sufficient statistics to directly determine how important RBEs and RREs
are to the heating of the TR and corona. We find, with high statistical
significance, that at least 11% of the low coronal brightenings detected
in a quiet-Sun region in He II 304 Å can be attributed to either RBEs
or RREs as observed in Hα, and a 6% match of Fe IX 171 Å detected
events to RBEs or RREs with very similar statistics for both types
of Hα features. We took a statistical approach that allows for noisy
detections in the coronal channels and provides us with a lower, but
statistical significant, bound. Further, we consider matches based on
overlapping features in both time and space, and find strong visual
indications of further correspondence between coronal events and
co-evolving but non-overlapping, RBEs and RREs.

---------------------------------------------------------
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
2015ApJ...813..125K Altcode: 2015arXiv151001877K
The asymmetries observed in the line profiles of solar flares can
provide important diagnostics of the properties and dynamics of the
flaring atmosphere. In this paper the evolution of the Hα and Ca ii
λ8542 lines are studied using high spatial, temporal, and spectral
resolution ground-based observations of an M1.1 flare obtained with
the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
line profiles from the flare kernel shows excess emission in the red
wing (red asymmetry) before flare maximum and excess in the blue wing
(blue asymmetry) after maximum. However, the Ca ii λ8542 line does
not follow the same pattern, showing only a weak red asymmetry during
the flare. RADYN simulations are used to synthesize spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. We show that the red asymmetry observed in
Hα is not necessarily associated with plasma downflows, and the blue
asymmetry may not be related to plasma upflows. Indeed, we conclude
that the steep velocity gradients in the flaring chromosphere modify
the wavelength of the central reversal in the Hα line profile. The
shift in the wavelength of maximum opacity to shorter and longer
wavelengths generates the red and blue asymmetries, respectively.

---------------------------------------------------------
Title: The Dynamics of Rapid Redshifted and Blueshifted Excursions
in the Solar Hα Line
Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Erdélyi, R.;
Zaqarashvili, T. V.; Shelyag, S.; Keys, P. H.; Keenan, F. P.
2015ApJ...802...26K Altcode: 2015arXiv150106205K
We analyze high temporal and spatial resolution time-series of spectral
scans of the Hα line obtained with the CRisp Imaging SpectroPolarimeter
instrument mounted on the Swedish Solar Telescope. The data reveal
highly dynamic, dark, short-lived structures known as Rapid Redshifted
and Blueshifted Excursions (RREs, RBEs) that are on-disk absorption
features observed in the red and blue wings of spectral lines formed
in the chromosphere. We study the dynamics of RREs and RBEs by tracking
their evolution in space and time, measuring the speed of the apparent
motion, line of sight (LOS) Doppler velocity, and transverse velocity
of individual structures. A statistical study of their measured
properties shows that RREs and RBEs have similar occurrence rates,
lifetimes, lengths, and widths. They also display non-periodic,
nonlinear transverse motions perpendicular to their axes at speeds of
4-31 km s-1. Furthermore, both types of structures either
appear as high speed jets and blobs that are directed outwardly from
a magnetic bright point with speeds of 50-150 km s-1,
or emerge within a few seconds. A study of the different velocity
components suggests that the transverse motions along the LOS of
the chromospheric flux tubes are responsible for the formation and
appearance of these redshifted/blueshifted structures. The short
lifetime and fast disappearance of the RREs/RBEs suggests that, similar
to type II spicules, they are rapidly heated to transition region
or even coronal temperatures. We speculate that the Kelvin-Helmholtz
instability triggered by observed transverse motions of these structures
may be a viable mechanism for their heating.

---------------------------------------------------------
Title: Magnetohydrodynamic oscillations in chromospheric fine
structures
Authors: Kuridze, David
2014PhDT.......537K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Characteristics of Transverse Waves in Chromospheric Mottles
Authors: Kuridze, D.; Verth, G.; Mathioudakis, M.; Erdélyi, R.;
Jess, D. B.; Morton, R. J.; Christian, D. J.; Keenan, F. P.
2013ApJ...779...82K Altcode: 2013arXiv1310.3628K
Using data obtained by the high temporal and spatial resolution
Rapid Oscillations in the Solar Atmosphere instrument on the Dunn
Solar Telescope, we investigate at an unprecedented level of detail
transverse oscillations in chromospheric fine structures near the solar
disk center. The oscillations are interpreted in terms of propagating
and standing magnetohydrodynamic kink waves. Wave characteristics
including the maximum transverse velocity amplitude and the phase
speed are measured as a function of distance along the structure's
length. Solar magnetoseismology is applied to these measured parameters
to obtain diagnostic information on key plasma parameters (e.g.,
magnetic field, density, temperature, flow speed) of these localized
waveguides. The magnetic field strength of the mottle along the ~2 Mm
length is found to decrease by a factor of 12, while the local plasma
density scale height is ~280 ± 80 km.

---------------------------------------------------------
Title: Failed filament eruption inside a coronal mass ejection in
active region 11121
Authors: Kuridze, D.; Mathioudakis, M.; Kowalski, A. F.; Keys, P. H.;
Jess, D. B.; Balasubramaniam, K. S.; Keenan, F. P.
2013A&A...552A..55K Altcode: 2013arXiv1302.5931K
 Aims: We study the formation and evolution of a failed filament
eruption observed in NOAA active region 11121 near the southeast limb on
November 6, 2010. Methods: We used a time series of SDO/AIA 304,
171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as
ROSA and ISOON Hα images to study the erupting active region. 
Results: We identify coronal loop arcades associated with a quadrupolar
magnetic configuration, and show that the expansion and cancellation
of the central loop arcade system over the filament is followed by
the eruption of the filament. The erupting filament reveals a clear
helical twist and develops the same sign of writhe in the form of
inverse γ-shape. Conclusions: The observations support the
"magnetic breakout" process in which the eruption is triggered by
quadrupolar reconnection in the corona. We propose that the formation
mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic
helical kink instability. The eruption has failed because of the
large-scale, closed, overlying magnetic loop arcade that encloses
the active region. Movies are available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Observations of ubiquitous compressive waves in the Sun's
chromosphere
Authors: Morton, Richard J.; Verth, Gary; Jess, David B.; Kuridze,
David; Ruderman, Michael S.; Mathioudakis, Mihalis; Erdélyi, Robertus
2012NatCo...3.1315M Altcode: 2012NatCo...3E1315M; 2013arXiv1306.4124M
The details of the mechanism(s) responsible for the observed
heating and dynamics of the solar atmosphere still remain a
mystery. Magnetohydrodynamic waves are thought to have a vital role
in this process. Although it has been shown that incompressible
waves are ubiquitous in off-limb solar atmospheric observations,
their energy cannot be readily dissipated. Here we provide, for the
first time, on-disk observation and identification of concurrent
magnetohydrodynamic wave modes, both compressible and incompressible,
in the solar chromosphere. The observed ubiquity and estimated energy
flux associated with the detected magnetohydrodynamic waves suggest
the chromosphere is a vast reservoir of wave energy with the potential
to meet chromospheric and coronal heating requirements. We are also
able to propose an upper bound on the flux of the observed wave energy
that is able to reach the corona based on observational constraints,
which has important implications for the suggested mechanism(s) for
quiescent coronal heating.

---------------------------------------------------------
Title: Transverse Oscillations in Chromospheric Mottles
Authors: Kuridze, D.; Morton, R. J.; Erdélyi, R.; Dorrian, G. D.;
Mathioudakis, M.; Jess, D. B.; Keenan, F. P.
2012ApJ...750...51K Altcode: 2012arXiv1202.5697K
A number of recent investigations have revealed that transverse
waves are ubiquitous in the solar chromosphere. The vast majority
of these have been reported in limb spicules and active region
fibrils. We investigate long-lived, quiet-Sun, on-disk features such as
chromospheric mottles (jet-like features located at the boundaries of
supergranular cells) and their transverse motions. The observations
were obtained with the Rapid Oscillations in the Solar Atmosphere
instrument at the Dunn Solar Telescope. The data set is comprised
of simultaneous imaging in the Hα core, Ca II K, and G band of an
on-disk quiet-Sun region. Time-distance techniques are used to study
the characteristics of the transverse oscillations. We detect over
40 transverse oscillations in both bright and dark mottles, with
periods ranging from 70 to 280 s, with the most frequent occurrence
at ~165 s. The velocity amplitudes and transverse displacements
exhibit characteristics similar to limb spicules. Neighboring mottles
oscillating in-phase are also observed. The transverse oscillations
of individual mottles are interpreted in terms of magnetohydrodynamic
kink waves. Their estimated periods and damping times are consistent
with phase mixing and resonant mode conversion.

---------------------------------------------------------
Title: Small-scale Hα jets in the solar chromosphere
Authors: Kuridze, D.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.;
Christian, D. J.; Keenan, F. P.; Balasubramaniam, K. S.
2011A&A...533A..76K Altcode: 2011arXiv1108.1043K
 Aims: High temporal and spatial resolution observations from
the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength
imager on the Dunn Solar Telescope are used to study the velocities
of small-scale Hα jets in an emerging solar active region. Methods: The dataset comprises simultaneous imaging in the Hα
core, Ca ii K, and G band, together with photospheric line-of-sight
magnetograms. Time-distance techniques are employed to determine
projected plane-of-sky velocities. Results: The Hα images
are highly dynamic in nature, with estimated jet velocities as high
as 45 km s-1. These jets are one-directional, with their
origin seemingly linked to underlying Ca ii K brightenings and G-band
magnetic bright points. Conclusions: It is suggested that the
siphon flow model of cool coronal loops is suitable for interpreting our
observations. The jets are associated with small-scale explosive events,
and may provide a mass outflow from the photosphere to the corona.

---------------------------------------------------------
Title: Network Loop Oscillations with EIS/Hinode
Authors: Srivastava, A. K.; Kuridze, D.; Zaqarashvili, T. V.; Dwivedi,
B. N.; Rani, B.
2010ASSP...19..437S Altcode: 2009arXiv0903.0212S; 2010mcia.conf..437S
We analyze a time sequence of He II 256.32 Å images obtained with
EIS/Hinode, sampling a small magnetic loop in magnetic network. Wavelet
analysis indicates 11-min periodicity close to the loop apex. We
interpret this oscillation as forcing through upward leakage by
the fundamental acoustic eigenmode of the underlying field-free
cavity. The observed loop length corresponds to the value predicted
from this mechanism.

---------------------------------------------------------
Title: Acoustic oscillations in the field-free, gravitationally
stratified cavities under solar bipolar magnetic canopies
Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.;
Poedts, S.
2009A&A...505..763K Altcode: 2009arXiv0905.2302K
Aims: The main goal here is to study the dynamics of the gravitationally
stratified, field-free cavities in the solar atmosphere, located
under small-scale, cylindrical magnetic canopies, in response to
explosive events in the lower-lying regions (due to granulation,
small-scale magnetic reconnection, etc.). Methods: We derive
the two-dimensional Klein-Gordon equation for isothermal density
perturbations in cylindrical coordinates. The equation is first solved
by a standard normal mode analysis to obtain the free oscillation
spectrum of the cavity. Then, the equation is solved in the case of
impulsive forcing associated to a pressure pulse specified in the lower
lying regions. Results: The normal mode analysis shows that the
entire cylindrical cavity of granular dimensions tends to oscillate
with frequencies of 5-8 mHz and also with the atmospheric cut-off
frequency. Furthermore, the passage of a pressure pulse, excited
in the convection zone, sets up a wake in the cavity oscillating
with the same cut-off frequency. The wake oscillations can resonate
with the free oscillation modes, which leads to an enhanced observed
oscillation power. Conclusions: The resonant oscillations of
these cavities explain the observed power halos near magnetic network
cores and active regions.

---------------------------------------------------------
Title: Acoustic oscillations in a field-free cavity under solar
small-scale bipolar magnetic canopy
Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.;
Poedts, S.
2008AnGeo..26.2983K Altcode: 2008arXiv0801.2877K
Observations show the increase of high-frequency wave power near
magnetic network cores and active regions in the solar lower
atmosphere. This phenomenon can be explained by the interaction
of acoustic waves with a magnetic field. We consider small-scale,
bipolar, magnetic field canopy structure near the network cores and
active regions overlying field-free cylindrical cavities of the
photosphere. Solving the plasma equations we get the analytical
dispersion relation of acoustic oscillations in the field-free
cavity area. We found that the m=1 mode, where m is azimuthal wave
number, cannot be trapped under the canopy due to energy leakage
upwards. However, higher (m≥2) harmonics can be easily trapped
leading to the observed acoustic power halos under the canopy.

---------------------------------------------------------
Title: Intensity oscillations observed with Hinode near the south
pole of the Sun: leakage of low frequency magneto-acoustic waves
into the solar corona
Authors: Srivastava, A. K.; Kuridze, D.; Zaqarashvili, T. V.; Dwivedi,
B. N.
2008A&A...481L..95S Altcode: 2008arXiv0802.0571S
Aims: We study intensity oscillations in the solar chromosphere and
corona, above a quiet-Sun magnetic network. Methods: We analyse
the time series of He II 256.32 Å, Fe XI 188.23 Å and Fe XII 195.12
Å spectral lines, observed close to the south pole, by the EUV Imaging
Spectrometer (EIS), onboard Hinode. We use a standard wavelet tool,
to produce power spectra of intensity oscillations above the magnetic
network. Results: For all spectral lines, we detect intensity
oscillations of period of approximately seven minutes; and for the He
II 256.32 Å line only, we detect an intensity oscillation of period
of thirteen minutes, with a probability of approximately 96-98%,
which provides the most likely signature of magneto-acoustic wave
propagation above the network. Conclusions: We propose that
field-free cavity areas under bipolar magnetic canopies, in the
vicinity of a magnetic network, are likely to serve as resonators for
the magneto-acoustic waves. The cavities with photospheric sound-speed,
and granular dimensions, can produce waves with observed periods. These
waves may propagate upwards in the transition region/corona and cause
observed intensity oscillations.

---------------------------------------------------------
Title: Resonant energy conversion of 3-min intensity oscillations
into Alfvén waves in the solar atmosphere
Authors: Kuridze, D.; Zaqarashvili, T. V.
2008JASTP..70..351K Altcode: 2007astro.ph..3482K
Nonlinear coupling between 3-min oscillations and Alfvén waves in
the solar lower atmosphere is studied. Three-minute oscillations are
considered as acoustic waves trapped in a chromospheric cavity and
oscillating along transversally inhomogeneous vertical magnetic
field. It is shown that under the action of the oscillations
the temporal dynamics of Alfvén waves is governed by Mathieu
equation. Consequently, the harmonics of Alfvén waves with twice
period and wavelength of 3-min oscillations grow exponentially
in time near the layer where the sound and Alfvén speeds equal
i.e. cs[approximate]vA. Thus the 3-min oscillations are resonantly
absorbed by pure Alfvén waves near this resonant layer. The resonant
Alfvén waves may penetrate into the solar corona taking energy from
the chromosphere. Therefore the layer cs[approximate]vA may play a
role of energy channel for otherwise trapped acoustic oscillations.

---------------------------------------------------------
Title: Resonant Conversion of Standing Acoustic Oscillations Into
ALFVÉN Waves in the β~1 Region of the Solar Atmosphere
Authors: Kuridze, D.; Zaqarashvili, T. V.; Roberts, B.
2005ESASP.600E..89K Altcode: 2005dysu.confE..89K; 2005ESPM...11...89K; 2005astro.ph.10437K
We show that 5-minute acoustic oscillations may resonantly convert
into Alfv{é}n waves in the $\beta{\sim}1$ region of the solar
atmosphere. Considering the 5-minute oscillations as pumping standing
acoustic waves oscillating along unperturbed vertical magnetic
field, we find on solving the ideal MHD equations that amplitudes
of Alfv{é}n waves with twice the period and wavelength of acoustic
waves exponentially grow in time when the sound and Alfv{é}n speeds
are equal, i.e. $c_s \approx v_A$. The region of the solar atmosphere
where this equality takes place we call a {\it swing layer}. The
amplified Alfv{é}n waves may easily pass through the chromosphere
and transition region carrying the energy of p-modes into the corona.