henriques

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Author name code: henriques
ADS astronomy entries on 2022-09-14
=author:"Henriques, V.M.J." OR author:"Henriques, Vasco"

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Title: The Solar ALMA Science Archive (SALSA). First release, SALAT,
and FITS header standard
Authors: Henriques, Vasco M. J.; Jafarzadeh, Shahin; Guevara Gómez,
Juan Camilo; Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikołaj;
Haugan, Stein Vidar H.; Mohan, Atul
2022A&A...659A..31H Altcode: 2021arXiv210902374H
In December 2016, the Atacama Large Millimeter/submillimeter Array
(ALMA) carried out the first regular observations of the Sun. These
early observations and the reduction of the respective data posed a
challenge due to the novelty and complexity of observing the Sun with
ALMA. The difficulties with producing science-ready, time-resolved
imaging products in a format familiar to and usable by solar physicists
based on the measurement sets delivered by ALMA had limited the
availability of such data to this point. With the development of the
Solar ALMA Pipeline, it has now become possible to routinely reduce
such data sets. As a result, a growing number of science-ready solar
ALMA data sets are now offered in the form of the Solar ALMA Science
Archive (SALSA). So far, SALSA contains primarily time series of
single-pointing interferometric images at cadences of one or two
seconds, accompanied by the respective single-dish full-disc solar
images. The data arrays are provided in FITS format. We also present
the first version of a standardised header format that accommodates
future expansions and fits within the scope of other standards
including the ALMA Science Archive itself and SOLARNET. The headers
include information designed to aid the reproduction of the imaging
products from the raw data. Links to co-observations, if available,
with a focus on those of the Interface Region Imaging Spectrograph,
are also provided. SALSA is accompanied by the Solar ALMA Library of
Auxiliary Tools (SALAT), which contains Interactive Data Language and
Python routines for convenient loading and a quick-look analysis of
SALSA data. Movies associated to Figs. 3 and 4 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142291/olm">https://www.aanda.org</A>

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Title: Evidence of the multi-thermal nature of spicular
downflows. Impact on solar atmospheric heating
Authors: Bose, Souvik; Rouppe van der Voort, Luc; Joshi, Jayant;
Henriques, Vasco M. J.; Nóbrega-Siverio, Daniel; Martínez-Sykora,
Juan; De Pontieu, Bart
2021A&A...654A..51B Altcode: 2021arXiv210802153B
Context. Spectroscopic observations of the emission lines formed in the
solar transition region commonly show persistent downflows on the order
of 10−15 km s−1. The cause of such downflows, however, is
still not fully clear and has remained a matter of debate. Aims:
We aim to understand the cause of such downflows by studying the coronal
and transition region responses to the recently reported chromospheric
downflowing rapid redshifted excursions (RREs) and their impact on the
heating of the solar atmosphere. Methods: We have used two sets
of coordinated data from the Swedish 1 m Solar Telescope, the Interface
Region Imaging Spectrograph, and the Solar Dynamics Observatory for
analyzing the response of the downflowing RREs in the transition
region and corona. To provide theoretical support, we use an already
existing 2.5D magnetohydrodynamic simulation of spicules performed
with the Bifrost code. Results: We find ample occurrences of
downflowing RREs and show several examples of their spatio-temporal
evolution, sampling multiple wavelength channels ranging from the cooler
chromospheric to the hotter coronal channels. These downflowing features
are thought to be likely associated with the returning components of
the previously heated spicular plasma. Furthermore, the transition
region Doppler shifts associated with them are close to the average
redshifts observed in this region, which further implies that these
flows could (partly) be responsible for the persistent downflows
observed in the transition region. We also propose two mechanisms -
(i) a typical upflow followed by a downflow and (ii) downflows along a
loop -from the perspective of a numerical simulation that could explain
the ubiquitous occurrence of such downflows. A detailed comparison
between the synthetic and observed spectral characteristics reveals a
distinctive match and further suggests an impact on the heating of the
solar atmosphere. Conclusions: We present evidence that suggests
that at least some of the downflowing RREs are the chromospheric
counterparts of the transition region and lower coronal downflows. Movies associated to Figs. 1-3, 8, and 10 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141404/olm">https://www.aanda.org</A>

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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.

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Title: Signatures of ubiquitous magnetic reconnection in the deep
atmosphere of sunspot penumbrae
Authors: Rouppe van der Voort, Luc H. M.; Joshi, Jayant; Henriques,
Vasco M. J.; Bose, Souvik
2021A&A...648A..54R Altcode: 2021arXiv210111321R
Context. Ellerman bombs are regions with enhanced Balmer line wing
emission and mark magnetic reconnection in the deep solar atmosphere
in active regions and the quiet Sun. They are often found in regions
where opposite magnetic polarities are in close proximity. Recent
high-resolution observations suggest that Ellerman bombs are more
prevalent than previously thought. Aims: We aim to determine
the occurrence of Ellerman bombs in the penumbra of sunspots. 
Methods: We analyzed high spatial resolution observations of sunspots
in the Balmer Hα and Hβ lines as well as auxiliary continuum channels
obtained with the Swedish 1-m Solar Telescope and applied the k-means
clustering technique to systematically detect and characterize Ellerman
Bombs. Results: Features with all the defining characteristics of
Ellerman bombs are found in large numbers over the entire penumbra. The
true prevalence of these events is only fully appreciated in the Hβ
line due to the highest spatial resolution and lower chromospheric
opacity. We find that the penumbra hosts some of the highest Ellerman
bomb densities, surpassed only by the moat in the immediate surroundings
of the sunspot. Some penumbral Ellerman bombs show flame morphology
and rapid dynamical evolution. Many penumbral Ellerman bombs are fast
moving with typical speed of 3.7 km s−1 and sometimes more
than 10 km s−1. Many penumbral Ellerman bombs migrate from
the inner to the outer penumbra over hundreds of km, and some continue
moving beyond the outer penumbral boundary into the moat. Many penumbral
Ellerman bombs are found in the vicinity of regions with opposite
magnetic polarity. Conclusions: We conclude that reconnection
is a near continuous process in the low atmosphere of the penumbra of
sunspots that manifest in the form of penumbral Ellerman bombs. These
are so prevalent that they may be a major sink of sunspot magnetic
energy. Movies associated to Figs. 1 and 6 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202040171/olm">https://www.aanda.org</A>

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Title: Spicules and downflows in the solar chromosphere
Authors: Bose, Souvik; Joshi, Jayant; Henriques, Vasco M. J.; Rouppe
van der Voort, Luc
2021A&A...647A.147B Altcode: 2021arXiv210107829B
Context. High-speed downflows have been observed in the solar
transition region (TR) and lower corona for many decades. Despite
their abundance, it has been hard to find signatures of such downflows
in the solar chromosphere. Aims: In this work, we target
an enhanced network region which shows ample occurrences of rapid
spicular downflows in the Hα spectral line, which could potentially
be linked to high-speed TR downflowing counterparts. Methods:
We used the k-means algorithm to classify the spectral profiles of
on-disk spicules in Hα and Ca II K data observed from the Swedish
1 m Solar Telescope and employed an automated detection method based
on advanced morphological image processing operations to detect such
downflowing features, in conjunction with rapid blue-shifted and
red-shifted excursions (RBEs and RREs). Results: We report
the existence of a new category of RREs (termed as downflowing RRE)
for the first time that, contrary to earlier interpretation, are
associated with chromospheric field aligned downflows moving toward
the strong magnetic field regions. Statistical analysis performed
on nearly 20 000 RBEs and 15 000 RREs (including the downflowing
counterparts), which were detected in our 97 min long dataset, shows
that the downflowing RREs are very similar to RBEs and RREs except
for their oppositely directed plane-of-sky motion. Furthermore, we
also find that RBEs, RREs, and downflowing RREs can be represented
by a wide range of spectral profiles with varying Doppler offsets,
and Hα line core widths, both along and perpendicular to the spicule
axis, that causes them to be associated with multiple substructures
which evolve together. Conclusions: We speculate that these
rapid plasma downflows could well be the chromospheric counterparts
of the commonly observed TR downflows. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202040014/olm">https://www.aanda.org</A>

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Title: An overall view of temperature oscillations in the solar
chromosphere with ALMA
Authors: Jafarzadeh, S.; Wedemeyer, S.; Fleck, B.; Stangalini, M.;
Jess, D. B.; Morton, R. J.; Szydlarski, M.; Henriques, V. M. J.; Zhu,
X.; Wiegelmann, T.; Guevara Gómez, J. C.; Grant, S. D. T.; Chen,
B.; Reardon, K.; White, S. M.
2021RSPTA.37900174J Altcode: 2021RSTPA.379..174J; 2020arXiv201001918J
By direct measurements of the gas temperature, the Atacama Large
Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic
tool to study the solar chromosphere. Here, we present an overview
of the brightness-temperature fluctuations from several high-quality
and high-temporal-resolution (i.e. 1 and 2 s cadence) time series
of images obtained during the first 2 years of solar observations
with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz)
and 1.25 mm (239 GHz), respectively. The various datasets represent
solar regions with different levels of magnetic flux. We perform
fast Fourier and Lomb-Scargle transforms to measure both the spatial
structuring of dominant frequencies and the average global frequency
distributions of the oscillations (i.e. averaged over the entire field
of view). We find that the observed frequencies significantly vary from
one dataset to another, which is discussed in terms of the solar regions
captured by the observations (i.e. linked to their underlying magnetic
topology). While the presence of enhanced power within the frequency
range 3-5 mHz is found for the most magnetically quiescent datasets,
lower frequencies dominate when there is significant influence from
strong underlying magnetic field concentrations (present inside and/or
in the immediate vicinity of the observed field of view). We discuss
here a number of reasons which could possibly contribute to the power
suppression at around 5.5 mHz in the ALMA observations. However,
it remains unclear how other chromospheric diagnostics (with an
exception of Hα line-core intensity) are unaffected by similar
effects, i.e. they show very pronounced 3-min oscillations dominating
the dynamics of the chromosphere, whereas only a very small fraction
of all the pixels in the 10 ALMA datasets analysed here show peak power
near 5.5 mHz. This article is part of the Theo Murphy meeting issue
`High-resolution wave dynamics in the lower solar atmosphere'.

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Title: Transverse motions in sunspot super-penumbral fibrils
Authors: Morton, R. J.; Mooroogen, K.; Henriques, V. M. J.
2021RSPTA.37900183M Altcode: 2020arXiv201207394M
Sunspots have played a key role in aiding our understanding of
magnetohydrodynamic (MHD) wave phenomena in the Sun's atmosphere, and
it is well known they demonstrate a number of wave phenomena associated
with slow MHD modes. Recent studies have shown that transverse wave
modes are present throughout the majority of the chromosphere. Using
high-resolution Ca II 8542 Å observations from the Swedish Solar
Telescope, we provide the first demonstration that the chromospheric
super-penumbral fibrils, which span out from the sunspot, also show
ubiquitous transverse motions. We interpret these motions as transverse
waves, in particular the MHD kink mode. We compile the statistical
properties of over 2000 transverse motions to find distributions
for periods and amplitudes, finding they are broadly consistent with
previous observations of chromospheric transverse waves in quiet Sun
fibrils. The very presence of the waves in super-penumbral fibrils
raises important questions about how they are generated, and could
have implications for our understanding of how MHD wave energy is
transferred through the atmosphere of a sunspot. This article is
part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.

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Title: Downflowing umbral flashes as evidence of standing waves in
sunspot umbrae
Authors: Felipe, T.; Henriques, V. M. J.; de la Cruz Rodríguez, J.;
Socas-Navarro, H.
2021A&A...645L..12F Altcode: 2021arXiv210104188F
Context. Umbral flashes are sudden brightenings commonly visible
in the core of some chromospheric lines. Theoretical and numerical
modeling suggests that they are produced by the propagation of shock
waves. According to these models and early observations, umbral flashes
are associated with upflows. However, recent studies have reported
umbral flashes in downflowing atmospheres. Aims: We aim to
understand the origin of downflowing umbral flashes. We explore how
the existence of standing waves in the umbral chromosphere impacts the
generation of flashed profiles. Methods: We performed numerical
simulations of wave propagation in a sunspot umbra with the code
MANCHA. The Stokes profiles of the Ca II 8542 Å line were synthesized
with the NICOLE code. Results: For freely propagating waves,
the chromospheric temperature enhancements of the oscillations are
in phase with velocity upflows. In this case, the intensity core of
the Ca II 8542 Å atmosphere is heated during the upflowing stage of
the oscillation. However, a different scenario with a resonant cavity
produced by the sharp temperature gradient of the transition region
leads to chromospheric standing oscillations. In this situation,
temperature fluctuations are shifted backward and temperature
enhancements partially coincide with the downflowing stage of the
oscillation. In umbral flash events produced by standing oscillations,
the reversal of the emission feature is produced when the oscillation
is downflowing. The chromospheric temperature keeps increasing while
the atmosphere is changing from a downflow to an upflow. During the
appearance of flashed Ca II 8542 Å cores, the atmosphere is upflowing
most of the time, and only 38% of the flashed profiles are associated
with downflows. Conclusions: We find a scenario that remarkably
explains the recent empirical findings of downflowing umbral flashes
as a natural consequence of the presence of standing oscillations
above sunspot umbrae.

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Title: Umbral chromospheric fine structure and umbral flashes modelled
as one: The corrugated umbra
Authors: Henriques, Vasco M. J.; Nelson, Chris J.; Rouppe van der
Voort, Luc H. M.; Mathioudakis, Mihalis
2020A&A...642A.215H Altcode: 2020arXiv200805482H
Context. The chromosphere of the umbra of sunspots features an
assortment of dynamic fine structures that are poorly understood and
often studied separately. Small-scale umbral brightenings (SSUBs),
umbral microjets, spikes or short dynamic fibrils (SDFs), and umbral
dark fibrils are found in any observation of the chromosphere with
sufficient spatial resolution performed at the correct umbral flash
stage and passband. Understanding these features means understanding
the dynamics of the umbral chromosphere. Aims: We aim to fully
understand the dynamics of umbral chromosphere through analysis of the
relationships between distinct observed fine features and to produce
complete models that explain both spectral profiles and the temporal
evolution of the features. We seek to relate such understanding to
umbral flashes. Methods: We studied the spatial and spectral
co-evolution of SDFs, SSUBs, and umbral flashes in Ca II 8542 Å
spectral profiles. We produced models that generate the spectral
profiles for all classes of features using non-local thermodynamic
equilibrium radiative transfer with a recent version of the NICOLE
inversion code. Results: We find that both bright SSUBs and dark
SDF structures are described with a continuous feature in the parameter
space that is distinct from the surroundings even in pixel-by-pixel
inversions. We find a phase difference between such features and
umbral flashes in both inverted line-of-sight velocities and timing
of the brightenings. For umbral flashes themselves we resolve,
for the first time in inversion-based semi-empirical modelling,
the pre-flash downflows, post-flash upflows, and the counter-flows
present during the umbral flash phase. We further present a simple
time-dependent cartoon model that explains the dynamics and spectral
profiles of both fine structure, dark and bright, and umbral flashes
in umbral chromospheres. Conclusions: The similarity of the
profiles between the brightenings and umbral flashes, the pattern of
velocities obtained from the inversions, and the phase relationships
between the structures all lead us to put forward that all dynamic
umbral chromospheric structures observed to this date are a locally
delayed or locally early portion of the oscillatory flow pattern that
generates flashes, secondary to the steepening large-scale acoustic
waves at its source. Essentially, SSUBs are part of the same shock or
merely compression front responsible for the spatially larger umbral
flash phenomenon, but out of phase with the broader oscillation.

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Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.

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Title: Characterization and formation of on-disk spicules in the Ca
II K and Mg II k spectral lines (Corrigendum)
Authors: Bose, Souvik; Henriques, Vasco M. J.; Joshi, Jayant; Rouppe
van der Voort, Luc
2020A&A...637C...1B Altcode:
No abstract at ADS

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Title: Multi-scale observations of thermal non-equilibrium cycles
in coronal loops
Authors: Froment, C.; Antolin, P.; Henriques, V. M. J.; Kohutova,
P.; Rouppe van der Voort, L. H. M.
2020A&A...633A..11F Altcode: 2019arXiv191109710F
Context. Thermal non-equilibrium (TNE) is a phenomenon that can
occur in solar coronal loops when the heating is quasi-constant and
highly-stratified. Under such heating conditions, coronal loops undergo
cycles of evaporation and condensation. The recent observations of
ubiquitous long-period intensity pulsations in coronal loops and their
relationship with coronal rain have demonstrated that understanding the
characteristics of TNE cycles is an essential step in constraining
the circulation of mass and energy in the corona. Aims:
We report unique observations with the Solar Dynamics Observatory
(SDO) and the Swedish 1-m Solar Telescope (SST) that link the captured
thermal properties across the extreme spatiotemporal scales covered by
TNE processes. Methods: Within the same coronal loop bundle,
we captured 6 h period coronal intensity pulsations in SDO/AIA and
coronal rain observed off-limb in the chromospheric Hα and Ca
II K spectral lines with SST/CRISP and SST/CHROMIS. We combined
a multi-thermal analysis of the cycles with AIA and an extensive
spectral characterisation of the rain clumps with the SST. 
Results: We find clear evidence of evaporation-condensation cycles in
the corona which are linked with periodic coronal rain showers. The
high-resolution spectroscopic instruments at the SST reveal the
fine-structured rain strands and allow us to probe the cooling
phase of one of the cycles down to chromospheric temperatures. 
Conclusions: These observations reinforce the link between long-period
intensity pulsations and coronal rain. They also demonstrate the
capability of TNE to shape the dynamics of active regions on the large
scales as well as on the smallest scales currently resolvable. Movies associated to Figs. 3-5, and 8 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936717/olm">https://www.aanda.org</A>

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Title: High-resolution spectropolarimetric observations of the
temporal evolution of magnetic fields in photospheric bright points
Authors: Keys, P. H.; Reid, A.; Mathioudakis, M.; Shelyag, S.;
Henriques, V. M. J.; Hewitt, R. L.; Del Moro, D.; Jafarzadeh, S.;
Jess, D. B.; Stangalini, M.
2020A&A...633A..60K Altcode: 2019arXiv191108436K
Context. Magnetic bright points (MBPs) are dynamic, small-scale
magnetic elements often found with field strengths of the order of a
kilogauss within intergranular lanes in the photosphere. Aims:
Here we study the evolution of various physical properties inferred from
inverting high-resolution full Stokes spectropolarimetry data obtained
from ground-based observations of the quiet Sun at disc centre. Methods: Using automated feature-tracking algorithms, we studied
300 MBPs and analysed their temporal evolution as they evolved to
kilogauss field strengths. These properties were inferred using
both the NICOLE and SIR Stokes inversion codes. We employ similar
techniques to study radiative magnetohydrodynamical simulations
for comparison with our observations. Results: Evidence was
found for fast (∼30-100 s) amplification of magnetic field strength
(by a factor of 2 on average) in MBPs during their evolution in our
observations. Similar evidence for the amplification of fields is seen
in our simulated data. Conclusions: Several reasons for the
amplifications were established, namely, strong downflows preceding
the amplification (convective collapse), compression due to granular
expansion and mergers with neighbouring MBPs. Similar amplification of
the fields and interpretations were found in our simulations, as well
as amplification due to vorticity. Such a fast amplification will have
implications for a wide array of topics related to small-scale fields
in the lower atmosphere, particularly with regard to propagating wave
phenomena in MBPs.

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Title: Characterization and formation of on-disk spicules in the Ca
II K and Mg II k spectral lines
Authors: Bose, Souvik; Henriques, Vasco M. J.; Joshi, Jayant; Rouppe
van der Voort, Luc
2019A&A...631L...5B Altcode: 2019arXiv191005533B
We characterize, for the first time, type-II spicules in Ca II K 3934
Å using the CHROMIS instrument at the Swedish 1 m Solar Telescope. We
find that their line formation is dominated by opacity shifts with
the K3 minimum best representing the velocity of the
spicules. The K2 features are either suppressed by the
Doppler-shifted K3 or enhanced via increased contribution
from the lower layers, leading to strongly enhanced but unshifted
K2 peaks, with widening towards the line core as consistent
with upper-layer opacity removal via Doppler-shift. We identify spicule
spectra in concurrent IRIS Mg II k 2796Å observations with very
similar properties. Using our interpretation of spicule chromospheric
line formation, we produce synthetic profiles that match observations.

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Title: The magnetic properties of photospheric magnetic bright points
with high-resolution spectropolarimetry
Authors: Keys, Peter H.; Reid, Aaron; Mathioudakis, Mihalis; Shelyag,
Sergiy; Henriques, Vasco M. J.; Hewitt, Rebecca L.; Del Moro, Dario;
Jafarzadeh, Shahin; Jess, David B.; Stangalini, Marco
2019MNRAS.488L..53K Altcode: 2019MNRAS.tmpL..98K; 2019MNRAS.tmpL..95K; 2019arXiv190607687K
Magnetic bright points (MBPs) are small-scale magnetic elements
ubiquitous across the solar disc, with the prevailing theory suggesting
that they form due to the process of convective collapse. Employing a
unique full Stokes spectropolarimetric data set of a quiet Sun region
close to disc centre obtained with the Swedish Solar Telescope, we look
at general trends in the properties of magnetic bright points. In total
we track 300 MBPs in the data set and we employ NICOLE inversions to
ascertain various parameters for the bright points such as line-of-sight
magnetic field strength and line-of-sight velocity, for comparison. We
observe a bimodal distribution in terms of maximum magnetic field
strength in the bright points with peaks at ∼480 G and ∼1700 G,
although we cannot attribute the kilogauss fields in this distribution
solely to the process of convective collapse. Analysis of MURAM
simulations does not return the same bimodal distribution. However,
the simulations provide strong evidence that the emergence of new flux
and diffusion of this new flux play a significant role in generating
the weak bright point distribution seen in our observations.

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Title: Semi-empirical model atmospheres for the chromosphere of the
sunspot penumbra and umbral flashes
Authors: Bose, Souvik; Henriques, Vasco M. J.; Rouppe van der Voort,
Luc; Pereira, Tiago M. D.
2019A&A...627A..46B Altcode: 2019arXiv190508264B
Context. The solar chromosphere and the lower transition region
are believed to play a crucial role in the heating of the solar
corona. Models that describe the chromosphere (and the lower transition
region), accounting for its highly dynamic and structured character
are, so far, found to be lacking. This is partly due to the breakdown
of complete frequency redistribution (CRD) in the chromospheric
layers and also because of the difficulty in obtaining complete sets
of observations that adequately constrain the solar atmosphere at
all relevant heights. Aims: We aim to obtain semi-empirical
model atmospheres that reproduce the features of the Mg II h&amp;k
line profiles that sample the middle chromosphere with focus on a
sunspot. Methods: We used spectropolarimetric observations
of the Ca II 8542 Å spectra obtained with the Swedish 1 m Solar
Telescope and used NICOLE inversions to obtain semi-empirical model
atmospheres for different features in and around a sunspot. These
were used to synthesize Mg II h&amp;k spectra using the RH1.5D
code, which we compared with observations taken with the Interface
Region Imaging Spectrograph (IRIS). Results: Comparison of
the synthetic profiles with IRIS observations reveals that there
are several areas, especially in the penumbra of the sunspot,
where most of the observed Mg II h&amp;k profiles are very well
reproduced. In addition, we find that supersonic hot down-flows,
present in our collection of models in the umbra, lead to synthetic
profiles that agree well with the IRIS Mg II h&amp;k profiles, with
the exception of the line core. Conclusions: We put forward
and make available four semi-empirical model atmospheres. Two for
the penumbra, reflecting the range of temperatures obtained for the
chromosphere, one for umbral flashes, and a model representative of
the quiet surroundings of a sunspot. Data of semi-empirical model
atmospheres are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A46">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A46</A>.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Sunspot penumbra and umbral
flashes models (Bose+, 2019)
Authors: Bose, S.; Henriques, V. M. J.; Rouppe van der Voort, L.;
Pereira, T. M. D.
2019yCat..36270046B Altcode:
The tables included in this paper describes the stratification of
atmospheric parameters for the cool and the hot penumbra, umbral flash
and the quiet surrounding respectively as a function of geometric
height and optical depth. (4 data files).

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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.

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Title: Penumbral Waves Driving Solar Fan-shaped Chromospheric Jets
Authors: Reid, A.; Henriques, V. M. J.; Mathioudakis, M.; Samanta, T.
2018ApJ...855L..19R Altcode:
We use Hα imaging spectroscopy taken via the Swedish 1 m Solar
Telescope to investigate the occurrence of fan-shaped jets at the solar
limb. We show evidence for near-simultaneous photospheric reconnection
at a sunspot edge leading to the jets appearance, with upward velocities
of 30 km s-1, and extensions up to 8 Mm. The brightening at
the base of the jets appears recurrent, with a periodicity matching that
of the nearby sunspot penumbra, implying running penumbral waves could
be the driver of the jets. The jets’ constant extension velocity
implies that a driver counteracting solar gravity exists, possibly
as a result of the recurrent reconnection erupting material into the
chromosphere. These jets also show signatures in higher temperature
lines captured from the Solar Dynamics Observatory, indicating a very
hot jet front, leaving behind optically thick cool plasma in its wake.

---------------------------------------------------------
Title: Penumbral Waves driving Solar chromospheric fan-shaped jets
Authors: Reid, A.; Henriques, V. M. J.; Mathioudakis, M.; Samanta, T.
2018arXiv180207537R Altcode:
We use H$\alpha$ imaging spectroscopy taken via the Swedish 1-m Solar
Telescope (SST) to investigate the occurrence of fan-shaped jets at
the solar limb. We show evidence for near-simultaneous photospheric
reconnection at a sunspot edge leading to the jets appearance, with
upward velocities of 30\ks, and extensions up to 8~Mm. The brightening
at the base of the jets appears recurrent, with a periodicity matching
that of the nearby sunspot penumbra, implying running penumbral waves
could be the driver of the jets. The jets' constant extension velocity
implies that a driver counteracting solar gravity exists, possibly
as a result of the recurrent reconnection erupting material into the
chromosphere. These jets also show signatures in higher temperature
lines captured from the Solar Dynamics Observatory (SDO), indicating
a very hot jet front, leaving behind optically thick cool plasma in
its wake.

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Title: Dynamics of internetwork chromospheric fibrils: Basic
properties and magnetohydrodynamic kink waves
Authors: Mooroogen, K.; Morton, R. J.; Henriques, V.
2017A&A...607A..46M Altcode: 2017arXiv170803500M
 Aims: Current observational instruments are now providing
data with the necessary temporal and spatial cadences required to
examine highly dynamic, fine-scale magnetic structures in the solar
atmosphere. Using the spectroscopic imaging capabilities of the
Swedish Solar Telescope, we aim to provide the first investigation on
the nature and dynamics of elongated absorption features (fibrils)
observed in Hα in the internetwork. Methods: We observe and
identify a number of internetwork fibrils, which form away from the
kilogauss, network magnetic flux, and we provide a synoptic view
on their behaviour. The internetwork fibrils are found to support
wave-like behaviour, which we interpret as magnetohydrodynamic (MHD)
kink waves. The properties of these waves, that is, amplitude, period,
and propagation speed, are measured from time-distance diagrams and we
attempt to exploit them via magneto-seismology in order to probe the
variation of plasma properties along the wave-guides. Results:
We found that the Internetwork (IN) fibrils appear, disappear, and
re-appear on timescales of tens of minutes, suggesting that they
are subject to repeated heating. No clear photospheric footpoints
for the fibrils are found in photospheric magnetograms or Hα wing
images. However, we suggest that they are magnetised features as the
majority of them show evidence of supporting propagating MHD kink
waves, with a modal period of 120 s. Additionally, one IN fibril is
seen to support a flow directed along its elongated axis, suggesting
a guiding field. The wave motions are found to propagate at speeds
significantly greater than estimates for typical chromospheric sound
speeds. Through their interpretation as kink waves, the measured speeds
provide an estimate for local average Alfvén speeds. Furthermore,
the amplitudes of the waves are also found to vary as a function of
distance along the fibrils, which can be interpreted as evidence of
stratification of the plasma in the neighbourhood of the IN fibril.

---------------------------------------------------------
Title: The formation of small-scale umbral brightenings in sunspot
atmospheres
Authors: Nelson, C. J.; Henriques, V. M. J.; Mathioudakis, M.; Keenan,
F. P.
2017A&A...605A..14N Altcode: 2017arXiv170505617N
Context. Sunspot atmospheres have been shown to be highly inhomogeneous
hosting both quasi-stable and transient features, such as small-scale
umbral brightenings (previously named "umbral micro-jets") and dark
fibril-like events. Aims: We seek to understand the morphological
properties and formation mechanisms of small-scale umbral brightenings
(analogous to umbral micro-jets). In addition, we aim to understand
whether links between these events and short dynamic fibrils,
umbral flashes, and umbral dots can be established. Methods:
A Swedish 1 m Solar Telescope (SST) filtergram time-series sampling
the Ca II H line and a CRisp Imaging Spectro-Polarimeter (SST/CRISP)
full-Stokes 15-point Ca II 8542 Å line scan dataset were used. The
spatial resolutions of these datasets are close to 0.1” and 0.18”
with cadences of 1.4 s and 29 s, respectively. These data allowed
us to construct light-curves, plot line profiles, and to perform
a weak-field approximation in order to infer the magnetic field
strength. Results: The average lifetime and lengths of the 54
small-scale brightenings identified in the sunspot umbra are found
to be 44.2 s (σ = 20 s) and 0.56” (σ = 0.14”), respectively. The
spatial positioning and morphological evolution of these events in
Ca II H filtergrams was investigated finding no evidence of parabolic
or ballistic profiles nor a preference for co-spatial formation with
umbral flashes. Line scans in Ca II 8542 Å and the presence of Stokes
V profile reversals provided evidence that these events could form in a
similar manner to umbral flashes in the chromosphere (I.e. through the
formation of shocks either due to the steepening of localised wavefronts
or due to the impact of returning material from short dynamic fibrils,
a scenario we find evidence for). The application of the weak-field
approximation indicated that changes in the line-of-sight magnetic
field were not responsible for the modifications to the line profile
and suggested that thermodynamic effects are, in fact, the actual
cause of the increased emission. Finally, a sub-set of small-scale
brightenings were observed to form at the foot-points of short dynamic
fibrils. Conclusions: The small-scale umbral brightenings studied
here do not appear to be jet-like in nature. Instead they appear to be
evidence of shock formation in the lower solar atmosphere. We found
no correlation between the spatial locations where these events were
observed and the occurrence of umbral dots and umbral flashes. These
events have lifetimes and spectral signatures comparable to umbral
flashes and are located at the footpoints of short dynamic fibrils,
during or at the end of the red-shifted stage. It is possible that
these features form due to the shocking of fibrilar material in the
lower atmosphere upon its return under gravity.

---------------------------------------------------------
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: A Hot Downflowing Model Atmosphere for Umbral Flashes and
the Physical Properties of Their Dark Fibrils
Authors: Henriques, V. M. J.; Mathioudakis, M.; Socas-Navarro, H.;
de la Cruz Rodríguez, J.
2017ApJ...845..102H Altcode: 2017arXiv170605311H
We perform non-LTE inversions in a large set of umbral flashes,
including the dark fibrils visible within them, and in the quiescent
umbra by using the inversion code NICOLE on a set of full Stokes
high-resolution Ca II λ8542 observations of a sunspot at disk
center. We find that the dark structures have Stokes profiles that are
distinct from those of the quiescent and flashed regions. They are
best reproduced by atmospheres that are more similar to the flashed
atmosphere in terms of velocities, even if with reduced amplitudes. We
also find two sets of solutions that finely fit the flashed profiles:
a set that is upflowing, featuring a transition region that is deeper
than in the quiescent case and preceded by a slight dip in temperature,
and a second solution with a hotter atmosphere in the chromosphere but
featuring downflows close to the speed of sound at such heights. Such
downflows may be related, or even dependent, on the presence of coronal
loops, rooted in the umbra of sunspots, as is the case in the region
analyzed. Similar loops have been recently observed to have supersonic
downflows in the transition region and are consistent with the earlier
“sunspot plumes,” which were invariably found to display strong
downflows in sunspots. Finally, we find, on average, a magnetic field
reduction in the flashed areas, suggesting that the shock pressure is
moving field lines in the upper layers.

---------------------------------------------------------
Title: Chromospheric Inversions of a Micro-flaring Region
Authors: Reid, A.; Henriques, V.; Mathioudakis, M.; Doyle, J. G.;
Ray, T.
2017ApJ...845..100R Altcode: 2017arXiv170700029R
We use spectropolarimetric observations of the Ca II 8542 Å line, taken
from the Swedish 1 m Solar Telescope, in an attempt to recover dynamic
activity in a micro-flaring region near a sunspot via inversions. These
inversions show localized mean temperature enhancements of ∼1000
K in the chromosphere and upper photosphere, along with co-spatial
bi-directional Doppler shifting of 5-10 km s-1. This heating
also extends along a nearby chromospheric fibril, which is co-spatial
to 10-15 km s-1 downflows. Strong magnetic flux cancellation
is also apparent in one of the footpoints, and is concentrated in the
chromosphere. This event more closely resembles that of an Ellerman
Bomb, though placed slightly higher in the atmosphere than what is
typically observed.

---------------------------------------------------------
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: The Effects of Transients on Photospheric and Chromospheric
Power Distributions
Authors: Samanta, T.; Henriques, V. M. J.; Banerjee, D.; Krishna
Prasad, S.; Mathioudakis, M.; Jess, D.; Pant, V.
2016ApJ...828...23S Altcode: 2016arXiv160406289S
We have observed a quiet-Sun region with the Swedish 1 m Solar Telescope
equipped with the CRISP Imaging SpectroPolarimeter. High-resolution,
high-cadence, Hα line scanning images were taken to observe
different layers of the solar atmosphere from the photosphere to upper
chromosphere. We study the distribution of power in different period
bands at different heights. Power maps of the upper photosphere
and the lower chromosphere show suppressed power surrounding the
magnetic-network elements, known as “magnetic shadows.” These also
show enhanced power close to the photosphere, traditionally referred
to as “power halos.” The interaction between acoustic waves and
inclined magnetic fields is generally believed to be responsible
for these two effects. In this study we explore whether small-scale
transients can influence the distribution of power at different
heights. We show that the presence of transients, like mottles, Rapid
Blueshifted Excursions (RBEs), and Rapid Redshifted Excursions (RREs),
can strongly influence the power maps. The short and finite lifetime of
these events strongly affects all power maps, potentially influencing
the observed power distribution. We show that Doppler-shifted transients
like RBEs and RREs that occur ubiquitously can have a dominant effect
on the formation of the power halos in the quiet Sun. For magnetic
shadows, transients like mottles do not seem to have a significant
effect on the power suppression around 3 minutes, and wave interaction
may play a key role here. Our high-cadence observations reveal that
flows, waves, and shocks manifest in the presence of magnetic fields
to form a nonlinear magnetohydrodynamic system.

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Title: Magnetic Flux Cancellation in Ellerman Bombs
Authors: Reid, A.; Mathioudakis, M.; Doyle, J. G.; Scullion, E.;
Nelson, C. J.; Henriques, V.; Ray, T.
2016ApJ...823..110R Altcode: 2016arXiv160307100R
Ellerman Bombs (EBs) are often found to be co-spatial with bipolar
photospheric magnetic fields. We use Hα imaging spectroscopy along with
Fe I 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope
(SST), combined with data from the Solar Dynamic Observatory, to study
EBs and the evolution of the local magnetic fields at EB locations. EBs
are found via an EB detection and tracking algorithm. Using NICOLE
inversions of the spectropolarimetric data, we find that, on average,
(3.43 ± 0.49) × 1024 erg of stored magnetic energy
disappears from the bipolar region during EB burning. The inversions
also show flux cancellation rates of 1014-1015
Mx s-1 and temperature enhancements of 200 K at the detection
footpoints. We investigate the near-simultaneous flaring of EBs due to
co-temporal flux emergence from a sunspot, which shows a decrease in
transverse velocity when interacting with an existing, stationary area
of opposite polarity magnetic flux, resulting in the formation of the
EBs. We also show that these EBs can be fueled further by additional,
faster moving, negative magnetic flux regions.

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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: 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: 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: Stable umbral chromospheric structures
Authors: Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman,
D.; Gallagher, P. T.; Keenan, F. P.
2015A&A...574A.131H Altcode: 2014arXiv1412.6100H
 Aims: We seek to understand the morphology of the chromosphere in
sunspot umbra. We investigate if the horizontal structures observed
in the spectral core of the Ca II H line are ephemeral visuals
caused by the shock dynamics of more stable structures, and examine
their relationship with observables in the H-alpha line. 
Methods: Filtergrams in the core of the Ca II H and H-alpha lines
as observed with the Swedish 1-m Solar Telescope are employed. We
utilise a technique that creates composite images and tracks the
flash propagation horizontally. Results: We find 0.̋15 wide
horizontal structures, in all of the three target sunspots, for every
flash where the seeing is moderate to good. Discrete dark structures
are identified that are stable for at least two umbral flashes, as well
as systems of structures that live for up to 24 min. We find cases of
extremely extended structures with similar stability, with one such
structure showing an extent of 5”. Some of these structures have a
correspondence in H-alpha, but we were unable to find a one-to-one
correspondence for every occurrence. If the dark streaks are formed at
the same heights as umbral flashes, there are systems of structures
with strong departures from the vertical for all three analysed
sunspots. Conclusions: Long-lived Ca II H filamentary horizontal
structures are a common and likely ever-present feature in the umbra
of sunspots. If the magnetic field in the chromosphere of the umbra
is indeed aligned with the structures, then the present theoretical
understanding of the typical umbra needs to be revisited. Movies
associated to Figs. 3 and 4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424664/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Ca II H sunspot tomography from the photosphere to the
chromosphere
Authors: Henriques, V. M. J.; Kiselman, D.
2013A&A...557A...5H Altcode:
 Aims: We aim at gaining insight into the thermal properties of
different small-scale structures related to sunspots. Methods: We
use filtergrams in the Ca ii H filter at the Swedish 1-m Solar Telescope
to study the relationship between fine structure at different heights
in a sunspot. Results: The methods for destretching and aligning
the different image data work well. The magnetic spine structure in
the outer parts of the sunspot penumbra is found to be associated with
higher intensities in the Ca ii H wing passbands but with less steep
vertical temperature gradients. Dark lanes in a light bridge behave
very similarly to dark cores in penumbral filaments. Fibril structures
are seen in the line-core images over the umbra and penumbra. 
Conclusions: The observations add support to the idea that penumbral
filaments, light bridges, and umbral dots are caused by similar
processes of overturning convection. Observations in the Ca ii H &amp;
K wings are a promising observable, complementing others, for testing
simulation results for sunspots at high spatial resolution.

---------------------------------------------------------
Title: Opposite polarity field with convective downflow and its
relation to magnetic spines in a sunspot penumbra
Authors: Scharmer, G. B.; de la Cruz Rodriguez, J.; Sütterlin, P.;
Henriques, V. M. J.
2013A&A...553A..63S Altcode: 2012arXiv1211.5776S
We discuss NICOLE inversions of Fe i 630.15 nm and 630.25 nm Stokes
spectra from a sunspot penumbra recorded with the CRISP imaging
spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial
resolution close to 0.15 arcsec. We report on narrow, radially extended
lanes of opposite polarity field, located at the boundaries between
areas of relatively horizontal magnetic field (the intra-spines) and
much more vertical field (the spines). These lanes harbor convective
downflows of about 1 km s-1. The locations of these downflows
close to the spines agree with predictions from the convective gap
model (the "gappy penumbra") proposed six years ago, and more recent
three-dimensional magnetohydrodynamic simulations. We also confirm the
existence of strong convective flows throughout the entire penumbra,
showing the expected correlation between temperature and vertical
velocity, and having vertical root mean square velocities of about
1.2 km s-1.

---------------------------------------------------------
Title: Three-dimensional mapping of fine structure in the solar
atmosphere
Authors: Henriques, Vasco M. J.
2013PhDT.........2H Altcode:
The effects on image formation through a tilted interference filter
in a converging beam are investigated and an adequate compensation
procedure is established. A method that compensates for small-scale
seeing distortions is also developed with the aim of co-aligning
non-simultaneous solar images from different passbands. These techniques
are applied to data acquired with a narrow tiltable filter at the
Swedish 1-meter Solar Telescope. Tilting provides a way to scan the
wing of the Ca II H line. The resulting images are used to map the
temperature stratification and vertical temperature gradients in a
solar active region containing a sunspot at a resolution approaching
0”10. The data are compared with hydro-dynamical quiet sun models
and magneto-hydrodynamic models of plage. The comparison gives
credence to the observational techniques, the analysis methods, and
the simulations. Vertical temperature gradients are lower in magnetic
structures than in non-magnetic. Line-of-sight velocities and
magnetic field properties in the penumbra of the same sunspot are
estimated using the CRISP imaging spectropolarimeter and straylight
compensation adequate for the data. These reveal a pattern of upflows
and downflows throughout the entire penumbra including the interior
penumbra. A correlation with intensity positively identifies these
flows as convective in origin. The vertical convective signatures are
observed everywhere, but the horizontal Evershed flow is observed to
be confined to areas of nearly horizontal magnetic field. The
relation between temperature gradient and total circular polarization
in magnetically sensitive lines is investigated in different structures
of the penumbra. Penumbral dark cores are prominent in total circular
polarization and temperature gradient maps. These become longer and
more contiguous with increasing height. Dark fibril structures over
bright regions are observed in the Ca II H line core, above both the
umbra and penumbra.

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Title: Three-dimensional mapping of fine structure in the solar
atmosphere
Authors: Henriques, Vasco Manuel de Jorge
2013PhDT.......405H Altcode:
No abstract at ADS

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Title: Three-dimensional temperature mapping of solar photospheric
fine structure using Ca ii H filtergrams
Authors: Henriques, V. M. J.
2012A&A...548A.114H Altcode: 2012arXiv1210.4168H
Context. The wings of the Ca ii H and K lines provide excellent
photospheric temperature diagnostics. At the Swedish 1-m Solar
Telescope (SST), the blue wing of Ca ii H is scanned with a narrowband
interference filter mounted on a rotation stage. This provides up
to 0farcs10 spatial resolution filtergrams at high cadence that are
concurrent with other diagnostics at longer wavelengths. Aims:
The aim is to develop observational techniques that provide photospheric
temperature stratification at the highest spatial resolution possible
and use them to compare simulations and observations at different
heights. Methods: We use filtergrams in the Ca ii H blue
wing that were obtained with a tiltable interference filter at the
SST. Synthetic observations are produced from three-dimensional (3D)
hydro and magneto-hydrodynamic numerical simulations and degraded
to match the observations. The temperature structure obtained from
applying the method to the synthetic data is compared with the
known structure in the simulated atmospheres and with observations
of an active region. Cross-correlation techniques using restored
non-simultaneous continuum images are used to reduce high-altitude,
small-scale seeing signal introduced from the non-simultaneity of
the frames when differentiating data. Results: Temperature
extraction using high-resolution filtergrams in the Ca ii H blue wing
works reasonably well when tested with simulated 3D atmospheres. The
cross-correlation technique successfully compensates for the problem
of small-scale seeing differences and provides a measure of the
spurious signal from this source in differentiated data. Synthesized
data from the simulated atmospheres (including pores) match well the
observations morphologically at different observed heights and in
vertical temperature gradients.

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Title: SST/CRISP observations of convective flows in a sunspot
penumbra
Authors: Scharmer, G. B.; Henriques, V. M. J.
2012A&A...540A..19S Altcode: 2011arXiv1109.1301S
Context. Recent discoveries of intensity correlated downflows in the
interior of a sunspot penumbra provide direct evidence for overturning
convection, adding to earlier strong indications of convection from
filament dynamics observed far from solar disk center, and supporting
recent simulations of sunspots. Aims: Using spectropolarimetric
observations obtained at a spatial resolution approaching 0.1 arcsec
with the Swedish 1-m Solar Telescope (SST) and its spectropolarimeter
CRISP, we investigate whether the convective downflows recently
discovered in the C i line at 538.03 nm can also be detected in the
wings of the Fe i line at 630.15 nm. Methods: We make azimuthal
fits of the measured LOS velocities in the core and wings of the
538 nm and 630 nm lines to disentangle the vertical and horizontal
flows. To investigate how these depend on the continuum intensity,
the azimuthal fits are made separately for each intensity bin. By
using spatially high-pass filtered measurements of the LOS component of
the magnetic field, the flow properties are determined separately for
magnetic spines (relatively strong and vertical field) and inter-spines
(weaker and more horizontal field). Results: The dark convective
downflows discovered recently in the 538.03 nm line are evident also
in the 630.15 nm line, and have similar strength. This convective
signature is the same in spines and inter-spines. However, the strong
radial (Evershed) outflows are found only in the inter-spines. 
Conclusions: At the spatial resolution of the present SST/CRISP data,
the small-scale intensity pattern seen in continuum images is strongly
related to a convective up/down flow pattern that exists everywhere
in the penumbra. Earlier failures to detect the dark convective
downflows in the interior penumbra can be explained by inadequate
spatial resolution in the observed data.

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Title: A tilted interference filter in a converging beam
Authors: Löfdahl, M. G.; Henriques, V. M. J.; Kiselman, D.
2011A&A...533A..82L Altcode: 2011arXiv1108.1234L
Context. Narrow-band interference filters can be tuned toward shorter
wavelengths by tilting them from the perpendicular to the optical
axis. This can be used as a cheap alternative to real tunable filters,
such as Fabry-Pérot interferometers and Lyot filters. At the Swedish
1-meter Solar Telescope, such a setup is used to scan through the
blue wing of the Ca ii H line. Because the filter is mounted in a
converging beam, the incident angle varies over the pupil, which
causes a variation of the transmission over the pupil, different for
each wavelength within the passband. This causes broadening of the
filter transmission profile and degradation of the image quality. Aims: We want to characterize the properties of our filter, at
normal incidence as well as at different tilt angles. Knowing the
broadened profile is important for the interpretation of the solar
images. Compensating the images for the degrading effects will improve
the resolution and remove one source of image contrast degradation. In
particular, we need to solve the latter problem for images that are
also compensated for blurring caused by atmospheric turbulence. 
Methods: We simulate the process of image formation through a tilted
interference filter in order to understand the effects. We test the
hypothesis that they are separable from the effects of wavefront
aberrations for the purpose of image deconvolution. We measure the
filter transmission profile and the degrading PSF from calibration
data. Results: We find that the filter transmission profile
differs significantly from the specifications. We demonstrate how to
compensate for the image-degrading effects. Because the filter tilt
effects indeed appear to be separable from wavefront aberrations in a
useful way, this can be done in a final deconvolution, after standard
image restoration with Multi-Frame Blind Deconvolution/Phase Diversity
based methods. We illustrate the technique with real data.

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Title: Detection of Convective Downflows in a Sunspot Penumbra
Authors: Scharmer, G. B.; Henriques, V. M. J.; Kiselman, D.; de la
Cruz Rodríguez, J.
2011Sci...333..316S Altcode:
The fine structure and dynamics of sunspots and the strong outflow in
their outer filamentary part—the penumbra—have puzzled astronomers
for more than a century. Recent theoretical models and three-dimensional
numerical simulations explain the penumbral filaments and their
radiative energy output as the result of overturning convection. Here,
we describe the detection of ubiquitous, relatively dark downward
flows of up to 1 kilometer per second (km/s) in the interior penumbra,
using imaging spectropolarimetric data from the Swedish 1-meter Solar
Telescope. The dark downflows are omnipresent in the interior penumbra,
distinguishing them from flows in arched flux tubes, and are associated
with strong (3 to 3.5 km/s) radial outflows. They are thus part of a
penumbral convective flow pattern, with the Evershed flow representing
the horizontal component of that convection.

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Title: Photospheric Temperatures from Ca IIH
Authors: Henriques, V. M. J.; Kiselman, D.; van Noort, M.
2010ASSP...19..511H Altcode: 2010mcia.conf..511H
The temperature stratification in the upper photosphere can be extracted
from Ca II H&amp;K spectrograms following Shine and Linsky (1974)
by assuming LTE, the Eddington-Barbier approximation, hydrostatic
equilibrium, and that Ca II is mostly in the ground state. Rouppe van
der Voort (2002) confirmed that these assumptions were solid for a wide
range in the Ca IIK wings and further developed the method including
forward computation using MULTI (Carlsson 1986).

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Title: Temperature stratification in the Sun's photosphere in high
horizontal resolution using Ca II H filtergrams.
Authors: Henriques, V. M. J.; Kiselman, D.
2009MmSAI..80..639H Altcode:
A method to extract the temperature stratification in the Sun's
photosphere using filtergrams is presented along with some high
resolution results. The data was acquired with the Swedish 1-m Solar
Telescope (SST) using a tunable filter in the Ca II H blue wing. Each
full scan is completed in the order of seconds thus allowing for
the full resolution of the SST and reasonable depth sampling to be
obtained simultaneously in a shorter time than that of the evolution
time scale of the photosphere. We test the quality of the method by
applying it to a set of synthetic images (obtained through radiative
transfer on 3D HD and MHD simulation snapshots followed by degradation)
and comparing the output with the known 3D simulated atmosphere. Fine
structure around bright points becomes evident in both the temperature
gradient maps computed from a set of test observations and synthetic
images obtained from MHD simulations.

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Title: Spectropolarimetry of Sunspots at 0.16 ARCSEC resolution
Authors: Scharmer, G.; Henriques, V.; Hillberg, T.; Kiselman, D.;
Löfdahl, M.; Narayan, G.; Sütterlin, P.; van Noort, M.; de la Cruz
Rodríguez, J.
2008ESPM...12..2.5S Altcode:
We present first observations of sunspots with the imaging
spectropolarimeter CRISP, recently installed at the Swedish 1-m
Solar Telescope (SST) on La Palma. This spectropolarimeter is based
on a high-fidelity dual Fabry-Perot filter system. Two liquid
crystals and a polarizing beam splitter are used to reduce seeing
induced I,Q,U,V crosstalk by simultaneously recording images with
two 1kx1k back-illuminated Sarnoff CCD's. A third CCD simultaneously
records broadband images through the pre-filter of the FPI filter
system, allowing image reconstruction and co-alignment of images of
different polarization states and at different wavelengths in Zeeman
sensitive spectral lines. The first data, recorded in April 2008,
demonstrate the capability of this system to record high cadence,
high S/N polarimetric data with a spatial resolution at or close to
the diffraction limit of the SST at 630 nm, 0.16 arcsec. We discuss
the analysis of first spectropolarimetric data for sunspots, based on
Milne-Eddington inversion techniques.

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Title: Temperature structure from Ca II H wing inversions
Authors: Henriques, V.; van Noort Kiselman, M. D.
2008ESPM...12.2.76H Altcode:
A method in development to extract temperature at different depths
from the Ca II H&amp;K lines using filtergrams is presented along
with preliminary inversion results. The inversions give information
up to a height of 200-300 km. We make use of the Swedish 1-m
Solar Telescope (SST) blue filter setup which allows for simultaneous
observations in four filter positions including a 1-Å tunable filter
that scans through the Ca H blue wing.