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Author name code: murabito
ADS astronomy entries on 2022-09-14
author:Murabito, Mariarita
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Title: Investigating of the nature of magnetic oscillations associated
with FIP effect
Authors: Murabito, Mariarita; Jafarzadeh, Shahin; Van Driel-Gesztelyi,
Lidia; Ermolli, Ilaria; Baker, Deborah; Brooks, David; Long, David;
Jess, David; Valori, Gherardo; Stangalini, Marco
2022cosp...44.2591M Altcode:
Observations of the photosphere, chromosphere, and corona combined with
magnetic field modeling of one of the biggest sunspots of the 24 solar
cycle, revealed that regions of high FIP bias plasma in the corona
were magnetically linked to the locations of the intrinsic magnetic
oscillations in the solar chromosphere. In order to characterize
the driver of the oscillations, we analyzed the relation between
the spatial distribution of the magnetic wave power and the overall
field geometry and plasma parameters obtained from the multi-height
spectropolarimetric non-local thermodynamic equilibrium (NLTE)
inversions. In correspondence with the locations where the magnetic
wave energy is observed at chromospheric heights, we found evidence
in support of locally excited acoustic waves that, after crossing the
equipartition layer located close to the umbra-penumbra boundary at
photospheric heights, are converted into magnetic-like waves. These
results indicate a direct connection between sunspot chromospheric
activity and observable changes in coronal plasma composition,
demonstrating the power of high resolution, multi-height studies of the
solar atmosphere that will become the gold standard in the era of DKIST.
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Title: The umbral filament of active region NOAA 12529
Authors: Guglielmino, Salvatore Luigi; Romano, Paolo; Zuccarello,
Francesca; Murabito, Mariarita; Ruiz Cobo, Basilio
2022cosp...44.2453G Altcode:
Umbral filaments are elongated, filamentary bright structures inside
sunspot umbrae, which differ in morphology, magnetic configuration,
and evolution from light bridges usually observed in sunspots. We
investigated an umbral filament (UF) observed in the umbra of the giant
leading sunspot of active region NOAA 12529, analyzing high-resolution
observations taken in the photosphere with the spectropolarimeter
aboard the \textit{Hinode} satellite and in the upper chromosphere and
transition region with the \textit{IRIS} telescope. We recognize in
the UF the presence of a strong horizontal field larger than 2500 G,
a significant portion of the UF with opposite polarity with respect
to the surroundings, and filaments in the upper atmospheric layers
corresponding to the UF in the photosphere. These findings suggest
that this UF is the photospheric manifestation of a flux rope hanging
above the sunspot and forming penumbral-like filaments within the
umbra via magneto-convection.
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Title: The identification of magnetic perturbations in the solar
atmosphere
Authors: Stangalini, Marco; Jafarzadeh, Shahin; Baker, Deborah; Jess,
David; Murabito, Mariarita; Valori, Gherardo
2022cosp...44.2590S Altcode:
Magneto-hydrodynamic (MHD) waves and, in particular, magnetic
perturbations associated with specific wave modes are thought to be
important mechanisms not only for the heating of the outer layers of
the Sun's atmosphere, but also for the elemental abundance anomaly
observed in the corona. High resolution spectropolarimetry is nowadays
progressively extending to the upper layers of the solar atmosphere,
and this provides invaluable insight into MHD wave processes up to
chromospheric heights. However, the identification of real magnetic
perturbations remains a difficult task due to a number of spurious
effects that can mimic the signals associated with them. In this
contribution we will show a novel approach to the identification
of real magnetic oscillations potentially linked to FIP and discuss
proxies to be used in statistical analyses.
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Title: IBIS-A: The IBIS data Archive. High-resolution observations
of the solar photosphere and chromosphere with contextual data
Authors: Ermolli, Ilaria; Giorgi, Fabrizio; Murabito, Mariarita;
Stangalini, Marco; Guido, Vincenzo; Molinaro, Marco; Romano, Paolo;
Guglielmino, Salvatore L.; Viavattene, Giorgio; Cauzzi, Gianna;
Criscuoli, Serena; Reardon, Kevin P.; Tritschler, Alexandra
2022A&A...661A..74E Altcode: 2022arXiv220209946E
Context. The IBIS data Archive (IBIS-A) stores data acquired with
the Interferometric BIdimensional Spectropolarimeter (IBIS), which
was operated at the Dunn Solar Telescope of the US National Solar
Observatory from June 2003 to June 2019. The instrument provided series
of high-resolution narrowband spectropolarimetric imaging observations
of the photosphere and chromosphere in the range 5800-8600 Å and
co-temporal broadband observations in the same spectral range and
with the same field of view as for the polarimetric data. <BR />
Aims: We present the data currently stored in IBIS-A, as well as the
interface utilized to explore such data and facilitate its scientific
exploitation. To this end, we also describe the use of IBIS-A data
in recent and undergoing studies relevant to solar physics and
space weather research. <BR /> Methods: IBIS-A includes raw and
calibrated observations, as well as science-ready data. The latter
comprise maps of the circular, linear, and net circular polarization,
and of the magnetic and velocity fields derived for a significant
fraction of the series available in the archive. IBIS-A furthermore
contains links to observations complementary to the IBIS data, such
as co-temporal high-resolution observations of the solar atmosphere
available from the instruments onboard the Hinode and IRIS satellites,
and full-disk multi-band images from INAF solar telescopes. <BR />
Results: IBIS-A currently consists of 30 TB of data taken with IBIS
during 28 observing campaigns performed in 2008 and from 2012 to 2019
on 159 days. Of the observations, 29% are released as Level 1 data
calibrated for instrumental response and compensated for residual seeing
degradation, while 10% of the calibrated data are also available as
Level 1.5 format as multi-dimensional arrays of circular, linear, and
net circular polarization maps, and line-of-sight velocity patterns;
81% of the photospheric calibrated series present Level 2 data with
the view of the magnetic and velocity fields of the targets, as derived
from data inversion with the Very Fast Inversion of the Stokes Vector
code. Metadata and movies of each calibrated and science-ready series
are also available to help users evaluate observing conditions. <BR />
Conclusions: IBIS-A represents a unique resource for investigating
the plasma processes in the solar atmosphere and the solar origin of
space weather events. The archive currently contains 454 different
series of observations. A recently undertaken effort to preserve
IBIS observations is expected to lead in the future to an increase in
the raw measurements and the fraction of processed data available in
IBIS-A. <P />Research supported by the H2020 SOLARNET grant no. 824135.
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Title: The Importance of Horizontal Poynting Flux in the Solar
Photosphere
Authors: Silva, Suzana S. A.; Murabito, Mariarita; Jafarzadeh, Shahin;
Stangalini, Marco; Verth, Gary; Ballai, Istvan; Fedun, Viktor
2022ApJ...927..146S Altcode: 2022arXiv220301221S
The electromagnetic energy flux in the lower atmosphere of the Sun is a
key tool to describe the energy balance of the solar atmosphere. Current
investigations on energy flux in the solar atmosphere focus primarily
on the vertical electromagnetic flux through the photosphere, ignoring
the Poynting flux in other directions and its possible contributions to
local heating. Based on a realistic Bifrost simulation of a quiet-Sun
(coronal hole) atmosphere, we find that the total electromagnetic energy
flux in the photosphere occurs mainly parallel to the photosphere,
concentrating in small regions along intergranular lanes. Thereby,
it was possible to define a proxy for this energy flux based on
only variables that can be promptly retrieved from observations,
namely, horizontal velocities of the small-scale magnetic elements
and their longitudinal magnetic flux. Our proxy accurately describes
the actual Poynting flux distribution in the simulations, with the
electromagnetic energy flux reaching 10<SUP>10</SUP> erg cm<SUP>-2</SUP>
s<SUP>-1</SUP>. To validate our findings, we extended the analysis
to SUNRISE/IMaX data. First, we show that Bifrost realistically
describes photospheric quiet-Sun regions, as the simulation presents
similar distributions for line-of-sight magnetic flux and horizontal
velocity field. Second, we found very similar horizontal Poynting flux
proxy distributions for the simulated photosphere and observational
data. Our results also indicate that the horizontal Poynting flux in the
observations is considerably larger than the vertical electromagnetic
flux from previous observational estimates. Therefore, our analysis
confirms that the electromagnetic energy flux in the photosphere
is mainly horizontal and is most intense in localized regions along
intergranular lanes.
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Title: Large scale coherent magnetohydrodynamic oscillations in
a sunspot
Authors: Stangalini, M.; Verth, G.; Fedun, V.; Aldhafeeri, A. A.;
Jess, D. B.; Jafarzadeh, S.; Keys, P. H.; Fleck, B.; Terradas, J.;
Murabito, M.; Ermolli, I.; Soler, R.; Giorgi, F.; MacBride, C. D.
2022NatCo..13..479S Altcode:
Although theoretically predicted, the simultaneous excitation of
several resonant modes in sunspots has not been observed. Like any
harmonic oscillator, a solar magnetic flux tube can support a variety
of resonances, which constitute the natural response of the system
to external forcing. Apart from a few single low order eigenmodes
in small scale magnetic structures, several simultaneous resonant
modes were not found in extremely large sunspots. Here we report
the detection of the largest-scale coherent oscillations observed
in a sunspot, with a spectrum significantly different from the Sun's
global acoustic oscillations, incorporating a superposition of many
resonant wave modes. Magnetohydrodynamic numerical modeling agrees
with the observations. Our findings not only demonstrate the possible
excitation of coherent oscillations over spatial scales as large as
30-40 Mm in extreme magnetic flux regions in the solar atmosphere,
but also paves the way for their diagnostic applications in other
astrophysical contexts.
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Title: Investigating the origin of magnetic perturbations associated
with the FIP Effect
Authors: Murabito, M.; Stangalini, M.; Baker, D.; Valori, G.; Jess,
D. B.; Jafarzadeh, S.; Brooks, D. H.; Ermolli, I.; Giorgi, F.; Grant,
S. D. T.; Long, D. M.; van Driel-Gesztelyi, L.
2021A&A...656A..87M Altcode: 2021arXiv210811164M
Recently, magnetic oscillations were detected in the chromosphere
of a large sunspot and found to be linked to the coronal locations
where a first ionization potential (FIP) effect was observed. In
an attempt to shed light on the possible excitation mechanisms
of these localized waves, we further investigate the same data
by focusing on the relation between the spatial distribution of
the magnetic wave power and the overall field geometry and plasma
parameters obtained from multi-height spectropolarimetric non-local
thermodynamic equilibrium (NLTE) inversions of IBIS data. We find,
in correspondence with the locations where the magnetic wave energy
is observed at chromospheric heights, that the magnetic fields have
smaller scale heights, meaning faster expansions of the field lines,
which ultimately results in stronger vertical density stratification
and wave steepening. In addition, the acoustic spectrum of the
oscillations at the locations where magnetic perturbations are
observed is broader than that observed at other locations, which
suggests an additional forcing driver to the p-modes. Analysis of the
photospheric oscillations in the sunspot surroundings also reveals
a broader spectrum between the two opposite polarities of the active
region (the leading spot and the trailing opposite polarity plage),
and on the same side where magnetic perturbations are observed in
the umbra. We suggest that strong photospheric perturbations between
the two polarities are responsible for this broader spectrum of
oscillations, with respect to the p-mode spectrum, resulting in locally
excited acoustic waves that, after crossing the equipartition layer,
located close to the umbra-penumbra boundary at photopheric heights,
are converted into magnetic waves and steepen due to the strong
density gradient. <P />Movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141504/olm">https://www.aanda.org</A>
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Title: On horizontal Poynting flux in the solar photosphere
Authors: Silva, Suzana; Murabito, Mariarita; Jafarzadeh, Shahin;
Stangalini, Marco; Verth, Gary; Ballai, Istvan; Fedun, Viktor
2021AGUFMSH44A..03S Altcode:
Describing the solar atmospheric energy balance and transport is an
essential step to understanding the high temperatures of the upper
atmosphere. This work analyses the 3D electromagnetic energy flux in
the lower atmosphere by combining Bifrost radiative MHD simulations
and Sunrise/IMaX data. Based on a simulated quiet Sun atmosphere, it
was found that only a minor fraction of the Poynting flux propagates
upwards in the photosphere. Most of the total electromagnetic energy
flows parallel to the solar surface, concentrating energy in small
regions along the intergranular lanes. The dominance of the horizontal
component of the electromagnetic energy flux allows an approximation for
the horizontal Poynting flux, which is based solely on the horizontal
velocity and the vertical magnetic field. The proxy to the horizontal
Poynting flux provides a very similar distribution of the total Poynting
flux and can describe the total flux for most of the photosphere with a
small relative error, <30%, in regions with an intense concentration
of electromagnetic energy. The results of the numerical data analysis
were validated by using observational data. First, it was shown that
both Bifrost and IMAX/sunrise data presents similar distributions
for line-of-sight magnetic field and velocity field, indicating
that the simulation realistically describes a quiet Sun region. The
horizontal Poynting flux proxy provided very similar distributions for
the numerical and observational data, which is considerably larger
than previous observational estimates for upwards electromagnetic
flux. Thereby, those findings corroborate that the electromagnetic
energy flux in the photosphere is mainly parallel to the solar surface
and can be properly described by approximated Poynting flux, based only
on the horizontal plasma flow and the vertical magnetic field. The
results also indicate that small scale intergranular motion may be
important to describe the properties of Poynting flux. Therefore,
further investigations based on the high-resolution data from DKIST
will be important for a valuable description of the energy transport
in the lower atmosphere.
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Title: Penumbral decay observed in active region NOAA 12585
Authors: Murabito, M.; Guglielmino, S. L.; Ermolli, I.; Romano, P.;
Jafarzadeh, S.; Rouppe van der Voort, L. H. M.
2021A&A...653A..93M Altcode: 2021arXiv210604936M
Context. The physical conditions leading the sunspot penumbra
decay are poorly understood so far. <BR /> Aims: We investigate the
photospheric magnetic and velocity properties of a sunspot penumbra
during the decay phase to advance the current knowledge of the
conditions leading to this process. <BR /> Methods: A penumbral
decay was observed with the CRISP instrument at the Swedish 1 m
Solar Telescope on 2016 September 4 and 5 in the active region NOAA
12585. During these days, full-Stokes spectropolarimetric scans
along the Fe I 630 nm line pair were acquired over more than one
hour. We inverted these observations with the VFISV code to obtain
the evolution of the magnetic and velocity properties. We complement
the study with data from instruments on board the Solar Dynamics
Observatory and Hinode space missions. <BR /> Results: The studied
penumbra disappears progressively in time and space. The magnetic
flux evolution seems to be linked to the presence of moving magnetic
features (MMFs). Decreasing Stokes V signals are observed. Evershed
flows and horizontal fields were detected even after the disappearance
of the penumbral sector. <BR /> Conclusions: The analyzed penumbral
decay seems to result from the interaction between opposite polarity
fields in type III MMFs and penumbra, while the presence of overlying
canopies regulates the evolution in the different penumbral
sectors. <P />Movies associated with Fig. 6 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141034/olm">https://www.aanda.org</A>
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Title: A novel approach to identify resonant MHD wave modes in solar
pores and sunspot umbrae: B − ω analysis
Authors: Stangalini, M.; Jess, D. B.; Verth, G.; Fedun, V.; Fleck, B.;
Jafarzadeh, S.; Keys, P. H.; Murabito, M.; Calchetti, D.; Aldhafeeri,
A. A.; Berrilli, F.; Del Moro, D.; Jefferies, S. M.; Terradas, J.;
Soler, R.
2021A&A...649A.169S Altcode: 2021arXiv210311639S
The umbral regions of sunspots and pores in the solar photosphere are
generally dominated by 3 mHz oscillations, which are due to p-modes
penetrating the magnetic region. In these locations, wave power is
also significantly reduced with respect to the quiet Sun. However,
here we study a pore where not only is the power of the oscillations
in the umbra comparable to, or even larger than, that of the quiet
Sun, but the main dominant frequency is not 3 mHz as expected, but
instead 5 mHz. By combining Doppler velocities and spectropolarimetry
and analysing the relationship between magnetic field strength and
frequency, the resultant B − ω diagram reveals distinct ridges that
are remarkably clear signatures of resonant magneto-hydrodynamic (MHD)
oscillations confined within the pore umbra. We demonstrate that these
modes, in addition to velocity oscillations, are also accompanied
by magnetic oscillations, as predicted from MHD theory. The novel
technique of B − ω analysis proposed in this article opens up
an exciting new avenue for identifying MHD wave modes in the umbral
regions of both pores and sunspots.
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Title: Analysis of Pseudo-Lyapunov Exponents of Solar Convection
Using State-of-the-Art Observations
Authors: Viavattene, Giorgio; Murabito, Mariarita; Guglielmino,
Salvatore L.; Ermolli, Ilaria; Consolini, Giuseppe; Giorgi, Fabrizio;
Jafarzadeh, Shahin
2021Entrp..23..413V Altcode: 2021arXiv210316980V
The solar photosphere and the outer layer of the Sun's interior are
characterized by convective motions, which display a chaotic and
turbulent character. In this work, we evaluated the pseudo-Lyapunov
exponents of the overshooting convective motions observed on the Sun's
surface by using a method employed in the literature to estimate
those exponents, as well as another technique deduced from their
definition. We analyzed observations taken with state-of-the-art
instruments at ground- and space-based telescopes, and we particularly
benefited from the spectro-polarimetric data acquired with the
Interferometric Bidimensional Spectrometer, the Crisp Imaging
SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following
previous studies in the literature, we computed maps of four quantities
which were representative of the physical properties of solar plasma in
each observation, and estimated the pseudo-Lyapunov exponents from the
residuals between the values of the quantities computed at any point
in the map and the mean of values over the whole map. In contrast to
previous results reported in the literature, we found that the computed
exponents hold negative values, which are typical of a dissipative
regime, for all the quantities derived from our observations. The values
of the estimated exponents increase with the spatial resolution of
the data and are almost unaffected by small concentrations of magnetic
field. Finally, we showed that similar results were also achieved by
estimating the exponents from residuals between the values at each
point in maps derived from observations taken at different times. The
latter estimation technique better accounts for the definition of
these exponents than the method employed in previous studies.
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Title: Spectropolarimetric fluctuations in a sunspot chromosphere
Authors: Stangalini, M.; Baker, D.; Valori, G.; Jess, D. B.;
Jafarzadeh, S.; Murabito, M.; To, A. S. H.; Brooks, D. H.; Ermolli,
I.; Giorgi, F.; MacBride, C. D.
2021RSPTA.37900216S Altcode: 2020arXiv200905302S
The instrumental advances made in this new era of 4 m class solar
telescopes with unmatched spectropolarimetric accuracy and sensitivity
will enable the study of chromospheric magnetic fields and their
dynamics with unprecedented detail. In this regard, spectropolarimetric
diagnostics can provide invaluable insight into magneto-hydrodynamic
(MHD) wave processes. MHD waves and, in particular, Alfvénic
fluctuations associated with particular wave modes were recently
recognized as important mechanisms not only for the heating of the outer
layers of the Sun's atmosphere and the acceleration of the solar wind,
but also for the elemental abundance anomaly observed in the corona
of the Sun and other Sun-like stars (also known as first ionization
potential) effect. Here, we take advantage of state-of-the-art and
unique spectropolarimetric Interferometric BIdimensional Spectrometer
observations to investigate the relation between intensity and circular
polarization (CP) fluctuations in a sunspot chromosphere. Our results
show a clear link between the intensity and CP fluctuations in a patch
which corresponds to a narrow range of magnetic field inclinations. This
suggests the presence of Alfvénic perturbations in the sunspot. <P
/>This article is part of the Theo Murphy meeting issue `High-resolution
wave dynamics in the lower solar atmosphere'.
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Title: IBIS2.0: The new Interferometric BIdimensional Spectrometer
Authors: Ermolli, Ilaria; Cirami, Roberto; Calderone, Giorgio; Del
Moro, Dario; Romano, Paolo; Viavattene, Giorgio; Coretti, Igor; Giorgi,
Fabrizio; Baldini, Veronica; Di Marcantonio, Paolo; Giovannelli, Luca;
Guglielmino, Salvatore Luigi; Murabito, Mariarita; Pedichini, Fernando;
Piazzesi, Roberto; Aliverti, Matteo; Redaelli, Edoardo Maria Alberto;
Berrilli, Francesco; Zuccarello, Francesca
2020SPIE11447E..0ZE Altcode:
We present the IBIS2.0 project, which aims to upgrade and to install
the Interferometric BIdimensional Spectrometer at the solar Vacuum Tower
Telescope (Tenerife, Spain) after its disassembling from the Dunn Solar
Telescope (New Mexico, USA). The instrument is undergoing a hardware and
software revision that will allow it to perform new spectropolarimetric
measurements of the solar atmosphere at high spatial, spectral and
temporal resolution in coordination with other ground- and space-based
instruments. Here we present the new opto-mechanical layout and control
system designed for the instrument, and describe future steps.
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Title: Restoring Process of Sunspot Penumbra
Authors: Romano, P.; Murabito, M.; Guglielmino, S. L.; Zuccarello,
F.; Falco, M.
2020ApJ...899..129R Altcode: 2020arXiv200609746R
We describe the disappearance of a sector of sunspot penumbra and its
restoring process observed in the preceding sunspot of active region
NOAA 12348. The evolution of the magnetic field and the plasma flows
supports the idea that the penumbra forms due to a change of inclination
of the magnetic field of the canopy. Moving magnetic features have
been observed during the disintegration phase of that sector of sunspot
penumbra. During the restoring phase we have not observed any magnetic
flux emergence around the sunspot. The restoring process of the penumbra
sector completed in about 72 hr and it was accompanied by the transition
from the counter-Evershed flow to the classical Evershed flow. The
inversion of photospheric spectropolarimetric measurements taken by the
Interferometric Bidimensional Spectroscopic Instrument (IBIS) allowed
us to reconstruct how the uncombed configuration of the magnetic field
forms during the new settlement of the penumbra, i.e., the vertical
component of the magnetic field seems to be progressively replaced by
some horizontal field lines, corresponding to the intraspines.
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Title: Unveiling the magnetic nature of chromospheric vortices
Authors: Murabito, Mariarita; Shetye, Juie; Stangalini, Marco;
Verwichte, Erwin; Arber, Tony; Ermolli, Ilaria; Giorgi, Fabrizio;
Goffrey, Tom
2020A&A...639A..59M Altcode: 2020arXiv200613776M
Context. Vortex structures in the Sun's chromosphere are believed to
channel energy between different layers of the solar atmosphere. <BR
/> Aims: We investigate the nature and dynamics of two small-scale
quiet-Sun rotating structures in the chromosphere. <BR /> Methods:
We analysed two chromospheric structures that show clear rotational
patterns in spectropolarimetric observations taken with the
Interferometric Bidimensional Spectrometer at the Ca II 8542 Å
line. <BR /> Results: We present the detection of spectropolarimetric
signals that manifest the magnetic nature of rotating structures in
the chromosphere. Our observations show two long-lived structures
of plasma that each rotate clockwise inside a 10 arcsec<SUP>2</SUP>
quiet-Sun region. Their circular polarisation signals are five to
ten times above the noise level. Line-of-sight Doppler velocity and
horizontal velocity maps from the observations reveal clear plasma flows
at and around the two structures. A magnetohydrodynamics simulation
shows these two structures are plausibly magnetically connected. Wave
analysis suggests that the observed rotational vortex pattern could be
due to a combination of slow actual rotation and a faster azimuthal
phase speed pattern of a magnetoacoustic mode. <BR /> Conclusions:
Our results imply that the vortex structures observed in the Sun's
chromosphere are magnetic in nature and that they can be connected
locally through the chromosphere <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038360/olm">https://www.aanda.org</A>
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Title: The penumbral solar filaments from the photosphere to the
chromosphere
Authors: Murabito, M.; Ermolli, I.; Giorgi, F.; Stangalini, M.;
Guglielmino, S. L.; Jafarzadeh, S.; Socas-Navarro, H.; Romano, P.;
Zuccarello, F.
2020JPhCS1548a2017M Altcode:
The magnetic field structure of sunspots above the photosphere remain
poorly understood due to limitations in observations and the complexity
of these atmospheric layers. In this regard, we studied the large
isolated sunspot (70”× 80”) located in the active region NOAA
12546 with spectro-polarimetric measurements acquired along the Fe I
617.3 nm and Ca II 854.2 nm lines with the IBIS/DST instrument, under
excellent seeing conditions lasting more than three hours. Using the
Non Local Thermodynamic Equilibrium inversion code we inverted both
line measurements simultaneously to retrieve the three-dimensional
magnetic and thermal structure of the penumbral region from the
bottom of the photosphere to the middle chromosphere. The analysis
of data acquired at spectral ranges unexplored allow us to show clear
evidence of the spine and intra-spine structure of the magnetic field at
chromospheric heights. In particular, we found a peak-to-peak variations
of the magnetic field strength and inclination of about 200 G and 10°
chromospheric heights, respectively, and of about 300 G and 20° in the
photosphere. We also investigated the structure of the magnetic field
gradient in the penumbra along the vertical and azimuthal directions,
confirming previous results reported in the literature from data taken
at the spectral region of the He I 1083 nm triplet.
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Title: Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres:
Chromospheric Detections of Intermediate Shocks
Authors: Houston, S. J.; Jess, D. B.; Keppens, R.; Stangalini, M.;
Keys, P. H.; Grant, S. D. T.; Jafarzadeh, S.; McFetridge, L. M.;
Murabito, M.; Ermolli, I.; Giorgi, F.
2020ApJ...892...49H Altcode: 2020arXiv200212368H
The formation of shocks within the solar atmosphere remains one of
the few observable signatures of energy dissipation arising from the
plethora of magnetohydrodynamic waves generated close to the solar
surface. Active region observations offer exceptional views of wave
behavior and its impact on the surrounding atmosphere. The stratified
plasma gradients present in the lower solar atmosphere allow for the
potential formation of many theorized shock phenomena. In this study,
using chromospheric Ca II λ8542 line spectropolarimetric data of a
large sunspot, we examine fluctuations in the plasma parameters in
the aftermath of powerful shock events that demonstrate polarimetric
reversals during their evolution. Modern inversion techniques are
employed to uncover perturbations in the temperatures, line-of-sight
velocities, and vector magnetic fields occurring across a range of
optical depths synonymous with the shock formation. Classification
of these nonlinear signatures is carried out by comparing the
observationally derived slow, fast, and Alfvén shock solutions with
the theoretical Rankine-Hugoniot relations. Employing over 200,000
independent measurements, we reveal that the Alfvén (intermediate)
shock solution provides the closest match between theory and
observations at optical depths of log<SUB>10</SUB>τ =-4, consistent
with a geometric height at the boundary between the upper photosphere
and lower chromosphere. This work uncovers first-time evidence of the
manifestation of chromospheric intermediate shocks in sunspot umbrae,
providing a new method for the potential thermalization of wave energy
in a range of magnetic structures, including pores, magnetic flux ropes,
and magnetic bright points.
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Title: Penumbral Brightening Events Observed in AR NOAA 12546
Authors: Murabito, Mariarita; Guglielmino, Salvo L.; Ermolli, Ilaria;
Stangalini, Marco; Giorgi, Fabrizio
2020ApJ...890...96M Altcode: 2019arXiv191206002M
Penumbral transient brightening events have been attributed to magnetic
reconnection episodes occurring in the low corona. We investigated
the trigger mechanism of these events in active region NOAA 12546 by
using multiwavelength observations obtained with the Interferometric
Bidimensional Spectrometer, by the Solar Dynamics Observatory, the
Interface Region Imaging Spectrograph, and the Hinode satellites. We
focused on the evolution of an area of the penumbra adjacent to two
small-scale emerging flux regions (EFRs), which manifested three
brightening events detected from the chromosphere to the corona. Two
of these events correspond to B-class flares. The same region showed
short-lived moving magnetic features (MMFs) that streamed out from the
penumbra. In the photosphere, the EFRs led to small-scale penumbral
changes associated with a counter-Evershed flow and to a reconfiguration
of the magnetic fields in the moat. The brightening events had one
of the footpoints embedded in the penumbra and seemed to result from
the distinctive interplay between the preexisting penumbral fields,
MMFs, and the EFRs. The IRIS spectra measured therein reveal enhanced
temperature and asymmetries in spectral lines, suggestive of event
triggering at different heights in the atmosphere. Specifically,
the blue asymmetry noted in C II and Mg II h&k lines suggests the
occurrence of chromospheric evaporation at the footpoint located in
the penumbra as a consequence of the magnetic reconnection process at
higher atmospheric heights.
---------------------------------------------------------
Title: Impact of small-scale emerging flux from the photosphere to
the corona: a case study from IRIS
Authors: Guglielmino, Salvo L.; Young, Peter R.; Zuccarello, Francesca;
Romano, Paolo; Murabito, Mariarita
2020IAUS..354..439G Altcode:
We report on multi-wavelength ultraviolet (UV) high-resolution
observations taken with the IRIS satellite during the emergence
phase of an emerging flux region embedded in the unipolar plage of
active region NOAA 12529. These data are complemented by measurements
taken with the spectropolarimeter aboard the Hinode satellite and by
observations from SDO.
---------------------------------------------------------
Title: The 3D structure of the penumbra at high resolution from the
bottom of the photosphere to the middle chromosphere
Authors: Murabito, Mariarita; Ermolli, Ilaria; Giorgi, Fabrizio;
Stangalini, Marco; Guglielmino, Salvo L.; Jafarzadeh, Shahin;
Socas-Navarro, Hector; Romano, Paolo; Zuccarello, Francesca
2020IAUS..354..448M Altcode:
Sunspots are the most prominent feature of the solar magnetism in the
photosphere. Although they have been widely investigated in the past,
their structure remains poorly understood. Indeed, due to limitations
in observations and the complexity of the magnetic field estimation
at chromospheric heights, the magnetic field structure of sunspot
above the photosphere is still uncertain. Improving the present
knowledge of sunspot is important in solar and stellar physics,
since spot generation is seen not only on the Sun, but also on other
solar-type stars. In this regard, we studied a large, isolated sunspot
with spectro-polarimeteric measurements that were acquired at the Fe
I 6173 nm and Ca II 8542 nm lines by the spectropolarimeter IBIS/DST
under excellent seeing conditions lasting more than three hours. Using
the Non-LTE inversion code NICOLE, we inverted both line measurements
simultaneously, to retrieve the three-dimensional magnetic and thermal
structure of the penumbral region from the bottom of the photosphere
to the middle chromosphere. Our analysis of data acquired at spectral
ranges unexplored in previous studies shows clear spine and intra-spine
structure of the penumbral magnetic field at chromopheric heights. Our
investigation of the magnetic field gradient in the penumbra along
the vertical and azimuthal directions confirms results reported in
the literature from analysis of data taken at the spectral region of
the He I 1083 nm triplet.
---------------------------------------------------------
Title: Continuum Enhancements, Line Profiles, and Magnetic Field
Evolution during Consecutive Flares
Authors: Zuccarello, Francesca; Guglielmino, Salvo L.; Capparelli,
Vincenzo; Mathioudakis, Mihalis; Keys, Peter H.; Criscuoli, Serena;
Falco, Mariachiara; Murabito, Mariarita
2020ApJ...889...65Z Altcode: 2019arXiv191200859Z
During solar flares, magnetic energy can be converted into
electromagnetic radiation from radio waves to γ-rays. Enhancements in
the continuum at visible wavelengths, as well as continuum enhancements
in the FUV and NUV passbands, give rise to white-light flares. In
addition, the strong energy release in these events can lead to
the rearrangement of the magnetic field at the photospheric level,
causing morphological changes in large and stable magnetic structures
like sunspots. In this context, we describe observations acquired
by satellite instruments (Interface Region Imaging Spectrograph
(IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager,
Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid
Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope)
during two consecutive C7.0 and X1.6 flares that occurred in active
region NOAA 12205 on 2014 November 7. The flare was accompanied by an
eruption. The results of the analysis show the presence of continuum
enhancements during the evolution of the events, observed both in ROSA
images and in IRIS spectra. In the latter, a prominent blueshifted
component is observed at the onset of the eruption. We investigate
the role played by the evolution of the δ sunspots of the active
region in the flare triggering, and finally we discuss the changes in
the penumbrae surrounding these sunspots as a further consequence of
these flares.
---------------------------------------------------------
Title: Properties of the Umbral Filament Observed in Active Region
NOAA 12529
Authors: Guglielmino, Salvo L.; Romano, Paolo; Ruiz Cobo, Basilio;
Zuccarello, Francesca; Murabito, Mariarita
2019ApJ...880...34G Altcode: 2019arXiv190600065G
Recent observations of the solar photosphere revealed the presence
of elongated filamentary bright structures inside sunspot umbrae,
called umbral filaments (UFs). These features differ in morphology,
magnetic configuration, and evolution from light bridges (LBs) that are
usually observed to intrude in sunspots. To characterize a UF observed
in the umbra of the giant leading sunspot of active region NOAA 12529,
we analyze high-resolution observations taken in the photosphere with
the spectropolarimeter on board the Hinode satellite and in the upper
chromosphere and transition region with the IRIS telescope. The results
of this analysis definitely rule out the hypothesis that the UF might
be a kind of LB. In fact, we find no field-free or low-field strength
region cospatial to the UF. Conversely, we recognize the presence of
a strong horizontal field larger than 2500 G, a significant portion
of the UF with opposite polarity with respect to the surroundings,
and filaments in the upper atmospheric layers corresponding to the
UF in the photosphere. These findings suggest that this structure
is the photospheric manifestation of a flux rope hanging above the
sunspot and forming penumbral-like filaments within the umbra via
magneto-convection. This reinforces a previously proposed scenario.
---------------------------------------------------------
Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
F.; Solanki, S. K.
2019ASPC..526..243M Altcode:
We analyze high-resolution observations of Active Region NOAA 11490,
acquired on 2012 May 28 and 29. Spectropolarimetric measurements of
the photospheric lines of Fe I at 617.3 nm and 630.25 nm were taken
with the Interferometric BIdimensional Spectrometer (IBIS), mounted on
NSO/DST, during about 30 minutes for each day. To study the evolution
of continuum intensity, LOS velocity, inclination and strength of the
magnetic field during the entire time interval, we also used data taken
by SDO/HMI. We used the SIR code to invert the Stokes profiles observed
with IBIS, using different initial models to take into account the
physical conditions of the plasma in the region of umbra, penumbra,
and quiet Sun. From the analysis of the SIR results, we found that,
before the formation of the penumbra, the annular zone is characterized
by downflows in the inner part. Furthermore, we observed that the onset
of the classical Evershed flow occurs on a short time scale, 1-3 hours,
while the penumbra is forming. In order to investigate the conditions
that lead to the establishment of the classical Evershed flow, we
analyzed the evolution of the continuum intensity, LOS velocity,
inclination and strength of the magnetic field in a segment in the
north-western part of the leading spot. In about 1 hour, we noted a
clear evolution from redshift to blueshift in the penumbral filaments
along the selected segment. We propose a scenario in which the penumbra
is formed by magnetic flux dragged down from the canopy surrounding
the initial pore: the Evershed flow starts when the sinking magnetic
field dips below the solar surface and magnetoconvection sets in.
---------------------------------------------------------
Title: Height Dependence of the Penumbral Fine-scale Structure in
the Inner Solar Atmosphere
Authors: Murabito, Mariarita; Ermolli, I.; Giorgi, F.; Stangalini,
M.; Guglielmino, S. L.; Jafarzadeh, S.; Socas-Navarro, H.; Romano,
P.; Zuccarello, F.
2019ApJ...873..126M Altcode: 2018arXiv181209029M
We studied the physical parameters of the penumbra in a large and fully
developed sunspot, one of the largest over the last two solar cycles,
by using full-Stokes measurements taken at the photospheric Fe I 617.3
nm and chromospheric Ca II 854.2 nm lines with the Interferometric
Bidimensional Spectrometer. Inverting measurements with the Non-LTE
inversion COde (NICOLE) code, we obtained the three-dimensional
structure of the magnetic field in the penumbra from the bottom
of the photosphere up to the middle chromosphere. We analyzed the
azimuthal and vertical gradient of the magnetic field strength and
inclination. Our results provide new insights on the properties of the
penumbral magnetic fields in the chromosphere at atmospheric heights
unexplored in previous studies. We found signatures of the small-scale
spine and intraspine structure of both the magnetic field strength and
inclination at all investigated atmospheric heights. In particular,
we report typical peak-to-peak variations of the field strength and
inclination of ≈300 G and ≈20°, respectively, in the photosphere,
and of ≈200 G and ≈10° in the chromosphere. In addition, we
estimated the vertical gradient of the magnetic field strength in
the studied penumbra: we find a value of ≈0.3 G km<SUP>-1</SUP>
between the photosphere and the middle chromosphere. Interestingly,
the photospheric magnetic field gradient changes sign from negative
in the inner to positive in the outer penumbra.
---------------------------------------------------------
Title: New atmosphere models to reconstruct solar irradiance
Authors: Ermolli, I.; Murabito, M.; Stangalini, M.; Giorgi, F.
2019NCimC..42....4E Altcode:
We aim at contributing to the refinement of the atmosphere
models employed in solar irradiance reconstructions by deriving
observation-based atmospheres from spectropolarimetric measurements of
the solar atmosphere. Here we present results obtained from analysis
of photospheric and chromospheric observations of quiet Sun, umbral,
and penumbral regions, performed on May 20th 2016 with the IBIS
Interferometric Bidimensional Spectrometer under excellent seeing
conditions.
---------------------------------------------------------
Title: High-resolution observations of the umbral filament in AR
NOAA 12529
Authors: Guglielmino, S. L.; Romano, P.; Ruiz Cobo, B.; Zuccarello,
, F.; Murabito, M.
2019NCimC..42...12G Altcode:
Recent observations have shown in some sunspots the presence of
structures that have been called umbral filaments (UFs). These consist
of bright filamentary features intruding sunspot umbrae, different in
morphology, evolution, and magnetic configuration from usually observed
light bridges. We report on the properties of an UF observed inside
the umbra of the giant leading sunspot in active region NOAA 12529. We
analysed high-resolution observations taken in the photosphere with
the spectropolarimeter aboard the Hinode satellite and in the upper
chromosphere and transition region with the IRIS telescope. These
observations were complemented with data from the Solar Dynamic
Observatory satellite and from the INAF-OACT equatorial spar to study
the evolution of this structure. We find that the UF harbours a strong
horizontal component of the magnetic field and a portion with polarity
opposite with respect to that of the umbra. In the upper atmospheric
layers, the structure is cospatial to a bundle of filaments, which
appears to be rooted in the sunspot umbra. We propose that the UF is the
photospheric counterpart of a flux rope touching the sunspot and giving
rise to penumbral-like filaments in the umbra via magneto-convection.
---------------------------------------------------------
Title: Continuum emission enhancements and penumbral changes observed
during flares by IRIS, ROSA, and Hinode
Authors: Zuccarello, F.; Guglielmino, S. L.; Capparelli, V.;
Mathioudakis, M.; Keys, P.; Fletcher, L.; Criscuoli, S.; Falco, M.;
Murabito, M.
2019NCimC..42...13Z Altcode: 2019arXiv190101732Z
In this paper we describe observations acquired by satellite instruments
( Hinode/SOT and IRIS) and ground-based telescopes (ROSA@DST) during
two consecutive C7.0 and X1.6 flares occurred in active region NOAA
12205 on 2014 November 7. The analysis of these data show the presence
of continuum enhancements during the evolution of the events, observed
both in ROSA images and in IRIS spectra. Moreover, we analyze the role
played by the evolution of the δ sunspots of the active region in the
flare triggering, indicating the disappearance of a large portion of
penumbra around these sunspots.
---------------------------------------------------------
Title: Satellite observations of reconnection between emerging and
pre-existing small-scale magnetic fields
Authors: Guglielmino, S. L.; Zuccarello, F.; Young, P. R.; Romano,
P.; Murabito, M.
2019NCimC..42...33G Altcode: 2019arXiv190101056G
We report multi-wavelength ultraviolet observations taken with the IRIS
satellite, concerning the emergence phase in the upper chromosphere
and transition region of an emerging flux region (EFR) embedded in
the unipolar plage of active region NOAA 12529. The photospheric
configuration of the EFR is analyzed in detail benefitting from
measurements taken with the spectropolarimeter aboard the Hinode
satellite, when the EFR was fully developed. In addition, these data
are complemented by full-disk, simultaneous observations of the
SDO satellite, relevant to the photosphere and the corona. In the
photosphere, magnetic flux emergence signatures are recognized in the
fuzzy granulation, with dark alignments between the emerging polarities,
cospatial with highly inclined fields. In the upper atmospheric
layers, we identify recurrent brightenings that resemble UV bursts,
with counterparts in all coronal passbands. These occur at the edges of
the EFR and in the region of the arch filament system (AFS) cospatial to
the EFR. Jet activity is also found at chromospheric and coronal levels,
near the AFS and the observed brightness enhancement sites. The analysis
of the IRIS line profiles reveals the heating of dense plasma in the
low solar atmosphere and the driving of bi-directional high-velocity
flows with speeds up to 100 km/s at the same locations. Furthermore,
we detect a correlation between the Doppler velocity and line width of
the Si IV 1394 and 1402 Å line profiles in the UV burst pixels and
their skewness. Comparing these findings with previous observations
and numerical models, we suggest evidence of several long-lasting,
small-scale magnetic reconnection episodes between the emerging bipole
and the ambient field. This process leads to the cancellation of a
pre-existing photospheric flux concentration of the plage with the
opposite polarity flux patch of the EFR. The reconnection appears to
occur higher in the atmosphere than usually observed.
---------------------------------------------------------
Title: Recent insights on the penumbra formation process
Authors: Murabito, M.; Romano, P.; Zuccarello, F.; Guglielmino, S. L.
2019NCimC..42...11M Altcode: 2019arXiv190105207M
Using high-resolution spectropolarimetric data acquired by IBIS,
as well as SDO/HMI observations, we studied the penumbra formation
in AR NOAA 11490 and in a sample of twelve ARs appeared on the solar
disk on 2011 and 2012, which were characterized by β -type magnetic
field configuration. The results show that the onset of the classical
Evershed flow occurs in a very short time scale, 1-3 hours. Studying
the formation of the first penumbral sector around the following
proto-spot, we found that a stable penumbra forms in the area facing
the opposite polarity, which appears to be co-spatial with an AFS,
i.e. in a flux emergence region, in contrast with the results of the
paper SCHLICHENMAIER R., REZAEI R. ET AL., Astron. Astrophys., 512
(2010) L1 concerning the leading polarity of AR NOAA 11490. Conversely,
analyzing the sample of twelve ARs, we noticed that there is not a
preferred location for the formation of the first penumbral sector. We
also observed before the penumbra formation an inverse Evershed flow,
which changes its sign when the penumbra appears. This confirms the
observational evidence that the appearance of the penumbral filaments
is correlated with the transition from the inverse Evershed to the
classical Evershed flow. Furthermore, the analysis suggests that the
time needed to form the penumbra may be related to the location where
the penumbra first appears. New high-resolution observations, like those
that will be provided by the European Solar Telescope, are expected
to increase our understanding of the penumbra formation process.
---------------------------------------------------------
Title: Propagating Spectropolarimetric Disturbances in a Large Sunspot
Authors: Stangalini, M.; Jafarzadeh, S.; Ermolli, I.; Erdélyi, R.;
Jess, D. B.; Keys, P. H.; Giorgi, F.; Murabito, M.; Berrilli, F.;
Del Moro, D.
2018ApJ...869..110S Altcode: 2018arXiv181012595S
We present results derived from the analysis of spectropolarimetric
measurements of active region AR12546, which represents one of the
largest sunspots to have emerged onto the solar surface over the last
20 years. The region was observed with full-Stokes scans of the Fe I
617.3 nm and Ca II 854.2 nm lines with the Interferometric BIdimensional
Spectrometer instrument at the Dunn Solar Telescope over an uncommon,
extremely long time interval exceeding three hours. Clear circular
polarization (CP) oscillations localized at the umbra-penumbra boundary
of the observed region were detected. Furthermore, the multi-height
data allowed us to detect the downward propagation of both CP and
intensity disturbances at 2.5-3 mHz, which was identified by a phase
delay between these two quantities. These results are interpreted as
a propagating magnetohydrodynamic surface mode in the observed sunspot.
---------------------------------------------------------
Title: IRIS Observations of Magnetic Interactions in the
Solar Atmosphere between Preexisting and Emerging Magnetic
Fields. I. Overall Evolution
Authors: Guglielmino, Salvo L.; Zuccarello, Francesca; Young, Peter
R.; Murabito, Mariarita; Romano, Paolo
2018ApJ...856..127G Altcode: 2018arXiv180205657G
We report multiwavelength ultraviolet observations taken with the IRIS
satellite, concerning the emergence phase in the upper chromosphere
and transition region of an emerging flux region (EFR) embedded in the
preexisting field of active region NOAA 12529 in the Sun. IRIS data are
complemented by full-disk observations of the Solar Dynamics Observatory
satellite, relevant to the photosphere and the corona. The photospheric
configuration of the EFR is also analyzed by measurements taken with
the spectropolarimeter on board the Hinode satellite, when the EFR was
fully developed. Recurrent intense brightenings that resemble UV bursts,
with counterparts in all coronal passbands, are identified at the edges
of the EFR. Jet activity is also observed at chromospheric and coronal
levels, near the observed brightenings. The analysis of the IRIS line
profiles reveals the heating of dense plasma in the low solar atmosphere
and the driving of bidirectional high-velocity flows with speed up to
100 km s<SUP>-1</SUP> at the same locations. Compared with previous
observations and numerical models, these signatures suggest evidence
of several long-lasting, small-scale magnetic reconnection episodes
between the emerging bipole and the ambient field. This process leads
to the cancellation of a preexisting photospheric flux concentration
and appears to occur higher in the atmosphere than usually found in
UV bursts, explaining the observed coronal counterparts.
---------------------------------------------------------
Title: Formation of Penumbra in a Sample of Active Regions Observed
by the SDO Satellite
Authors: Murabito, Mariarita; Zuccarello, Francesca; Guglielmino,
Salvo L.; Romano, Paolo
2018ApJ...855...58M Altcode:
Recently, high-resolution observations improved our understanding of
the penumbra formation process around sunspots. In particular, two
aspects have been carefully investigated: whether the settlement of
the penumbra can occur between the main opposite magnetic polarities
where new magnetic flux is still emerging, and the establishment
of the Evershed flow. In this paper, we present the analysis of
twelve active regions (ARs) where both the penumbra formation and
the onset of the Evershed flow were observed. We used data acquired
by the Helioseismic and Magnetic Imager (HMI) instrument on board
the Solar Dynamic Observatory (SDO) satellite analyzing continuum
images, magnetograms, and Dopplergrams of the selected ARs. The
results obtained in our sample provided the following information
about the stable settlement of the penumbra: eight spots formed the
first stable penumbral sector in the region between the two opposite
polarities, and nine spots formed on the opposite side. Moreover,
eleven sunpots showed an inverse Evershed flow (i.e., a plasma motion
directed toward the protospot border) before the penumbra formation,
which changes within 1-6 hr into the classical Evershed flow as soon
as the penumbra forms. Comparing our results with recent observations,
we are able to discriminate between the different ways of penumbra
formation. Moreover, we suggest that the change from inverse Evershed
flow, visible before the penumbra appears, into the classical Evershed
flow may be a signature of the formation of penumbral filaments.
---------------------------------------------------------
Title: Long-term optical monitoring of the solar atmosphere in Italy
Authors: Guglielmino, S. L.; Ermolli, I.; Romano, P.; Zuccarello,
F.; Giorgi, F.; Falco, M.; Piazzesi, R.; Stangalini, M.; Murabito,
M.; Ferrucci, M.; Mangano, A.
2018IAUS..340..251G Altcode: 2019arXiv190101050G
Probably, the long-term monitoring of the solar atmosphere started
in Italy with the first telescopic observations of the Sun made by
Galileo Galilei in the early 17<SUP>th</SUP> century. His recorded
observations and science results, as well as the work carried out by
other following outstanding Italian astronomers inspired the start of
institutional programs of regular solar observations at the Arcetri,
Catania, and Rome Observatories. <P />These programs have accumulated
daily images of the solar photosphere and chromosphere taken at various
spectral bands over a time span larger than 80 years. In the last
two decades, regular solar observations were continued with digital
cameras only at the Catania and Rome Observatories, which are now part
of the INAF National Institute for Astrophysics. At the two sites,
daily solar images are taken at the photospheric G-band, Blue (λ =
409.4 nm), and Red (λ = 606.9 nm) continua spectral ranges and at the
chromospheric Ca II K and Hα lines, with a 2” spatial resolution. <P
/>Solar observation in Italy, which benefits from over 2500 hours
of yearly sunshine, currently aims at the operational monitoring of
solar activity and long-term variability and at the continuation of the
historical series as well. Existing instruments will be soon enriched
by the SAMM double channel telescope equipped with magneto-optical
filters that will enable the tomography of the solar atmosphere with
simultaneous observations at the K I 769.9 nm and Na I D 589.0 nm
lines. In this contribution, we present the available observations
and outline their scientific relevance.
---------------------------------------------------------
Title: Observation of a 3D Magnetic Null Point
Authors: Romano, P.; Falco, M.; Guglielmino, S. L.; Murabito, M.
2017ApJ...837..173R Altcode: 2017arXiv170300665R
We describe high-resolution observations of a GOES B-class flare
characterized by a circular ribbon at the chromospheric level,
corresponding to the network at the photospheric level. We interpret
the flare as a consequence of a magnetic reconnection event that
occurred at a three-dimensional (3D) coronal null point located above
the supergranular cell. The potential field extrapolation of the
photospheric magnetic field indicates that the circular chromospheric
ribbon is cospatial with the fan footpoints, while the ribbons of
the inner and outer spines look like compact kernels. We found new
interesting observational aspects that need to be explained by models:
(1) a loop corresponding to the outer spine became brighter a few
minutes before the onset of the flare; (2) the circular ribbon was
formed by several adjacent compact kernels characterized by a size
of 1″-2″ (3) the kernels with a stronger intensity emission were
located at the outer footpoint of the darker filaments, departing
radially from the center of the supergranular cell; (4) these kernels
started to brighten sequentially in clockwise direction; and (5)
the site of the 3D null point and the shape of the outer spine were
detected by RHESSI in the low-energy channel between 6.0 and 12.0
keV. Taking into account all these features and the length scales
of the magnetic systems involved in the event, we argue that the low
intensity of the flare may be ascribed to the low amount of magnetic
flux and to its symmetric configuration.
---------------------------------------------------------
Title: On the Formation of a Stable Penumbra in a Region of Flux
Emergence in the Sun
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello, F.
2017ApJ...834...76M Altcode: 2016arXiv161104749M
We studied the formation of the first penumbral sector around a pore
in the following polarity of the NOAA Active Region (AR) 11490. We used
a high spatial, spectral, and temporal resolution data set acquired by
the Interferometric BIdimensional Spectrometer operating at the NSO/Dunn
Solar Telescope, as well as data taken by the Helioseismic and Magnetic
Imager on board the Solar Dynamics Observatory satellite. On the side
toward the leading polarity, elongated granules in the photosphere
and an arch filament system (AFS) in the chromosphere are present,
while the magnetic field shows a sea-serpent configuration, indicating
a region of magnetic flux emergence. We found that the formation of
a stable penumbra in the following polarity of the AR begins in the
area facing the opposite polarity located below the AFS in the flux
emergence region, different from what was found by Schlichenmaier
and colleagues. Moreover, during the formation of the first penumbral
sector, the area characterized by magnetic flux density larger than
900 G and the area of the umbra increase.
---------------------------------------------------------
Title: Polarization signatures in the chromosphere during an X1.6
flare
Authors: Guglielmino, S. L.; Zuccarello, F.; Murabito, M.; Romano, P.
2017psio.confE.119G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of a stable penumbra in a region of flux emergence
Authors: Murabito, Mariarita
2017psio.confE..52M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
F.; Solanki, S. K.
2016ApJ...825...75M Altcode: 2016arXiv160405610M
We studied the variations of line of sight photospheric plasma flows
during the formation phase of the penumbra around a pore in active
region NOAA 11490. We used a high spatial, spectral, and temporal
resolution data set acquired by the Interferometric BIdimensional
Spectrometer operating at the NSO/Dunn Solar Telescope as well as
data taken by the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory satellite (SDO/HMI). Before the penumbra
formed we observed a redshift of the spectral line in the inner part
of the annular zone surrounding the pore as well as a blueshift of
material associated with opposite magnetic polarity farther away from
the pore. We found that the onset of the classical Evershed flow
occurs on a very short timescale (1 to 3 hr) while the penumbra is
forming. During the same time interval we found changes in the magnetic
field inclination in the penumbra, with the vertical field actually
changing sign near the penumbral edge, while the total magnetic field
showed a significant increase, about 400 G. To explain these and other
observations related to the formation of the penumbra and the onset
of the Evershed flow we propose a scenario in which the penumbra is
formed by magnetic flux dragged down from the canopy surrounding the
initial pore. The Evershed flow starts when the sinking magnetic field
dips below the solar surface and magnetoconvection sets in.
