explanation blue bibcodes open ADS page with paths to full text
Author name code: jafarzadeh
ADS astronomy entries on 2022-09-14
=author:"Jafarzadeh, S." OR =author:"Jafarzadeh, Shahin"
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Title: Propagation of transverse waves in the solar chromosphere
probed at different heights with ALMA sub-bands
Authors: Guevara Gómez, Juan Camilo; Jafarzadeh, Shahin; Wedemeyer,
Sven; Szydlarski, Mikolaj
2022arXiv220812070G Altcode:
The Atacama Large Millimeter/sub-millimeter Array (ALMA) has provided
us with an excellent diagnostic tool for studies of the dynamics of
the Solar chromosphere, albeit through a single receiver band at one
time presently. Each ALMA band consists of four sub-bands that are
comprised of several spectral channels. To date, however, the spectral
domain has been neglected in favour of ensuring optimal imaging, so
that time-series observations have been mostly limited to full-band
data products, thereby limiting studies to a single chromospheric
layer. Here, we report the first observations of a dynamical event
(i.e. wave propagation) for which the ALMA Band 3 data (centred at
3\,mm; 100\,GHz) is split into a lower and an upper sideband. In
principle, this approach is aimed at mapping slightly different
layers in the Solar atmosphere. The side-band data were reduced
together with the Solar ALMA Pipeline (SoAP), resulting in time
series of brightness-temperature maps for each side-band. Through a
phase analysis of a magnetically quiet region, where purely acoustic
waves are expected to dominate, the average height difference between
the two side-bands is estimated as $73\pm16$~km. Furthermore, we
examined the propagation of transverse waves in small-scale bright
structures by means of wavelet phase analysis between oscillations at
the two atmospheric heights. We find 6\% of the waves to be standing,
while 54\% and 46\% of the remaining waves are propagating upwards and
downwards, respectively, with absolute propagating speeds on the order
of $\approx96$~km/s, resulting in a mean energy flux of $3800$\,W/m$^2$.
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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: Characterisation of bright chromospheric and oscillating
small-scale features observed with ALMA
Authors: Guevara Gómez, Juan Camilo; Jafarzadeh, Shahin; Wedemeyer,
Sven
2022cosp...44.2549G Altcode:
Small-scale chromospheric bright features exhibiting oscillations in
brightness temperature, size and horizontal velocity were identified
and traced in both solar ALMA observations in Bands 3 ($\sim$3
mm) and 6 ($\sim$1.2 mm) and in a Bifrost simulation resembling
the ALMA observation. In total, 492 and 175 features were present
in the observations and simulation respectively. Particularly, an
anti-correlation between brightness temperature and size is present in
the oscillations which might imply that these features are associated
with fast-sausage MHD modes. We have performed a wavelet analysis to
quantify the periods of oscillation for these three quantities as
well as the phase angles between temperature and size. The outcome
of a statistical analysis shows that the found periods correspond
to high frequency oscillations in photosphere and chromosphere by
diagnostics at other wavelengths. We have also estimated the energy
carried by these waves and discussed the results from a statistical
point of view. Specifically, we compared the outcomes between the
the two ALMA frequency bands as they are considered to be formed at
distinct heights and used the simulation to discuss the context of
the observational results.
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Title: Quantifying Properties of Photospheric Magnetic Cancellations
in the Quiet Sun Internetwork
Authors: Ledvina, Vincent E.; Kazachenko, Maria D.; Criscuoli, Serena;
Tilipman, Dennis; Ermolli, Ilaria; Falco, Mariachiara; Guglielmino,
Salvatore; Jafarzadeh, Shahin; van der Voort, Luc Rouppe; Zuccarello,
Francesca
2022ApJ...934...38L Altcode: 2022arXiv220604644L
We analyzed spectropolarimetric data from the Swedish 1 m Solar
Telescope to investigate the physical properties of small-scale magnetic
cancellations in the quiet Sun photosphere. Specifically, we looked at
the full Stokes polarization profiles along the Fe I 557.6 nm and of the
Fe I 630.1 nm lines measured by the CRisp Imaging SpectroPolarimeter to
study the temporal evolution of the line-of-sight magnetic field during
42.5 minutes of quiet Sun evolution. From this magnetogram sequence, we
visually identified 38 cancellation events. We then used the Yet Another
Feature Tracking Algorithm to characterize the physical properties of
these magnetic cancellations. We found on average 1.6 × 10<SUP>16</SUP>
Mx of magnetic flux canceled in each event with an average cancellation
rate of 3.8 × 10<SUP>14</SUP> Mx s<SUP>-1</SUP>. The derived canceled
flux is associated with strong downflows, with an average speed of V
<SUB>LOS</SUB> ≍ 1.1 km s<SUP>-1</SUP>. Our results show that the
average lifetime of each event is 9.2 minutes with an average of 44.8%
of initial magnetic flux being canceled. Our estimates of magnetic
fluxes provide a lower limit since studied magnetic cancellation events
have magnetic field values that are very close to the instrument noise
level. We observed no horizontal magnetic fields at the cancellation
sites and therefore cannot conclude whether the events are associated
with structures that could cause magnetic reconnection.
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Title: High frequency waves in chromospheric spicules
Authors: Bate, William; Nakariakov, Valery; Jafarzadeh, Shahin; Jess,
David; Stangalini, Marco; Grant, Samuel; Keys, Peter; Christian,
Damian; Keenan, Francis
2022cosp...44.2548B Altcode:
Using high cadence observations from the Hydrogen-alpha Rapid
Dynamics camera imaging system on the Dunn Solar Telescope, we
present an investigation of the statistical properties of transverse
oscillations in spicules captured above the solar limb. At five equally
separated atmospheric heights, spanning approximately $4900-7500$~km,
we have detected a total of $15{\,}959$ individual wave events,
with a mean displacement amplitude of $151\pm 124$~km, a mean
period of $54\pm 45$~s, and a mean projected velocity amplitude
of $21\pm 13$~km{\,}s$^{-1}$. We find that both the displacement
and velocity amplitudes increase with height above the solar limb,
ranging from $132\pm 111$~km and $17.7\pm 10.6$~km{\,}s$^{-1}$ at
$\approx4900$~km, and $168\pm 125$~km and $26.3\pm 14.1$~km{\,}s$^{-1}$
at $\approx7500$~km, respectively. Following the examination of
neighboring oscillations in time and space, we find 45% of the waves
to be upwardly propagating, 49% to be downwardly propagating, and 6%
to be standing, with mean absolute phase velocities for the propagating
waves on the order of $75-150$~km{\,}s$^{-1}$. While the energy flux
of the waves propagating downwards does not appear to depend on height,
we find the energy flux of the upwardly propagating waves decreases with
atmospheric height at a rate of $-13{\,}200\pm6500$~W{\,}m$^{-2}$/Mm. As
a result, this decrease in energy flux as the waves propagate upwards
may provide significant thermal input into the local plasma.
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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: High-frequency Waves in Chromospheric Spicules
Authors: Bate, W.; Jess, D. B.; Nakariakov, V. M.; Grant, S. D. T.;
Jafarzadeh, S.; Stangalini, M.; Keys, P. H.; Christian, D. J.; Keenan,
F. P.
2022ApJ...930..129B Altcode: 2022arXiv220304997B
Using high-cadence observations from the Hydrogen-alpha Rapid
Dynamics camera imaging system on the Dunn Solar Telescope, we
present an investigation of the statistical properties of transverse
oscillations in spicules captured above the solar limb. At five equally
separated atmospheric heights, spanning approximately 4900-7500 km,
we have detected a total of 15,959 individual wave events, with a
mean displacement amplitude of 151 ± 124 km, a mean period of 54
± 45 s, and a mean projected velocity amplitude of 21 ± 13 km
s<SUP>-1</SUP>. We find that both the displacement and velocity
amplitudes increase with height above the solar limb, ranging from
132 ± 111 km and 17.7 ± 10.6 km s<SUP>-1</SUP> at ≍4900 km,
and 168 ± 125 km and 26.3 ± 14.1 km s<SUP>-1</SUP> at ≍7500 km,
respectively. Following the examination of neighboring oscillations in
time and space, we find 45% of the waves to be upwardly propagating,
49% to be downwardly propagating, and 6% to be standing, with mean
absolute phase velocities for the propagating waves on the order of
75-150 km s<SUP>-1</SUP>. While the energy flux of the waves propagating
downwards does not appear to depend on height, we find the energy flux
of the upwardly propagating waves decreases with atmospheric height
at a rate of -13,200 ± 6500 W m<SUP>-2</SUP>/Mm. As a result, this
decrease in energy flux as the waves propagate upwards may provide
significant thermal input into the local plasma.
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Title: Power distribution of oscillations in the atmosphere of a
plage region. Joint observations with ALMA, IRIS, and SDO
Authors: Narang, Nancy; Chandrashekhar, Kalugodu; Jafarzadeh, Shahin;
Fleck, Bernhard; Szydlarski, Mikołaj; Wedemeyer, Sven
2022A&A...661A..95N Altcode: 2022arXiv220211547N
Context. Joint observations of the Atacama Large
Millimeter/Submillimeter Array (ALMA) with other solar observatories
can provide a wealth of opportunities for understanding the coupling
between different layers of the solar atmosphere. <BR /> Aims: We
present a statistical analysis of the power distribution of oscillations
in a plage region in active region NOAA AR12651, which was observed
jointly with ALMA, the Interface Region Imaging Spectrograph (IRIS),
and the Solar Dynamics Observatory (SDO). <BR /> Methods: We employ
coordinated ALMA Band 6 (1.25 mm) brightness temperature maps,
IRIS slit-jaw images in the 2796 Å passband, and observations in
six passbands (1600 Å, 304 Å, 131 Å, 171 Å, 193 Å, and 211 Å)
from the Atmospheric Imaging Assembly (AIA) on board SDO. We perform
Lomb-Scargle transforms to study the distribution of oscillation power
by means of dominant period maps and power maps. We study the spatial
association of oscillations through the atmosphere, with a focus on
the correlation of the power distribution of ALMA oscillations with
others. <BR /> Results: We do not observe any significant association
of ALMA oscillations with IRIS and AIA oscillations. While the global
behavior of the dominant ALMA oscillations shows a similarity with
that of the transition region and coronal passbands of AIA, the ALMA
dominant period maps and power maps do not show any correlation with
those from the other passbands. The spatial distribution of dominant
periods and power in different period intervals of ALMA oscillations
is uncorrelated with those of any other passbands. <BR /> Conclusions:
We speculate that the non-association of ALMA oscillations with those
of IRIS and AIA is due to significant variations in the height of
formation of the millimeter continuum observed by ALMA. Additionally,
the fact that ALMA directly maps the brightness temperature, in contrast
to the intensity observations by IRIS and AIA, can result in the very
different intrinsic nature of the ALMA oscillations compared to the
IRIS and AIA oscillations.
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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. <P />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: 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: The Sun at millimeter wavelengths. III. Impact of the spatial
resolution on solar ALMA observations
Authors: Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikołaj;
Jafarzadeh, Shahin
2021A&A...656A..68E Altcode: 2021arXiv210913826E
Context. Interferometric observations of the Sun with the Atacama
Large Millimeter/sub-millimeter Array (ALMA) provide valuable
diagnostic tools for studying the small-scale dynamics of the solar
atmosphere. <BR /> Aims: The aims are to perform estimations of the
observability of the small-scale dynamics as a function of spatial
resolution for regions with different characteristic magnetic field
topology facilitate a more robust analysis of ALMA observations
of the Sun. <BR /> Methods: A three-dimensional model of the solar
atmosphere from the radiation-magnetohydrodynamic code Bifrost was used
to produce high-cadence observables at millimeter and submillimeter
wavelengths. The synthetic observables for receiver bands 3-10 were
degraded to the angular resolution corresponding to ALMA observations
with different configurations of the interferometric array from the
most compact, C1, to the more extended, C7. The observability of
the small-scale dynamics was analyzed in each case. The analysis
was thus also performed for receiver bands and resolutions that
are not commissioned so far for solar observations as a means for
predicting the potential of future capabilities. <BR /> Results:
The minimum resolution required to study the typical small spatial
scales in the solar chromosphere depends on the characteristic
properties of the target region. Here, a range from quiet Sun to
enhanced network loops is considered. Limited spatial resolution
affects the observable signatures of dynamic small-scale brightening
events in the form of reduced brightness temperature amplitudes,
potentially leaving them undetectable, and even shifts in the times
at which the peaks occur of up to tens of seconds. Conversion factors
between the observable brightness amplitude and the original amplitude
in the fully resolved simulation are provided that can be applied to
observational data in principle, but are subject to wavelength-dependent
uncertainties. Predictions of the typical appearance at the different
combinations of receiver band, array configuration, and properties of
the target region are conducted. <BR /> Conclusions: The simulation
results demonstrate the high scientific potential that ALMA already has
with the currently offered capabilities for solar observations. For the
study of small-scale dynamic events, however, the spatial resolution
is still crucial, and wide array configurations are preferable. In
any case, it is essential to take the effects due to limited spatial
resolution into account in the analysis of observational data. Finally,
the further development of observing capabilities including wider
array configurations and advanced imaging procedures yields a high
potential for future ALMA observations of the Sun.
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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: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
---------------------------------------------------------
Title: 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.
---------------------------------------------------------
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. <P />This article is part of the Theo Murphy meeting issue
`High-resolution wave dynamics in the lower solar atmosphere'.
---------------------------------------------------------
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'.
---------------------------------------------------------
Title: High-frequency oscillations in small chromospheric bright
features observed with Atacama Large Millimetre/Submillimetre Array
Authors: Guevara Gómez, J. C.; Jafarzadeh, S.; Wedemeyer, S.;
Szydlarski, M.; Stangalini, M.; Fleck, B.; Keys, P. H.
2021RSPTA.37900184G Altcode: 2020arXiv200804179G
We report detection of oscillations in brightness temperature,
size and horizontal velocity of three small bright features in the
chromosphere of a plage/enhanced-network region. The observations,
which were taken with high temporal resolution (i.e. 2 s cadence)
with the Atacama large millimetre/ submillimetre array (ALMA) in Band
3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with
oscillatory behaviour with different, but overlapping, distributions of
period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ±
23 s, respectively. We find anti-correlations between perturbations in
brightness, temperature and size of the three features, which suggest
the presence of fast sausage-mode waves in these small structures. In
addition, the detection of transverse oscillations (although with
a larger uncertainty) may also suggest the presence of Alfvénic
oscillations which are likely representative of kink waves. This work
demonstrates the diagnostic potential of high-cadence observations with
ALMA for detecting high-frequency magnetohydrodynamic waves in the
solar chromosphere. Such waves can potentially channel a vast amount
of energy into the outer atmosphere of the Sun. <P />This article is
part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.
---------------------------------------------------------
Title: High-resolution wave dynamics in the lower solar atmosphere
Authors: Jess, D. B.; Keys, P. H.; Stangalini, M.; Jafarzadeh, S.
2021RSPTA.37900169J Altcode: 2020arXiv201113940J
The magnetic and convective nature of the Sun's photosphere provides
a unique platform from which generated waves can be modelled,
observed and interpreted across a wide breadth of spatial and
temporal scales. As oscillations are generated in-situ or emerge
through the photospheric layers, the interplay between the rapidly
evolving densities, temperatures and magnetic field strengths provides
dynamic evolution of the embedded wave modes as they propagate into
the tenuous solar chromosphere. A focused science team was assembled
to discuss the current challenges faced in wave studies in the lower
solar atmosphere, including those related to spectropolarimetry and
radiative transfer in the optically thick regions. Following the
Theo Murphy international scientific meeting held at Chicheley Hall
during February 2020, the scientific team worked collaboratively to
produce 15 independent publications for the current Special Issue,
which are introduced here. Implications from the current research
efforts are discussed in terms of upcoming next-generation observing
and high-performance computing facilities. <P />This article is part
of the Theo Murphy meeting issue `High-resolution wave dynamics in
the lower solar atmosphere'.
---------------------------------------------------------
Title: Characterization of shock wave signatures at millimetre
wavelengths from Bifrost simulations
Authors: Eklund, Henrik; Wedemeyer, Sven; Snow, Ben; Jess, David B.;
Jafarzadeh, Shahin; Grant, Samuel D. T.; Carlsson, Mats; Szydlarski,
Mikołaj
2021RSPTA.37900185E Altcode: 2020arXiv200805324E
Observations at millimetre wavelengths provide a valuable tool to study
the small-scale dynamics in the solar chromosphere. We evaluate the
physical conditions of the atmosphere in the presence of a propagating
shock wave and link that to the observable signatures in mm-wavelength
radiation, providing valuable insights into the underlying physics
of mm-wavelength observations. A realistic numerical simulation from
the three-dimensional radiative magnetohydrodynamic code Bifrost
is used to interpret changes in the atmosphere caused by shock wave
propagation. High-cadence (1 s) time series of brightness temperature
(T<SUB>b</SUB>) maps are calculated with the Advanced Radiative Transfer
code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite
sides of spectral band 6 of the Atacama Large Millimeter/submillimeter
Array (ALMA). An example of shock wave propagation is presented. The
brightness temperatures show a strong shock wave signature with large
variation in formation height between approximately 0.7 and 1.4 Mm. The
results demonstrate that millimetre brightness temperatures efficiently
track upwardly propagating shock waves in the middle chromosphere. In
addition, we show that the gradient of the brightness temperature
between wavelengths within ALMA band 6 can potentially be used as
a diagnostics tool in understanding the small-scale dynamics at the
sampled layers. <P />This article is part of the Theo Murphy meeting
issue `High-resolution wave dynamics in the lower solar atmosphere'.
---------------------------------------------------------
Title: Magnetoacoustic wave energy dissipation in the atmosphere of
solar pores
Authors: Gilchrist-Millar, Caitlin A.; Jess, David B.; Grant, Samuel
D. T.; Keys, Peter H.; Beck, Christian; Jafarzadeh, Shahin; Riedl,
Julia M.; Van Doorsselaere, Tom; Ruiz Cobo, Basilio
2021RSPTA.37900172G Altcode: 2020arXiv200711594G
The suitability of solar pores as magnetic wave guides has been a key
topic of discussion in recent years. Here, we present observational
evidence of propagating magnetohydrodynamic wave activity in a group
of five photospheric solar pores. Employing data obtained by the
Facility Infrared Spectropolarimeter at the Dunn Solar Telescope,
oscillations with periods of the order of 5 min were detected at
varying atmospheric heights by examining Si ɪ 10827 Å line bisector
velocities. Spectropolarimetric inversions, coupled with the spatially
resolved root mean square bisector velocities, allowed the wave energy
fluxes to be estimated as a function of atmospheric height for each
pore. We find propagating magnetoacoustic sausage mode waves with
energy fluxes on the order of 30 kW m<SUP>-2</SUP> at an atmospheric
height of 100 km, dropping to approximately 2 kW m<SUP>-2</SUP>
at an atmospheric height of around 500 km. The cross-sectional
structuring of the energy fluxes reveals the presence of both body-
and surface-mode sausage waves. Examination of the energy flux decay
with atmospheric height provides an estimate of the damping length,
found to have an average value across all five pores of L<SUB>d</SUB>
≈ 268 km, similar to the photospheric density scale height. We find
the damping lengths are longer for body mode waves, suggesting that
surface mode sausage oscillations are able to more readily dissipate
their embedded wave energies. This work verifies the suitability of
solar pores to act as efficient conduits when guiding magnetoacoustic
wave energy upwards into the outer solar atmosphere. <P />This article
is part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.
---------------------------------------------------------
Title: Reply to: Signatures of sunspot oscillations and the case
for chromospheric resonances
Authors: Jess, David B.; Snow, Ben; Fleck, Bernhard; Stangalini,
Marco; Jafarzadeh, Shahin
2021NatAs...5....5J Altcode: 2020NatAs.tmp..149J
No abstract at ADS
---------------------------------------------------------
Title: Alfvénic Perturbations in a Sunspot Chromosphere Linked to
Fractionated Plasma in the Corona
Authors: Baker, Deborah; Stangalini, Marco; Valori, Gherardo; Brooks,
David H.; To, Andy S. H.; van Driel-Gesztelyi, Lidia; Démoulin,
Pascal; Stansby, David; Jess, David B.; Jafarzadeh, Shahin
2021ApJ...907...16B Altcode: 2020arXiv201204308B
In this study, we investigate the spatial distribution of highly
varying plasma composition around one of the largest sunspots of solar
cycle 24. Observations of the photosphere, chromosphere, and corona
are brought together with magnetic field modeling of the sunspot
in order to probe the conditions that regulate the degree of plasma
fractionation within loop populations of differing connectivities. We
find that, in the coronal magnetic field above the sunspot umbra,
the plasma has photospheric composition. Coronal loops rooted in the
penumbra contain fractionated plasma, with the highest levels observed
in the loops that connect within the active region. Tracing field
lines from regions of fractionated plasma in the corona to locations
of Alfvénic fluctuations detected in the chromosphere shows that they
are magnetically linked. These results indicate a connection between
sunspot chromospheric activity and observable changes in coronal
plasma composition.
---------------------------------------------------------
Title: ALMA and IRIS Observations of the Solar
Chromosphere. II. Structure and Dynamics of Chromospheric Plages
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...83C Altcode: 2020arXiv201205970C
We propose and employ a novel empirical method for determining
chromospheric plage regions, which seems to better isolate a plage from
its surrounding regions than other methods commonly used. We caution
that isolating a plage from its immediate surroundings must be done
with care in order to successfully mitigate statistical biases that,
for instance, can impact quantitative comparisons between different
chromospheric observables. Using this methodology, our analysis suggests
that λ = 1.25 mm free-free emission in plage regions observed with
the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may
not form in the low chromosphere as previously thought, but rather
in the upper chromospheric parts of dynamic plage features (such as
spicules and other bright structures), i.e., near geometric heights
of transition-region temperatures. We investigate the high degree of
similarity between chromospheric plage features observed in ALMA/Band6
(at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph
(IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are
not as well correlated with ALMA/Band6 as was previously thought,
and we discuss discrepancies with previous works. Lastly, we report
indications of chromospheric heating due to propagating shocks supported
by the ALMA/Band6 observations.
---------------------------------------------------------
Title: ALMA and IRIS Observations of the Solar Chromosphere. I. An
On-disk Type II Spicule
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...82C Altcode: 2020arXiv200512717C
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph. The observatories
targeted a chromospheric plage region of which the spatial distribution
(split between strongly and weakly magnetized regions) allowed the
study of linear-like structures in isolation, free of contamination
from background emission. Using these observations in conjunction with
a radiative magnetohydrodynamic 2.5D model covering the upper convection
zone all the way to the corona that considers nonequilibrium ionization
effects, we report the detection of an on-disk chromospheric spicule
with ALMA and confirm its multithermal nature.
---------------------------------------------------------
Title: ALMA and IRIS Observations Highlighting the Dynamics and
Structure of Chromospheric Plage
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.;
Hansteen, V. H.; de la Cruz Rodriguez, J.; Szydlarski, M.; Jafarzadeh,
S.; Wedemeyer, S.; Bastian, T.; Sainz Dalda, A.
2020AGUFMSH0010009C Altcode:
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph (IRIS). The
observatories targeted a chromospheric plage region of which the spatial
distribution (split between strongly and weakly magnetized regions)
allowed the study of linear-like structures in isolation, free of
contamination from background emission. Using these observations
in conjunction with a radiative magnetohydrodynamic 2.5D model
covering the upper convection zone all the way to the corona
that considers non-equilibrium ionization effects, we report the
detection of an on-disk chromospheric spicule with ALMA and confirm
its multithermal nature. In addition, we discuss the strikingly high
degree of similarity between chromospheric plage features observed
in ALMA/Band6 and IRIS/\ion{Si}{4} (also reproduced in our model)
suggesting that ALMA/Band6 does not observe in the low chromosphere as
previously thought but rather observes the upper chromospheric parts
of structures such as spicules and other bright structures above plage
at geometric heights near transition region temperatures. We also show
that IRIS/\ion{Mg}{2} is not as well correlated with ALMA/Band6 as was
previously thought. For these comparisons, we propose and employ a novel
empirical method for the determination of plage regions, which seems
to better isolate plage from its surrounding regions as compared to
other methods commonly used. We caution that isolating plage from its
immediate surroundings must be done with care to mitigate statistical
bias in quantitative comparisons between different chromospheric
observables. Lastly, we report indications for chromospheric heating
due to traveling shocks supported by the ALMA/Band6 observations.
---------------------------------------------------------
Title: The Sun at millimeter wavelengths. II. Small-scale dynamic
events in ALMA Band 3
Authors: Eklund, Henrik; Wedemeyer, Sven; Szydlarski, Mikolaj;
Jafarzadeh, Shahin; Guevara Gómez, Juan Camilo
2020A&A...644A.152E Altcode: 2020arXiv201006400E
Context. Solar observations with the Atacama Large
Millimeter/sub-millimeter Array (ALMA) facilitate studies of the
atmosphere of the Sun at chromospheric heights at high spatial and
temporal resolution at millimeter wavelengths. <BR /> Aims: ALMA
intensity data at millimeter(mm)-wavelengths are used for a first
detailed systematic assessment of the occurrence and properties of
small-scale dynamical features in the quiet Sun. <BR /> Methods: We
analyzed ALMA Band 3 data (∼3 mm/100 GHz) with a spatial resolution
of ∼1.4-2.1 arcsec and a duration of ∼40 min together with SDO/HMI
magnetograms. The temporal evolution of the mm maps is studied to
detect pronounced dynamical features, which then are connected to
dynamical events via a k-means clustering algorithm. We studied the
physical properties of the resulting events and explored whether or
not they show properties consistent with propagating shock waves. For
this purpose, we calculated observable shock wave signatures at mm
wavelengths from one- and three-dimensional model atmospheres. <BR />
Results: We detect 552 dynamical events with an excess in brightness
temperature (ΔT<SUB>b</SUB>) of at least ≥400 K. The events show a
large variety in size up to ∼9″, amplitude ΔT<SUB>b</SUB> up to
∼1200 K with typical values in the range ∼450-750 K, and lifetime
at full width at half maximum of ΔT<SUB>b</SUB> of between ∼43 and
360 s, with typical values between ∼55 and 125 s. Furthermore, many
of the events show signature properties suggesting that they are likely
produced by propagating shock waves. <BR /> Conclusions: There are a
lot of small-scale dynamic structures detected in the Band 3 data,
even though the spatial resolution sets limitations on the size of
events that can be detected. The number of dynamic signatures in the
ALMA mm data is very low in areas with photospheric footpoints with
stronger magnetic fields, which is consistent with the expectation
for propagating shock waves.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: The Sun at millimeter wavelengths. I. Introduction to ALMA
Band 3 observations
Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin;
Eklund, Henrik; Guevara Gomez, Juan Camilo; Bastian, Tim; Fleck,
Bernhard; de la Cruz Rodriguez, Jaime; Rodger, Andrew; Carlsson, Mats
2020A&A...635A..71W Altcode: 2020arXiv200102185W
Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started
regular observations of the Sun in 2016, first offering receiver Band
3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around
1.25 mm (239 GHz). <BR /> Aims: Here we present an initial study
of one of the first ALMA Band 3 observations of the Sun. Our aim is
to characterise the diagnostic potential of brightness temperatures
measured with ALMA on the Sun. <BR /> Methods: The observation covers
a duration of 48 min at a cadence of 2 s targeting a quiet Sun region
at disc-centre. Corresponding time series of brightness temperature
maps are constructed with the first version of the Solar ALMA Pipeline
and compared to simultaneous observations with the Solar Dynamics
Observatory (SDO). <BR /> Results: The angular resolution of the
observations is set by the synthesised beam, an elliptical Gaussian
that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit
network patches, internetwork regions, and elongated thin features
that are connected to large-scale magnetic loops, as confirmed by a
comparison with SDO maps. The ALMA Band 3 maps correlate best with
the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit
network features and, although very weak in the ALMA maps, imprints
of large-scale loops. A group of compact magnetic loops is very
clearly visible in ALMA Band 3. The brightness temperatures in the
loop tops reach values of about 8000-9000 K and in extreme moments
up to 10 000 K. <BR /> Conclusions: ALMA Band 3 interferometric
observations from early observing cycles already reveal temperature
differences in the solar chromosphere. The weak imprint of magnetic
loops and the correlation with the 171, 131, and 304 SDO channels
suggests, however, that the radiation mapped in ALMA Band 3 might
have contributions from a wider range of atmospheric heights than
previously assumed, but the exact formation height of Band 3 needs to
be investigated in more detail. The absolute brightness temperature
scale as set by total power measurements remains less certain and
must be improved in the future. Despite these complications and the
limited angular resolution, ALMA Band 3 observations have a large
potential for quantitative studies of the small-scale structure and
dynamics of the solar chromosphere. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201937122/olm">https://www.aanda.org</A>
---------------------------------------------------------
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.
---------------------------------------------------------
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. <BR /> 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. <BR
/> 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. <BR /> 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. <BR /> 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.
---------------------------------------------------------
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: A chromospheric resonance cavity in a sunspot mapped with
seismology
Authors: Jess, David B.; Snow, Ben; Houston, Scott J.; Botha, Gert
J. J.; Fleck, Bernhard; Krishna Prasad, S.; Asensio Ramos, Andrés;
Morton, Richard J.; Keys, Peter H.; Jafarzadeh, Shahin; Stangalini,
Marco; Grant, Samuel D. T.; Christian, Damian J.
2020NatAs...4..220J Altcode: 2019NatAs...4..220J; 2019NatAs.tmp..502J
Sunspots are intense collections of magnetic fields that pierce through
the Sun's photosphere, with their signatures extending upwards into the
outermost extremities of the solar corona<SUP>1</SUP>. Cutting-edge
observations and simulations are providing insights into the
underlying wave generation<SUP>2</SUP>, configuration<SUP>3,4</SUP> and
damping<SUP>5</SUP> mechanisms found in sunspot atmospheres. However,
the in situ amplification of magnetohydrodynamic waves<SUP>6</SUP>,
rising from a few hundreds of metres per second in the photosphere to
several kilometres per second in the chromosphere<SUP>7</SUP>, has,
until now, proved difficult to explain. Theory predicts that the
enhanced umbral wave power found at chromospheric heights may come
from the existence of an acoustic resonator<SUP>8-10</SUP>, which
is created due to the substantial temperature gradients experienced
at photospheric and transition region heights<SUP>11</SUP>. Here,
we provide strong observational evidence of a resonance cavity
existing above a highly magnetic sunspot. Through a combination of
spectropolarimetric inversions and comparisons with high-resolution
numerical simulations, we provide a new seismological approach to
mapping the geometry of the inherent temperature stratifications across
the diameter of the underlying sunspot, with the upper boundaries of the
chromosphere ranging between 1,300 ± 200 km and 2,300 ± 250 km. Our
findings will allow the three-dimensional structure of solar active
regions to be conclusively determined from relatively commonplace
two-dimensional Fourier power spectra. The techniques presented are
also readily suitable for investigating temperature-dependent resonance
effects in other areas of astrophysics, including the examination of
Earth-ionosphere wave cavities<SUP>12</SUP>.
---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array - from continuum to magnetic fields
Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Rodriguez, Jaime de
la Cruz; Jafarzadeh, Shahin
2020IAUS..354...24W Altcode:
The Atacama Large Millimeter/submillimeter Array offers regular
observations of our Sun since 2016. After an extended period of
further developing and optimizing the post-processing procedures,
first scientific results are now produced. While the first observing
cycles mostly provided mosaics and time series of continuum brightness
temperature maps with a cadence of 1-2s, additional receiver bands and
polarization capabilities will be offered in the future. Currently,
polarization capabilities are offered for selected receiver bands but
not yet for solar observing. An overview of the recent development,
first scientific results and potential of solar magnetic field
measurements with ALMA will be presented.
---------------------------------------------------------
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.
---------------------------------------------------------
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: The solar chromosphere at millimetre and ultraviolet
wavelengths. I. Radiation temperatures and a detailed comparison
Authors: Jafarzadeh, S.; Wedemeyer, S.; Szydlarski, M.; De Pontieu,
B.; Rezaei, R.; Carlsson, M.
2019A&A...622A.150J Altcode: 2019arXiv190105763J
Solar observations with the Atacama Large Millimeter/submillimeter
Array (ALMA) provide us with direct measurements of the brightness
temperature in the solar chromosphere. We study the temperature
distributions obtained with ALMA Band 6 (in four sub-bands at 1.21,
1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of,
a sunspot, comprising quasi-quiet and active regions with different
amounts of underlying magnetic fields. We compare these temperatures
with those obtained at near- and far-ultraviolet (UV) wavelengths
(and with the line-core intensities of the optically-thin far-UV
spectra), co-observed with the Interface Region Imaging Spectrograph
(IRIS) explorer. These include the emission peaks and cores of the Mg
II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores
of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the
mid-to-high chromosphere and the low transition region. Splitting the
ALMA sub-bands resulted in an slight increase of spatial resolution in
individual temperature maps, thus, resolving smaller-scale structures
compared to those produced with the standard averaging routines. We
find that the radiation temperatures have different, though somewhat
overlapping, distributions in different wavelengths and in the various
magnetic regions. Comparison of the ALMA temperatures with those of
the UV diagnostics should, however, be interpreted with great caution,
the former is formed under the local thermodynamic equilibrium (LTE)
conditions, the latter under non-LTE. The mean radiation temperature
of the ALMA Band 6 is similar to that extracted from the IRIS C II
line in all areas with exception of the sunspot and pores where the C
II poses higher radiation temperatures. In all magnetic regions, the
Mg II lines associate with the lowest mean radiation temperatures in
our sample. These will provide constraints for future numerical models.
---------------------------------------------------------
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: Linear Polarization Features in the Quiet-Sun Photosphere:
Structure and Dynamics
Authors: Kianfar, S.; Jafarzadeh, S.; Mirtorabi, M. T.; Riethmüller,
T. L.
2018SoPh..293..123K Altcode: 2018arXiv180704633K
We present detailed characteristics of linear polarization features
(LPFs) in the quiet-Sun photosphere from high-resolution observations
obtained with SUNRISE/IMaX. We explore differently treated data
with various noise levels in linear polarization signals, from which
structure and dynamics of the LPFs are studied. Physical properties
of the detected LPFs are also obtained from the results of Stokes
inversions. The number of LPFs and their sizes and polarization signals
are found to be strongly dependent on the noise level and on the spatial
resolution. While the linear polarization with a signal-to-noise ratio
≥4.5 covers about 26% of the entire area in the least noisy data in
our study (with a noise level of 1.7 ×10<SUP>−4</SUP> in the unit of
Stokes I continuum), the detected (spatially resolved) LPFs cover about
10% of the area at any given time, with an occurrence rate on the order
of 8 ×10<SUP>−3</SUP><SUP>s−1</SUP> arcsec<SUP>−2</SUP>. The LPFs
were found to be short lived (in the range of 30 - 300 s), relatively
small structures (radii of ≈0.1 - 1.5 arcsec), highly inclined,
posing hG fields, and they move with an average horizontal speed of
1.2 km s<SUP>−1</SUP>. The LPFs were observed (almost) equally on
both upflow and downflow regions, with an intensity contrast always
larger than that of the average quiet Sun.
---------------------------------------------------------
Title: Solar Magnetoconvection and Small-Scale Dynamo
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
2018smf..book..275B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intermittent Reconnection and Plasmoids in UV Bursts in the
Low Solar Atmosphere
Authors: Rouppe van der Voort, L.; De Pontieu, B.; Scharmer, G. B.;
de la Cruz Rodríguez, J.; Martínez-Sykora, J.; Nóbrega-Siverio,
D.; Guo, L. J.; Jafarzadeh, S.; Pereira, T. M. D.; Hansteen, V. H.;
Carlsson, M.; Vissers, G.
2017ApJ...851L...6R Altcode: 2017arXiv171104581R
Magnetic reconnection is thought to drive a wide variety of dynamic
phenomena in the solar atmosphere. Yet, the detailed physical mechanisms
driving reconnection are difficult to discern in the remote sensing
observations that are used to study the solar atmosphere. In this
Letter, we exploit the high-resolution instruments Interface Region
Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at
the Swedish 1-m Solar Telescope (SST) to identify the intermittency
of magnetic reconnection and its association with the formation of
plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV
1403 Å UV burst spectra from the transition region show evidence of
highly broadened line profiles with often non-Gaussian and triangular
shapes, in addition to signatures of bidirectional flows. Such profiles
had previously been linked, in idealized numerical simulations, to
magnetic reconnection driven by the plasmoid instability. Simultaneous
CHROMIS images in the chromospheric Ca II K 3934 Å line now provide
compelling evidence for the presence of plasmoids by revealing highly
dynamic and rapidly moving brightenings that are smaller than 0.″2 and
that evolve on timescales of the order of seconds. Our interpretation
of the observations is supported by detailed comparisons with synthetic
observables from advanced numerical simulations of magnetic reconnection
and associated plasmoids in the chromosphere. Our results highlight
how subarcsecond imaging spectroscopy sensitive to a wide range of
temperatures combined with advanced numerical simulations that are
realistic enough to compare with observations can directly reveal the
small-scale physical processes that drive the wide range of phenomena
in the solar atmosphere.
---------------------------------------------------------
Title: Solar Magnetoconvection and Small-Scale Dynamo. Recent
Developments in Observation and Simulation
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
2017SSRv..210..275B Altcode: 2015SSRv..tmp..113B; 2015arXiv151104214B
A number of observational and theoretical aspects of solar
magnetoconvection are considered in this review. We discuss recent
developments in our understanding of the small-scale structure of
the magnetic field on the solar surface and its interaction with
convective flows, which is at the centre of current research. Topics
range from plage areas in active regions over the magnetic network
shaped by supergranulation to the ubiquituous `turbulent' internetwork
fields. On the theoretical side, we focus upon magnetic field generation
by small-scale dynamo action.
---------------------------------------------------------
Title: Erratum: Morphological Properties of
Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..230...11G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polarized Kink Waves in Magnetic Elements: Evidence for
Chromospheric Helical Waves
Authors: Stangalini, M.; Giannattasio, F.; Erdélyi, R.; Jafarzadeh,
S.; Consolini, G.; Criscuoli, S.; Ermolli, I.; Guglielmino, S. L.;
Zuccarello, F.
2017ApJ...840...19S Altcode: 2017arXiv170402155S
In recent years, new high spatial resolution observations of the Sun's
atmosphere have revealed the presence of a plethora of small-scale
magnetic elements down to the resolution limit of the current cohort
of solar telescopes (∼100-120 km on the solar photosphere). These
small magnetic field concentrations, due to the granular buffeting,
can support and guide several magnetohydrodynamic wave modes that
would eventually contribute to the energy budget of the upper layers
of the atmosphere. In this work, exploiting the high spatial and
temporal resolution chromospheric data acquired with the Swedish
1 m Solar Telescope, and applying the empirical mode decomposition
technique to the tracking of the solar magnetic features, we analyze
the perturbations of the horizontal velocity vector of a set of
chromospheric magnetic elements. We find observational evidence that
suggests a phase relation between the two components of the velocity
vector itself, resulting in its helical motion.
---------------------------------------------------------
Title: High-frequency Oscillations in Small Magnetic Elements Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Stangalini, M.; Steiner,
O.; Cameron, R. H.; Danilovic, S.
2017ApJS..229...10J Altcode: 2016arXiv161109302J
We characterize waves in small magnetic elements and investigate
their propagation in the lower solar atmosphere from observations at
high spatial and temporal resolution. We use the wavelet transform to
analyze oscillations of both horizontal displacement and intensity
in magnetic bright points found in the 300 nm and the Ca II H 396.8
nm passbands of the filter imager on board the Sunrise balloon-borne
solar observatory. Phase differences between the oscillations at the
two atmospheric layers corresponding to the two passbands reveal
upward propagating waves at high frequencies (up to 30 mHz). Weak
signatures of standing as well as downward propagating waves are also
obtained. Both compressible and incompressible (kink) waves are found
in the small-scale magnetic features. The two types of waves have
different, though overlapping, period distributions. Two independent
estimates give a height difference of approximately 450 ± 100 km
between the two atmospheric layers sampled by the employed spectral
bands. This value, together with the determined short travel times of
the transverse and longitudinal waves provide us with phase speeds of 29
± 2 km s<SUP>-1</SUP> and 31 ± 2 km s<SUP>-1</SUP>, respectively. We
speculate that these phase speeds may not reflect the true propagation
speeds of the waves. Thus, effects such as the refraction of fast
longitudinal waves may contribute to an overestimate of the phase speed.
---------------------------------------------------------
Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Schmidt, W.
2017ApJS..229...11J Altcode: 2016arXiv161003104J
A dense forest of slender bright fibrils near a small solar active
region is seen in high-quality narrowband Ca II H images from the SuFI
instrument onboard the Sunrise balloon-borne solar observatory. The
orientation of these slender Ca II H fibrils (SCF) overlaps with the
magnetic field configuration in the low solar chromosphere derived
by magnetostatic extrapolation of the photospheric field observed
with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
qualitatively aligned with small-scale loops computed from a novel
inversion approach based on best-fit numerical MHD simulation. Such
loops are organized in canopy-like arches over quiet areas that differ
in height depending on the field strength near their roots.
---------------------------------------------------------
Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....9J Altcode: 2016arXiv161007449J
We present observations of transverse oscillations in slender Ca II
H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
time series of high- (spatial and temporal-) resolution seeing-free
observations in a 1.1 Å wide passband covering the line core of Ca
II H 3969 Å from the second flight of the Sunrise balloon-borne solar
observatory. The entire field of view, spanning the polarity inversion
line of an active region close to the solar disk center, is covered with
bright, thin, and very dynamic fine structures. Our analysis reveals
the prevalence of transverse waves in SCFs with median amplitudes and
periods on the order of 2.4 ± 0.8 km s<SUP>-1</SUP> and 83 ± 29 s,
respectively (with standard deviations given as uncertainties). We
find that the transverse waves often propagate along (parts of) the
SCFs with median phase speeds of 9 ± 14 km s<SUP>-1</SUP>. While the
propagation is only in one direction along the axis in some of the
SCFs, propagating waves in both directions, as well as standing waves
are also observed. The transverse oscillations are likely Alfvénic
and are thought to be representative of magnetohydrodynamic kink
waves. The wave propagation suggests that the rapid high-frequency
transverse waves, often produced in the lower photosphere, can
penetrate into the chromosphere with an estimated energy flux of ≈15
kW m<SUP>-2</SUP>. Characteristics of these waves differ from those
reported for other fibrillar structures, which, however, were observed
mainly in the upper solar chromosphere.
---------------------------------------------------------
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
2017ApJS..229....8J Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km<SUP>2</SUP> s<SUP>-1</SUP>, 80-90 km<SUP>2</SUP> s<SUP>-1</SUP>,
and 25-70 km<SUP>2</SUP> s<SUP>-1</SUP>, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.
---------------------------------------------------------
Title: Morphological Properties of Slender Ca II H Fibrils Observed
by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....6G Altcode: 2016arXiv161200319G
We use seeing-free high spatial resolution Ca II H data obtained by
the SUNRISE observatory to determine properties of slender fibrils
in the lower solar chromosphere. In this work we use intensity images
taken with the SuFI instrument in the Ca II H line during the second
scientific flight of the SUNRISE observatory to identify and track
elongated bright structures. After identification, we analyze theses
structures to extract their morphological properties. We identify
598 slender Ca II H fibrils (SCFs) with an average width of around
180 km, length between 500 and 4000 km, average lifetime of ≈400
s, and average curvature of 0.002 arcsec<SUP>-1</SUP>. The maximum
lifetime of the SCFs within our time series of 57 minutes is ≈2000
s. We discuss similarities and differences of the SCFs with other
small-scale, chromospheric structures such as spicules of type I and
II, or Ca II K fibrils.
---------------------------------------------------------
Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....7G Altcode: 2017arXiv170102801G
We report the detection of oscillations in slender Ca II H fibrils
(SCFs) from high-resolution observations acquired with the Sunrise
balloon-borne solar observatory. The SCFs show obvious oscillations in
their intensity, but also their width. The oscillatory behaviors are
investigated at several positions along the axes of the SCFs. A large
majority of fibrils show signs of oscillations in intensity. Their
periods and phase speeds are analyzed using a wavelet analysis. The
width and intensity perturbations have overlapping distributions
of the wave period. The obtained distributions have median values
of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
find that the fluctuations of both parameters propagate in
the SCFs with speeds of {11}<SUB>-11</SUB><SUP>+49</SUP> km
s<SUP>-1</SUP> and {15}<SUB>-15</SUB><SUP>+34</SUP> km s<SUP>-1</SUP>,
respectively. Furthermore, the width and intensity oscillations have a
strong tendency to be either in anti-phase or, to a smaller extent, in
phase. This suggests that the oscillations of both parameters are caused
by the same wave mode and that the waves are likely propagating. Taking
all the evidence together, the most likely wave mode to explain all
measurements and criteria is the fast sausage mode.
---------------------------------------------------------
Title: Kinematics and Magnetic Properties of a Light Bridge in a
Decaying Sunspot
Authors: Falco, M.; Borrero, J. M.; Guglielmino, S. L.; Romano, P.;
Zuccarello, F.; Criscuoli, S.; Cristaldi, A.; Ermolli, I.; Jafarzadeh,
S.; Rouppe van der Voort, L.
2016SoPh..291.1939F Altcode: 2016arXiv160607229F; 2016SoPh..tmp..107F
We present the results obtained by analysing high spatial and spectral
resolution data of the solar photosphere acquired by the CRisp Imaging
SpectroPolarimeter at the Swedish Solar Telescope on 6 August 2011 of a
large sunspot with a light bridge (LB) observed in NOAA AR 11263. These
data are complemented by simultaneous Hinode Spectropolarimeter (SP)
observation in the Fe I 630.15 nm and 630.25 nm lines. The continuum
intensity map shows a discontinuity in the radial distribution of the
penumbral filaments in correspondence with the LB, which shows a dark
lane (≈0.3<SUP>″</SUP> wide and ≈8.0<SUP>″</SUP> long) along its
main axis. The available data were inverted with the Stokes Inversion
based on Response functions (SIR) code and physical parameters maps were
obtained. The line-of-sight (LOS) velocity of the plasma along the LB
derived from the Doppler effect shows motions towards and away from the
observer up to 0.6 kms−<SUP>1</SUP> that are lower in value than the
LOS velocities observed in the neighbouring penumbral filaments. The
noteworthy result is that we find motions towards the observer of up to
0.6 kms−<SUP>1</SUP> in the dark lane where the LB is located between
two umbral cores, while the LOS velocity motion towards the observer
is strongly reduced where the LB is located between an umbral core
at one side and penumbral filaments on the other side. Statistically,
the LOS velocities correspond to upflows or downflows, and comparing
these results with Hinode/SP data, we conclude that the surrounding
magnetic field configuration (whether more or less inclined) could have
a role in maintaining the conditions for the process of plasma pile-up
along the dark lane. The results obtained from our study support and
confirm outcomes of recent magneto-hydrodynamic simulations showing
upflows along the main axis of an LB.
---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W Altcode:
This document was created by the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) in preparation of
the first regular observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), which are anticipated to start
in ALMA Cycle 4 in October 2016. The science cases presented here
demonstrate that a large number of scientifically highly interesting
observations could be made already with the still limited solar
observing modes foreseen for Cycle 4 and that ALMA has the potential
to make important contributions to answering long-standing scientific
questions in solar physics. With the proposal deadline for ALMA Cycle
4 in April 2016 and the Commissioning and Science Verification campaign
in December 2015 in sight, several of the SSALMON Expert Teams composed
strategic documents in which they outlined potential solar observations
that could be feasible given the anticipated technical capabilities
in Cycle 4. These documents have been combined and supplemented
with an analysis, resulting in recommendations for solar observing
with ALMA in Cycle 4. In addition, the detailed science cases also
demonstrate the scientific priorities of the solar physics community
and which capabilities are wanted for the next observing cycles. The
work on this White Paper effort was coordinated in close cooperation
with the two international solar ALMA development studies led by
T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
further updated until the beginning of Cycle 4 in October 2016. In
particular, we plan to adjust the technical capabilities of the solar
observing modes once finally decided and to further demonstrate the
feasibility and scientific potential of the included science cases by
means of numerical simulations of the solar atmosphere and corresponding
simulated ALMA observations.
---------------------------------------------------------
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
2015ApJ...813..125K Altcode: 2015arXiv151001877K
The asymmetries observed in the line profiles of solar flares can
provide important diagnostics of the properties and dynamics of the
flaring atmosphere. In this paper the evolution of the Hα and Ca ii
λ8542 lines are studied using high spatial, temporal, and spectral
resolution ground-based observations of an M1.1 flare obtained with
the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
line profiles from the flare kernel shows excess emission in the red
wing (red asymmetry) before flare maximum and excess in the blue wing
(blue asymmetry) after maximum. However, the Ca ii λ8542 line does
not follow the same pattern, showing only a weak red asymmetry during
the flare. RADYN simulations are used to synthesize spectral line
profiles for the flaring atmosphere, and good agreement is found
with the observations. We show that the red asymmetry observed in
Hα is not necessarily associated with plasma downflows, and the blue
asymmetry may not be related to plasma upflows. Indeed, we conclude
that the steep velocity gradients in the flaring chromosphere modify
the wavelength of the central reversal in the Hα line profile. The
shift in the wavelength of maximum opacity to shorter and longer
wavelengths generates the red and blue asymmetries, respectively.
---------------------------------------------------------
Title: Magnetic Upflow Events in the Quiet-Sun
Photosphere. I. Observations
Authors: Jafarzadeh, S.; Rouppe van der Voort, L.; de la Cruz
Rodríguez, J.
2015ApJ...810...54J Altcode: 2015arXiv150707355J
Rapid magnetic upflows in the quiet-Sun photosphere were recently
uncovered from both Sunrise/IMaX and Hinode/SOT observations. Here, we
study magnetic upflow events (MUEs) from high-quality, high- (spatial,
temporal, and spectral) resolution, and full Stokes observations
in four photospheric magnetically sensitive Fe i lines centered at
5250.21, 6173.34, 6301.51, and 6302.50 Å acquired with the Swedish
Solar Telescope (SST)/CRISP. We detect MUEs by subtracting in-line
Stokes V signals from those in the far blue wing whose signal-to-noise
ratio (S/N) ≥slant 7. We find a larger number of MUEs at any given
time (2.0× {10}<SUP>-2</SUP> arcsec<SUP>-2</SUP>), larger by one to
two orders of magnitude, than previously reported. The MUEs appear
to fall into four classes presenting different shapes of Stokes V
profiles with (I) asymmetric double lobes, (II) single lobes, (III)
double-humped (two same-polarity lobes), and (IV) three lobes (an
extra blueshifted bump in addition to double lobes), of which less
than half are single-lobed. We also find that MUEs are almost equally
distributed in network and internetwork areas and they appear in the
interior or at the edge of granules in both regions. Distributions
of physical properties, except for horizontal velocity, of the MUEs
(namely, Stokes V signal, size, line-of-sight velocity, and lifetime)
are almost identical for the different spectral lines in our data. A
bisector analysis of our spectrally resolved observations shows that
these events host modest upflows and do not show a direct indication of
the presence of supersonic upflows reported earlier. Our findings reveal
that the numbers, types (classes), and properties determined for MUEs
can strongly depend on the detection techniques used and the properties
of the employed data, namely, S/Ns, resolutions, and wavelengths.
---------------------------------------------------------
Title: Non-linear propagation of kink waves to the solar chromosphere
Authors: Stangalini, M.; Giannattasio, F.; Jafarzadeh, S.
2015A&A...577A..17S Altcode: 2015arXiv150207213S
Small-scale magnetic field concentrations (magnetic elements) in
the quiet Sun are believed to contribute to the energy budget of the
upper layers of the Sun's atmosphere, as they are observed to support
a large number of magneto-hydrodynamic modes. In recent years, kink
waves in magnetic elements were observed at different heights in
the solar atmosphere, from the photosphere to the corona. However,
the propagation of these waves has not been fully evaluated. Our aim
is to investigate the propagation of kink waves in small magnetic
elements in the solar atmosphere. We analysed high-quality, long
duration spectropolarimetric data of a photospheric quiet Sun region
observed near the disk centre with the spectropolarimeter CRISP at
the Swedish Solar Telescope (SST). We complemented these data with
simultaneous and co-spatial broadband chromospheric observations
of the same region. Our findings reveal a clear upward propagation
of kink waves with frequency above 2.6 mHz. Moreover, the signature
of a non-linear propagation process is also observed. By comparing
photospheric to chromospheric power spectra, no signature of an energy
dissipation is found at least at the atmospheric heights at which the
data analysed originate. This implies that most of the energy carried
by the kink waves (within the frequency range under study < 17 mHz)
flows to upper layers in the Sun's atmosphere.
---------------------------------------------------------
Title: Inclinations of small quiet-Sun magnetic features based on
a new geometric approach
Authors: Jafarzadeh, S.; Solanki, S. K.; Lagg, A.; Bellot Rubio,
L. R.; van Noort, M.; Feller, A.; Danilovic, S.
2014A&A...569A.105J Altcode: 2014arXiv1408.2443J
Context. High levels of horizontal magnetic flux have been reported
in the quiet-Sun internetwork, often based on Stokes profile
inversions. <BR /> Aims: Here we introduce a new method for deducing
the inclination of magnetic elements and use it to test magnetic field
inclinations from inversions. <BR /> Methods: We determine accurate
positions of a set of small, bright magnetic elements in high spatial
resolution images sampling different photospheric heights obtained by
the Sunrise balloon-borne solar observatory. Together with estimates
of the formation heights of the employed spectral bands, these provide
us with the inclinations of the magnetic features. We also compute
the magnetic inclination angle of the same magnetic features from the
inversion of simultaneously recorded Stokes parameters. <BR /> Results:
Our new, geometric method returns nearly vertical fields (average
inclination of around 14° with a relatively narrow distribution
having a standard deviation of 6°). In strong contrast to this, the
traditionally used inversions give almost horizontal fields (average
inclination of 75 ± 8°) for the same small magnetic features,
whose linearly polarised Stokes profiles are adversely affected by
noise. We show that for such magnetic features inversions overestimate
the flux in horizontal magnetic fields by an order of magnitude. <BR />
Conclusions: The almost vertical field of bright magnetic features from
our geometric method is clearly incompatible with the nearly horizontal
magnetic fields obtained from the inversions. This indicates that the
amount of magnetic flux in horizontal fields deduced from inversions is
overestimated in the presence of weak Stokes signals, in particular if
Stokes Q and U are close to or under the noise level. Inversions should
be used with great caution when applied to data with no clear Stokes Q
and no U signal. By combining the proposed method with inversions we are
not just improving the inclination, but also the field strength. This
technique allows us to analyse features that are not reliably treated
by inversions, thus greatly extending our capability to study the
complete magnetic field of the quiet Sun.
---------------------------------------------------------
Title: Migration of Ca II H bright points in the internetwork
Authors: Jafarzadeh, S.; Cameron, R. H.; Solanki, S. K.; Pietarila,
A.; Feller, A.; Lagg, A.; Gandorfer, A.
2014A&A...563A.101J Altcode: 2014arXiv1401.7522J
Context. The migration of magnetic bright point-like features (MBP)
in the lower solar atmosphere reflects the dispersal of magnetic
flux as well as the horizontal flows of the atmospheric layer they
are embedded in. <BR /> Aims: We analyse trajectories of the proper
motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs
(mean lifetime 461 ± 9 s) to obtain their diffusivity behaviour. <BR
/> Methods: We use seeing-free high spatial and temporal resolution
image sequences of quiet-Sun, disc-centre observations obtained in
the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI)
onboard the Sunrise balloon-borne solar observatory. Small MBPs in
the internetwork are automatically tracked. The trajectory of each
MBP is then calculated and described by a diffusion index (γ) and
a diffusion coefficient (D). We also explore the distribution of the
diffusion indices with the help of a Monte Carlo simulation. <BR />
Results: We find γ = 1.69 ± 0.08 and D = 257 ± 32 km<SUP>2</SUP>
s<SUP>-1</SUP> averaged over all MBPs. Trajectories of most MBPs are
classified as super-diffusive, i.e. γ > 1, with the determined γ
being the largest obtained so far to our knowledge. A direct correlation
between D and timescale (τ) determined from trajectories of all MBPs is
also obtained. We discuss a simple scenario to explain the diffusivity
of the observed, relatively short-lived MBPs while they migrate within
a small area in a supergranule (i.e. an internetwork area). We show
that the scatter in the γ values obtained for individual MBPs is due
to their limited lifetimes. <BR /> Conclusions: The super-diffusive
MBPs can be described as random walkers (due to granular evolution and
intergranular turbulence) superposed on a large systematic (background)
velocity, caused by granular, mesogranular, and supergranular flows.
---------------------------------------------------------
Title: Dynamics of magnetic bright points in the lower solar
atmosphere
Authors: Jafarzadeh, Shahin
2013PhDT........35J Altcode:
In this thesis we have investigated the structure and dynamics of
small-scale magnetic bright points (MBPs) in quiet, internetwork
regions of the lower solar atmosphere. Such MBPs are associated with
small-scale, intense (generally kG) magnetic elements. The internetwork
(IN) areas cover the largest fraction of the solar surface and
it has been argued that the IN may contain most of the existing
unsigned magnetic flux on the surface at any given time. However,
the distribution of the magnetic field's properties in the IN regions
is still being debated. Thus, only recently has the presence of kG
fields in the IN been confirmed of which the studied MBPs are thought
to be manifestations. In addition, interaction between intense magnetic
features and convective flows on the solar surface (in particular in
IN areas) have been proposed to excite waves which can carry energy to
the upper solar atmosphere. The properties of these waves and their
contribution to the heating of the upper solar atmosphere is still
unclear. Moreover, the migration of the small magnetic elements owing
to the convective flows/turbulence is not known (due to, e.g., lack
of high spatial and temporal resolution observations not affected by
seeing). We used high spatial and temporal resolution observations,
obtained by the Sunrise balloon-borne solar observatory, to address
the above issues. We concentrate on the study of the smallest MBPs
visible in the data; whose apparent lack of internal fine-structure
facilitates their precise location and tracking in time-series of
images. The analyses were performed using an algorithm we developed
to identify, locate and track the MBPs as well as to determine their
physical properties at any given time. These findings have implications
for, e.g., our understanding of the heating mechanisms in the higher
layers of the solar atmosphere, estimates of the solar magnetic flux as
well as the structure of the convection flows (within a supergranule)
advecting small magnetic elements.
---------------------------------------------------------
Title: Structure and dynamics of isolated internetwork Ca II H bright
points observed by SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.;
Pietarila, A.; Danilovic, S.; Riethmüller, T. L.; Martínez Pillet, V.
2013A&A...549A.116J Altcode: 2012arXiv1211.4836J
<BR /> Aims: We aim to improve our picture of the low chromosphere in
the quiet-Sun internetwork by investigating the intensity, horizontal
velocity, size and lifetime variations of small bright points (BPs;
diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 Å
passband along with their magnetic field parameters, derived from
photospheric magnetograms. <BR /> Methods: Several high-quality
time series of disc-centre, quiet-Sun observations from the Sunrise
balloon-borne solar telescope, with spatial resolution of around 100
km on the solar surface, have been analysed to study the dynamics
of BPs observed in the Ca II H passband and their dependence on the
photospheric vector magnetogram signal. <BR /> Results: Parameters such
as horizontal velocity, diameter, intensity and lifetime histograms of
the isolated internetwork and magnetic Ca II H BPs were determined. Mean
values were found to be 2.2 km s<SUP>-1</SUP>, 0.2 arcsec (≈150 km),
1.48 ⟨ I<SUB>Ca</SUB> ⟩ and 673 s, respectively. Interestingly, the
brightness and the horizontal velocity of BPs are anti-correlated. Large
excursions (pulses) in horizontal velocity, up to 15 km s<SUP>-1</SUP>,
are present in the trajectories of most BPs. These could excite kink
waves travelling into the chromosphere and possibly the corona, which we
estimate to carry an energy flux of 310 W m<SUP>-2</SUP>, sufficient to
heat the upper layers, although only marginally. <BR /> Conclusions:
The stable observing conditions of Sunrise and our technique for
identifying and tracking BPs have allowed us to determine reliable
parameters of these features in the internetwork. Thus we find, e.g.,
that they are considerably longer lived than previously thought. The
large velocities are also reliable, and may excite kink waves. Although
these wave are (marginally) energetic enough to heat the quiet corona,
we expect a large additional contribution from larger magnetic elements
populating the network and partly also the internetwork.
---------------------------------------------------------
Title: First Results from the SUNRISE Mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Jafarzadeh, S.; Lagg, A.; Riethmüller,
T. L.; Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; González,
M. J. M.; Pillet, V. M.; Khomenko, E.; Yelles Chaouche, L.; Iniesta,
J. C. d. T.; Domingo, V.; Palacios, J.; Knölker, M.; González,
N. B.; Borrero, J. M.; Berkefeld, T.; Franz, M.; Roth, M.; Schmidt,
W.; Steiner, O.; Title, A. M.
2012ASPC..455..143S Altcode:
The SUNRISE balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that reveal the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the SUNRISE data, which include a number of discoveries.
---------------------------------------------------------
Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
2012decs.confE..99J Altcode:
We analyze trajectories of the proper motion of intrinsically magnetic,
isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
obtain their diffusivity behaviors. We use high spatial and temporal
resolution image sequences of quiet-Sun, disc-centre observations
obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
(SuFI) on board the SUNRISE balloon-borne solar observatory. In
order to avoid misidentification, the BPs are semi-manually selected
and then automatically tracked. The trajectory of each BP is then
calculated and its diffusion index is described by a power law
exponent, using which we classify the BPs' trajectories into sub-,
normal and super- diffusive. In addition, the corresponding diffusion
coefficients (D) based on the observed displacements are consequently
computed. We find a strong super-diffusivity at a height sampled by the
SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
the temperature minimum). We find that 74% of the identified tiny BPs
are super-diffusive, 18% move randomly (i.e. their motion corresponds
to normal diffusion) and only 8% belong to the sub-diffusion regime. In
addition, we find that 53% of the super-diffusion regime (i.e. 39% of
all BPs) have the diffusivity index of 2 which are termed as "Ballistic
BPs". Finally, we explore the distribution of diffusion index with the
help of a simple simulation. The results suggest that the BPs are random
walkers superposed by a systematic (background) velocity in which the
magnitude of each component (and hence their ratio) depends on the time
and spatial scales. We further discuss a simple sketch to explain the
diffusivity of observed BPs while they migrate within a supergranule
(i.e. internetwork areas) or close to the network regions.
---------------------------------------------------------
Title: Relation between the Sunrise photospheric magnetic field and
the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
2010cosp...38.2856J Altcode: 2010cosp.meet.2856J
Recent observations from the Sunrise balloon-borne solar telescope
have enabled us to reach an unprecedented high spatial resolution
on the solar surface with the near-ultraviolet photo-spheric and
chromospheric images as well as the magnetograms. We use these high
resolution observations to investigate the structure of the solar
upper photosphere and lower chromosphere as well as their temporal
evolutions. We study the relation between the inter-granular Ca II
397 nm bright structures in images obtained by the Sunrise Filter
Imager (SuFI) and their corresponding photospheric vector magnetic
field computed from the Imaging Magnetogram eXperiment (IMaX)
observations. The targets under study are in a quiet Sun region and
close to disc-centre.
---------------------------------------------------------
Title: Abundance Analysis of Red Horizontal Branch Stars
Authors: Jafarzadeh, S.; Lagerholm, C.; Mikolaitis, Š.
2008osa..conf...53J Altcode:
During the Observational Stellar Astrophysics research course in
Lithuania, we analyzed the spectra of four red horizontal branch stars
obtained on the Nordic Optical Telescope and FIES spectrograph. For
the analysis we used the program SIU running under IDL. Overall, the
metallicity for these stars seems to be higher than what is listed in
the literature. We have determined the main atmospheric parameters and
abundances of C, N, O and Mg chemical elements. We were only able to
get the [O/Fe] abundance for one star because of telluric lines. The
abundances were compared with stellar evolutionary models, both for
finding the stellar mass and to investigate how well these stars follow
theoretical predictions of evolutionary abundance alterations.
---------------------------------------------------------
Title: Photoelectric Observations, Light Curves Analysis and Period
Study of the Eclipsing Variable DO Cas
Authors: Jafarzadeh, Shahin
2006astro.ph.10647J Altcode:
The new B and V photoelectric observations of the beta Lyrae eclipsing
binary DO Cas were obtained on 6 nights form December 2000 to January
2001. The observations were made at the Biruni Observatory, Shiraz,
Iran and the light curves are analyzed using the Wilson light curve
synthesis and differential correction code. So, the relative surface
luminosities, new light elements, and new orbital elements have been
obtained, and from times of minimum the period is improved. With these
and previously published times, the period variation is studied and
a constant period is approved, though some authors has mentioned some
variations. The solutions of the light curves suggest that DO Cas is
a contact binary.
---------------------------------------------------------
Title: Observations and Analysis of the Eclipsing Variable do CAS
Authors: Jafarzadeh, Shahin
2003IAUJD..13E..13J Altcode:
The new B and V photoelectric observations of the β Lyrae eclipsing
binary DO Cas were obtained on 6 nights form December 2000 to January
2001. The observations were made at the Biruni Observatory Shiraz Iran
and the light curves are analyzed using the Wilson-Devinny light curve
synthesis and differential correction code. So the relative surface
luminosities limb darkening coefficient new light elements and new
orbital elements have been obtained and from times of minimum the
period is improved. The solutions of the light curves suggest that DO
Cas is a contact binary.