Author name code: criscuoli
ADS astronomy entries on 2022-09-14
author:"Criscuoli, Serena"
------------------------------------------------------------------------
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
Bibcode: 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 × 1016
Mx of magnetic flux canceled in each event with an average cancellation
rate of 3.8 × 1014 Mx s-1. The derived canceled
flux is associated with strong downflows, with an average speed of V
LOS ≍ 1.1 km s-1. 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.
Title: IBIS-A: The IBIS data Archive. High-resolution observations
of the solar photosphere and chromosphere with contextual data
Authors: Ermolli, Ilaria; Giorgi, Fabrizio; Murabito, Mariarita;
Stangalini, Marco; Guido, Vincenzo; Molinaro, Marco; Romano, Paolo;
Guglielmino, Salvatore L.; Viavattene, Giorgio; Cauzzi, Gianna;
Criscuoli, Serena; Reardon, Kevin P.; Tritschler, Alexandra
Bibcode: 2022A&A...661A..74E
Altcode: 2022arXiv220209946E
Context. The IBIS data Archive (IBIS-A) stores data acquired with
the Interferometric BIdimensional Spectropolarimeter (IBIS), which
was operated at the Dunn Solar Telescope of the US National Solar
Observatory from June 2003 to June 2019. The instrument provided series
of high-resolution narrowband spectropolarimetric imaging observations
of the photosphere and chromosphere in the range 5800-8600 Å and
co-temporal broadband observations in the same spectral range and
with the same field of view as for the polarimetric data.
Aims: We present the data currently stored in IBIS-A, as well as the
interface utilized to explore such data and facilitate its scientific
exploitation. To this end, we also describe the use of IBIS-A data
in recent and undergoing studies relevant to solar physics and
space weather research.
Methods: IBIS-A includes raw and
calibrated observations, as well as science-ready data. The latter
comprise maps of the circular, linear, and net circular polarization,
and of the magnetic and velocity fields derived for a significant
fraction of the series available in the archive. IBIS-A furthermore
contains links to observations complementary to the IBIS data, such
as co-temporal high-resolution observations of the solar atmosphere
available from the instruments onboard the Hinode and IRIS satellites,
and full-disk multi-band images from INAF solar telescopes.
Results: IBIS-A currently consists of 30 TB of data taken with IBIS
during 28 observing campaigns performed in 2008 and from 2012 to 2019
on 159 days. Of the observations, 29% are released as Level 1 data
calibrated for instrumental response and compensated for residual seeing
degradation, while 10% of the calibrated data are also available as
Level 1.5 format as multi-dimensional arrays of circular, linear, and
net circular polarization maps, and line-of-sight velocity patterns;
81% of the photospheric calibrated series present Level 2 data with
the view of the magnetic and velocity fields of the targets, as derived
from data inversion with the Very Fast Inversion of the Stokes Vector
code. Metadata and movies of each calibrated and science-ready series
are also available to help users evaluate observing conditions.
Conclusions: IBIS-A represents a unique resource for investigating
the plasma processes in the solar atmosphere and the solar origin of
space weather events. The archive currently contains 454 different
series of observations. A recently undertaken effort to preserve
IBIS observations is expected to lead in the future to an increase in
the raw measurements and the fraction of processed data available in
IBIS-A. Research supported by the H2020 SOLARNET grant no. 824135.
Title: Revisiting the Solar Research Cyberinfrastructure Needs:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena;
Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal;
Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens,
Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov,
Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L.
Bibcode: 2022arXiv220309544N
Altcode:
Solar and Heliosphere physics are areas of remarkable data-driven
discoveries. Recent advances in high-cadence, high-resolution
multiwavelength observations, growing amounts of data from realistic
modeling, and operational needs for uninterrupted science-quality data
coverage generate the demand for a solar metadata standardization and
overall healthy data infrastructure. This white paper is prepared as
an effort of the working group "Uniform Semantics and Syntax of Solar
Observations and Events" created within the "Towards Integration of
Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research
Coordination Network (@HDMIEC RCN), with primary objectives to discuss
current advances and identify future needs for the solar research
cyberinfrastructure. The white paper summarizes presentations and
discussions held during the special working group session at the
EarthCube Annual Meeting on June 19th, 2020, as well as community
contribution gathered during a series of preceding workshops and
subsequent RCN working group sessions. The authors provide examples
of the current standing of the solar research cyberinfrastructure, and
describe the problems related to current data handling approaches. The
list of the top-level recommendations agreed by the authors of the
current white paper is presented at the beginning of the paper.
Title: Final Report for SAG 21: The Effect of Stellar Contamination
on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
Bibcode: 2022arXiv220109905R
Altcode:
Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
Analysis Group (ExoPAG) was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method for
studying exoplanetary atmospheres by measuring the wavelength-dependent
radius of a planet as it transits its star. Transmission spectroscopy
relies on a precise understanding of the spectrum of the star being
occulted. However, stars are not homogeneous, constant light sources
but have temporally evolving photospheres and chromospheres with
inhomogeneities like spots, faculae, and plages. This SAG has brought
together an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar astrophysics,
planetary science, and exoplanetary atmosphere research communities,
to study the current needs that can be addressed in this context to
make the most of transit studies from current NASA facilities like
HST and JWST. The analysis produced 14 findings, which fall into
three Science Themes encompassing (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars") and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies").
Title: Spectral Runway: An Analysis of Solar Balmer Lines through
both Observations and Models
Authors: Burnham, Emilie; Criscuoli, Serena; Kowalski, Adam; Harder,
Jerald; Meisner, Randy
Bibcode: 2021AGUFMSH45B2367B
Altcode:
Spectral analysis provides a glimpse into the physical properties of
stellar atmospheres, which includes temperature, density, magnetic
signatures, and so on. Balmer lines specifically are used as proxies
for atmospheric activity, as they have been used to determine stellar
effective temperatures, and used to constrain stellar atmospheric
models. Here, we are interested in the variations of Balmer lines
induced by stellar surface magnetism, which is known to affect the
atmospheres of orbiting planets and is a factor in determining
their habitability. As direct solar measurements and spatially
resolved stellar spectra are not always available, models are vital
to the understanding of the magnetic contribution to stellar spectral
variability. In this context, the Sun offers a unique opportunity for
direct observations of the effects of magnetic features on spectral
irradiance and further validation with state-of-the-art models. In this
study we utilize high spatial resolution spectroscopic observations
obtained at the Dunn Solar Telescope to investigate how surface
magnetism affects the shape of Balmer line profiles, specifically
H-alpha and H-gamma. Observational results are then compared with
theoretical spectra obtained with the Rybiki and Hummer synthesis
code using two sets of one-dimensional solar atmospheric models (each
describing different types of quiet and active regions) published
in Fontenla et al. 1999 and Fontenla et al. 2011, respectively. At
this point, it seems that the 2011 models are an overall better
representation of our quiet sun observations than the 1999 models, for
the 1999 models have far deeper line profiles than would be expected for
the quiet sun atmospheric structures that were observed. By determining
the atmospheric models that best fit the observations, our results
provide important information for improving the understanding of the
solar atmosphere and for the modeling of stellar spectral variability
that would, in turn, impact the search for habitable exoplanets.
Title: Solar Atmosphere Radiative Transfer Model Comparison based
on 3D MHD Simulations
Authors: Haberreiter, Margit; Criscuoli, Serena; Rempel, Matthias;
Mendes Domingos Pereira, Tiago
Bibcode: 2021AGUFMSH43A..06H
Altcode:
The reconstruction of the solar spectral irradiance (SSI) on various
time scales is essential for the understanding of the Earths climate
response to the SSI variability. The driver of the SSI variability
is understood to be the intensity contrast of magnetic features
present on the Sun with respect to the largely non-magnetic quiet
Sun. However, different spectral synthesis codes lead to diverging
projections of SSI variability. We present a study in which we compare
three different radiative transfer codes and carry out a a detailed
analysis of their performance. We perform the spectral synthesis at
the continuum wavelength of 665 nm with the Code for Solar Irradiance
(COSI), and the Rybicki-Hummer (RH), and Max Planck University of
Chicago Radiative MHD (MURaM) codes for three 3D MHD simulations
snapshots, a non-magnetic case, and MHD simulations with 100 G, and 200
G magnetic field strength. We determine the intensity distributions, the
intensity differences and ratios for the spectral synthesis codes. We
identify that the largest discrepancies originate in the intergranular
lanes where the most field concentration occurs. Overall, the applied
radiative transfer codes give consistent intensity distributions. Also,
the intensity variation as a function of magnetic field strength for
the particular 100 G and 200 G snapshots agree within the 2-3% range.
Title: Prediction of Sunspot and Plage Coverage for Solar Cycle 25
Authors: Penza, Valentina; Berrilli, Francesco; Bertello, Luca;
Cantoresi, Matteo; Criscuoli, Serena
Bibcode: 2021ApJ...922L..12P
Altcode: 2021arXiv211102928P
Solar variability occurs over a broad range of spatial and temporal
scales, from the Sun's brightening over its lifetime to the fluctuations
commonly associated with magnetic activity over minutes to years. The
latter activity includes most prominently the 11 yr sunspot solar
cycle and its modulations. Space weather events, in the form of
solar flares, solar energetic particles, coronal mass ejections,
and geomagnetic storms, have long been known to approximately follow
the solar cycle occurring more frequently at solar maximum than solar
minimum. These events can significantly impact our advanced technologies
and critical infrastructures, making the prediction for the strength of
future solar cycles particularly important. Several methods have been
proposed to predict the strength of the next solar cycle, cycle 25,
with results that are generally not always consistent. Most of these
methods are based on the international sunspot number time series,
or other indicators of solar activity. We present here a new approach
that uses more than 100 yr of measured fractional areas of the visible
solar disk covered by sunspots and plages and an empirical relationship
for each of these two indices of solar activity in even-odd cycles. We
anticipate that cycle 25 will peak in 2024 and will last for about 12
yr, slightly longer than cycle 24. We also found that, in terms of
sunspot and plage areas coverage, the amplitude of cycle 25 will be
substantially similar or slightly higher than cycle 24.
Title: Solar atmosphere radiative transfer model comparison based
on 3D MHD simulations
Authors: Haberreiter, M.; Criscuoli, S.; Rempel, M.; Pereira, T. M. D.
Bibcode: 2021A&A...653A.161H
Altcode: 2021arXiv210902681H
Context. The reconstruction of the solar spectral irradiance (SSI)
on various time scales is essential for the understanding of the
Earth's climate response to the SSI variability.
Aims: The
driver of the SSI variability is understood to be the intensity
contrast of magnetic features present on the Sun with respect to
the largely non-magnetic quiet Sun. However, different spectral
synthesis codes lead to diverging projections of SSI variability. In
this study we compare three different radiative transfer codes and
carry out a detailed analysis of their performance.
Methods:
We perform the spectral synthesis at the continuum wavelength of
665 nm with the Code for Solar Irradiance, and the Rybicki-Hummer,
and Max Planck University of Chicago Radiative MHD codes for three 3D
MHD simulations snapshots, a non-magnetic case, and MHD simulations
with 100 G, and 200 G magnetic field strength.
Results: We
determine the intensity distributions, the intensity differences and
ratios for the spectral synthesis codes. We identify that the largest
discrepancies originate in the intergranular lanes where the most
field concentration occurs.
Conclusions: Overall, the applied
radiative transfer codes give consistent intensity distributions. Also,
the intensity variation as a function of magnetic field strength for
the particular 100 G and 200 G snapshots agree within the 2-3% range.
Title: Deep Learning Based Reconstruction of Total Solar Irradiance
Authors: Abduallah, Yasser; Wang, Jason T. L.; Shen, Yucong; Alobaid,
Khalid A.; Criscuoli, Serena; Wang, Haimin
Bibcode: 2021arXiv210711042A
Altcode:
The Earth's primary source of energy is the radiant energy generated
by the Sun, which is referred to as solar irradiance, or total solar
irradiance (TSI) when all of the radiation is measured. A minor
change in the solar irradiance can have a significant impact on the
Earth's climate and atmosphere. As a result, studying and measuring
solar irradiance is crucial in understanding climate changes and solar
variability. Several methods have been developed to reconstruct total
solar irradiance for long and short periods of time; however, they
are physics-based and rely on the availability of data, which does not
go beyond 9,000 years. In this paper we propose a new method, called
TSInet, to reconstruct total solar irradiance by deep learning for
short and long periods of time that span beyond the physical models'
data availability. On the data that are available, our method agrees
well with the state-of-the-art physics-based reconstruction models. To
our knowledge, this is the first time that deep learning has been used
to reconstruct total solar irradiance for more than 9,000 years.
Title: Measuring and modeling the variability of solar Balmer lines
Authors: Criscuoli, S.; Marchenko, S.; Deland, M.; Choudhary, D.;
Kopp, G.
Bibcode: 2021AAS...23811312C
Altcode:
We investigate the variability of solar Balmer lines (H-alpha,
beta, gamma, delta) observed by space-borne radiometers (SORCE,
SCIAMACHY, GOME-2, OMI, and TROPOMI), combining these precise,
long-term observations with abundant, high-resolution data from the
ground-based NSO/ISS spectrograph. We relate the detected variability
to the appearance of magnetic features on the solar disk. We find that
on solar-rotation timescales Balmer line activity indices (defined as
line-core to line-wing ratios) closely follow variations in the total
solar irradiance (which is predominantly photospheric), thus frequently
(specifically, during passages of big sunspot groups) deviates from
behavior of the line-activity indices that track chromospheric activity
levels. At longer timescales (years), the correlation with chromospheric
indices increases, with periods of low- or even anti- correlation found
at intermediate timescales. Comparisons with Balmer-line variability
patterns obtained from a semi-empirical model indicate that it is
unlikely that the periods of low/anti correlations can be ascribed to
the presence of filaments, in contradiction to some previous studies.
Title: The National Science Foundation's Daniel K. Inouye Solar
Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
Mathioudakis, M.; Dkist Team
Bibcode: 2021AAS...23810601R
Altcode:
The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
(DKIST) on Haleakala, Maui is now the largest solar telescope in the
world. DKIST's superb resolution and polarimetric sensitivity will
enable astronomers to unravel many of the mysteries the Sun presents,
including the origin of solar magnetism, the mechanisms of coronal
heating and drivers of flares and coronal mass ejections. Five
instruments, four of which provide highly sensitive measurements
of solar magnetic fields, including the illusive magnetic field of
the faint solar corona. The DKIST instruments will produce large and
complex data sets, which will be distributed through the NSO/DKIST Data
Center. DKIST has achieved first engineering solar light in December
of 2019. Due to COVID the start of the operations commissioning phase
is delayed and is now expected for fall of 2021. We present a status
update for the construction effort and progress with the operations
commissioning phase.
Title: Solar Magnetism and Radiation
Authors: Petrie, Gordon; Criscuoli, Serena; Bertello, Luca
Bibcode: 2021GMS...258...83P
Altcode:
No abstract at ADS
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
Bibcode: 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: Understanding variability of solar Balmer lines
Authors: Criscuoli, Serena; Marchenko, Sergey; DeLand, Matthew;
Choudary, Debi; Kopp, Greg
Bibcode: 2021csss.confE.290C
Altcode:
Precise, adequately high-cadence, long-term records of spectral
variability at different temporal scales lead to better understanding of
a wide variety of phenomena including stellar atmospheres and dynamos,
evolution of the magnetic fields on a stellar photosphere, convective
motions, and rotational periods. These, in turn, are fundamental
for the detectability of exoplanets, the characterization of their
atmospheres and habitability, as well as characterization of stellar
magnetospheres and winds. The Sun, viewed as a star via spectral
irradiance measurements, offers a means of exploring such measurements
while also having the imaging capability to help discern the causes
of observed spectral variations. In this study, we investigate the
variability of solar Balmer lines (H-α, β, γ and δ) observed by
space-borne radiometers, combining these precise, long-term observations
with abundant, high-resolution data from the ground-based NSO/ISS
spectrograph. We relate the detected variability to magnetic features
on the solar disk. We find that on solar-rotation timescales (~month),
the Balmer line activity indices (defined as line-core to line-wing
ratios) closely follow variations in the total solar irradiance
(which is predominantly photospheric), thus frequently (specifically,
during passages of big sunspot groups) deviates from behavior of the
line-activity indices that track chromospheric activity levels. At
longer timescales (years), the correlation with chromospheric indices
increases, with periods of low- or even anti- correlation found at
intermediate timescales. Comparisons with Balmer-line variability
patterns obtained from a semi-empirical model indicate the periods
of low/anti correlations should be attributed to the increase of the
relative abundance of network, which affects the Ca-index while leaving
almost un-altered the Hα-index.
Title: Solar activity and responses observed in Balmer lines
Authors: Marchenko, S.; Criscuoli, S.; DeLand, M. T.; Choudhary,
D. P.; Kopp, G.
Bibcode: 2021A&A...646A..81M
Altcode:
Context. Many stars show Sun-like magnetic activity cycles, which
are frequently observed by tracking changes in the chromospherically
sensitive CaII H&K doublet. However, relationships between the
line profile changes related to the magnetic activity seen in strong
spectral transitions in other portions of a stellar spectrum are
yet to be understood.
Aims: We follow variability patterns in
various solar lines in order to relate them to the emergence, passage,
and decay of active solar regions.
Methods: The line activity
indices (core-to-wing ratio) for the upper Balmer lines - Hβ, Hγ,
and Hδ - are constructed from the near-daily solar measurements
acquired by the Ozone Monitoring Instrument and the TROPOspheric
Monitoring Instrument.
Results: On solar rotation timescales,
the upper Balmer line activity indices closely follow variations in
the total solar irradiance, r ∼ -(0.6 - 0.7), and thus frequently
deviate from the behavior of the line activity indices that track
chromospheric activity levels (e.g., the CH 430 nm band used in this
study), specifically during passages of big sunspot groups.
Title: Multi-Wavelength Modeling and Analysis of the Center-to-Limb
Effects of Solar Spectroscopy and Helioseismology
Authors: Kitiashvili, I.; Zhao, J.; Sadykov, V. M.; Criscuoli, S.;
Kosovichev, A. G.; Wray, A. A.
Bibcode: 2020AGUFMSH0020003K
Altcode:
An accurate interpretation of observed solar dynamics with different
instruments requires modeling solar magnetoconvection in different
regimes, as well as taking into account center-to-limb effects,
magnetic fields, and turbulence. Realistic 3D radiative MHD modeling
of the solar magnetoconvection and atmosphere allows us to generate
synthetic observables that directly link the physical properties of
the solar plasma to spectroscopic and helioseismic observables. In
this work, we investigate the influence of the center-to-limb effects
for a wide range of wavelengths, which correspond to the operational
lines of HMI/SDO, Hinode, DKIST, and other instruments. In particular,
we discuss the wavelength-dependency of the center-to-limb helioseismic
observations of acoustic travel times that are used for diagnostics of
the deep meridional circulation, as well as 'concave' Sun effect. The
presented study will support interpretation of helioseismic inversion
results by taking into account realistic coupling of subsurface and
atmosphere, and geometry-related effects. In particular, it allows us
to improve accuracy of solar subsurface measurements from the SoHO and
SDO missions, and resolve the long-standing problem of the meridional
circulation and evolution with the solar cycle.
Title: Investigation of the X1.6 Flare Occurred in the Great Active
Region 12192
Authors: Zuccarello, F.; Guglielmino, S. L.; Ferrente, F.; Criscuoli,
S.; Romano, P.
Bibcode: 2020AGUFMSH0430003Z
Altcode:
The X1.6 flare observed on 22 October 2014 (SOL2014-10-22T14:28)
was among the strongest flares occurred in the magnetically complex,
great active region NOAA 12192. It was a confined flare, without an
accompanying CME, despite the large amount of released energy. Here,
we report on full spectro-polarimetric observations acquired by
the IBIS/DST instrument along the Ca II 8542 line, analyzing the
polarization signatures during the flare, together with complementary
data from SDO and IRIS. We attempt to derive new information about
the chromospheric magnetic field topology, which can help to explain
the lack of ejecta.
Title: Challenges and Advances in Modeling of the Solar Atmosphere:
A White Paper of Findings and Recommendations
Authors: Criscuoli, Serena; Kazachenko, Maria; Kitashvili, Irina;
Kosovichev, Alexander; Martínez Pillet, Valentín; Nita, Gelu;
Sadykov, Viacheslav; Wray, Alan
Bibcode: 2021arXiv210100011C
Altcode:
The next decade will be an exciting period for solar astrophysics, as
new ground- and space-based instrumentation will provide unprecedented
observations of the solar atmosphere and heliosphere. The synergy
between modeling effort and comprehensive analysis of observations
is crucial for the understanding of the physical processes behind
the observed phenomena. However, the unprecedented wealth of data on
one hand, and the complexity of the physical phenomena on the other,
require the development of new approaches in both data analysis and
numerical modeling. In this white paper, we summarize recent numerical
achievements to reproduce structure, dynamics, and observed phenomena
from the photosphere to the low corona and outline challenges we expect
to face for the interpretation of future observations.
Title: A new spectroscopic method for measuring the temperature
gradient in the solar photosphere. Generalized application in
magnetized regions
Authors: Faurobert, M.; Criscuoli, S.; Carbillet, M.; Contursi, G.
Bibcode: 2020A&A...642A.186F
Altcode:
Context. The contribution of quiet-Sun regions to the solar irradiance
variability is currently unclear. Certain solar-cycle variations of
the quiet-Sun's physical structure, such as the temperature gradient,
might affect the irradiance. Accurate measurements of this quantity
over the course of the activity cycle would improve our understanding
of long-term irradiance variations.
Aims: In a previous work,
we introduced and successfully tested a new spectroscopic method
for measuring the photospheric temperature gradient directly on a
geometric scale in the case of non-magnetic regions. In this paper,
we generalize this method for moderately magnetized regions that
may be encountered in the quiet solar photosphere.
Methods:
To simulate spectroscopic observations, we used synthetic Stokes
profiles I and V of the magnetic FeI 630.15 nm line and intensity
profiles of the non-magnetic FeI 709 nm line computed from realistic
three-dimensional magneto-hydrodynamical simulations of the photospheric
granulation and line radiative transfer under local thermodynamical
equilibrium conditions. We then obtained maps at different levels
in the line-wings by convolution with the instrumental point spread
function (PSF) under various conditions of atmospheric turbulence -
with and without correction by an adaptive optics (AO) system. The
PSF were obtained with the PAOLA software and the AO performance is
inspired by the system that will be operating on the Daniel K. Inouye
Solar Telescope.
Results: We considered different conditions
of atmospheric turbulence and photospheric regions with different
mean magnetic strengths of 100 G and 200 G. As in non-magnetic cases
studied in our previous work, the image correction by the AO system
is mandatory for obtaining accurate measurements of the temperature
gradient. We show that the non-magnetic line at 709 nm may be safely
used in all the cases we have investigated. However, the intensity
profile of the magnetic-sensitive line is broadened by the Zeeman
effect, which would bias our temperature-gradient measurement. We thus
implemented a correction procedure of the line profile for this magnetic
broadening in the case of weakly magnetized regions. In doing so, we
remarked that in the weak-field regime, the right- and left-hand (I +
V and I - V) components have similar shapes, however, they are shifted
in opposite directions due to the Zeeman effect. We thus reconstructed
the intensity profile by shifting back the I + V and I - V profiles
and by adding the re-centered profiles. The measurement then proceeds
as in the non-magnetic case. We find that this correction procedure
is efficient in regions where the mean magnetic strength is smaller or
on the order of 100 G.
Conclusions: The new method we implement
here may be used to measure the temperature gradient in the quiet Sun
from ground-based telescopes equipped with an efficient AO system. We
stress that we derive the gradient on a geometrical scale and not on an
optical-depth scale as we would do with other standard methods. This
allows us to avoid any confusion due to the effect of temperature
variations on the continuum opacity in the solar photosphere.
Title: Quantifying Properties of Photospheric Magnetic Cancellations
in the Quiet Sun Internetwork
Authors: Ledvina, V.; Kazachenko, M.; Criscuoli, S.
Bibcode: 2020AAS...23633003L
Altcode:
We use spectropolarimetric data from the Swedish 1-meter Solar
Telescope to investigate the physical properties of small-scale
magnetic cancellations in the quiet sun photosphere. The CRisp Imaging
SpectroPolarimeter (CRISP) captured a full Stokes polarization profile
at Fe I 557.6 nm, which allowed to derive temporal evolution of the
line-of-sight magnetic field during 42.5 minutes of QS evolution. From
this magnetogram, we identified 38 cancellation events. We then
used YAFTA magnetic element-tracking technique to derive various
statistical physical properties of these cancellations. We found on
average 1.558×1016 Mx of magnetic flux being canceled in
each event with an average cancellation rate of 3.816×1014
Mx s-1. We found that derived canceled flux is associated
with strong downflows, with an average speed of ΔVLOS of
1.1 km s-1. Based on previous studies we surmise that these
downflows lead to omega-loop submergence and magnetic reconnection. We
found an average lifetime of each event to be 9.2 minutes with an
average 44.8% of initial magnetic flux being canceled; these estimates,
however, provide a lower limit since during cancellation events magnetic
fields are frequently below the instrument noise level.
Title: Comparing Radiative Transfer Codes and Opacity Samplings for
Solar Irradiance Reconstructions
Authors: Criscuoli, Serena; Rempel, Matthias; Haberreiter, Margit;
Pereira, Tiago M. D.; Uitenbroek, Han; Fabbian, Damian
Bibcode: 2020SoPh..295...50C
Altcode:
Some techniques developed to reproduce solar irradiance variations make
use of synthetic radiative fluxes of quiet and magnetic features. The
synthesis of radiative fluxes of astronomical objects is likely
to be affected by uncertainties resulting from approximations and
specific input employed for the synthesis. In this work we compare
spectra obtained with three radiative transfer codes with the
purpose of investigating differences in reproducing solar irradiance
variations. Specifically, we compare spectral synthesis produced in
non-local thermodynamic equilibrium obtained with COSI and RH using
1-D atmosphere models. We also compare local thermodynamic equilibrium
syntheses emerging from 3-D MURaM simulations of the solar atmosphere
obtained with two sets of opacity tables generated with the ATLAS9
package and with the RH code, and test the effects of opacity sampling
on the emergent spectra. We find that, although the different codes
and methodologies employed to synthesize the spectrum reproduce overall
the observed solar spectrum with a similar degree of accuracy, subtle
differences in quiet Sun spectra may translate into larger differences
in the computation of the contrasts of magnetic features, which,
in turn, critically affect the estimates of solar variability.
Title: Recent progresses in the use of 3D MHD simulations for solar
irradiance reconstructions
Authors: Criscuoli, Serena
Bibcode: 2020IAUGA..30..333C
Altcode:
The use of 3D magneto-hydrodynamic simulations of the solar
atmosphere in modeling irradiance variations seems a natural
evolution of the current irradiance reconstruction techniques making
use of one-dimensional, static, atmosphere models. Nevertheless,
the development of such new models poses serious computational
challenges. This contribution focuses on recent progresses made in
the development of novel irradiance reconstruction models making use
of 3D MHD simulations and discusses current and future challenges.
Title: Long-term (1749-2015) Variations of Solar UV Spectral Indices
Authors: Berrilli, Francesco; Criscuoli, Serena; Penza, Valentina;
Lovric, Mija
Bibcode: 2020SoPh..295...38B
Altcode:
Solar radiation variability spans a wide range in time, ranging from
seconds to decadal and longer. The nearly 40 years of measurements of
solar irradiance from space established that the total solar irradiance
varies by ≈0.1 % in phase with the Sun's magnetic cycle. Specific
intervals of the solar spectrum, e.g., ultraviolet (UV), vary by orders
of magnitude more. These variations can affect the Earth's climate
in a complex non-linear way. Specifically, some of the processes
of interaction between solar UV radiation and the Earth's atmosphere
involve threshold processes and do not require a detailed reconstruction
of the solar spectrum. For this reason a spectral UV index based on the
(FUV-MUV) color has been recently introduced. This color is calculated
using SORCE SOLSTICE integrated fluxes in the FUV and MUV bands. We
present in this work the reconstructions of the solar (FUV-MUV) color
and Ca II K and Mg II indices, from 1749-2015, using a semi-empirical
approach based on the reconstruction of the area coverage of different
solar magnetic features, i.e., sunspot, faculae and network. We remark
that our results are in noteworthy agreement with latest solar UV proxy
reconstructions that exploit more sophisticated techniques requiring
historical full-disk observations. This makes us confident that our
technique can represent an alternative approach which can complement
classical solar reconstruction efforts. Moreover, this technique,
based on broad-band observations, can be utilized to estimate the
activity on Sun-like stars, that cannot be resolved spatially, hosting
extra-solar planetary systems.
Title: Continuum Enhancements, Line Profiles, and Magnetic Field
Evolution during Consecutive Flares
Authors: Zuccarello, Francesca; Guglielmino, Salvo L.; Capparelli,
Vincenzo; Mathioudakis, Mihalis; Keys, Peter H.; Criscuoli, Serena;
Falco, Mariachiara; Murabito, Mariarita
Bibcode: 2020ApJ...889...65Z
Altcode: 2019arXiv191200859Z
During solar flares, magnetic energy can be converted into
electromagnetic radiation from radio waves to γ-rays. Enhancements in
the continuum at visible wavelengths, as well as continuum enhancements
in the FUV and NUV passbands, give rise to white-light flares. In
addition, the strong energy release in these events can lead to
the rearrangement of the magnetic field at the photospheric level,
causing morphological changes in large and stable magnetic structures
like sunspots. In this context, we describe observations acquired
by satellite instruments (Interface Region Imaging Spectrograph
(IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager,
Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid
Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope)
during two consecutive C7.0 and X1.6 flares that occurred in active
region NOAA 12205 on 2014 November 7. The flare was accompanied by an
eruption. The results of the analysis show the presence of continuum
enhancements during the evolution of the events, observed both in ROSA
images and in IRIS spectra. In the latter, a prominent blueshifted
component is observed at the onset of the eruption. We investigate
the role played by the evolution of the δ sunspots of the active
region in the flare triggering, and finally we discuss the changes in
the penumbrae surrounding these sunspots as a further consequence of
these flares.
Title: Solar Cycle-Related Variability of Sun-as-a-Star Spectral
Line Profiles
Authors: Kalscheur, M.; Criscuoli, S.; Bertello, L.; Pevtsov, A. A.
Bibcode: 2019AGUFMSH11D3390K
Altcode:
We use daily observations of the Sun-as-a-star by the high resolution
Integrated Sunlight Spectrometer (ISS), one of three instruments
which comprise the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) facility, to investigate solar cycle-related variability
in line profiles from three ISS spectral bands. Preliminary results
show an anti-correlation between the magnitude of the CN band-head
jump and total unsigned magnetic flux through the decline phase of
Solar Cycle 23 and the rise and fall of Solar Cycle 24, consistent
with magnetohydrodynamic simulations. Additional line parameters
(core intensity, full width at half maximum and equivalent width)
show correlations with the solar cycle, but may require correction
for stray light. We investigate two such corrections. Varied line
parameter responses to thermodynamic and magnetic structures in the
solar atmosphere may provide a means of disentangling thermal and
magnetic effects in disk-integrated solar spectra. These line parameter
responses could in turn inform spectroscopic observations of other
stars. Ultimately, this work is a step towards a better understanding
of magnetic activity cycles in other Sun-like stars.
Title: Quantifying Properties of Photospheric Magnetic Field
Cancellation Events in the Quiet Sun Internetwork
Authors: Ledvina, V.; Kazachenko, M.; Criscuoli, S.
Bibcode: 2019AGUFMSH43E3386L
Altcode:
The behavior of the small-scale internetwork (IN) magnetic fields on
the quiet sun is a frontier poorly understood. Since the quiet sun
represents a majority of the Sun's flux output even during solar
maximum, analyzing its processes is a key step in understanding
the fundamental aspects of solar magnetism. IN cancellations in
particular are important to characterize since they represent the
major process occurring constantly on the quiet Sun. By observing
these IN cancellations with high spatial and temporal resolutions
with the Swedish 1m Solar Telescope (SST), we were able to analyze
twelve cancellation events and describe their magnetic field
properties. Applying a polarity-tracking algorithm, YAFTA, to a
sequence of line-of-sight magnetograms, we found a mean cancellation
flux of 1.11*1017 Mx and a mean cancellation rate of
1.61*1014 Mx s-1. Using the Doppler
velocity at the PIL we found that all magnetic cancellations are
associated with omega-loop submergence with a mean peak downflow speed
of 1.02 km s-1, a figure statistically greater than regional
convective downflow behavior. Analyzing the convergence speeds of the
polarities suggests granular motions are the primary catalyst for IN
cancellation events. Data gathered in this study complements existing
understanding of magnetic behavior on the quiet Sun.
Title: On the Challenges of synthetizing solar and stellar spectra
for Irradiance reconstructions
Authors: Criscuoli, Serena; Rempel, Matthias D.; Haberreiter, Margit;
Pereira, Tiago; Uitenbroek, Han; Fabbian, Damian
Bibcode: 2019AAS...23421702C
Altcode:
Syntheses of solar and stellar spectra strongly depend on the adopted
approximations and atomic and molecular databases. We compare LTE and
NLTE syntheses of solar spectra obtained with widely used radiative
transfer codes, utilizing both 3D-MHD simulations and 1D-static
atmosphere models. We show that although different codes reproduce
reasonably well the observed spectrum, subtle differences may translate
into discrepancies of several tens of percents in the estimate of
solar and stellar spectral irradiance variability.
Title: Historical reconstruction of UV spectral indices
Authors: Criscuoli, Serena; Berrilli, Francesco; Lovric, Mia; Penza,
Valentina
Bibcode: 2019AAS...23430205C
Altcode:
Solar radiation is one of the major natural drivers of Earth
climate changes observed from the Maunder minimum. UV radiation in
particular plays a major role in the ozone production/destruction
processes and is known to affect the circulation patterns. Here we
present reconstructions of the FUV-MUV color index and CaII and MgII
core-to-wing indeces from 1749-2015, performed with a semi-epirical
approach. We also present a reconstruction of the TSI variability. Our
results are compared with reconstructions obtained with models employed
in climatological studies.
Title: Developing a vision for exoplanetary transit spectroscopy:
a shared window on the analysis of planetary atmospheres and of
stellar magnetic structure
Authors: Kowalski, Adam; Schrijver, Karel; Pillet, Valentin; Criscuoli,
Serena
Bibcode: 2019BAAS...51c.149K
Altcode: 2019astro2020T.149K; 2019arXiv190405976K
We describe how accurate exoplanet atmospheres' characterization will
inevitably require taking into consideration stellar inhomogeneities
caused by convection and magnetic fields. Disentangling these two
components requires a multipronged approach with new solar reference
spectra, MHD modeling, and collaborations among astrophysics
communities.
Title: Long-term reconstruction of Solar UV indices
Authors: Criscuoli, Serena; Berrilli, Francesco; Lovric, Mia; Penza,
Valentina
Bibcode: 2019shin.confE..80C
Altcode:
Solar radiation is one of the major natural drivers of Earth climate
variations. UV radiation in particular plays a major role in the ozone
production/destruction processes and is known to affect the Earth's
global circulation patterns. We present reconstructions of the FUV-MUV
color index and CaII and MgII core-to-wing indices from 1749 to 2015,
performed with a 4-components semi-empirical approach . Our model makes
use of the Sunspot Number to estimate the UV color index and facula,
network and sunspot area. The reconstructed UV indices, as well as
the estimated area of magnetic structures, well compare with modern
observations and historical records.
Title: Effects of Continuum Fudging on Non-LTE Synthesis of Stellar
Spectra. I. Effects on Estimates of UV Continua and Solar Spectral
Irradiance Variability
Authors: Criscuoli, Serena
Bibcode: 2019ApJ...872...52C
Altcode: 2018arXiv181205201C
Syntheses performed under non-LTE conditions usually overestimate
stellar spectra. An approach widely adopted in the literature to
reduce the excess of UV radiation consists of artificially increasing
the continuum opacity by using multiplicative fudge factors, which
are empirically derived to impose that the synthetized spectrum
match the observed one. Although the method was initially developed
to improve non-LTE synthesis of spectral lines, it has been recently
employed to model solar spectral irradiance variability. Such irradiance
reconstruction techniques combine spectral synthesis of different types
of structures, which are performed making use of factors derived from
a reference, quiet-Sun model. Because the opacity scales in a complex
way with plasma physical properties, the question arises whether, and
to what extent, fudge factors derived using a reference model can be
used to adjust the opacity of models representing different types of
quiet and magnetic features. Here we investigate the effects of opacity
fudging on estimates of solar and stellar irradiance variability in UV
bands. We find that the use of fudge factors might underestimate the
variability by 19% and up to 20% in the ranges 230-300 nm and 300-400
nm, respectively. These estimates are model dependent and should be
considered as upper limits. Finally, our analysis suggests that the
uncertainties generated by the use of fudge factors increase with the
decrease of stellar metallicity and are significant for stars whose
variability is facula dominated and whose effective temperature is
larger than ∼4000 K.
Title: The Solar Photospheric Continuum Brightness as a Function of
Mean Magnetic Flux Density. I. The Role of the Magnetic Structure
Size Distribution
Authors: Peck, C. L.; Rast, M. P.; Criscuoli, S.; Rempel, M.
Bibcode: 2019ApJ...870...89P
Altcode:
Solar irradiance models indicate that irradiance variations are
dominated by changes in the disk-coverage of magnetic structures,
whose brightness is thought to be determined by their size and average
magnetic flux density. Recent results suggest that the brightness of
small-scale magnetic structures also depends on the mean magnetic flux
of the extended region surrounding them due to reduced convective
vigor. Low spatial resolution, however, may limit the ability to
distinguish the role of magnetic structure size distributions from that
of the mean magnetic flux. Using high-resolution 3D MHD simulations,
we investigate the brightness of magnetic structures embedded in
regions characterized by different mean magnetic flux. In agreement
with previous results, we find reduced brightness with increasing
mean magnetic flux when comparing the pixel-by-pixel continuum
brightness versus magnetic field strength. Evaluating equivalently
sized magnetic structures, however, we find no significant dependence
of the magnetic structure brightness on the mean magnetic flux of the
region in which they are embedded. Rather, we find that simulations
with larger mean magnetic flux generate larger, and therefore darker,
magnetic structures whose contributions result in an overall darkening
of the region. The differences in magnetic structure size distributions
alone can explain the reduced brightness of regions with larger mean
magnetic flux. This implies that, for the range of mean magnetic flux
of the simulations, convective suppression plays at most a secondary
role in determining radiative output of magnetized regions. Quantifying
the role of convective transport over a wider range of mean magnetic
flux is the subject of the second paper in this series.
Title: Preface
Authors: Bemporad, A.; Criscuoli, S.; Del Moro, D.; Guglielmino,
S. L.; Landi, S.; Laurenza, M.; Reale, F.; Straus, T.; Vecchio, A.
Bibcode: 2019NCimC..42....1B
Altcode:
No abstract at ADS
Title: Continuum emission enhancements and penumbral changes observed
during flares by IRIS, ROSA, and Hinode
Authors: Zuccarello, F.; Guglielmino, S. L.; Capparelli, V.;
Mathioudakis, M.; Keys, P.; Fletcher, L.; Criscuoli, S.; Falco, M.;
Murabito, M.
Bibcode: 2019NCimC..42...13Z
Altcode: 2019arXiv190101732Z
In this paper we describe observations acquired by satellite instruments
( Hinode/SOT and IRIS) and ground-based telescopes (ROSA@DST) during
two consecutive C7.0 and X1.6 flares occurred in active region NOAA
12205 on 2014 November 7. The analysis of these data show the presence
of continuum enhancements during the evolution of the events, observed
both in ROSA images and in IRIS spectra. Moreover, we analyze the role
played by the evolution of the δ sunspots of the active region in the
flare triggering, indicating the disappearance of a large portion of
penumbra around these sunspots.
Title: The Correlation of Synthetic UV Color versus Mg II Index
along the Solar Cycle
Authors: Criscuoli, Serena; Penza, Valentina; Lovric, Mija; Berrilli,
Francesco
Bibcode: 2018ApJ...865...22C
Altcode: 2018arXiv180808439C
UV solar irradiance strongly affects the chemical and physical
properties of the Earth’s atmosphere. UV radiation is also a
fundamental input for modeling the habitable zones of stars and
the atmospheres of their exoplanets. Unfortunately, measurements
of solar irradiance are affected by instrumental degradation and
are not available before 1978. For other stars, the situation is
worsened by interstellar medium absorption. Therefore, estimates
of solar and stellar UV radiation and variability often rely on
modeling. Recently, Lovric et al. used Solar Radiation and Climate
Experiment (SORCE)/Stellar Irradiance Comparison Experiment (SOLSTICE)
data to investigate the variability of a color index that is a
descriptor of the UV radiation that modulates the photochemistry of
planets’ atmospheres. After correcting the SOLSTICE data for residual
instrumental effects, the authors found the color index to be strongly
correlated with the Mg II index, a solar activity proxy. In this paper,
we employ an irradiance reconstruction to synthetize the UV color and Mg
II index with the purpose of investigating the physical mechanisms that
produce the strong correlation between the color index and the solar
activity. Our reconstruction, which extends back to 1989, reproduces
very well the observations, and shows that the two indices can be
described by the same linear relation for almost three cycles, thus
ruling out an overcompensation of SORCE/SOLTICE data in the analysis
of Lovric et al. We suggest that the strong correlation between the
indices results from the UV radiation analyzed originating in the
chromosphere, where atmosphere models of quiet and magnetic features
present similar temperature and density gradients.
Title: Harmonizing Mangnetograph Data with end-to-end Instrument
Simulations
Authors: Plowman, J.; Petrie, G. J. D.; Pillet, V. M.; Criscuoli,
S.; Harvey, J. W.; Marble, A.; Uitenbroek, H.
Bibcode: 2017AGUFMSH13A2460P
Altcode:
There are a number of instruments, such as NSO's GONG and SOLIS/VSM,
which measure the magnetic field of the Sun's photosphere. However,
their measurements are not fully consistent, and the factors responsible
for the differences have yet to be isolated. I report on a new effort
to resolve them - we simulate the observing processes from end to
end, beginning with 3D MHD simulations. This allows us to compare the
synthetic observations produced with the MHD simulations' 'ground truth'
and identify the effects of the observational factors at play. The
result will be the best ever calibration of a magnetograph, giving
magnetic field models based on these data a much firmer foundation.
Title: An Assessment of and Solution to the Intensity Diffusion
Error Intrinsic to Short-characteristic Radiative Transfer Methods
Authors: Peck, C. L.; Criscuoli, S.; Rast, M. P.
Bibcode: 2017ApJ...850....9P
Altcode: 2017arXiv170809362P
Radiative transfer coupled with highly realistic simulations of the
solar atmosphere is routinely used to infer the physical properties
underlying solar observations. Due to its computational efficiency,
the method of short-characteristics is often employed, despite it
introducing numerical diffusion as an interpolation artifact. In this
paper, we quantify the effect of the numerical diffusion on the spatial
resolution of synthesized emergent intensity images, and derive a
closed form analytical model of the diffusive error made as a function
of viewing angle when using linear interpolation. We demonstrate that
the consequent image degradation adversely affects the comparison
between simulated data and observations away from disk center, unless
the simulations are computed at much higher intrinsic resolutions than
the observations. We also show that the diffusive error is readily
avoided by interpolating the simulation solution on a viewing angle
aligned grid prior to computing the radiative transfer. Doing this
will be critical for comparisons with observations using the upcoming
large aperture telescopes—the Daniel K. Inouye Solar Telescope and
the European Solar Telescope.
Title: Photometric Properties of Network and Faculae Derived from
HMI Data Compensated for Scattered Light
Authors: Criscuoli, Serena; Norton, Aimee; Whitney, Taylor
Bibcode: 2017ApJ...847...93C
Altcode: 2017arXiv170901593C
We report on the photometric properties of faculae and network,
as observed in full-disk, scattered-light-corrected images from the
Helioseismic Magnetic Imager. We use a Lucy-Richardson deconvolution
routine that corrects an image in less than one second. Faculae are
distinguished from network through proximity to active regions. This is
the first report that full-disk observations, including center-to-limb
variations, reproduce the photometric properties of faculae and
network observed previously only in sub-arcsecond-resolution; small
field-of-view studies, I.e. that network, as defined by distance from
active regions, exhibit higher photometric contrasts. Specifically,
for magnetic flux values larger than approximately 300 G, the network
is brighter than faculae and the contrast differences increase toward
the limb, where the network contrast is about twice the facular one. For
lower magnetic flux values, network appear darker than faculae. Contrary
to reports from previous full-disk observations, we also found that
network exhibits a higher center-to-limb variation. Our results are
in agreement with reports from simulations that indicate magnetic
flux alone is a poor proxy of the photometric properties of magnetic
features. We estimate that the contribution of faculae and network
to Total Solar Irradiance variability of the current Cycle 24 is
overestimated by at least 11%, due to the photometric properties of
network and faculae not being recognized as different. This estimate
is specific to the method employed in this study to reconstruct
irradiance variations, so caution should be paid when extending it to
other techniques.
Title: The variability of magnetic activity in solar-type stars
Authors: Fabbian, D.; Simoniello, R.; Collet, R.; Criscuoli, S.;
Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.;
Alvarado-Gómez, J. D.; Booth, R.; García, R. A.; Lehtinen, J.;
See, V.
Bibcode: 2017AN....338..753F
Altcode:
No abstract at ADS
Title: Photometric Properties of Network and faculae derived by HMI
data compensated for scattered-light
Authors: Criscuoli, Serena; Norton, Aimee Ann; Whitney, Taylor
Bibcode: 2017SPD....4820703C
Altcode:
We report on the photometric properties of faculae and network
as observed in full-disk,scattered-light corrected images from
the Helioseismic Magnetic Imager (HMI). We usea Lucy-Richardson
deconvolution routine that corrects a full-disk intensity image in
lessthan one second. Faculae are distinguished from network through
proximity to activeregions in addition to continuum intensity and
magnetogram thresholds. This is the firstreport that full-disk image
data, including center-to-limb variations, reproduce the photometric
properties of faculae and network observed previously only in
sub-arcsecond resolution, small field-of-view studies, i.e. that network
exhibit in general higher photometric contrasts. More specifically,
for magnetic flux values larger than approximately 300 G, the network
is always brighter than faculae and the contrast differences increases
toward the limb, where the network contrast is about twice the facular
one. For lower magnetic flux values, pixels in network regions appear
always darker than facular ones. Contrary to reports from previous
full-disk observations, we also found that network exhibits a higher
center-to-limb variation. Our results are in agreement with reports
from simulations that indicate magnetic flux alone is a poor proxy
of the photometric properties of magnetic features. We estimate
that the facular and network contribution to irradiance variability
of the current Cycle 24 is overestimated by at least 11% due to the
photometric properties of network and faculae not being recognized as
distinctly different.
Title: Assessing the Impact of Small-Scale Magnetic Morphology on
Solar Variability
Authors: Peck, Courtney; Rast, Mark; Criscuoli, Serena
Bibcode: 2017SPD....48.0503P
Altcode:
Spectral solar irradiance (SSI), the radiant energy flux per wavelength
of the Sun received at Earth, is an important driver of chemical
reactions in the Earth’s atmosphere. Accurate measurements of SSI are
therefore necessary as an input for global climate models. While models
and observations of the spectrally-integrated total solar irradiance
(TSI) variations agree within ∼ 95%, they can disagree on the sign
and magnitude of the SSI variations. In this work, we examine the
contribution of currently-unresolved small-scale magnetic structures
to SSI variations in the photosphere. We examine the emergent spectra
of two atmospheres with differing imposed-field conditions — one
with a small-scale dynamo and the other with a predominantly vertical
magnetic field — with similar mean field strengths at wavelengths
spanning from visible to infrared. Comparing the radiative output at
various viewing angles of pixels of equal vertical magnetic field
strength between the two simulations, we find that the small-scale
dynamo simulations produce higher radiative output than those in the
predominantly vertical field simulation. This implies that the radiative
output of a small magnetic structure depends on the magnetic morphology
of the environment in which it is embedded, which is currently not
included in SSI models. We deduce the effect on inferred irradiance
by comparing the disk-integrated irradiance of these two atmospheres
with standard 1D model atmospheres used in SSI modeling.
Title: Assessment of and a Solution to the Intensity Diffusion Error
Intrinsic in Short-Characteristic Radiative Transfer
Authors: Peck, Courtney; Rast, Mark; Criscuoli, Serena
Bibcode: 2017SPD....4820701P
Altcode:
Short characteristic radiative transfer coupled with 3D MHD simulations
are routinely used to compare simulations with observations of the
solar atmosphere. While it has been known that the method of short
characteristics radiative transfer results in intensity diffusion,
it has been routinely employed to solve radiative transfer due to
its computational expediency. In this talk, we discuss the effect
of spatial smearing due to short characteristics radiative transfer
under both linear and high-order interpolation. We then demonstrate
that linear interpolation results in an effective spatial smearing
related to the number of grid heights above the τ = 1 surface and
conserves intensity. Additionally, we show that the use of high-order
strict monotonic interpolation reduces the amount of smearing, but at
the expense of error in the integrated emergent intensity. Finally,
we demonstrate that these issues can be easily avoided at no
added computational expense by interpolating the atmosphere onto a
ray-directed grid and computing the radiative transfer for vertical
rays through the grid.
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.
Bibcode: 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: A Study of Solar Photospheric Temperature Gradient Variation
Using Limb Darkening Measurements
Authors: Criscuoli, Serena; Foukal, Peter
Bibcode: 2017ApJ...835...99C
Altcode: 2016arXiv161110201C
The variation in area of quiet magnetic network measured over the
sunspot cycle should modulate the spatially averaged photospheric
temperature gradient, since temperature declines with optical depth
more gradually in magnetic flux tube atmospheres. Yet, limb darkening
measurements show no dependence upon activity level, even at an rms
precision of 0.04%. We study the sensitivity of limb darkening to
changes in area filling factor using a 3D MHD model of the magnetized
photosphere. The limb darkening change expected from the measured
11-year area variation lies below the level of measured limb darkening
variations, for a reasonable range of magnetic flux in quiet network
and internetwork regions. So the remarkably constant limb darkening
observed over the solar activity cycle is not inconsistent with
the measured 11-year change in area of quiet magnetic network. Our
findings offer an independent constraint on photospheric temperature
gradient changes reported from measurements of the solar spectral
irradiance from the Spectral Irradiance Monitor, and recently, from
wavelength-differential spectrophotometry using the Solar Optical
Telescope aboard the HINODE spacecraft.
Title: Lower solar atmosphere and magnetism at ultra-high spatial
resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
Bibcode: 2016arXiv161202348C
Altcode:
We present the scientific case for a future space-based telescope
aimed at very high spatial and temporal resolution imaging of the
solar photosphere and chromosphere. Previous missions (e.g., HINODE,
SUNRISE) have demonstrated the power of observing the solar photosphere
and chromosphere at high spatial resolution without contamination from
Earth's atmosphere. We argue here that increased spatial resolution
(from currently 70 km to 25 km in the future) and high temporal cadence
of the observations will vastly improve our understanding of the
physical processes controlling solar magnetism and its characteristic
scales. This is particularly important as the Sun's magnetic field
drives solar activity and can significantly influence the Sun-Earth
system. At the same time a better knowledge of solar magnetism can
greatly improve our understanding of other astrophysical objects.
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.
Bibcode: 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″ wide and ≈8.0″ 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−1 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−1 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: Angular Dependence of the Facular-Sunspot Coverage Relation
as Derived by MDI Magnetograms
Authors: Criscuoli, S.
Bibcode: 2016SoPh..291.1957C
Altcode: 2016SoPh..tmp..108C; 2016arXiv160604851C
Previous studies have shown that the variation over the solar magnetic
activity cycle of the area of facular/network features identified from
broad-band and narrow-band imagery is positively correlated with the
sunspot area and number, the relation being described as either linear
or quadratic. On the other hand, the temporal variation of the spatial
distributions of faculae, network and sunspots follows patterns that
are less obviously correlated, so that we expect the relation that
describes variation of the area coverage of different types of magnetic
features to vary with the position over the disk. In this work we employ
Michelson Doppler Interferometer (MDI) full-disk magnetograms acquired
during solar cycle 23 and at the beginning of cycle 24 to investigate
the relation between the coverage of magnetic elements characterized
by different amounts of magnetic flux and located at different angular
distances from disk center with the sunspot number. In agreement with
some previous studies we find that daily data are best described by
a quadratic function while data averaged over six months are best
described by a linear function. In both cases the coefficients of
the fits show large dependence on the position over the disk and
the magnetic flux. We also find that toward disk center six-month
averaged data show asymmetries between the ascending and the descending
phases. The implications for solar irradiance modeling are discussed.
Title: Relation between Intensity Contrast and Magnetic Field for
Active and Quiet Regions Observed on the Solar Photosphere
Authors: Whitney, Taylor; Criscuoli, Serena; Norton, Aimee Ann
Bibcode: 2016SPD....47.1209W
Altcode:
Current solar modeling techniques assume that active and quiet regions
can be considered in the same manner. However, recent results from
numerical simulations and high-spatial resolution observations indicate
that radiative properties of small magnetic elements depend on whether
they are located in plages, network, or quiet areas. These studies have
been carried out typically at, or close to, disk center. In this study,
data from the Helioseismic Magnetic Imager (HMI) are used to investigate
the differences between magnetic elements located in Network/Quiet and
Active Regions (AR) observed at different positions over the solar disk.
Title: Investigation of photospheric temperature gradient variations
using limb darkening measurements and simulations
Authors: Criscuoli, Serena; Foukal, Peter V.
Bibcode: 2016SPD....4730301C
Altcode:
The temperature stratifications of magnetic elements and unmagnetized
plasma are different, so that changes of the facular and network
filling factor over the cycle modify the average temperature gradient
in the photosphere.Such variations have been suggested to explain
irradiance measurements obtained by the SIM spectrometers in he
visible and infrared spectral ranges. On the other hand, limb darkening
measurements show no dependence upon activity level. We investigate the
sensitivity of limb darkening to changes in network area filling factor
using a 3-D MHD model of the magnetized photosphere. We find that the
expected limb darkening change due to the measured 11- yr variation
in filling factor lies outside the formal 99% confidence limit of
the limb darkening measurements. This poses important constraints for
observational validation of 3D-MHD simulations.
Title: Facular-sunspot coverage relation derived by MDI magnetograms
Authors: Criscuoli, Serena
Bibcode: 2016SPD....47.1003C
Altcode:
We employ MDI full-disk magnetograms acquired during Cycle 23 and
at the beginning of Cycle 24 to investigate the relation between
the filling factor of magnetic elements characterized by different
amount of magnetic flux and located at different angular distance from
disk center with the sunspot number. In agreement with some previous
studies we find that daily data are best described by a quadratic
function while data averaged over 6-months are best described by a
linear function. In both cases the coefficients of the fits show large
dependence on the position over the disk and the magnetic flux. We also
find that toward disk center 6-months averaged data show asymmetries
between the ascending and the descending phase.
Title: Interpreting Irradiance Distributions Using High-Resolution
3D MHD Simulations
Authors: Peck, Courtney; Rast, Mark; Criscuoli, Serena; Uitenbroek,
Han; Rempel, Matthias D.
Bibcode: 2016SPD....4730302P
Altcode:
We present initial results of studies aimed at understanding the
impact of the unresolved magnetic field distribution on solar spectral
irradiance. Using high-resolution 3D MHD simulations (from MURaM code)
and spectral synthesis (with the RH code), we examine the emergent
spectra of two atmospheres with similar mean field strengths but
differing imposed-field conditions at wavelengths spanning from
visible to infrared. Comparing the contrast against the magnetic
field strength for the two magnetic simulations, we find differences
in the distributions of contrasts versus field strength. We repeat
the analysis after convolving the images with the PSF of a typical
solar telescope (1-meter) and discuss the potential implications for
irradiance modeling and future steps.
Title: A Multi-instrument Analysis of a C4.1 Flare Occurring in a
δ Sunspot
Authors: Guglielmino, S. L.; Zuccarello, F.; Romano, P.; Cristaldi,
A.; Ermolli, I.; Criscuoli, S.; Falco, M.; Zuccarello, F. P.
Bibcode: 2016ApJ...819..157G
Altcode:
We present an analysis of multi-instrument space- and ground-based
observations relevant to a C4.1 solar flare that occurred in the
active region (AR) NOAA 11267 on 2011 August 6. Solar Dynamics
Observatory observations indicate that at the flare’s beginning,
it was localized in the preceding sunspot of the AR, which exhibits
a δ configuration. Along the polarity inversion line between its
opposite polarities we find a large shear angle of about 80°. The
helicity accumulation shows that the AR does not obey the general
hemispheric helicity rule. At the flare peak, unique observations
taken with the X-Ray Telescope aboard Hinode reveal that the bulk
of the X-ray emission takes place in the δ-spot region, where
the plasma heats up to ≈ 1.9\cdot {10}7 K. During the
gradual phase, we observe the development of a Y-shaped structure in
the corona and in the high chromosphere. An extruding structure forms,
being directed from the emitting region above the δ spot toward the
following sunspot. This structure cools down in a few tens of minutes
while moving eastward along a direction opposite to the flare ribbon
expansion. Finally, remote brightenings are found at the easternmost
footpoint of this structure, appearing as a third flare ribbon in the
chromosphere. After some minutes, RHESSI measurements show that the
X-ray emission is localized in the region close to the crossing point
of the coronal Y-shaped structure. Simultaneously, high-resolution
(0.″15) observations performed at the Swedish 1 m Solar Telescope
indicate a decreasing trend of the Ca II H intensity in the flare
ribbons with some transient enhancements. All these findings suggest
that this event is a manifestation of magnetic reconnection, likely
induced by an asymmetric magnetic configuration in a highly sheared
region.
Title: The Effects of Magnetic Field Morphology on the Determination
of Oxygen and Iron Abundances in the Solar Photosphere
Authors: Moore, Christopher S.; Uitenbroek, Han; Rempel, Matthias;
Criscuoli, Serena; Rast, Mark
Bibcode: 2016AAS...22712501M
Altcode:
The solar chemical abundance (or a scaled version of it) is
implemented in numerous astrophysical analyses. Thus, an accurate
and precise estimation of the solar elemental abundance is crucial
in astrophysics.We have explored the impact of magnetic fields
on the determination of the solar photospheric oxygen andiron
abundances using 3D radiation-magnetohydrodynamic (MHD) simulations
of convection. Specifically, weexamined differences in abundance
deduced from three classes of atmospheres simulated with the MURaM
code: apure hydrodynamic (HD) simulation, an MHD simulation with
a local dynamo magnetic field that has saturated withan unsigned
vertical field strength of 80 G at the optical depth unity surface,
and an MHD simulation with an initially imposed vertical mean field
of 80 G. We use differential equivalent width analysis for diagnosing
abundances derived from five oxygen and four iron spectral lines of
differing wavelength, oscillator strength, excitation potential, and
Lande g-factor, and find that the morphology of the magnetic field
is important to the outcome of abundance determinations. The largest
deduced abundance differences are found in the vertical mean field
simulations and small scale unresolved field resulting from the local
dynamo has a smaller impact on abundance determinations.
Title: Merging of small-size magnetic elements observed at the
Swedish Solar Tower
Authors: Criscuoli, Serena
Bibcode: 2015TESS....120105C
Altcode:
We investigate the evolution of physical properties of small-size
magnetic elements of the same polarity during merging. We found
that at the merging the line of sight velocity and magnetic flux
abruptly change, while the photometric contrast increases with a
delay proportional to the formation height of the observed wavelength
range. These results suggest that the merging causes MHD perturbations
propagating from the photosphere to the higher layers of the atmosphere.
Title: Understanding the Fe I Line Measurements Returned by the
Helioseismic and Magnetic Imager (HMI)
Authors: Cohen, D. P.; Criscuoli, S.; Farris, L.; Tritschler, A.
Bibcode: 2015SoPh..290..689C
Altcode: 2015SoPh..tmp...17C; 2015arXiv150202559C
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) observes the Sun at the Fe I 6173 Å line and
returns full-disk maps of line-of-sight (LOS) observables including
the magnetic flux density, velocities, Fe I line width, line depth, and
continuum intensity. These data are estimated through an algorithm (the
MDI-like algorithm, hereafter) that combines observables obtained at six
wavelength positions within the Fe I 6173 Å line. To properly interpret
such data, it is important to understand any effects of the instrument
and of the pipeline that generates these data products. We tested
the accuracy of the line width, line depth, and continuum intensity
returned by the MDI-like algorithm using various one-dimensional (1D)
atmosphere models. It was found that HMI estimates of these quantities
are highly dependent on the shape of the line, therefore on the LOS
angle and the magnetic flux density associated with the model, and less
to line shifts with respect to the central positions of the instrument
transmission profiles. In general, the relative difference between
synthesized values and HMI estimates increases toward the limb and
with the increase of the field; the MDI-like algorithm seems to fail
in regions with fields larger than approximately 2000 G. Instrumental
effects were investigated by analyzing HMI data obtained at daily
intervals for a span of three years at disk center in the quiet Sun
and hourly intervals for a span of 200 hours. The analysis revealed
periodicities induced by the variation of the orbital velocity of the
observatory with respect to the Sun, and long-term trends attributed to
instrument adjustments, re-calibrations, and instrumental degradation.
Title: The Signature of Flare Activity in Multifractal Measurements
of Active Regions Observed by SDO/HMI
Authors: Giorgi, F.; Ermolli, I.; Romano, P.; Stangalini, M.;
Zuccarello, F.; Criscuoli, S.
Bibcode: 2015SoPh..290..507G
Altcode: 2017arXiv170506708G; 2014SoPh..tmp..132G
Recent studies indicate that measurements of fractal and multifractal
parameters of active regions (ARs) are inefficient tools for
distinguishing ARs on the basis of the flare activity or to predict
flare events. In an attempt to validate this result on a large
observation data set of higher spatial and temporal resolution and
higher flux sensitivity than employed in previous studies, we analyzed
high-cadence time series of line-of-sight magnetograms of 43 ARs
characterized by different flare activity, which were observed with
SDO/HMI from May 2010 to December 2013. On these data, we estimated
four parameters, the generalized fractal dimensions D0 and
D8, and the multifractal parameters Cdiv and
Ddiv. We found distinct average values of the parameters
measured on ARs that have hosted flares of different class. However,
the dispersion of values measured on ARs that have produced the same
class of events is such that the parameters deduced from distinct
classes of flaring regions can also largely overlap. Based on the
results of our measurements, C- and M-class flaring ARs are practically
indistinguishable, and the same is true for M- and X-class flaring
ARs. We only found consistent changes on the time series of the
measured parameters on ≈ 50 % of the ARs and ≈ 50 % of the M-
and X-class events. We show that these results hold for fractal and
multifractal parameter estimates based on total unsigned and signed
flux data of the ARs.
Title: The Effects of Magnetic Field Morphology on the Determination
of Oxygen and Iron Abundances in the Solar Photosphere
Authors: Moore, Christopher S.; Uitenbroek, Han; Rempel, Matthias;
Criscuoli, Serena; Rast, Mark P.
Bibcode: 2015ApJ...799..150M
Altcode:
We have explored the impact of magnetic fields on the determination
of the solar photospheric oxygen and iron abundances using
three-dimensional radiation-magnetohydrodynamic (MHD) simulations
of convection. Specifically, we examined differences in abundance
deduced from three classes of atmospheres simulated with the MURaM
code: a pure hydrodynamic (HD) simulation, an MHD simulation with
a local dynamo magnetic field that has saturated with an unsigned
vertical field strength of 80 G at τ = 1, and an MHD simulation with
an initially imposed vertical mean field of 80 G. We use differential
equivalent width analysis for diagnosing abundances derived from
five oxygen and four iron lines of differing wavelength, oscillator
strength, excitation potential, and Landé g-factor, and find that
the morphology of the magnetic field is important to the outcome of
abundance determinations. The largest deduced abundance differences are
found in the vertical mean field simulations, where the O I and Fe I
abundance corrections compared to the pure HD case are ~+0.011 dex and
+0.065 dex respectively. Small scale unresolved field resulting from
the local dynamo has a smaller impact on abundance determinations,
with corrections of -0.0001 dex and +0.0044 dex in the magnetized
compared to the pure HD simulations. While the overall influence of
magnetic field on abundance estimates is found to be small, we stress
that such estimates are sensitive not only to the magnitude of magnetic
field but also to its morphology.
Title: Angular Variation of Solar Feature Contrast in Full-Disk
G-Band Images
Authors: Blunt, Sarah Caroline; Criscuoli, Serena; Ermolli, Ilaria;
Giorgi, Fabrizio
Bibcode: 2015AAS...22513703B
Altcode:
We investigate the center-to-limb variation (CLV) of the contrasts of
four types of solar surface features observed in the G-Band (430.6 nm,
FWHM 1.2 nm) by analyzing 12 high quality full-disk images obtained
from the Rome Precision Solar Photometric Telescope. The studied
features, specifically network, enhanced network, plage, and bright
plage, were singled out based on their brightness signatures in mean
simultaneous Ca II K images using an intensity threshold technique. We
compared our results with those obtained from high-resolution (HR)
observations, and with the outputs of the spectral synthesis performed
on semi-empirical models and magneto hydrodynamic (MHD) simulations. We
find that the measured contrasts are systematically lower than those of
HR observational results, as was expected due to the lower resolution
of the analyzed observations. We also find that our observations best
reflect the CLV derived from the recent one-dimensional atmospheric
models described in Fontenla et al 2011 with respect to results obtained
from earlier similar models. The measured CLV also agrees with those
derived from the syntheses of MHD simulations and HR observations,
if spatial resolution effects are properly taken into account. This
work was carried out through the National Solar Observatory Summer
Research Assistantship (SRA) Program. The National Solar Observatory is
operated by the Association of Universities for Research in Astronomy,
Inc. (AURA) under cooperative agreement with the National Science
Foundation. This work was also partially supported by the European
Union's Seventh Programme for Research, Technological Development
and Demonstration under the grant agreements in 312495 (SOLARNET)
and 313188 (SOLID).
Title: Dynamical behaviour of photospheric bright points during
merging
Authors: Criscuoli, S.; Stangalini, M.; Ermolli, I.; Zuccarello, F.;
Cristaldi, A.; Falco, M.; Guglielmino, S.; Giorgi, F.
Bibcode: 2014AGUFMSH41C4152C
Altcode:
We investigate the merging of bright points observed at high spatial
and temporal resolution with CRISP/SST in a quiet region region. We
analyze the MHD perturbations excited during the merging, their role
in the energy budget of the magnetic structure and the potential role
that they can play in heating the upper layers of the Sun's atmosphere.
Title: "Future Solar Physics with the Daniel K. Inouye Solar Telescope
(DKIST)"
Authors: Criscuoli, S.
Bibcode: 2014AGUFMSH31C..02C
Altcode:
During the last decades, the synergistic development of large
aperture telescopes and real time and post facto techniques for
image degradation correction, have allowed observations of the solar
atmosphere at resolutions up to tens of arcsecond. The analysis of
these data, together with the development of sophisticated inversion
techniques to infer properties of the magnetic field, have largely
improved our understanding of many aspects of solar physics which
include the nature and properties of small scale magnetic elements,
the fine structuring of sunspots, the properties of granulation and
its interaction with the magnetic field, the propagation of waves
from the photosphere to the chromosphere, the highly dynamics and
fine structuring of the chromosphere. Still several issues, like the
origin and nature of the photospheric magnetism, especially in the
quiet Sun, the properties of the chromospheric magnetic field, the
chromospheric energy budget, and the properties of the photospheric
and chromospheric plasma and magnetic field during eruptive events,
remain open. Moreover, state-of-the-art magneto hydrodynamic simulations
produce structures down to the spatial resolution of the simulations
themselves (generally, few kilometers per pixel), which are unresolved
in current observations. The Daniel K. Inouye Solar Telescope (DKIST),
with its four meter aperture and state-of-the-art adaptive optics, will
allow the acquisition of hundredths of arcsecond spatial resolution
data. In this contribution I review the main open questions that the
analysis of DKIST observations will allow to address.
Title: Fractal and Multifractal Properties of Active Regions as Flare
Precursors: A Case Study Based on SOHO/MDI and SDO/HMI Observations
Authors: Ermolli, I.; Giorgi, F.; Romano, P.; Zuccarello, F.;
Criscuoli, S.; Stangalini, M.
Bibcode: 2014SoPh..289.2525E
Altcode: 2014SoPh..tmp...38E
Several studies indicate that fractal and multifractal parameters
inferred from solar photospheric magnetic field measurements may
help assessing the eruptive potential of Active Regions (ARs) and
also predicting their flare activity. We further investigate this
topic, by exploring the sensitivity of some parameters already
used in the literature on data and methods employed for their
estimation. In particular, we measured the generalized fractal
dimensions D0 and D8, and the multifractal
parameters Cdiv and Ddiv, on the time series of
photospheric magnetograms of the flaring AR NOAA 11158 obtained with
the SOHO/MDI and SDO/HMI. The observations by the latter instrument are
characterized by a higher spatial and temporal resolution, as well as
higher flux sensitivity, than the ones obtained from SOHO/MDI, which
were widely employed in earlier studies. We found that the average
and peak values of complexity parameters measured on the two data sets
agree within measurement uncertainties. The temporal evolution of the
parameters measured on the two data sets show rather similar trends,
but the ones derived from the SOHO/MDI observations show larger and
spurious variations over time than those deduced from analysis of
the corresponding SDO/HMI data. We also found a larger sensitivity
of these measurements to characteristics of the data analyzed than
reported by earlier studies. In particular, analysis of the higher
resolution and higher cadence SDO/HMI data allows us also to detect
slight variations of the complexity indicators that cannot be derived
from the analysis of the SOHO/MDI data. These variations occur right
after the major events in the analyzed AR. They may be the signature
of photospheric effects of coronal magnetic field re-arrangement.
Title: Dynamic Properties along the Neutral Line of a Delta Spot
Inferred from High-resolution Observations
Authors: Cristaldi, A.; Guglielmino, S. L.; Zuccarello, F.; Romano,
P.; Falco, M.; Rouppe van der Voort, L.; de la Cruz Rodríguez, J.;
Ermolli, I.; Criscuoli, S.
Bibcode: 2014ApJ...789..162C
Altcode:
Delta (δ) spots are complex magnetic configurations of sunspots
characterized by umbrae of opposite polarity sharing a common
penumbra. In order to investigate the fine structure of the region
separating the two magnetic polarities of a δ spot, we studied the
morphology, the magnetic configuration, and the velocity field in
such a region using observations of active region (AR) NOAA 11267
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the
Swedish Solar Telescope on 2011 August 6. The analysis of CRISP data
shows upflows and downflows of ~ ± 3 km s-1 in proximity
of the δ spot polarity inversion line (PIL), and horizontal motions
along the PIL of the order of ~1 km s-1. The results
obtained from the SIR inversion of CRISP data also indicate that the
transverse magnetic field in the brighter region separating the two
opposite magnetic polarities of the δ spot is tilted about ~45°
with respect to the PIL. Solar Dynamics Observatory/Helioseismic and
Magnetic Imager observations confirm the presence of motions of ~
± 3 km s-1 in proximity of the PIL, which were observed
to last 15 hr. From the data analyzed, we conclude that the steady,
persistent, and subsonic motions observed along the δ spot PIL can be
interpreted as being due to Evershed flows occurring in the penumbral
filaments that show a curved, wrapped configuration. The fluting of
the penumbral filaments and their bending, continuously increased by
the approaching motion of the negative umbra toward the positive one,
give rise to the complex line-of-sight velocity maps that we observed.
Title: Understanding Measurements Returned by the Helioseismic and
Magnetic Imager
Authors: Cohen, Daniel Parke; Criscuoli, Serena
Bibcode: 2014AAS...22412351C
Altcode:
The Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics
Observatory (SDO) observes the Sun at the FeI 6173 Å line and returns
full disk maps of line-of-sight observables including the magnetic
field flux, FeI line width, line depth, and continuum intensity. To
properly interpret such data it is important to understand any issues
with the HMI and the pipeline that produces these observables. At this
aim, HMI data were analyzed at both daily intervals for a span of 3
years at disk center in the quiet Sun and hourly intervals for a span
of 200 hours around an active region. Systematic effects attributed to
issues with instrument adjustments and re-calibrations, variations in
the transmission filters and the orbital velocities of the SDO were
found while the actual physical evolutions of such observables were
difficult to determine. Velocities and magnetic flux measurements are
less affected, as the aforementioned effects are partially compensated
for by the HMI algorithm; the other observables are instead affected
by larger uncertainties. In order to model these uncertainties, the
HMI pipeline was tested with synthetic spectra generated through
various 1D atmosphere models with radiative transfer code (the RH
code). It was found that HMI estimates of line width, line depth, and
continuum intensity are highly dependent on the shape of the line,
and therefore highly dependent on the line-of-sight angle and the
magnetic field associated to the model. The best estimates are found
for Quiet regions at disk center, for which the relative differences
between theoretical and HMI algorithm values are 6-8% for line width,
10-15% for line depth, and 0.1-0.2% for continuum intensity. In general,
the relative difference between theoretical values and HMI estimates
increases toward the limb and with the increase of the field; the
HMI algorithm seems to fail in regions with fields larger than ~2000
G. This work is carried out through the National Solar Observatory
Research Experiences for Undergraduate (REU) site program, which
is co-funded by the Department of Defense in partnership with the
NSF REU Program. The National Solar Observatory is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA)
under cooperative agreement with the National Science Foundation.
Title: Interpretation of Solar Irradiance Monitor Measurements
through Analysis of 3D MHD Simulations
Authors: Criscuoli, S.; Uitenbroek, H.
Bibcode: 2014ApJ...788..151C
Altcode: 2014arXiv1404.4651C
Measurements from the Spectral Irradiance Monitor (SIM) on board the
Solar Radiation and Climate Experiment mission indicate that solar
spectral irradiance at visible and IR wavelengths varies in counter
phase with the solar activity cycle. The sign of these variations is not
reproduced by most of the irradiance reconstruction techniques based on
variations of surface magnetism employed so far, and it is not yet clear
whether SIM calibration procedures need to be improved or if instead
new physical mechanisms must be invoked to explain such variations. We
employ three-dimensional magnetohydrodynamic simulations of the solar
photosphere to investigate the dependence of solar radiance in SIM
visible and IR spectral ranges on variations of the filling factor of
surface magnetic fields. We find that the contribution of magnetic
features to solar radiance is strongly dependent on the location on
the disk of the features, which are negative close to disk center and
positive toward the limb. If features are homogeneously distributed over
a region around the equator (activity belt), then their contribution
to irradiance is positive with respect to the contribution of HD
snapshots, but decreases with the increase of their magnetic flux for
average magnetic flux larger than 50 G in at least two of the visible
and IR spectral bands monitored by SIM. Under the assumption that the
50 G snapshots are representative of quiet-Sun regions, we thus find
that the Spectral Irradiance can be in counter-phase with the solar
magnetic activity cycle.
Title: Interpretation of Solar Spectral Irradiance variations from
analysis of 3D MHD simulations
Authors: Criscuoli, Serena
Bibcode: 2014AAS...22432361C
Altcode:
Recent measurements by SIM radiometers show that the solar irradiance
varies in the Visible and IR bands in counterphase with the magnetic
activity cycle. Such variations have been largely debated, as they
do not agree with measurements obtained with other radiometers, while
the majority of reconstruction techniques employed to reconstruct the
total irradiance do not reproduce such signals. It is therefore yet
not clear whether the SIM measurements are still not fully compensated
for residual instrumental degradation, or if instead new physical
phenomena must be invoked to explain such variations. A large part
of reconstruction techniques employ semiempirical one-dimensional
models. In this contribution I will explain the limitations of such
models and why we expect a noticeable improvement of reconstructions
obtained by 3-D magnetohydrodynamic simulations. I will also present
some preliminary results obtained with the STAGGER simulations which
indicate that solar irradiance in the Visible and IR bands might be in
counterphase with the magnetic activity, as measured by SIM radiometers.
Title: The statistical distribution of the magnetic-field strength
in G-band bright points
Authors: Criscuoli, S.; Uitenbroek, H.
Bibcode: 2014A&A...562L...1C
Altcode: 2013arXiv1312.2611C
Context. G-band bright points are small-sized features characterized
by high photometric contrast. Theoretical investigations indicate
that these features have associated magnetic-field strengths of 1
to 2 kG. Results from observations, however, lead to contradictory
results, indicating magnetic fields of only kG strength in some and
including hG strengths in others.
Aims: To understand the
differences between measurements reported in the literature, and to
reconcile them with results from theory, we analyzed the distribution
of the magnetic-field strength of G-band bright features identified
in synthetic images of the solar photosphere and its sensitivity
to observational and methodological effects.
Methods: We
investigated the dependence of magnetic-field strength distributions of
G-band bright points identified in 3D magnetohydrodynamic simulations
on feature selection method, data sampling, alignment, and spatial
resolution.
Results: The distribution of the magnetic-field
strength of G-band bright features shows two peaks, one at about 1.5
kG and one below 1 hG. The former corresponds to magnetic features,
the second mostly to bright granules. Peaks at several hG are obtained
only on spatially degraded or misaligned data.
Conclusions:
Simulations show that magnetic G-band bright points have typically
associated field strengths of a few kG. Field strengths in the hG
range can result from observational effects, which explains the
discrepancies presented in the literature. Our results also indicate
that results from spectro-polarimetric inversions with an imposed unit
filling-factor should be employed with great caution.
Title: Comparison of Physical Properties of Quiet and Active Regions
Through the Analysis of Magnetohydrodynamic Simulations of the
Solar Photosphere
Authors: Criscuoli, S.
Bibcode: 2013ApJ...778...27C
Altcode: 2013arXiv1309.5494C
Recent observations have shown that the photometric and dynamic
properties of granulation and small-scale magnetic features depend on
the amount of magnetic flux of the region they are embedded in. We
analyze results from numerical hydrodynamic and magnetohydrodynamic
simulations characterized by different amounts of average magnetic
flux and find qualitatively the same differences as those reported
from observations. We show that these different physical properties
result from the inhibition of convection induced by the presence of
the magnetic field, which changes the temperature stratification of
both quiet and magnetic regions. Our results are relevant for solar
irradiance variations studies, as such differences are still not
properly taken into account in irradiance reconstruction models.
Title: Effects of Unresolved Magnetic Field on Fe I 617.3 and 630.2
nm Line Shapes
Authors: Criscuoli, S.; Ermolli, I.; Uitenbroek, H.; Giorgi, F.
Bibcode: 2013ApJ...763..144C
Altcode: 2012arXiv1212.2190C
The contribution of the quiet Sun to solar irradiance variability,
either due to changes of the solar effective temperature or
to the presence of unresolved magnetic field, is still poorly
understood. In this study we investigate spectral line diagnostics
that are sensitive to both temperature variations and the presence of
small-scale unresolved magnetic features in these areas of the solar
atmosphere. Specifically, we study the dependence on the magnetic flux
density of three parameters describing the shape of two magnetically
sensitive Fe I lines, at 630.2 nm and 617.3 nm, namely the line core
intensity (IC), the FWHM, and the equivalent width (EQW). To this end
we analyze observations of active region NOAA 11172, acquired with
Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope,
as well as results from numerical synthesis. Our results show that IC
is sensitive to both temperature and magnetic flux density variations,
FWHM is mostly affected by magnetic field changes, and EQW is mostly
sensitive to temperature. Variations of a few percent of the measured
line parameters are found in observational data that were spatially
degraded to represent quiet-Sun, disk-center, medium-resolution
observations. It is therefore possible to disentangle magnetic from
pure thermodynamic effects by the comparison of temporal variations
of the EQW and the FWHM of either of the two Fe I lines.
Title: A novel method to estimate temperature gradients in stellar
photospheres.
Authors: Uitenbroek, H.; Criscuoli, S.
Bibcode: 2013MmSAI..84..369U
Altcode:
Inversions utilizing one-dimensional atmospheric models provide
information about the thermal stratification of stars, but these
models are in general not unique nor sufficiently descriptive of the
physical conditions of a star. Here we propose a novel model-independent
method to better constrain the temperature stratification in a stellar
atmosphere. In our method we employ intensities measured at opacity
conjugate wavelength pairs to improve the estimate of temperature
stratification that is obtained from radiation temperatures in
combination with the Eddington-Barbier relation. This relation can
lead to significant errors because of the non-linear dependence of the
source function on optical depth, even in the case of continua. Such
errors are substantially reduced by combining observations at pairs of
conjugate continua, which have the same H- opacity between
them, and therefore pairwise form at the same height.
Title: Small-scale brightenings observed in active regions with SST
and Hinode
Authors: Cristaldi, A.; Guglielmino, S. L.; Zuccarello, F.; Ermolli,
I.; Falco, M.; Criscuoli, S.
Bibcode: 2013MmSAI..84..339C
Altcode:
Ca II H brightenings are good proxies of transient phenomena occurring
in the solar chromosphere. We analyze temporal series of Ca II H
filtergrams taken with SST at extreme high resolution (0.15 arcsec)
at different line positions, simultaneously with spectropolarimetric
data in the Fe I pair at 630.2 nm and Hinode/SOT data, to study the
interactions between flux systems. Ca II H core brightenings have
been observed in areas surrounding the sunspot penumbra, following
their evolution.
Title: On the sensitivity of FeI 617.3 and 630.2 nm line shapes to
unresolved magnetic fields
Authors: Criscuoli, S.; Ermolli, I.; Uitenbroek, H.; Giorgi, F.
Bibcode: 2013MmSAI..84..335C
Altcode:
Our study was aimed at obtaining line diagnostics sensitive to
effects of small scale magnetic features that are unresolved in
observations. We studied the dependence on the magnetic flux of
parameters describing the two Fe I lines at 630.2 and 617.3 nm. In
particular, we analyzed the line core intensity (IC), full width
half maximum (FWHM), and equivalent width (EQW) of Stokes I in NOAA
11172 observed with IBIS at the Dunn Solar Telescope on March 17th,
2011. Our results show that IC is sensitive to both temperature and
magnetic flux variations, while FWHM is sensitive mostly to magnetic
flux variations. The EQW is almost insensitive to magnetic flux and
mostly sensitive to temperature. Variations of a few percents of line
parameters are found in data spatially degraded to represent quiet
Sun, disk-centre conditions in medium resolution observations. Such
variations can be observed with instruments as SOLIS/VSM, SDO/HMI,
HINODE/SOT. Shapes of investigated lines can therefore be employed to
investigate physical properties of quiet Sun regions, and in particular
to disentangle magnetic and thermodynamic effects an d their variations
over the magnetic cycle.
Title: Sunspot evolution observed with SST.
Authors: Falco, M.; Zuccarello, F.; Criscuoli, S.; Cristaldi, A.;
Guglielmino, S. L.; Ermolli, I.
Bibcode: 2013MmSAI..84..345F
Altcode:
We report on the evolution of an active region NOAA 11263 observed
with SST at extreme high spatial resolution (0.15 arcsec). We analyzed
spectral and spectropolarimetric data acquired at Fe I 557.6 nm and
630.2 nm spectral ranges, respectively, to study the magnetic field
properties and the dynamics of the plasma in the umbral and penumbral
region of the sunspot. Interestingly, images acquired in photospheric
continuum show twisting motions of the penumbral filaments. Moreover,
we investigate if MMFs are present during the evolution of the
sunspot. Brightenings in Ca II H line are also noticed, indicating
the occurrence of transient phenomena in the chromosphere.
Title: Spectro-polarimetric Observations of Moving Magnetic Features
around a Pore
Authors: Zuccarello, F.; Berrilli, F.; Criscuoli, S.; Del Moro, D.;
Ermolli, I.; Giannattasio, F.; Giorgi, F.; Romano, P.; Viticchiè, B.
Bibcode: 2012ASPC..463...51Z
Altcode:
Moving Magnetic Features (MMFs) are small-size magnetic elements that
are seen to stream-out from sunspots. Although several observations
suggest that MMFs are closely related to the existence and presence
of penumbral filaments, there are some very few observations that
report MMFs streaming from pores and sunspots after the penumbra has
disappeared. Here we report on the first high spectral, spatial and
temporal resolution observations of type II and III MMFs streaming out
from a small pore and compare our results with previous observations of
features streaming out from penumbrae. We analyzed spectro-polarimetric
observations of NOAA 11005 acquired with the IBIS instrument at
the Dunn Solar Telescope in the Fe I 617.3 nm and the Ca II 854.2 nm
spectral lines, and in the G-band. We show that the characteristics of
the investigated MMFs agree with those reported in the literature for
MMFs which stream out from spots with penumbrae. We believe that our
results provide new information that might be helpful in the future
development and upgrade of numerical modeling of the generation of
MMFs in the lack of a penumbra.
Title: IBIS: High-Resolution Multi-Height Observations and Magnetic
Field Retrieval
Authors: Del Moro, D. .; Berrilli, F.; Stangalini, M.; Giannattasio,
F.; Piazzesi, R.; Giovannelli, L.; Viticchiè, B.; Vantaggiato, M.;
Sobotka, M.; Jurčák, J.; Criscuoli, S.; Giorgi, F.; Zuccarello, F.
Bibcode: 2012ASPC..463...33D
Altcode:
IBIS (Interferometric BIdimensional Spectrometer) allows us to measure
the four Stokes parameters in several spectroscopic lines with high
spatial and spectral resolutions. With this information, we can
retrieve both the dynamics and the magnetic field at different layers
of the Photosphere and Chromosphere. The high spectral, spatial and
temporal resolutions and the polarimetric sensitivity of IBIS allows
us to study different phenomena taking place in the solar atmosphere
with new tools. As an example, we highlight some applications of
IBIS observations and analysis:
· Radiative and dynamical
properties of Photospheric Bright Points versus their magnetic field
concentration.
· Close up analysis of magnetic, velocity and
temperature field in a solar pore.
· MHD wave propagation from
the photosphere to the chromosphere in complex magnetic configuration.
Title: High cadence spectropolarimetry of moving magnetic features
observed around a pore
Authors: Criscuoli, S.; Del Moro, D.; Giannattasio, F.; Viticchié,
B.; Giorgi, F.; Ermolli, I.; Zuccarello, F.; Berrilli, F.
Bibcode: 2012A&A...546A..26C
Altcode: 2012arXiv1208.2039C
Context. Moving magnetic features (MMFs) are small-size magnetic
elements that are seen to stream out from sunspots, generally during
their decay phase. Several observational results presented in the
literature suggest them to be closely related to magnetic filaments
that extend from the penumbra of the parent spot. Nevertheless,
few observations of MMFs streaming out from spots without penumbra
have been reported. The literature still lacks analyses of the
physical properties of these features.
Aims: We investigate
physical properties of monopolar MMFs observed around a small pore
that had developed penumbra in the days preceding our observations
and compare our results with those reported in the literature for
features observed around sunspots.
Methods: We analyzed NOAA
11005 during its decay phase with data acquired at the Dunn Solar
Telescope in the Fe i 617.3 nm and the Ca ii 854.2 nm spectral lines
with IBIS, and in the G-band. The field of view showed monopolar
MMFs of both polarities streaming out from the leading negative
polarity pore of the observed active region. Combining different
analyses of the data, we investigated the temporal evolution of the
relevant physical quantities associated with the MMFs as well as the
photospheric and chromospheric signatures of these features.
Results: We show that the characteristics of the investigated MMFs
agree with those reported in the literature for MMFs that stream out
from spots with penumbrae. Moreover, observations of at least two of the
observed features suggest them to be manifestations of emerging magnetic
arches. Appendices A and B, and a movie are available in electronic
form at http://www.aanda.org
Title: A Comparative Analysis of Photospheric Bright Points in an
Active Region and in the Quiet Sun
Authors: Romano, P.; Berrilli, F.; Criscuoli, S.; Del Moro, D.;
Ermolli, I.; Giorgi, F.; Viticchié, B.; Zuccarello, F.
Bibcode: 2012SoPh..280..407R
Altcode: 2012SoPh..tmp...26R
We present a comparative study of photometric and dynamic properties
of photospheric bright points (BPs) observed at the disk centre in
the active region (AR) NOAA 10912 and in the quiet Sun. We found that
the average concentration of BPs is 54% larger in the AR than in the
quiet Sun. We also measure a decrease of the BP concentration and an
increase of their size moving away from the AR centre. However, these
variations can be ascribed to the variation of the spatial resolution
and image quality in the field of view of the AR dataset. We also found
that BPs in the quiet Sun are associated with larger downflow motions
than those measured within the AR. Finally, from our measurements of
contrast and velocity along the line of sight, we deduced that BPs
are less bright in high magnetic flux density regions than in quiet
regions, due to a lower efficiency of convection in the former regions.
Title: Physical properties of Moving Magnetic Features observed
around a pore
Authors: Criscuoli, S.; Del Moro, D.; Giannattasio, F.; Viticchié,
B.; Giorgi, F.; Ermolli, I.; Zuccarello, F.; Berrilli, F.
Bibcode: 2012EAS....55...87C
Altcode:
Movies of magnetograms of sunspots often show small-size magnetic
patches that move radially away and seem to be expelled from the
field of the spot. These patches are named Moving Magnetic Features
(MMFs). They have been mostly observed around spots and have been
interpreted as manifestations of penumbral filaments. Nevertheless,
few observations of MMFS streaming out from spots without penumbra
have been reported. He we investigate the physical properties of MMFs
observed around the field of a pore derived by the analyses of high
spectral, spatial and temporal resolution data acquired at the Dunn
Solar Telescope with IBIS. We find that the main properties of the
investigated features agree with those reported for MMFs observed
around regular spots. These results indicate that an improvement of
current numerical simulations is required to understand the generation
of MMFs in the lack of penumbrae.
Title: Properties of G-band Bright Points derived from IBIS
observations
Authors: Criscuoli, S.; Del Moro, D.; Giorgi, F.; Romano, P.; Berrilli,
F.; Ermolli, I.; Viticchié, B.; Zuccarello, F.
Bibcode: 2012MSAIS..19...93C
Altcode: 2010arXiv1011.4890C
We have investigated properties of photospheric Bright Points (BPs)
observed in an Active Region during its decay phase and in a quiet Sun
region. We have analyzed two sets of photospheric observations taken
with IBIS (Interferometric Bidimensioal Spectrometer) at the NSO Dunn
Solar Telescope. The first set consists of spectral data acquired in the
Fe I 709.0 nm and Ca I 854.2 nm lines and simultaneous broad-band and
of G-band observations. The second set consists of spectro-polarimetric
observations in the Fe I 630.15 nm - 630.25 nm doublet and simultaneous
white light and G-band observations. The relation between BP
filling factor and RMS image contrast indicates that, on average,
BPs cover up to 3% of the solar surface outside Active Regions. The
relation between area and intensity values of the features identified
on both data sets suggests that they are composed of aggregations of
magnetic flux elements. The horizontal velocity values are as high
as 2 km/s, thus supporting the scenario of BPs motion contributing to
the coronal heating.
Title: Recent results from optical synoptic observations of the
solar atmosphere with ground-based instruments
Authors: Ermolli, I.; Criscuoli, S.; Giorgi, F.
Bibcode: 2011CoSka..41...73E
Altcode:
This brief review summarizes three research topics recently addressed
with synoptic observations carried out at the Ca II K line and other
continuum spectral ranges and relating to solar variability occurring
on time scales from a day to a few decades. Namely, the irradiance
reconstructions from intensity images, the radiative emission of solar
features in the Ca II K line, and the comparison of time series of Ca
II K spectroheliograms.
Title: Why One-dimensional Models Fail in the Diagnosis of Average
Spectra from Inhomogeneous Stellar Atmospheres
Authors: Uitenbroek, Han; Criscuoli, Serena
Bibcode: 2011ApJ...736...69U
Altcode: 2011arXiv1101.2643U
We investigate the feasibility of representing a structured
multi-dimensional stellar atmosphere with a single one-dimensional
average stratification for the purpose of spectral diagnosis of the
atmosphere's average spectrum. In particular, we construct four
different one-dimensional stratifications from a single snapshot
of a magnetohydrodynamic simulation of solar convection: one by
averaging its properties over surfaces of constant height and three
by averaging over surfaces of constant optical depth at 500 nm. Using
these models, we calculate continuum and atomic and molecular line
intensities and their center-to-limb variations. From an analysis of
the emerging spectra, we identify three main reasons why these average
representations are inadequate for accurate determination of stellar
atmospheric properties through spectroscopic analysis. These reasons are
nonlinearity in the Planck function with temperature, which raises the
average emergent intensity of an inhomogeneous atmosphere above that of
an average-property atmosphere, even if their temperature-optical depth
stratification is identical; nonlinearities in molecular formation with
temperature and density, which raise the abundance of molecules of an
inhomogeneous atmosphere over that in a one-dimensional model with the
same average properties; and the anisotropy of convective motions,
which strongly affects the center-to-limb variation of line-core
intensities. We argue therefore that a one-dimensional atmospheric
model that reproduces the mean spectrum of an inhomogeneous atmosphere
necessarily does not reflect the average physical properties of that
atmosphere and is therefore inherently unreliable.
Title: Evolution of Small-scale Magnetic Features Streaming-out from
a Pore
Authors: Criscuoli, S.; Del Moro, D.; Romano, P.; Berrilli, F.;
Ermolli, I. : Giorgi, F.; Vitichhié, B.; Zuccarello, F.
Bibcode: 2011ASPC..437..493C
Altcode:
We present results from observations of Moving Magnetic Features
(MMFs) of different types observed on region NOAA 11005. The analyses
is based on spectro-polarimetric data obtained with the Interferometric
Bidimensional Spectrometer (IBIS) at various spectral ranges. We present
new evidences of bipolar MMFs observed to stream out from pores and
show the temporal evolution of magnetic, dynamic and morphological
properties of these features.
Title: Line Shape Effects on Intensity Measurements of Solar Features:
Brightness Correction to SOHO MDI Continuum Images
Authors: Criscuoli, S.; Ermolli, I.; Del Moro, D.; Giorgi, F.;
Tritschler, A.; Uitenbroek, H.; Vitas, N.
Bibcode: 2011ApJ...728...92C
Altcode: 2010arXiv1012.2561C
Continuum intensity observations obtained with the Michelson
Doppler Imager (MDI) on board the SOHO mission provide long time
series of filtergrams that are ideal for studying the evolution of
large-scale phenomena in the solar atmosphere and their dependence on
solar activity. These filtergrams, however, are not taken in a pure
continuum spectral band, but are constructed from a proxy, namely a
combination of filtergrams sampling the Ni I 6768 Å line. We studied
the sensitivity of this continuum proxy to the shape of the nickel line
and to the degradation in the instrumental transmission profiles. We
compared continuum intensity measurements near the nickel line with
MDI proxy values in three sets of high-resolution spectro-polarimetric
data obtained with the Interferometric Bidimensional Spectrometer,
and in synthetic data, obtained from multi-dimensional simulations of
magneto-convection and one-dimensional atmosphere models. We found that
MDI continuum measurements require brightness corrections which depend
on magnetic field strength, temperature and, to a smaller extent, plasma
velocity. The correction ranges from 2% to 25% in sunspots, and is,
on average, less than 2% for other features. The brightness correction
also varies with position on the disk, with larger variations obtained
for sunspots, and smaller variations obtained for quiet Sun, faculae,
and micropores. Correction factors derived from observations agree
with those deduced from the numerical simulations when observational
effects are taken into account. Finally, we found that the investigated
potential uncertainties in the transmission characteristics of MDI
filters only slightly affect the brightness correction to proxy
measurements.
Title: Imaging Spectropolarimetry with IBIS. II. On the Fine Structure
of G-band Bright Features
Authors: Viticchié, B.; Del Moro, D.; Criscuoli, S.; Berrilli, F.
Bibcode: 2010ApJ...723..787V
Altcode: 2010arXiv1009.0721V
We present new results from first observations of the quiet solar
photosphere performed through the Interferometric BIdimensional
Spectrometer (IBIS) in spectropolarimetric mode. IBIS allowed us to
measure the four Stokes parameters in the Fe I 630.15 nm and Fe I
630.25 nm lines with high spatial and spectral resolutions for 53
minutes; the polarimetric sensitivity achieved by the instrument is
3 × 10-3 the continuum intensity level. We focus on the
correlation which emerges between the G-band bright feature brightness
and magnetic filling factor of ~103 G (kG) fields derived
by inverting the Stokes I and V profiles. In more detail, we present
the correlation first in a pixel-by-pixel study of a sime3'' wide
bright feature (a small network patch) and then we show that such a
result can be extended to all the bright features found in the data
set at any instant of the time sequence. The higher the kilo-Gauss
filling factor associated to a feature, the higher the brightness of
the feature itself. Filling factors up to sime35% are obtained for
the brightest features. Considering the values of the filling factors
derived from the inversion analysis of spectropolarimetric data and the
brightness variation observed in the G-band data we put forward an upper
limit for the smallest scale over which magnetic flux concentrations
in intergranular lanes produce a G-band brightness enhancement
(sime0farcs1). Moreover, the brightness saturation observed for feature
sizes comparable to the resolution of the observations is compatible
with the large G-band bright features being clusters of sub-arcsecond
bright points. This conclusion deserves to be confirmed by forthcoming
spectropolarimetric observations at higher spatial resolution.
Title: Radiative emission of solar features in the Ca II K line:
comparison of measurements and models
Authors: Ermolli, I.; Criscuoli, S.; Uitenbroek, H.; Giorgi, F.;
Rast, M. P.; Solanki, S. K.
Bibcode: 2010A&A...523A..55E
Altcode: 2010arXiv1009.0227E
Context. The intensity of the Ca II K resonance line observed with
spectrographs and Lyot-type filters has long served as a diagnostic of
the solar chromosphere. However, the literature contains a relative
lack of photometric measurements of solar features observed at this
spectral range.
Aims: We study the radiative emission of various
types of solar features, such as quiet Sun, enhanced network, plage,
and bright plage regions, identified on filtergrams taken in the Ca II
K line.
Methods: We analysed full-disk images obtained with the
PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative
emission of disk features on the filter bandpass. We also performed a
non-local thermal equilibrium (NLTE) spectral synthesis of the Ca II
K line integrated over the bandpass of PSPT filters. The synthesis
was carried out by utilizing the partial frequency redistribution
(PRD) with the most recent set of semi-empirical atmosphere models
in the literature and some earlier atmosphere models. As the studied
models were computed by assuming the complete redistribution formalism
(CRD), we also performed simulations with this approximation for
comparison.
Results: We measured the center-to-limb variation
of intensity values for various solar features identified on PSPT
images and compared the results obtained with those derived from the
synthesis. We find that CRD calculations derived using the most recent
quiet Sun model, on average, reproduce the measured values of the
quiet Sun regions slightly more accurately than PRD computations with
the same model. This may reflect that the utilized atmospheric model
was computed assuming CRD. Calculations with PRD on earlier quiet Sun
model atmospheres reproduce measured quantities with a similar accuracy
as to that achieved here by applying CRD to the recent model. We
also find that the median contrast values measured for most of the
identified bright features, disk positions, and filter bandpasses
are, on average, a factor ≈1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The
discrepancy between measured and modeled values decreases by ≈12%
after taking into account straylight effects on PSPT images. When
moving towards the limb, PRD computations display closer agreement with
the data than performed in CRD. Moreover, PRD computations on either
the most recent or the earlier atmosphere models of bright features
reproduce measurements from plage and bright plage regions with a
similar accuracy. Appendix A is only available in electronic form
at http://www.aanda.org
Title: A decline and fall in the future of Italian Astronomy?
Authors: Antonelli, Angelo; Antonuccio-Delogu, Vincenzo; Baruffolo,
Andrea; Benetti, Stefano; Bianchi, Simone; Biviano, Andrea; Bonafede,
Annalisa; Bondi, Marco; Borgani, Stefano; Bragaglia, Angela; Brescia,
Massimo; Brucato, John Robert; Brunetti, Gianfranco; Brunino, Riccardo;
Cantiello, Michele; Casasola, Viviana; Cassano, Rossella; Cellino,
Alberto; Cescutti, Gabriele; Cimatti, Andrea; Comastri, Andrea;
Corbelli, Edvige; Cresci, Giovanni; Criscuoli, Serena; Cristiani,
Stefano; Cupani, Guido; De Grandi, Sabrina; D'Elia, Valerio; Del
Santo, Melania; De Lucia, Gabriella; Desidera, Silvano; Di Criscienzo,
Marcella; D'Odorico, Valentina; Dotto, Elisabetta; Fontanot, Fabio;
Gai, Mario; Gallerani, Simona; Gallozzi, Stefano; Garilli, Bianca;
Gioia, Isabella; Girardi, Marisa; Gitti, Myriam; Granato, Gianluigi;
Gratton, Raffaele; Grazian, Andrea; Gruppioni, Carlotta; Hunt, Leslie;
Leto, Giuseppe; Israel, Gianluca; Magliocchetti, Manuela; Magrini,
Laura; Mainetti, Gabriele; Mannucci, Filippo; Marconi, Alessandro;
Marelli, Martino; Maris, Michele; Matteucci, Francesca; Meneghetti,
Massimo; Mennella, Aniello; Mercurio, Amata; Molendi, Silvano; Monaco,
Pierluigi; Moretti, Alessia; Murante, Giuseppe; Nicastro, Fabrizio;
Orio, Marina; Paizis, Adamantia; Panessa, Francesca; Pasian, Fabio;
Pentericci, Laura; Pozzetti, Lucia; Rossetti, Mariachiara; Santos,
Joana S.; Saro, Alexandro; Schneider, Raffaella; Silva, Laura;
Silvotti, Roberto; Smart, Richard; Tiengo, Andrea; Tornatore, Luca;
Tozzi, Paolo; Trussoni, Edoardo; Valentinuzzi, Tiziano; Vanzella, Eros;
Vazza, Franco; Vecchiato, Alberto; Venturi, Tiziana; Vianello, Giacomo;
Viel, Matteo; Villalobos, Alvaro; Viotto, Valentina; Vulcani, Benedetta
Bibcode: 2010arXiv1007.1455A
Altcode:
On May 27th 2010, the Italian astronomical community learned with
concern that the National Institute for Astrophysics (INAF) was going
to be suppressed, and that its employees were going to be transferred to
the National Research Council (CNR). It was not clear if this applied to
all employees (i.e. also to researchers hired on short-term contracts),
and how this was going to happen in practice. In this letter, we give
a brief historical overview of INAF and present a short chronicle of
the few eventful days that followed. Starting from this example, we
then comment on the current situation and prospects of astronomical
research in Italy.
Title: Radiative emission of solar features in Ca II K
Authors: Criscuoli, S.; Ermolli, I.; Fontenla, J.; Giorgi, F.; Rast,
M.; Solanki, S. K.; Uitenbroek, H.
Bibcode: 2010MmSAI..81..773C
Altcode: 2010arXiv1002.0244C
We investigated the radiative emission of different types of solar
features in the spectral range of the Ca II K line. We analyzed
full-disk 2k × 2k observations from the Precision Solar Photometric
Telescope (PSPT). The data were obtained by using three narrow-band
interference filters that sample the Ca II K line with different pass
bands. Two filters are centered in the line core, the other in the red
wing of the line. We measured the intensity and contrast of various
solar features, specifically quiet Sun (inter-network), network,
enhanced network, plage, and bright plage (facula) regions. Moreover,
we compared the results obtained with those derived from the numerical
synthesis performed for the three PSPT filters with a widely used
radiative code on a set of reference semi-empirical atmosphere models.
Title: Magnetic evolution of superactive regions. Complexity and
potentially unstable magnetic discontinuities
Authors: Criscuoli, S.; Romano, P.; Giorgi, F.; Zuccarello, F.
Bibcode: 2009A&A...506.1429C
Altcode: 2009arXiv0908.3608C
Context: It is widely accepted that solar flares are manifestations
of magnetic reconnection events taking place in the solar
atmosphere. Several aspects of these events remain unclear, although
many efforts have been devoted to the investigation of magnetic
field configurations at flare occurrence sites.
Aims: In this
work, we have studied the temporal evolution of some properties of
a sample of superactive regions with the aim to single out the most
significant for flare activity forecasting.
Methods: We have
investigated properties of 14 superactive regions, observed between
January 1st 2000 and December 31st 2006 with MDI/SOHO instrument and
characterized by a particularly intense flare activity during their
passage on the solar disk. We have analyzed the temporal evolution of
fractal and multifractal properties of photospheric magnetic fields,
namely the generalized fractal dimension and the contribution and
dimensional diversities, which describe geometrical properties of
the magnetic field, as well as the potential unstable volumes of
magnetic discontinuities above the studied ARs, which may provide
information about the magnetic field configuration in upper layers of
the atmosphere. Correlations of these quantities with the flare index,
which provides information about the flare activity of a region, have
also been estimated.
Results: We found that in 50% of our sample
the generalized fractal dimension is correlated with the flare index
computed over windows of 50 h, while the contribution diversity and the
dimensional diversity are anticorrelated with the same index. A clear
increase of the potential unstable volume of magnetic discontinuities in
the corona is observed before the phases characterized by more frequent
and intense flares. We also found that the free energy distribution
functions of unstable volumes of the analyzed superactive regions can be
fitted with straight lines whose slope is larger than the values found
in previous works for less active magnetic regions.
Conclusions:
The generalized fractal dimension and the potential unstable volume
of magnetic discontinuities are the most suitable for statistical
investigations of relations with flare activity over longer (50 h)
and shorter (few hours) time intervals, respectively. Appendix
A is only available in electronic form at http://www.aanda.org
Title: Observation of bipolar moving magnetic features streaming
out from a naked spot
Authors: Zuccarello, F.; Romano, P.; Guglielmino, S. L.; Centrone,
M.; Criscuoli, S.; Ermolli, I.; Berrilli, F.; Del Moro, D.
Bibcode: 2009A&A...500L...5Z
Altcode:
Context: Mechanisms responsible for active-region formation, evolution,
and decay have been investigated by many authors and several common
features have been identified. In particular, a key element in the
dispersal of the magnetic field seems to be the presence of magnetic
elements, called moving magnetic features (MMFs).
Aims: We
analyze the short-lived sunspot group NOAA 10977, which appeared on
the solar disk between 2 and 8 December 2007, to study the details of
its emergence and decay phases.
Methods: We performed a multi
wavelength analysis of the region using images at visible (G band
and Hα) and near-IR (Ca II) wavelengths acquired by both the IBIS
instrument and SOT/HINODE, EUV images (17.1 nm) acquired by TRACE, and
MDI and SOT magnetograms.
Results: The observed region exhibits
some peculiarities. During the emergence phase the formation of the
f-pore was initially observed, while the p-polarity later formed a
naked spot, i.e., a sunspot without a penumbra. We measured a moat
flow around this spot, and observed some MMFs streaming out from it
during the decay phase. The characteristics of these MMFs allowed us
to classify them as type I (U-shaped) MMFs. They were also cospatial
with sites of increased brightness both in the photosphere and the
chromosphere.
Conclusions: The presence of bipolar MMFs in a
naked spot indicates that current interpretation of bipolar MMFs,
as extensions of the penumbral filaments beyond the sunspot outer
boundaries, should be revised, to take into account this observational
evidence. We believe that our results provide new insights into
improving models of sunspot evolution.
Title: Photometric Properties of Magnetic Elements: Resolved and
Unresolved Features
Authors: Criscuoli, S.
Bibcode: 2009ASPC..405..303C
Altcode:
We investigate, by numerical simulations, the photometric signature of
magnetic flux tubes in the solar photosphere. We show that the observed
contrast profiles are determined not only by the physical properties
of the tube and its surroundings, but also by the peculiarities of the
observations, including the line/continuum formation height and the
spatial resolution. The aim is to understand these contributions well
enough so that multi-wavelength observations can begin to disentangle
them.
Title: The digitized archive of the Arcetri
spectroheliograms. Preliminary results from the analysis of Ca II
K images
Authors: Ermolli, I.; Marchei, E.; Centrone, M.; Criscuoli, S.;
Giorgi, F.; Perna, C.
Bibcode: 2009A&A...499..627E
Altcode:
Context: The increasing interest in the recovery of historic data and
the availability of new hardware resources is leading to projects to
digitize photographic archives of astronomical observations. In addition
to preservation, solar archives are digitized because the observations
stored in such archives have the potential of providing unique
information about solar magnetism, which can improve knowledge about
long-term solar changes.
Aims: The solar tower of the Arcetri
Astrophysical Observatory produced synoptic observations of the solar
atmosphere from 1926 to 1974. The photographic archive contains about
13 000 plates of full-disk Ca II K and Hα spectroheliograms acquired
during about 5000 observing days. The program for the digitization and
distribution of the images of this archive was carried out at the Rome
Astronomical Observatory and is now complete.
Methods: Nearly 13
000 plates were scanned with a commercial device and stored on DVD, as
well as in a database accessible online. Image processing was developed
for the reduction of the data and their photographic calibration.
Results: The obtained digital archive provides the astronomical
community with the Arcetri historical solar observations and with
measurements of solar features identified in such observations. As
an example, we show some preliminary results concerning the temporal
variability of facular regions identified in the time-series of Ca
II K observations.
Conclusions: Existing programs studying
solar activity and variability, as well as new scientific projects,
will benefit from the Arcetri digital archive, since it extends the
temporal baseline of digital full-disk solar observations, and it
provides data for the inter-calibration of results obtained from
measurements performed in similar observations.
Title: Photometric properties of resolved and unresolved magnetic
elements
Authors: Criscuoli, S.; Rast, M. P.
Bibcode: 2009A&A...495..621C
Altcode: 2008arXiv0812.1727C
Aims: We investigate the photometric signature of magnetic flux tubes
in the solar photosphere.
Methods: We developed two-dimensional,
static numerical models of isolated and clustered magnetic flux
tubes. We investigated the emergent intensity profiles at different
lines-of-sight for various spatial resolutions and opacity models.
Results: We found that both geometric and photometric properties
of bright magnetic features are determined not only by the physical
properties of the tube and its surroundings, but also by the
particularities of the observations, including the line/continuum
formation height, the spatial resolution, and the image analysis
techniques applied. We show that some observational results presented
in the literature can be interpreted by considering bright magnetic
features to be clusters of smaller elements, rather than a monolithic
flux tube.
Title: Enhancing the spatial resolution of IBIS spectrograms via
Multi-Frame Blind Deconvolution.
Authors: Del Moro, D.; Centrone, M.; Giorgi, F.; Criscuoli, S.
Bibcode: 2009MmSAI..80..270D
Altcode:
We compare the spatial resolution between observed and restored
spectrographs of the solar photosphere, acquired with IBIS
(Interferometric BIdimensional Spectrometer) currently feeded by
the HOAO (High-Order Adaptive Optics) channel of the DST (Dunn Solar
Telescope). The observations consist of 3×120 sequences, containing
a 25 images scan of the NiI 676.8 nm line, a 15 images scan of the FeI
709.0 nm line and a 13 images scan of the CaI 854.2 nm line. For each
spectral image a broadband (661± 5 nm) and a G-band (430.5 ± 1 nm)
counterpart were acquired simultaneously. The images were successively
restored via the MFBD (Multi-Frame Blind Deconvolution) procedure to
achieve near diffraction limit resolution in the whole FOV for the
whole dataset duration.
Title: Studying the decay phase of a short-lived active region
with coordinated DST/IBIS, Hinode/EIS+SOT+XRT, SOHO/MDI and TRACE
observations
Authors: Zuccarello, F.; Berrilli, F.; Centrone, M.; Contarino, L.;
Criscuoli, S.; Del Moro, D.; Ermolli, I.; Giorgi, F.; Guglielmino,
L. S.; Salerno, C.; Spadaro, D.; Romano, P.
Bibcode: 2008ESPM...12.2.56Z
Altcode:
This study concerns the physical processes occurring during the decay
phase of the short-lived active region NOAA 10977, as evaluated from
analysis of data gathered using ground- (DST/IBIS) and space-based
(Hinode/EIS+SOT+XRT, SOHO/MDI and TRACE) facilities. The coordinated
observing campaign was performed from December 1st to 9th, 2007,
covering several spectral ranges, with unprecedented spatial and
spectral resolution. We present preliminary results of the Doppler
analysis of plasma motions evaluated from monochromatic images taken
along the Ca II (8542 Å) and the Fe I (7049 Å) spectral lines with
IBIS. We also report results concerning the horizontal displacements of
photospheric magnetic structures and advection flows as obtained from
application of Local Correlation Tracking (LCT) and Two-Level Structure
Tracking (TST) techniques to both the LoS magnetograms taken by MDI
and to high resolution intensity maps obtained by IBIS at DST/NSO. Further contributions to understanding the mechanisms at the base
of the magnetic field diffusion are provided from the inversion of
the Stokes profiles of the photospheric Fe I lines at 6301.5 Å and
6302.5 Å, obtained with SOT/SP, and the analysis of filtergrams in
the core of the Ca II H line (3968.5 ± 3 Å) and images in G-band
(4305 ± 8 Å) taken by SOT/BFI, as well as EIS data and images taken
by the thin Be of XRT, and by TRACE at 171 Å and 1600 Å.
Title: Temporal Evolution of Magnetic Properties of Super Active
Regions
Authors: Criscuoli, S.; Giorgi, F.; Romano, P.; Zuccarello, F.
Bibcode: 2008ESPM...12.2.57C
Altcode:
It is widely accepted that solar flares are manifestations of magnetic
reconnection events taking place in the solar atmosphere. Several
aspects of these events remain unclear, although many efforts have
been devoted to the investigation of magnetic field configurations at
flares occurrence. In this work we investigate some properties of
26 super active regions, observed between Jan 1 2000 and Dec 31 2006
with MDI/SOHO instrument and characterized by a particularly intense
flare activity during their passage on the solar disc. We analyzed
the temporal evolution of some fractal and multifractal estimators, as
well as other parameters like the distorsion of the magnetic inversion
line and the number of the singular points in potential fields with
the aim to single out the most significant for flare forecasting.
Title: Radiative Properties of Magnetic Elements at the Spectral
Range of the Ni I 676.8 nm Line
Authors: Ermolli, I.; Centrone, M.; Criscuoli, S.; Giorgi, F.;
Berrilli, F.; Del Moro, D.
Bibcode: 2008ESPM...12.2.48E
Altcode:
We present measurements of the radiative properties of magnetic
elements at some spectral ranges, including the NiI 676.8 nm line. This
mid-photospheric absorption line is used to derive the continuum
intensity data and helioseismic measurements provided by the MDI and
GONG instruments, respectively. We show the results obtained from the
analysis of high resolution spatial and spectral measurement of two
magnetic regions observed on November 2007 at DST/IBIS. We investigate
the line profile changes in presence of magnetic field. We quantify
the effects of such changes in the continuum intensity derived by
SOI/MDI measurements.
Title: Stray-light restoration of full-disk CaII K solar observations:
a case study
Authors: Criscuoli, S.; Ermolli, I.
Bibcode: 2008A&A...484..591C
Altcode: 2008arXiv0804.1010C
Aims: We investigate whether restoration techniques, such as those
developed for application to current observations, can be used to
remove stray-light degradation effects on archive CaII K full-disk
observations. We analyze to what extent these techniques can recover
homogeneous time series of data.
Methods: We develop a restoration
algorithm based on a method presented by Walton & Preminger (1999,
ApJ, 514, 959). We apply this algorithm to data for both present-day
and archive CaII K full-disk observations, which were acquired using
the PSPT mounted at the Rome Observatory, or obtained by digitization
of Mt Wilson photographic-archive spectroheliograms.
Results: We
show that the restoring algorithm improves both spatial resolution and
photometric contrast of the analyzed solar observations. We find that
the improvement in spatial resolution is similar for analyzed recent
and archive data. On the other hand, the improvement of photometric
contrast is quite poor for the archive data, with respect to the
one obtained for the present-day images. We show that the quality of
restored archive data depends on the photographic calibration applied to
the original observations. In particular, photometry can be recovered
with a restoring algorithm if the photographic-calibration preserves
the intensity information stored in the original data, principally
outside the solar-disk observations.
Title: Photometric properties of magnetic elements: resolved and
unresolved features
Authors: Criscuoli, Serena
Bibcode: 2007arXiv0712.3294C
Altcode:
We investigate, by numerical simulations, the photometric signature of
magnetic flux tubes in the solar photosphere. We show that the observed
contrast profiles are determined not only by the physical properties
of the tube and its surroundings, but also by the peculiarities of
the observations, including the line/continuum formation height and
the spatial and spectral resolution. The aim is to understand these
contributions well enough so that multi-wavelength observations can
begin to disentangle them.
Title: Photometric properties of facular features over the activity
cycle
Authors: Ermolli, I.; Criscuoli, S.; Centrone, M.; Giorgi, F.;
Penza, V.
Bibcode: 2007A&A...465..305E
Altcode:
Aims:We have analyzed the contrast of facular features identified
in a large dataset of PSPT full-disk photometric images and SoHO/MDI
magnetograms, obtained from 1998 to 2005. The aim of this work is to
contribute to the improvement of semi-empirical atmospheric models
and of irradiance studies and to understand the reasons for the
controversial results of facular contrast already presented in the
literature.
Methods: We used different identification methods
to analyze their effects upon the results obtained. We also analyzed
the effects of the limited information content in the analyzed
images.
Results: We show that selection effects associated
with the identification method may produce significant differences
in the results. The facular contrast is not only a function of both
selection methods and the heliocentric angle, but also of feature size,
activity level, and content of the analyzed images. Comparisons of the
results obtained with computations of the most recent semi-empirical
atmospheric models of facular features show that these models reproduce
limb-angle corrected contrast measurements with an offset up to ≈1%
from the disk center to μ = 0.3.
Title: Photometric Properties Of Complex Magnetic Elements In The
Solar Photosphere
Authors: Criscuoli, Serena
Bibcode: 2007PhDT.......314C
Altcode:
In this thesis I investigate the photometric and geometric properties
of bright magnetic features in the lower solar atmosphere. The
contribution of these features to Total Solar Irradiance (TSI here
after) variations observed at different temporal scales has been broadly
showed during the last years. Nevertheless, measurements and theoretical
investigations of their properties, on which reconstructions of TSI
variations are based, have produced discrepant results. In order to
interpret discrepancies presented in the literature and to improve
our understanding of physical properties of magnetic elements, both
experimental and theoretical aspects have been investigated. In the
first part of the thesis I show results obtained by the analysis
of full disk PSPT broad band images from Rome and Hawaii. Geometric
properties and the possible connection with photometric properties
have been investigated through the measurement of fractal dimension
of features observed in chromosphere. Results I obtain agree very well
with the ones presented in the literature carried out on similar data
and with the same fractal dimension estimator. The fractal dimension
increases in fact with features area and reaches a plateau at areas
larger than about 1000-2000 Mm2. Nevertheless, by the analyses of images
of fractals whose dimension is known by the theory, I show that fractal
dimension estimation is critically effected by pixelization, technique
employed to select magnetic structures on images and resolution. In
particular the increase of fractal dimension with object size is an
effect of pixelization and thus some conclusions previously drawn
in the literature should be revisited. Photometric properties are
investigated by the analyses of contrast of identified features in two
photospheric bands and in the chromosphere. In particular the variation
of the contrast with position on the solar disk and with object size
is investigated. I show that the contrast in the chromosphere is not
dependent on disk position and that in the photosphere monotonically
increases from the center toward the limb. A comparison with previously
published results shows a better agreement with authors that employed
an identification methods similar to the ones I employed to select
magnetic features on images. The contrast, especially at the limb,
is also critically affected by seeing. Comparison of the scaling of
average and maximum contrast with object size suggests that the smaller
magnetic elements, whose clustering forms the features analyzed,
are characterized by different photometric properties. The increase
of average contrast with object size, very similar to the increase
observed for the fractal dimension, is instead an effect of filling
factor. In order to investigate the physical origin of the results
and validate some of the conclusions drawn, 2D numerical codes based
on the magnetic flux tube model have been developed. Plane parallel
gray atmosphere in LTE is supposed and radiative and convective energy
transport mechanisms have been taken into account. In particular two
classes of models are investigated. In the first one convection is
modelled by the Mixing length theory and radiation by the radiative
diffusion approximation. In the second one only radiation is taken
into account, but radiative diffusion approximation is dropped and
radiative equilibrium is imposed by an iterative scheme. The presence
of the magnetic field is mimicked by imposing a lower pressure and
density in the magnetic region. In order to evaluate the radiation
field a numerical code, based on the short characteristic technique,
was developed. A detailed description of the code, as well as results
obtained by tests aimed to investigate and compare different numerical
techniques and spurious effects, are presented. The radiative flux
is finally evaluated by a quadrature scheme. At this aim two schemes
have been developed and compared. The software developed has allowed to
investigate radiation field through the flux tube models studied. I show
that the presence of a magnetic structure generates areas of different
shapes and contrast around it. These features vary with the position
of the structures on the solar disk (the sight angle) and have spatial
scales smaller than the typical scale of a flux tube (about 100 km),
so resolution better than 0.1 arcsec is required to observe them. The
contrast of magnetic features varies also in function of the optical
depth, so that for the same model different center to limb variations
of the contrast can be observed. This indicates that when observing
magnetic structures at different wavelengths the contrast can be very
different, thus partially explaining the discrepant results obtained
in the literature. Investigation of the results also shows that the
center to limb variation of the contrast reflects the temperature
stratification inside and outside the tube. Measurements carried out
at different wavelengths are thus fundamental for the determination
of temperature of magnetic structures and for the investigation of
their physical properties. ii
Title: On the reliability of the fractal dimension measure of solar
magnetic features and on its variation with solar activity
Authors: Criscuoli, S.; Rast, M. P.; Ermolli, I.; Centrone, M.
Bibcode: 2007A&A...461..331C
Altcode: 2006astro.ph..9748C
Context: Several studies have investigated the fractal and multifractal
nature of magnetic features in the solar photosphere and its variation
with the solar magnetic activity cycle.
Aims: Here we extend
those studies by examining the fractal geometry of bright magnetic
features at higher atmospheric levels, specifically in the solar
chromosphere. We analyze structures identified in CaIIK images obtained
with the Precision Solar Photometric Telescopes (PSPTs) at Osservatorio
Astronomico di Roma (OAR) and Mauna Loa Solar Observatory (MLSO).
Methods: Fractal dimension estimates depend on the estimator employed,
the quality of the images, and the structure identification techniques
used. We examine both real and simulated data and employ two different
perimeter-area estimators in order to understand the sensitivity of
the deduced fractal properties to pixelization and image quality.
Results: The fractal dimension of bright “magnetic” features
in CaIIK images ranges between values of 1.2 and 1.7 for small and
large structures respectively. This size dependency largely reflects
the importance of image pixelization in the measurement of small
objects. The fractal dimension of chromospheric features does not show
any clear systematic variation with time over the period examined,
the descending phase of solar cycle 23.
Conclusions: .These
conclusions, and the analysis of both real and synthetic images on
which they are based, are important in the interpretation of previously
reported results.
Title: SINERGIES (Sun, INterplanetary, EaRth Ground-based InstrumEntS)
or the potential of the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena.
Authors: Amata, E.; Candidi, M.; Centrone, M.; Consolini, G.;
Contarino, L.; Criscuoli, S.; De Lauretis, M.; Diego, P.; Ermolli,
I.; Francia, P.; Giorgi, F.; Laurenza, M.; Magrí, M.; Marcucci, F.;
Massetti, S.; Messerotti, M.; Oliviero, M.; Penza, V.; Perna, C.;
Pietropaolo, E.; Romano, P.; Severino, G.; Spadaro, D.; Storini, M.;
Vellante, M.; Villante, U.; Zlobec, P.; Zuccarello, F.
Bibcode: 2006MSAIS...9...82A
Altcode:
The Italian Network for Ground-Based Observations of Sun-Earth
Phenomena, whose instruments monitor the Sun, the Interplanetary
Space, and the Earth's Magnetosphere, has recently started to operate
in a coordinated scheme. In this paper, we describe few significant
examples of this coordination effort. 1) During the year 2003, several
coordinated observational campaigns were carried out in order to study
the solar photospheric dynamics. 2) Reconstruction of TSI in time, for
periods spanning from a solar rotation up to the whole current solar
cycle. 3) Extreme solar events occurring during the late October -
early November 2003.
Title: SINERGIES, the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena .
Authors: Amata, E.; Berrilli, F.; Candidi, M.; Cantarano, S.; Centrone,
M.; Consolini, G.; Contarino, L.; Criscuoli, S.; De Lauretis, M.;
Del Moro, D.; Egidi, A.; Ermolli, I.; Francia, P.; Giordano, S.;
Giorgi, F.; Oliviero, M.; Magrí, M.; Marcucci, F.; Massetti, S.;
Messerotti, M.; Parisi, M.; Perna, C.; Pietropaolo, E.; Romano, P.;
Severino, G.; Spadaro, D.; Storini, M.; Vellante, M.; Villante, U.;
Zlobec, P.; Zuccarello, F.
Bibcode: 2006MSAIS...9...79A
Altcode:
Since many years, the complex phenomena occurring on the Sun have
been continuously monitored by different and complementary ground
based instruments managed by groups of the Italian Astrophysics
Community. Recently some of these instruments have started to operate in
a coordinated scheme, the Italian Network for Ground-Based Observations
of Sun-Earth Phenomena. In this paper, we describe the characteristics
of the nodes belonging to the Network, called SINERGIES, the scientific
objectives, the facilities and the data storage system of the Network
itself. Due to its capabilities, the Network allows the Italian Solar
Terrestrial Physics Community to monitor solar activity and its effect
on the Earth.
Title: First Implementation Of Phase Diversity At Themis
Authors: Criscuoli, S.; Moro, D. Del; Bonet, J. A.; Márquez, I.
Bibcode: 2005SoPh..228..177C
Altcode:
Phase diversity techniques are robust post-processing tools for image
enhancement and correction of telescopic and atmospheric induced
aberrations. We present results obtained applying the Partitioned
Phase-Diverse Speckle (PPDS) technique to images acquired at THEMIS. We
also present an image quality estimator based on image power spectrum
content we developed in order to automatically evaluate the results
of large amount of data.
Title: A study of the photometrical properties of solar magnetic
features by numerical simulation
Authors: Criscuoli, S.; Rast, M. P.
Bibcode: 2005MmSAI..76..945C
Altcode:
Existing numerical simulations reproduce many of the observed
geometrical and photometrical characteristics of solar magnetic
structures. Nonetheless, some quite fundemental properties, such as
network center-to-limb variation and facular contrast, which depend on
both the structure's size and magnetic field intensity, are still only
partially understood. In order to investigate these problems, we have
developed a radiative transfer code, based on the short characteristics
method, that enables detailed study of the radiative properties of
individual magnetic flux tubes and unresolved aggregates of them.
Title: Phase diversity at THEMIS : first implementation
Authors: Del Moro, D.; Criscuoli, S.; Bonet, J. A.; Márquez, I.;
Lemen, C.; Briand, C.
Bibcode: 2003MmSAI..74..811D
Altcode:
Phase diversity techniques actually provide robust post-processing
methods to restore solar images degraded by seeing-optical
aberrations. We present preliminary results of the application of a
Partitioned Phase-Diverse Speckle (PPDS) technique at THEMIS. The images
have been acquired using the IPM broad-band CCD camera and reduced
using a suitable IDL code. The spectral analysis of unrestored/restored
images shows a significant improvement of image quality, achieving
diffraction limited resolution.
Title: Phase diversity at THEMIS : first implementation
Authors: Del Moro, D.; Lemen, C.; Bonet, J. A.; Márquez, I.;
Criscuoli, S.; Briand, C.
Bibcode: 2003AN....324..299D
Altcode:
No abstract at ADS
Title: Restoring full-disk images for atmospheric and instrumental
degradation effects
Authors: Criscuoli, S.; Ermolli, I.
Bibcode: 2003MmSAI..74..607C
Altcode:
A numerical technique developed to recover atmospheric and instrumental
degradation effects on full-disk images of the solar atmosphere
acquired with a medium resolution will be presented. This technique,
based on the method proposed by Walton and Preminger (1999), allows
simultaneous determination of the undisturbed solar limb darkening
profile and the characterization of the Point Spread Function in
terms of a small number of analytic parameters. The application
of the technique allows to remove stray light effects from images,
to a great extent, while preserves the data photometry. The results
obtained applying this technique to a sample of full-disk images taken
with the PSPT telescopes will be summarized.
Title: CONCORDIASTRO/Italy: A Solar High-Resolution Observation
Program at Dome-C
Authors: Severino, G.; Andretta, V.; Berrilli, F.; Cascone, E.;
Centrone, M.; Criscuoli, S.; Del Moro, D.; Ermolli, I.; Giorgi, F.;
Jefferies, S. M.; Magri, M.; Moretti, P. F.; Oliviero, M.; Parisi,
L.; V; Porzio; Smaldone, L. A.; Straus, Th.
Bibcode: 2003MSAIS...2..181S
Altcode:
CONCORDIASTRO is the Nice-Napoli joint project for site
testing of the Dome C for solar and stellar astronomy in the
visible. CONCORDIASTRO/Italy is the solar physics part of this project,
whose the Napoli team has the principal responsibility. Beyond the
well-known interest for the helioseismology, CONCORDIASTRO/Italy pointed
out that, because of its special atmospheric conditions, Dome C promises
to be one of the best sites on Earth to perform high-resolution solar
physics. Here we review the basis for this statement and the solar
observations program planned by CONCORDIASTRO/Italy.
Title: From the minimum to the maximum: the quality of Rome-PSPT
images
Authors: Fazzari, C.; Ermolli, I.; Centrone, M.; Criscuoli, S.;
Giorgi, F.
Bibcode: 2003MmSAI..74..667F
Altcode:
In response to the need for both measurement and interpretation of
irradiance variations, two PSPTs (Precision Solar Photometric Telescope)
have been designed and produced in the framework of the RISE (Radiative
Inputs of the Sun to Earth) project, to provide high-precision (0.1%)
photometric observations of the solar disk, with about 1 arcsec
spatial resolution at three wavelength bands. As well known, these
two PSPTs, installed at the Rome and the Mauna Loa Observatories,
since 1996 provide daily observation of the Sun available to the
community at the internet addresses http://www.mporzio.astro.it and
http://www.rise.hao.ucar.edu. We present the results obtained analyzing
the quality of the images acquired by the two PSPTs, with particular
regard to photometric accuracy, spatial scale, scattered light level
and temporal variations of the image quality.
Title: Analysis of high resolution and full disk solar images
Authors: Berrilli, F.; Caccin, B.; Cantarano, S.; Egidi, A.; Penza,
V.; Criscuoli, S.; del Moro, D.; Pietropaolo, E.; Consolini, G.;
Ermolli, I.; Lepreti, F.; Mainella, G.; Severino, G.; Zuccarello, F.
Bibcode: 2001ESASP.493..173B
Altcode: 2001sefs.work..173B
No abstract at ADS