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Author name code: sainz-dalda
ADS astronomy entries on 2022-09-14
author:"Sainz Dalda, Alberto"
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Title: Solar surges related to UV bursts: Characterization through
k-means, inversions, and density diagnostics
Authors: Nóbrega Siverio, Daniel; Guglielmino, Salvatore Luigi;
Sainz Dalda, A.
2022cosp...44.2530N Altcode:
Surges are dynamic, cool and dense ejections typically observed in
chromospheric lines and closely related to other solar phenomena
like UV bursts or coronal jets. Even though surges have been observed
for decades now, fundamental questions regarding the temperature and
density distribution, as well as their connection and impact on upper
layers of the solar atmosphere remain open. Our aim is to characterize
the chromospheric and transition region properties of these phenomena
taking advantage of high-resolution observations combined with advanced
techniques. We have analyzed four surges that appear related to UV
bursts observed with the Interface Region Imaging Spectrograph (IRIS)
on 2016 April. We have studied the mid- and low-chromosphere of the
surges by getting their representative Mg II h$&$k line profiles
through the k-means algorithm and performing inversions on them using
the STIC code. We have also studied the far-UV spectra, focusing
on the O IV 1399.8 and 1401.2 Å lines, and carrying out density
diagnostics. We obtain that the mid- and low-chromosphere of the surges
are characterized by temperatures between 5.5 and 6.9 kK, electronic
number densities from ∼1.5$\times$10$^{11}$ to 2.5$\times$10$ ^{12}$
cm$^{‑3}$, and line-of-sight velocities of a few km/s at optical
depths ranging from log$ _{10}$($\tau$)=‑6.0 to ‑3.2. We find,
for the first time, observational evidence of O IV emission within
the surges, indicating that these phenomena have a transition region
counterpart even in the weakest lines. The O IV emitting layers of the
surges have an electron number density between 2.5$\times$10$ ^{10}$
and 10$ ^{12}$ cm$ ^{‑3}$.
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Title: Emergence of internetwork magnetic fields into the chromosphere
and transition region
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R.; Sainz
Dalda, A.; Esteban Pozuelo, Sara
2022cosp...44.2511G Altcode:
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they are spread all over the Sun, they may hold a
significant fraction of the total magnetic energy stored in the
photosphere. Therefore, it is crucial to understand their role in the
quiet Sun magnetism and impact on the energetics and dynamics of the
solar atmosphere. To provide new insights into this topic, we studied
three flux emergence events and followed them as they emerge into the
photosphere and reach the chromosphere and transition region. We used
coordinated, high-resolution, multiwavelength observations obtained with
the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging
Spectrograph (IRIS). SST Fe I 6173 and Mg I b$_2$ 5173 magnetograms
show the footpoints of the IN bipoles emerging at the solar surface
and rising toward the upper solar atmosphere. For the first time, our
spectropolarimetric measurements in the Ca II 8542 \AA\/ line provide
direct observational evidence that IN fields are capable of reaching
the chromosphere. IRIS observations reveal another important piece of
information - small-scale IN loops can even reach transition region
heights, and locally heat the upper solar atmosphere.
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Title: Unsupervised Machine Learning for the Identification of
Preflare Spectroscopic Signatures
Authors: Woods, Magnus M.; Sainz Dalda, Alberto; De Pontieu, Bart
2021ApJ...922..137W Altcode:
The study of the preflare environment is of great importance to
understanding what drives solar flares. k-means clustering, an
unsupervised machine-learning technique, has the ability to cluster
large data set in a way that would be impractical or impossible for a
human to do. In this paper we present a study using k-means clustering
to identify possible preflare signatures in spectroscopic observations
of the Mg II h and k spectral lines made by NASA's Interface Region
Imaging Spectrometer. Our analysis finds that spectral profiles showing
single-peak Mg II h and k and single-peaked emission in the Mg II UV
triplet lines are associated with preflare activity up to 40 minutes
prior to flaring. Subsequent inversions of these spectral profiles
reveal increased temperature and electron density in the chromosphere,
which suggest that significant heating events in the chromosphere may
be associated with precursor signals to flares.
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Title: Solar surges related to UV bursts. Characterization through
k-means, inversions, and density diagnostics
Authors: Nóbrega-Siverio, D.; Guglielmino, S. L.; Sainz Dalda, A.
2021A&A...655A..28N Altcode: 2021arXiv210813960N
Context. Surges are cool and dense ejections typically observed in
chromospheric lines and closely related to other solar phenomena
such as UV bursts or coronal jets. Even though surges have been
observed for decades now, questions regarding their fundamental
physical properties such as temperature and density, as well as their
impact on upper layers of the solar atmosphere remain open. <BR />
Aims: Our aim is to address the current lack of inverted models and
diagnostics of surges, as well as to characterize the chromospheric
and transition region plasma of these phenomena. <BR /> Methods: We
have analyzed an episode of recurrent surges related to UV bursts
observed with the Interface Region Imaging Spectrograph (IRIS)
in April 2016. The mid- and low-chromosphere of the surges were
unprecedentedly examined by getting their representative Mg IIh&k
line profiles through the k-means algorithm and performing inversions
on them using the state-of-the-art STiC code. We have studied the
far-UV spectra focusing on the O IV 1399.8 Å and 1401.2 Å lines,
which were previously unexplored for surges, carrying out density
diagnostics to determine the transition region properties of these
ejections. We have also used numerical experiments performed with
the Bifrost code for comparisons. <BR /> Results: Thanks to the
k-means clustering, we reduced the number of Mg IIh&k profiles
to invert by a factor 43.2. The inversions of the representative
profiles show that the mid- and low-chromosphere of the surges are
characterized, with a high degree of reliability, by temperatures
mainly around T = 6 kK at −6.0 ≤ log<SUB>10</SUB>(τ)≤
− 3.2. For the electronic number density, n<SUB>e</SUB>, and
line-of-sight velocity, V<SUB>LOS</SUB>, the most reliable results
from the inversions are within −6.0 ≤ log<SUB>10</SUB>(τ)≤
− 4.8, with n<SUB>e</SUB> ranging from ∼1.6 × 10<SUP>11</SUP>
cm<SUP>−3</SUP> up to 10<SUP>12</SUP> cm<SUP>−3</SUP>, and
V<SUB>LOS</SUB> of a few km s<SUP>−1</SUP>. We find, for the first
time, observational evidence of enhanced O IV emission within the
surges, indicating that these phenomena have a considerable impact
on the transition region even in the weakest far-UV lines. The O IV
emitting layers of the surges have an electron number density ranging
from 2.5 × 10<SUP>10</SUP> cm<SUP>−3</SUP> to 10<SUP>12</SUP>
cm<SUP>−3</SUP>. The numerical simulations provide theoretical
support in terms of the topology and location of the O IV emission
within the surges. <P />Movie associated with Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141472/olm">https://www.aanda.org</A>
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Title: Emergence of Internetwork Magnetic Fields through the Solar
Atmosphere
Authors: Gošić, M.; De Pontieu, B.; Bellot Rubio, L. R.; Sainz Dalda,
A.; Pozuelo, S. Esteban
2021ApJ...911...41G Altcode: 2021arXiv210302213G
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they emerge all over the Sun, these small-scale fields
bring a substantial amount of flux, and therefore energy, to the solar
surface. Because of this, IN fields are crucial for understanding
the quiet Sun (QS) magnetism. However, they are weak and produce very
small polarization signals, which is the reason why their properties
and impact on the energetics and dynamics of the solar atmosphere are
poorly known. Here we use coordinated, high-resolution, multiwavelength
observations obtained with the Swedish 1 m Solar Telescope and the
Interface Region Imaging Spectrograph (IRIS) to follow the evolution
of IN magnetic loops as they emerge into the photosphere and reach
the chromosphere and transition region. We studied in this paper three
flux emergence events having total unsigned magnetic fluxes of 1.9 ×
10<SUP>18</SUP>, 2.5 × 10<SUP>18</SUP>, and 5.3 × 10<SUP>18</SUP>
Mx. The footpoints of the emerging IN bipoles are clearly seen
to appear in the photosphere and to rise up through the solar
atmosphere, as observed in Fe I 6173 Å and Mg I b<SUB>2</SUB> 5173
Å magnetograms, respectively. For the first time, our polarimetric
measurements taken in the chromospheric Ca II 8542 Å line provide
direct observational evidence that IN fields are capable of reaching the
chromosphere. Moreover, using IRIS data, we study the effects of these
weak fields on the heating of the chromosphere and transition region.
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Title: Compression of Solar Spectroscopic Observations: a Case Study
of Mg II k Spectral Line Profiles Observed by NASA's IRIS Satellite
Authors: Sadykov, Viacheslav M; Kitiashvili, Irina N; Sainz Dalda,
Alberto; Oria, Vincent; Kosovichev, Alexander G; Illarionov, Egor
2021arXiv210307373S Altcode:
In this study we extract the deep features and investigate the
compression of the Mg II k spectral line profiles observed in quiet
Sun regions by NASA's IRIS satellite. The data set of line profiles
used for the analysis was obtained on April 20th, 2020, at the
center of the solar disc, and contains almost 300,000 individual
Mg II k line profiles after data cleaning. The data are separated
into train and test subsets. The train subset was used to train the
autoencoder of the varying embedding layer size. The early stopping
criterion was implemented on the test subset to prevent the model from
overfitting. Our results indicate that it is possible to compress the
spectral line profiles more than 27 times (which corresponds to the
reduction of the data dimensionality from 110 to 4) while having a 4 DN
average reconstruction error, which is comparable to the variations in
the line continuum. The mean squared error and the reconstruction error
of even statistical moments sharply decrease when the dimensionality of
the embedding layer increases from 1 to 4 and almost stop decreasing
for higher numbers. The observed occasional improvements in training
for values higher than 4 indicate that a better compact embedding may
potentially be obtained if other training strategies and longer training
times are used. The features learned for the critical four-dimensional
case can be interpreted. In particular, three of these four features
mainly control the line width, line asymmetry, and line dip formation
respectively. The presented results are the first attempt to obtain
a compact embedding for spectroscopic line profiles and confirm the
value of this approach, in particular for feature extraction, data
compression, and denoising.
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Title: ALMA and IRIS Observations of the Solar
Chromosphere. II. Structure and Dynamics of Chromospheric Plages
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...83C Altcode: 2020arXiv201205970C
We propose and employ a novel empirical method for determining
chromospheric plage regions, which seems to better isolate a plage from
its surrounding regions than other methods commonly used. We caution
that isolating a plage from its immediate surroundings must be done
with care in order to successfully mitigate statistical biases that,
for instance, can impact quantitative comparisons between different
chromospheric observables. Using this methodology, our analysis suggests
that λ = 1.25 mm free-free emission in plage regions observed with
the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may
not form in the low chromosphere as previously thought, but rather
in the upper chromospheric parts of dynamic plage features (such as
spicules and other bright structures), i.e., near geometric heights
of transition-region temperatures. We investigate the high degree of
similarity between chromospheric plage features observed in ALMA/Band6
(at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph
(IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are
not as well correlated with ALMA/Band6 as was previously thought,
and we discuss discrepancies with previous works. Lastly, we report
indications of chromospheric heating due to propagating shocks supported
by the ALMA/Band6 observations.
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Title: ALMA and IRIS Observations of the Solar Chromosphere. I. An
On-disk Type II Spicule
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
2021ApJ...906...82C Altcode: 2020arXiv200512717C
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph. The observatories
targeted a chromospheric plage region of which the spatial distribution
(split between strongly and weakly magnetized regions) allowed the
study of linear-like structures in isolation, free of contamination
from background emission. Using these observations in conjunction with
a radiative magnetohydrodynamic 2.5D model covering the upper convection
zone all the way to the corona that considers nonequilibrium ionization
effects, we report the detection of an on-disk chromospheric spicule
with ALMA and confirm its multithermal nature.
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Title: Expected spectropolarimetric observables in the lower solar
atmosphere from 3D radiative MHD models
Authors: Sainz Dalda, A.; Gosic, M.; Martinez-Sykora, J.
2020AGUFMSH0010019S Altcode:
No abstract at ADS
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Title: ALMA and IRIS Observations Highlighting the Dynamics and
Structure of Chromospheric Plage
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.;
Hansteen, V. H.; de la Cruz Rodriguez, J.; Szydlarski, M.; Jafarzadeh,
S.; Wedemeyer, S.; Bastian, T.; Sainz Dalda, A.
2020AGUFMSH0010009C Altcode:
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph (IRIS). The
observatories targeted a chromospheric plage region of which the spatial
distribution (split between strongly and weakly magnetized regions)
allowed the study of linear-like structures in isolation, free of
contamination from background emission. Using these observations
in conjunction with a radiative magnetohydrodynamic 2.5D model
covering the upper convection zone all the way to the corona
that considers non-equilibrium ionization effects, we report the
detection of an on-disk chromospheric spicule with ALMA and confirm
its multithermal nature. In addition, we discuss the strikingly high
degree of similarity between chromospheric plage features observed
in ALMA/Band6 and IRIS/\ion{Si}{4} (also reproduced in our model)
suggesting that ALMA/Band6 does not observe in the low chromosphere as
previously thought but rather observes the upper chromospheric parts
of structures such as spicules and other bright structures above plage
at geometric heights near transition region temperatures. We also show
that IRIS/\ion{Mg}{2} is not as well correlated with ALMA/Band6 as was
previously thought. For these comparisons, we propose and employ a novel
empirical method for the determination of plage regions, which seems
to better isolate plage from its surrounding regions as compared to
other methods commonly used. We caution that isolating plage from its
immediate surroundings must be done with care to mitigate statistical
bias in quantitative comparisons between different chromospheric
observables. Lastly, we report indications for chromospheric heating
due to traveling shocks supported by the ALMA/Band6 observations.
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Title: Chromospheric response to emergence of internetwork magnetic
fields
Authors: Gosic, M.; De Pontieu, B.; Bellot Rubio, L.; Sainz Dalda, A.
2020AGUFMSH0010006G Altcode:
Internetwork (IN) magnetic fields are weak, short-lived, but highly
dynamic magnetic structures that emerge all over the Sun. They
bring an enormous amount of magnetic flux and energy to the solar
surface. Therefore, IN fields are of paramount importance for
maintenance of the QS magnetism. Since these fields are ubiquitous,
they may have a substantial impact on the energetics and dynamics of the
solar atmosphere. In this work, we use coordinated, high-resolution,
multiwavelength observations obtained with the Interface Region
Imaging Spectrograph (IRIS) and the Swedish 1 m Solar Telescope (SST)
to follow the evolution of IN magnetic loops as they emerge into the
photosphere. The footpoints of the emerging IN bipoles are clearly
visible as they appear in the photosphere and rise up through the
solar atmosphere, as seen in SST magnetograms taken in the Fe I
6173 Å and Mg I b2 5173 Å lines, respectively. Our polarimetric
measurements, taken in the Ca II 8542 Å line, provide the first
direct observational evidence that IN fields are capable of reaching
the chromosphere. Moreover, using IRIS data, we describe in detail
how individual IN bipoles affect the dynamics and energetics of the
chromosphere and transition region.
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Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.
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Title: Investigating Pre-flare Signatures with K-means Clustering
Authors: Woods, M.; De Pontieu, B.; Sainz Dalda, A.
2019AGUFMSH31E3348W Altcode:
We present the results of a large statistical study of pre-flare
activity using spectroscopic data from the IRIS spacecraft, analysed
using K-means clustering. Solar flares are large energy releases
whose effects are observed throughout the solar atmosphere. They
are also heavily correlated with eruptions and CMEs, which extend
their influence into the greater heliosphere. Many models exist
that attempt to explain the triggering of flares and eruptions,
but not all have clear observational signatures related to them. The
identification of reliable pre-flare signatures is therefore highly
important to not only furthering our understanding the processes
that lead to flaring and eruptions, but also to efforts to predict
the occurrence of such events. <P />We compiled a data set of over
100 flare events with pre-flare coverage, comprising a range of GOES
classes and eruptivities. The individual spectra from these data were
then standardised for direct comparison, and the unsupervised machine
learning technique K-means clustering was run upon them. This allowed
us to investigate the types of spectra that were observed prior to
flaring, and how these spectra are distributed both spatially and
temporally. Additionally we investigated how these spectral clusters
are related to the eruptivity of the flares that they precede.
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Title: A comprehensive three-dimensional radiative magnetohydrodynamic
simulation of a solar flare
Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.;
Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.;
Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen,
B.; McIntosh, S. W.
2019NatAs...3..160C Altcode: 2018NatAs...3..160C
Solar and stellar flares are the most intense emitters of X-rays and
extreme ultraviolet radiation in planetary systems<SUP>1,2</SUP>. On
the Sun, strong flares are usually found in newly emerging sunspot
regions<SUP>3</SUP>. The emergence of these magnetic sunspot groups
leads to the accumulation of magnetic energy in the corona. When
the magnetic field undergoes abrupt relaxation, the energy released
powers coronal mass ejections as well as heating plasma to temperatures
beyond tens of millions of kelvins. While recent work has shed light
on how magnetic energy and twist accumulate in the corona<SUP>4</SUP>
and on how three-dimensional magnetic reconnection allows for rapid
energy release<SUP>5,6</SUP>, a self-consistent model capturing how
such magnetic changes translate into observable diagnostics has remained
elusive. Here, we present a comprehensive radiative magnetohydrodynamics
simulation of a solar flare capturing the process from emergence to
eruption. The simulation has sufficient realism for the synthesis of
remote sensing measurements to compare with observations at visible,
ultraviolet and X-ray wavelengths. This unifying model allows us to
explain a number of well-known features of solar flares<SUP>7</SUP>,
including the time profile of the X-ray flux during flares, origin
and temporal evolution of chromospheric evaporation and condensation,
and sweeping of flare ribbons in the lower atmosphere. Furthermore,
the model reproduces the apparent non-thermal shape of coronal X-ray
spectra, which is the result of the superposition of multi-component
super-hot plasmas<SUP>8</SUP> up to and beyond 100 million K.
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Title: Radiative MHD Simulation of a Solar Flare
Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats;
De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W.
2019AAS...23431005C Altcode:
We present a radiative MHD simulation of a solar flare. The
computational domain captures the near-surface layers of the convection
zone and overlying atmosphere. Inspired by the observed evolution of
NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed
to emerge in the vicinity of a pre-existing sunspot. The emergence of
twisted magnetic flux generates shear flows that create a pre-existing
flux rope underneath the canopy field of the sunspot. Following erosion
of the overlying bootstrapping field, the flux rope erupts. Rapid
release of magnetic energy results in multi-wavelength synthetic
observables (including X-ray spectra, narrowband EUV images, Doppler
shifts of EUV lines) that are consistent with flare observations. This
works suggests the super-position of multi-thermal, superhot (up
to 100 MK) plasma may be partially responsible for the apparent
non-thermal shape of coronal X-ray sources in flares. Implications
for remote sensing observations of other astrophysical objects is also
discussed. This work is an important stepping stone toward high-fidelity
data-driven MHD models.
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Title: Recovering Thermodynamics from Spectral Profiles observed by
IRIS: A Machine and Deep Learning Approach
Authors: Sainz Dalda, Alberto; de la Cruz Rodríguez, Jaime; De
Pontieu, Bart; Gošić, Milan
2019ApJ...875L..18S Altcode: 2019arXiv190408390S
Inversion codes allow the reconstruction of a model atmosphere from
observations. With the inclusion of optically thick lines that form in
the solar chromosphere, such modeling is computationally very expensive
because a non-LTE evaluation of the radiation field is required. In this
study, we combine the results provided by these traditional methods
with machine and deep learning techniques to obtain similar-quality
results in an easy-to-use, much faster way. We have applied these
new methods to Mg II h and k lines observed by the Interface Region
Imaging Spectrograph (IRIS). As a result, we are able to reconstruct the
thermodynamic state (temperature, line-of-sight velocity, nonthermal
velocities, electron density, etc.) in the chromosphere and upper
photosphere of an area equivalent to an active region in a few CPU
minutes, speeding up the process by a factor of 10<SUP>5</SUP> -
10<SUP>6</SUP>. The open-source code accompanying this Letter will
allow the community to use IRIS observations to open a new window to
a host of solar phenomena.
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Title: A Statistical Comparison between Photospheric Vector
Magnetograms Obtained by SDO/HMI and Hinode/SP
Authors: Sainz Dalda, Alberto
2017ApJ...851..111S Altcode: 2018arXiv180107374S
Since 2010 May 1, we have been able to study (almost) continuously
the vector magnetic field in the Sun, thanks to two space-based
observatories: the Solar Dynamics Observatory (SDO) and Hinode. Both
are equipped with instruments able to measure the Stokes parameters
of Zeeman-induced polarization of photospheric line radiation. But
the observation modes; the spectral lines; the spatial, spectral, and
temporal sampling; and even the inversion codes used to recover magnetic
and thermodynamic information from the Stokes profiles are different. We
compare the vector magnetic fields derived from observations with the
HMI instrument on board SDO with those observed by the SP instrument on
Hinode. We have obtained relationships between components of magnetic
vectors in the umbra, penumbra, and plage observed in 14 maps of NOAA
Active Region 11084. Importantly, we have transformed SP data into
observables comparable to those of HMI, to explore possible influences
of the different modes of operation of the two instruments and the
inversion schemes used to infer the magnetic fields. The assumed filling
factor (fraction of each pixel containing a Zeeman signature) produces
the most significant differences in derived magnetic properties,
especially in the plage. The spectral and angular samplings have
the next-largest effects. We suggest to treat the disambiguation in
the same way in the data provided by HMI and SP. That would make the
relationship between the vector magnetic field recovered from these
data stronger, which would favor the simultaneous or complementary
use of both instruments.
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Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
2017SPD....4840001R Altcode:
We present a recently developed version of the MURaM radiative
MHD code that includes coronal physics in terms of optically thin
radiative loss and field aligned heat conduction. The code employs
the "Boris correction" (semi-relativistic MHD with a reduced speed
of light) and a hyperbolic treatment of heat conduction, which allow
for efficient simulations of the photosphere/corona system by avoiding
the severe time-step constraints arising from Alfven wave propagation
and heat conduction. We demonstrate that this approach can be used
even in dynamic phases such as a flare. We consider a setup in which
a flare is triggered by flux emergence into a pre-existing bipolar
active region. After the coronal energy release, efficient transport
of energy along field lines leads to the formation of flare ribbons
within seconds. In the flare ribbons we find downflows for temperatures
lower than ~5 MK and upflows at higher temperatures. The resulting
soft X-ray emission shows a fast rise and slow decay, reaching a peak
corresponding to a mid C-class flare. The post reconnection energy
release in the corona leads to average particle energies reaching 50
keV (500 MK under the assumption of a thermal plasma). We show that
hard X-ray emission from the corona computed under the assumption of
thermal bremsstrahlung can produce a power-law spectrum due to the
multi-thermal nature of the plasma. The electron energy flux into the
flare ribbons (classic heat conduction with free streaming limit) is
highly inhomogeneous and reaches peak values of about 3x10<SUP>11</SUP>
erg/cm<SUP>2</SUP>/s in a small fraction of the ribbons, indicating
regions that could potentially produce hard X-ray footpoint sources. We
demonstrate that these findings are robust by comparing simulations
computed with different values of the saturation heat flux as well as
the "reduced speed of light".
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Title: Physics & Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
2016SPD....47.0607C Altcode:
We provide an update on our NASA Heliophysics Grand Challenges Research
(HGCR) project on the ‘Physics & Diagnostics of the Drivers of
Solar Eruptions’. This presentation will focus on results from a
data-inspired, 3D radiative MHD model of a solar flare. The model
flare results from the interaction of newly emerging flux with a
pre-existing active region. Synthetic observables from the model
reproduce observational features compatible with actual flares. These
include signatures of coronal magnetic reconnection, chromospheric
evaporation, EUV flare arcades, sweeping motion of flare ribbons
and sunquakes.
---------------------------------------------------------
Title: SDO/HMI Vector Magnetic Field Observations of the Solar
Polar Region
Authors: Sun, X.; Hoeksema, J. T.; Liu, Y.; Norton, A. A.; Sainz Dalda,
A.; Hayashi, K.
2015AGUFMSH23A2429S Altcode:
SDO/HMI is now providing full-disk vector magnetograms of the
Sun. Although the instrument is optimized for strong field in active
regions, data from the quieter regions can still provide valuable
diagnostics if treated carefully. Here we present our first attempt at
inferring the vector field in the polar regions. Through deep averaging
(96 min) of the Stokes profiles, we find that many unipolar patches
reach 5-sigma signal-to-noise ratio, so magnetic field can be inferred
with confidence. The inclination of the field in these patches appears
to deviate from the radial direction. We discuss the implications for
global coronal field topology and our next steps of work.
---------------------------------------------------------
Title: A self-consistent combined radiative transfer hydrodynamic and
particle acceleration model for the X1.0 class flare on March 29, 2014
Authors: Rubio da Costa, F.; Kleint, L.; Sainz Dalda, A.; Petrosian,
V.; Liu, W.
2015AGUFMSH31B2419R Altcode:
The X1.0 flare on March 29, 2014 was well observed, covering its
emission at several wavelengths from the photosphere to the corona. The
RHESSI spectra images allow us to estimate the temporal variation of
the electron spectra using regularized inversion techniques. Using
this as input for a combined particle acceleration and transport
(Stanford-Flare) and radiative transfer hydrodynamic (Radyn) code, we
calculate the response of the atmosphere to the electron heating. We
will present the evolution of the thermal continuum and several line
emissions. Comparing them with GOES soft X-ray and high resolution
observations from IRIS, SDO and DST/IBIS allows us to test the basic
mechanism(s) of acceleration and to constrain its characteristics. We
will also present perspectives on how to apply this methodology and
related diagnostics to other flares.
---------------------------------------------------------
Title: On Helium 1083 nm Line Polarization during the Impulsive
Phase of an X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Sainz Dalda, Alberto
2015ApJ...814..100J Altcode: 2015arXiv151009218J
We analyze spectropolarimetric data of the He i 1083 nm multiplet
(1s2s{}<SUP>3</SUP>{S}<SUB>1</SUB>-1s2p{}<SUP>3</SUP>{P}<SUB>2,1,0</SUB><SUP>o</SUP>)
during the X1 flare SOL2014-03-29T17:48, obtained with the Facility
Infrared Spectrometer (FIRS) at the Dunn Solar Telescope. While scanning
active region NOAA 12017, the FIRS slit crossed a flare ribbon during
the impulsive phase, when the helium line intensities turned into
emission at ≲twice the continuum intensity. Their linear polarization
profiles are of the same sign across the multiplet including 1082.9
nm, intensity-like, at ≲5% of the continuum intensity. Weaker
Zeeman-induced linear polarization is also observed. Only the strongest
linear polarization coincides with hard X-ray (HXR) emission at 30-70
keV observed by RHESSI. The polarization is generally more extended and
lasts longer than the HXR emission. The upper J = 0 level of the 1082.9
nm component is unpolarizable thus, lower-level polarization is the
culprit. We make non-LTE radiative transfer calculations in thermal
slabs optimized to fit only intensities. The linear polarizations
are naturally reproduced, through a systematic change of sign with
wavelength of the radiation anisotropy when slab optical depths of
the 1082.9 component are ≲1. Neither are collisions with beams of
particles needed, nor can they produce the same sign of polarization
of the 1082.9 and 1083.0 nm components. The He i line polarization
merely requires heating sufficient to produce slabs of the required
thickness. Widely different polarizations of Hα, reported previously,
are explained by different radiative anisotropies arising from slabs
of different optical depths.
---------------------------------------------------------
Title: The Fast Filament Eruption Leading to the X-flare on 2014
March 29
Authors: Kleint, Lucia; Battaglia, Marina; Reardon, Kevin; Sainz Dalda,
Alberto; Young, Peter R.; Krucker, Säm
2015ApJ...806....9K Altcode: 2015arXiv150400515K
We investigate the sequence of events leading to the solar X1 flare
SOL2014-03-29T17:48. Because of the unprecedented joint observations of
an X-flare with the ground-based Dunn Solar Telescope and the spacecraft
IRIS, Hinode, RHESSI, STEREO, and the Solar Dynamics Observatory, we can
sample many solar layers from the photosphere to the corona. A filament
eruption was observed above a region of previous flux emergence, which
possibly led to a change in magnetic field configuration, causing
the X-flare. This was concluded from the timing and location of the
hard X-ray emission, which started to increase slightly less than a
minute after the filament accelerated. The filament showed Doppler
velocities of ∼2-5 km s<SUP>-1</SUP> at chromospheric temperatures
for at least one hour before the flare occurred, mostly blueshifts,
but also redshifts near its footpoints. Fifteen minutes before the
flare, its chromospheric Doppler shifts increased to ∼6-10 km
s<SUP>-1</SUP> and plasma heating could be observed before it lifted
off with at least 600 km s<SUP>-1</SUP> as seen in IRIS data. Compared
to previous studies, this acceleration (∼3-5 km s<SUP>-2</SUP>) is
very fast, while the velocities are in the common range for coronal
mass ejections. An interesting feature was a low-lying twisted second
filament near the erupting filament, which did not seem to participate
in the eruption. After the flare ribbons started on each of the second
filament’s sides, it seems to have untangled and vanished during the
flare. These observations are some of the highest resolution data of
an X-class flare to date and reveal some small-scale features yet to
be explained.
---------------------------------------------------------
Title: Solar Flare Chromospheric Line Emission: Comparison Between
IBIS High-resolution Observations and Radiative Hydrodynamic
Simulations
Authors: Rubio da Costa, Fatima; Kleint, Lucia; Petrosian, Vahé;
Sainz Dalda, Alberto; Liu, Wei
2015ApJ...804...56R Altcode: 2015ApJ...804...56D; 2014arXiv1412.1815R
Solar flares involve impulsive energy release, which results in enhanced
radiation over a broad spectral range and a wide range of heights. In
particular, line emission from the chromosphere can provide critical
diagnostics of plasma heating processes. Thus, a direct comparison
between high-resolution spectroscopic observations and advanced
numerical modeling results could be extremely valuable, but has not
yet been attempted. In this paper, we present such a self-consistent
investigation of an M3.0 flare observed by the Dunn Solar Telescope’s
Interferometric Bi-dimensional Spectrometer (IBIS) on 2011 September 24
which we have modeled using the radiative hydrodynamic code RADYN. We
obtained images and spectra of the flaring region with IBIS in Hα
6563 Å and Ca ii 8542 Å, and with RHESSI in X-rays. The latter
observations were used to infer the non-thermal electron population,
which was passed to RADYN to simulate the atmospheric response to
electron collisional heating. We then synthesized spectral lines and
compared their shapes and intensities to those observed by IBIS and
found a general agreement. In particular, the synthetic Ca ii 8542
Å profile fits well to the observed profile, while the synthetic Hα
profile is fainter in the core than for the observation. This indicates
that Hα emission is more responsive to the non-thermal electron flux
than the Ca ii 8542 Å emission. We suggest that it is necessary to
refine the energy input and other processes to resolve this discrepancy.
---------------------------------------------------------
Title: Study of a sunspot umbra using spatially deconvolved Hinode
spectropolarometric data
Authors: Sainz Dalda, A.; Cheung, C. M. M.
2014AGUFMSH41C4160S Altcode:
We have studied the properties of the umbra of NOAA AR 10933 using a
2-step deconvolution method to improve the quality of the data. We have
implemented a simple, fast deconvolution technique for observations
from the Solar Optical Telescope (SOT, Tsuneta et al 2008) on-board
Hinode (Kosugi et al 2007). By performing Richardson-Lucy iterative
deconvolution (Richardson 1972, Lucy 1974) on the polarization images
one wavelength at a time, we remove the diffraction pattern of SOT from
SP data before feeding them into a conventional inversion scheme (SIR,
Ruiz Cobo & del Toro Iniesta 1992), which performs the inversion
independently pixel-by-pixel. As result, we obtain well-contrasted,
well-detailed physical maps of the vector magnetic field and other
thermodynamic parameters that may shed light on the nature of the umbra.
---------------------------------------------------------
Title: Comparison between IBIS Observations and Radiative Transfer
Hydrodynamic Simulations of a Solar Flare
Authors: Rubio da Costa, F.; Kleint, L.; Liu, W.; Sainz Dalda, A.;
Petrosian, V.
2014AGUFMSH13B4104R Altcode:
High-resolution spectroscopic observations of solar flares are
rare but can provide valuable diagnostics. On September 24, 2011 an
M3.0 class flare was observed by the Interferometric BIdimensional
Spectropolarimeter (IBIS) in chromospheric Hα and CaII 8542 Å
lines and by the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) in X-rays. We fitted the RHESSI spectra at different times
with a power-law plus isothermal component. We then used the fitted
real-time spectral parameters of nonthermal electrons as the input to
the RADYN radiative hydrodynamic code (Carlsson et al, 1992, 1996;
Allred et al, 2005) to simulate the low-chromospheric response to
collisional heating by energetic electrons. We synthesized both the
Hα and CaII 8542 Å lines from the simulation results and compare
them with the IBIS observations. We discuss the constraints from this
comparison on particle acceleration mechanisms in solar flares.
---------------------------------------------------------
Title: High-resolution Observations of the X-flare on 2014-03-29
Authors: Kleint, L.; Battaglia, M.; Krucker, S.; Reardon, K.; Sainz
Dalda, A.
2014AGUFMSH31C..06K Altcode:
We investigate the sequence of events leading to the X1 flare
SOL2014-03-29T17:48. Because of the unprecedented joint observations of
an X-flare with the ground-based Dunn Solar Telescope and the spacecraft
IRIS, Hinode, RHESSI, STEREO, and SDO, we can sample many solar layers
from the photosphere to the corona. We find that a filament eruption,
which was possibly caused by a thermal instability, was the cause of
this X-flare. The filament was rising in the chromosphere for at least
one hour before the flare occurred with a velocity of ∼2--5 km/s. 15
minutes before the flare, its chromospheric rise velocity increased to
∼6--10 km/s, before it lifted off with at least 600 km/s, as seen by
IRIS in the transition region. Doppler velocities from H-alpha images
reveal intriguing small scale flows along the filament and enable us to
derive its probable shape. An unusual feature was a low-lying twisted
flux rope near the filament, which did not participate in the filament
eruption. After the flare ribbons started on each of its sides, the
flux rope seems to have untangled and vanished during the flare. We
present a comprehensive overview of the flare, including polarimetric
and spectroscopic data at subarcsecond resolution.
---------------------------------------------------------
Title: On the Origin of a Sunquake during the 2014 March 29 X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Donea, Alina; Sainz Dalda,
Alberto; Fletcher, Lyndsay
2014ApJ...796...85J Altcode: 2014arXiv1409.6268J
Helioseismic data from the Helioseismic Magnetic Imager instrument have
revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48
in active region NOAA 12017. We try to discover if acoustic-like
impulses or actions of the Lorentz force caused the sunquake. We
analyze spectropolarimetric data obtained with the Facility Infrared
Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortunately,
the FIRS slit crossed the flare kernel close to the acoustic source
during the impulsive phase. The infrared FIRS data remain unsaturated
throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He
I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm
core intensity increases by a factor of several, and the IR continuum
increases by 4% ± 1%. Remarkably, the Si I core resembles the classical
Ca II K line's self-reversed profile. With nLTE radiative models of
H, C, Si, and Fe, these properties set the penetration depth of flare
heating to 100 ± 100 km (i.e., photospheric layers). Estimates of the
non-magnetic energy flux are at least a factor of two less than the
sunquake energy flux. Milne-Eddington inversions of the Si I line show
that the local magnetic energy changes are also too small to drive the
acoustic pulse. Our work raises several questions. Have we missed the
signature of downward energy propagation? Is it intermittent in time
and/or non-local? Does the 1-2 s photospheric radiative damping time
discount compressive modes? <P />The National Center for Atmospheric
Research is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: A particular seismic event generated during the solar flare
2014 March 29
Authors: Donea, Alina C.; Judge, P.; Kleint, L.; Sainz-Dalda, Alberto
2014shin.confE..49D Altcode:
The X1.3 solar flare of 2014 March 29 from AR 2017 was extremely well
observed, from both space and the ground. Helioseismic observations
from the Helioseismic Magnetic Imager (HMI) aboard the Solar Dynamics
Observatory (SDO) indicate that this flare generated a weak seismic
transient. All previous strong seismic transients to date have
emanated from sunspot penumbrae, but the source of this transient
lay outside the active-region penumbra close to a magnetic pore. <P
/>Uniquely, Kleint and Sainz Dalda captured ground based imaging
and slit spectropolarimetry of this flare using the IBIS and FIRS
instruments respectively, at the Dunn Solar Telescope in Sunspot,
New Mexico. Here we report only on FIRS data along with space-based
data, IBIS data will be reported elsewhere. The FIRS infrared data
are not saturated even during the flare, which was observed through
the rise and decay phases. We are still investigating the origins of
peculiar, Zeeman-induced polarization in the He I 1083 nm multiplet. <P
/>Using spectropolarimetric data of Si I and He I lines from FIRS, we
investigate the evolution of both photosphere and chromosphere above
and around the seismic source. Together with data from AIA and from
RHESSI, these data offer unique new insight into how the flare energy
is channeled into and through the photosphere into the Sun's interior
as a seismic transient. We present acoustic properties of the seismic
event and their relationship to photospheric and chromospheric plasma
and magnetic fields from FIRS, and to the evolving plasmas seen from
space from UV to X-ray wavelengths.
---------------------------------------------------------
Title: Relationship between unusual features in umbrae and flares
Authors: Sainz Dalda, Alberto; Kleint, Lucia
2014AAS...22412314S Altcode:
The influence of photospheric and chromospheric dynamics and
morphologies on flare activity are still unclear. We present a study
of two flaring active regions (ARs) with complementary instruments
(DST/IBIS, Hinode/SOT-SP, SDO/HMI and SDO/AIA) to investigate the
temporal evolution of the sunspots and their magnetic and thermodynamic
properties. In spite of vast differences in flare occurrence and flare
magnitudes, both ARs show similar features in the lower solar atmosphere
during flares. We investigate common magnetic topologies and dynamics,
which may favor flare activity.
---------------------------------------------------------
Title: Unusual Filaments inside the Umbra
Authors: Kleint, L.; Sainz Dalda, A.
2013ApJ...770...74K Altcode: 2013arXiv1305.7263K
We analyze several unusual filamentary structures which appeared in
the umbra of one of the sunspots in AR 11302. They do not resemble
typical light bridges in morphology or in evolution. We analyze data
from SDO/HMI to investigate their temporal evolution, Hinode/SP
for photospheric inversions, IBIS for chromospheric imaging, and
SDO/AIA for the overlying corona. Photospheric inversions reveal a
horizontal, inverse Evershed flow along these structures, which we
call umbral filaments. Chromospheric images show brightenings and
energy dissipation, while coronal images indicate that bright coronal
loops seem to end in these umbral filaments. These rapidly evolving
features do not seem to be common, and are possibly related to the
high flare-productivity of the active region. Their analysis could
help to understand the complex evolution of active regions.
---------------------------------------------------------
Title: Differences between the vector magnetic field provided by
the SDO/HMI and Hinode-SOT/SP databases.
Authors: Sainz Dalda, A.
2013enss.confE.115S Altcode:
Since April 7, 2010, SDO/HMI has been observing the photosphere of the
full solar disk with almost continuous coverage. Because of its high
temporal cadence, SDO/HMI data are especially useful to study those
dynamic phenomena that involve the vector magnetic field and its derived
quantities, e.g.: electric current density or helicity. Hinode-SOT/SP
has a better spectral and spatial resolution, but a worse temporal
sampling than SDO/HMI. Hinode SOT/SP takes about 0.5-1h to scan a
typical AR. We can overcome both instruments' disadvantages by combining
their data. We compare the vector magnetic field of NOAA AR 11410,
obtained from inversions of data from both instruments. We found that
the magnetic field observed by both instruments is mainly the same for
the umbra and penumbra, but it is slightly different for the plage. The
most important difference is due to the spectral sampling. However,
the spatial sampling also plays an important role in the derived
quantities, i.e. those that require calculating derivatives on the
spatial coordinates. While we cannot validate which inversion code
or instrument gives 'better' estimates of the vector magnetic field,
we can provide a conversion between SDO/HMI and Hinode-SOT/SP data.
---------------------------------------------------------
Title: Towards Measuring the Magnetic Energy Spectrum at
Sub-Resolution Scales
Authors: López Ariste, A.; Sainz Dalda, A.
2012ASPC..463..243L Altcode:
Area asymmetries in the Stokes V profile of the Zeeman-sensitive Fe
I line at 630.25 nm shed light on gradients of velocity and magnetic
field along the photon path. We use that information on observations
of Hinode-SOT/SP of the quiet sun at different heliocentric angles
to further investigate turbulent field models in those regions. The
relationship between the asymmetry value and a correlation length
scale for the field strength in the framework of stochastic radiative
transfer for polarized light allows us to identify in the data
subresolution scales of change of the magnetic field. From these we
make a crude first attempt to determine the energy spectrum of the
turbulent magnetic field down to the km scale as a proof-of-concept
of the potential of this technique.
---------------------------------------------------------
Title: The Dynamic Polar Magnetic Field Before Its Polarity Reversal
Authors: Sun, X.; Hoeksema, J. T.; Liu, Y.; Sainz Dalda, A.; Norton,
A.; Hayashi, K.
2012AGUFMSH41D2130S Altcode:
We characterize the magnetic field in the Sun's polar region using the
spectropolarimetric measurement from the Helioseismic and Magnetic
Imager (HMI) on board the Solar Dynamics Observatory (SDO). With
HMI's high cadence, continuous time coverage, and moderate spectral and
spatial resolution, we are able to estimate the polar magnetic flux, its
latitudinal distribution, and its temporal variation over three years
(2010-2012) during Cycle 24's rising phase. A comparison with higher
spectral resolution observations from Hinode SOT/SP provides constraints
on the flux estimates. The tracking of individual magnetic element
movements yields new insight on the polar field's dynamic behavior
leading up to the polarity reversal. We compare the result with that
from the HMI line-of-sight data, as well as MDI data for Cycle 23. All
observations indicate an earlier reversal of the northern hemisphere
owing to more solar activity in the rising phase, which resulted in
a significant hemispheric asymmetry.
---------------------------------------------------------
Title: Bipolar Magnetic Structures in Sunspot Penumbrae
Authors: Sainz Dalda, A.; Bellot Rubio, L. R.
2012ASPC..454..221S Altcode:
We present a study of bipolar, sea-serpent-like structures in
the penumbra of sunspots. Our analysis is based on longitudinal
magnetograms and full Stokes spectra of AR 10923 taken with the
NFI and SP instruments of Hinode. The circular polarization maps
reveal the presence of many elongated structures in the mid penumbra
and beyond. They consist of two opposite-polarity patches that move
together as a single entity toward the outer penumbral boundary, where
they become moving magnetic features. Their Stokes profiles suggest
a complex magnetic topology. The existence of opposite polarities in
the penumbra is well known from previous analyses, but this is the
first time that their bipolar nature is unveiled. Our observations
also demonstrate that they are intimately connected with the Evershed
flow. These structures provide new constraints to theoretical and
numerical models of sunspots.
---------------------------------------------------------
Title: Scales of the magnetic fields in the quiet Sun
Authors: López Ariste, A.; Sainz Dalda, A.
2012A&A...540A..66L Altcode: 2012arXiv1202.5436L
Context. The presence of a turbulent magnetic field in the quiet Sun has
been unveiled observationally using different techniques. The magnetic
field is quasi-isotropic and has field strengths weaker than 100
G. It is pervasive and may host a local dynamo. <BR /> Aims: We aim to
determine the length scale of the turbulent magnetic field in the quiet
Sun. <BR /> Methods: The Stokes V area asymmetry is sensitive to minute
variations in the magnetic topology along the line of sight. Using
data provided by Hinode-SOT/SP instrument, we performed a statistical
study of this quantity. We classified the different magnetic regimes
and infer properties of the turbulent magnetic regime. In particular
we measured the correlation length associated to these fields for the
first time. <BR /> Results: The histograms of Stokes V area asymmetries
reveal three different regimes: one organized, quasi-vertical and
strong field (flux tubes or other structures of the like); a strongly
asymmetric group of profiles found around field concentrations; and a
turbulent isotropic field. For the last, we confirm its isotropy and
measure correlation lengths from hundreds of kilometers down to 10 km,
at which point we lost sensitivity. A crude attempt to measure the
power spectra of these turbulent fields is made. <BR /> Conclusions: In
addition to confirming the existence of a turbulent field in the quiet
Sun, we give further prove of its isotropy. We also measure correlation
lengths down to 10 km. The combined results show magnetic fields with
a large span of length scales, as expected from a turbulent cascade.
---------------------------------------------------------
Title: Spectropolarimetry of the photosphere and the chromosphere
with IBIS
Authors: Kleint, L.; Sainz Dalda, A.
2012decs.confE...4K Altcode:
We have obtained quasi-simultaneous spectropolarimetric imaging
observations of various chromospheric and photospheric features in the
lines Fe I 6302 A, Ca II 8542 A, H-alpha 6563 A and Na I 5896 A with
the IBIS instrument at Sac Peak. Our targets include the quiet Sun,
pores, sunspots, and flaring regions and our goal is to analyze the
3D magnetic field structure of the solar atmosphere. We carry out
NTLE inversions with the NICOLE code to investigate interpretation
techniques for chromospheric spectropolarimetric observations. The very
faint polarization signatures make chromospheric inversions of the
quiet Sun challenging. On the other hand, they are quite pronounced
during flares and show us that the chromospheric magnetic structure
is seemingly unrelated to the photosphere during these events.
---------------------------------------------------------
Title: Observation, inversion and numerical simulation of single-lobed
Stokes V profiles in the quiet sun.
Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.;
Title, A.
2012decs.confE..89S Altcode:
We have studied characteristics and statistics of strong asymmetric
profiles in Stokes V, i.e., single-lobed profiles, in quiet sun using
Hinode/SOT. These profiles require the existence of a velocity gradient
along the line-of-sight, possibly associated with gradients of magnetic
field strength, inclination and/or azimuth. For a better understanding,
observations, inversions and numerical simulations are compared. We
focus our analysis of the observations on the statistical properties
of the single-lobed Stokes V profiles and the results provided by the
inversions using SIRJUMP, which is an LTE inversion code that can
reproduce sharp discontinuities or jump in the magnetic field and
line-of-sight velocity of the atmosphere model. In the quiet sun,
magnetic field is continuously appearing and disappearing at small
scales due to the convective motions and the input of new flux from
deeper layers. From radiative MHD 3D simulations, using Bifrost code, we
note that most of these small scale processes have stratifications with
gradients of magnetic field strength, inclination and velocities. As
result, those stratifications showing jumps in the magnetic field
configuration are associated with the existence of single-lobe Stokes
V profiles in the solar photosphere, as we previously assumed for the
inversions. We show that most of these profiles come from emerging and
disappearance magnetic flux in small scales in the simulations. Finally,
we emphasize importance of the comparison between the synthetic profiles
from the simulations with the observed ones and the atmospheres that
produce them. This comparison will ultimately improve the realism of
the simulations and quantify the emerging and disappearance flux in
the quiet sun.
---------------------------------------------------------
Title: Study of Single-lobed Circular Polarization Profiles in the
Quiet Sun
Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.;
Title, A.
2012ApJ...748...38S Altcode: 2012arXiv1202.0593S
The existence of asymmetries in the circular polarization (Stokes V)
profiles emerging from the solar photosphere has been known since
the 1970s. These profiles require the presence of a velocity gradient
along the line of sight (LOS), possibly associated with gradients of
magnetic field strength, inclination, and/or azimuth. We have focused
our study on the Stokes V profiles showing extreme asymmetry in the
form of only one lobe. Using Hinode spectropolarimetric measurements,
we have performed a statistical study of the properties of these
profiles in the quiet Sun. We show their spatial distribution, their
main physical properties, how they are related with several physical
observables, and their behavior with respect to their position on
the solar disk. The single-lobed Stokes V profiles occupy roughly
2% of the solar surface. For the first time, we have observed their
temporal evolution and have retrieved the physical conditions of the
atmospheres from which they emerged using an inversion code implementing
discontinuities of the atmospheric parameters along the LOS. In
addition, we use synthetic Stokes profiles from three-dimensional
magnetoconvection simulations to complement the results of the
inversion. The main features of the synthetic single-lobed profiles
are in general agreement with the observed ones, lending support to
the magnetic and dynamic topologies inferred from the inversion. The
combination of all these different analyses suggests that most of the
single-lobed Stokes V profiles are signals coming from the magnetic
flux emergence and/or submergence processes taking place in small
patches in the photosphere of the quiet Sun.
---------------------------------------------------------
Title: Magnetic Topology of a Naked Sunspot: Is It Really Naked?
Authors: Sainz Dalda, A.; Vargas Domínguez, S.; Tarbell, T. D.
2012ApJ...746L..13S Altcode: 2012arXiv1202.0591S
The high spatial, temporal, and spectral resolution achieved by Hinode
instruments gives much better understanding of the behavior of some
elusive solar features, such as pores and naked sunspots. Their fast
evolution and, in some cases, their small sizes have made their study
difficult. The moving magnetic features (MMFs) have been studied during
the last 40 years. They have been always associated with sunspots,
especially with the penumbra. However, a recent observation of a naked
sunspot (one with no penumbra) has shown MMF activity. The authors
of this reported observation expressed their reservations about the
explanation given to the bipolar MMF activity as an extension of the
penumbral filaments into the moat. How can this type of MMF exist when
a penumbra does not? In this Letter, we study the full magnetic and
(horizontal) velocity topology of the same naked sunspot, showing how
the existence of a magnetic field topology similar to that observed
in sunspots can explain these MMFs, even when the intensity map of
the naked sunspot does not show a penumbra.
---------------------------------------------------------
Title: Spectropolarimetric Comparison Between SDO/HMI and
Hinode-SOT/SP Through THEMIS/MTR
Authors: Sainz Dalda, A.; Lopez Ariste, A.; Gelly, B.; Tarbell, T. D.;
Centeno, R.; DeRosa, M. L.; Hoeksema, J. T.
2011AGUFMSH31A1986S Altcode:
In the golden age of solar spacecraft observatories, the use of similar
instruments observing same targets offers us the possibility to get
more accurate information of the physical processes taking place on
them. We present a comparison between the vector magnetic field and
thermodynamic quantities obtained by three different spectropolarimetric
instruments. We have used the simultaneous multi-wavelength capabilities
of THEMIS/MTR as bridge between the observations at Fe I 6173 Å
provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP
observations. The official inversion codes for these instruments (PCA
based-on, VFISV and MERLIN respectively) have been used with the data
properly arranged for them. Therefore, we compare the final products
usually offered to the community, i.e. after the inversion, using
different codes and these different wavelengths. The cross-calibration
of these products shall allow us to go forward from one instrument
result to other one in an easy, convenient way.
---------------------------------------------------------
Title: Spectropolarimetric Study of Sea-serpent Penumbral Filaments
and a Naked Sunspot
Authors: Sainz Dalda, Alberto; Tarbell, T.; Title, A.; Vargas
Dominguez, S.; Bellot Rubio, L. R.
2011SPD....42.0303S Altcode: 2011BAAS..43S.0303S
We present a spectropolarimetric study of the sea-serpent penumbral
filaments in AR NOAA 10944 and of a naked sunspot (i.e. a sunspot-like
feature without penumbra) in AR NOAA 10977. Both active regions were
observed by Hinode-SOT/SP in the photospheric lines Fe I 6301 &
6302 [[Unable to Display Character: &#506]]. The high spatial and
temporal resolution combined with the high polarimetric sensitivity
of these observations enables us to get a better understanding of the
dynamics of the penumbra and the moving magnetic feature (herafter MMF)
activity in and around both traditional and naked sunspots. Our results
show how the temporal evolution of the sea-serpent filaments fits
very well with the thin-tube flux model for the penumbra presented by
Schlichenmaier (2003). In addition, the spectropolarmetric analysis of
the naked sunspot addresses the issue posed by Zuccarello et al. (2009)
about the existence of bipolar MMFs around naked sunspots even when
they cannot be explained as an extension of the penumbral filaments.
---------------------------------------------------------
Title: Temporal Evolution of the Sea-Serpent Penumbral Filaments
Authors: Sainz Dalda, A.; Bellost Rubio, L.
2010AGUFMSH11B1644S Altcode:
The high spectral and spatial resolution provided by Hinode allows us
to investigate the temporal evolution of magnetic structures in and
around of the sunspot penumbra. Such structures show behavior similar
to the penumbral bright points, i.e. they migrate inward from 2/3 of the
penumbra and outward from the outer part of the penumbra. This dynamical
process can be explained by the so-called thin-flux tube penumbral
model that takes into account the magneto-convective overshoot.
---------------------------------------------------------
Title: Sunspot Umbra Atmosphere from Full Stokes Inversion
Authors: Wenzel, R.; Berdyugina, S. V.; Fluri, D. M.; Arnaud, J.;
Sainz-Dalda, A.
2010ASPC..428..117W Altcode: 2010arXiv1003.5114W
Sunspots are prominent manifestations of the solar cycle and provide
key constraints for understanding its operation. Also, knowing
the internal structure of sunspots allows us to gain insights on
the energy transport in strong magnetic fields and, thus, on the
processes inside the convection zone, where solar magnetic fields
are generated and amplified before emerging at the surface on various
scales, even during solar minima. In this paper, we present results
of a spectropolarimetric analysis of a sunspot observed during the
declining phase of solar cycle 23. By inversion of the full Stokes
spectra, observed in several spectral regions in the optical at the
THEMIS facility, we infer the height dependence of physical quantities
such as the temperature and the magnetic field strength for different
sunspot regions. The simultaneous use of atomic (Fe I 5250.2 and 5250.6
Å) and highly temperature-sensitive molecular (TiO 7055 Å and MgH
5200 Å) lines allows us to improve a model of the sunspot umbra.
---------------------------------------------------------
Title: Explanation of the Sea-serpent Magnetic Structure of Sunspot
Penumbrae
Authors: Kitiashvili, I. N.; Bellot Rubio, L. R.; Kosovichev, A. G.;
Mansour, N. N.; Sainz Dalda, A.; Wray, A. A.
2010ApJ...716L.181K Altcode: 2010arXiv1003.0049K
Recent spectro-polarimetric observations of a sunspot showed the
formation of bipolar magnetic patches in the mid-penumbra and their
propagation toward the outer penumbral boundary. The observations
were interpreted as being caused by sea-serpent magnetic fields near
the solar surface. In this Letter, we develop a three-dimensional
radiative MHD numerical model to explain the sea-serpent structure
and the wave-like behavior of the penumbral magnetic field lines. The
simulations reproduce the observed behavior, suggesting that the
sea-serpent phenomenon is a consequence of magnetoconvection in
a strongly inclined magnetic field. It involves several physical
processes: filamentary structurization, high-speed overturning
convective motions in strong, almost horizontal magnetic fields with
partially frozen field lines, and traveling convective waves. The
results demonstrate a correlation of the bipolar magnetic patches with
high-speed Evershed downflows in the penumbra. This is the first time
that a three-dimensional numerical model of the penumbra results in
downward-directed magnetic fields, an essential ingredient of sunspot
penumbrae that has eluded explanation until now.
---------------------------------------------------------
Title: Sea-Serpent Magnetic Structure of Sunspot Penumbrae:
Observations and MHD Simulations
Authors: Kitiashvili, Irina; Bellot Rubio, L. R.; Kosovichev, A. G.;
Mansour, N. N.; Sainz Dalda, A.; Wray, A. A.
2010AAS...21631706K Altcode: 2010BAAS...41..899K
Recent high-resolution spectro-polarimetric observations of a sunspot
detected formation of bipolar magnetic patches in the mid penumbra and
propagation of these patches toward the outer penumbral boundary. The
observations have been interpreted as an evidence of sea-serpent field
lines near the solar surface. Using a radiative 3D MHD code, we model
the behavior of solar magnetoconvection in strongly inclined magnetic
field of penumbra. The numerical simulation results reproduce the
moving bipolar magnetic elements observed in high-resolution SOHO/MDI
and Hinode/SOT data and also their physical properties, supporting the
sea-serpent model. The simulations explain the sea-serpent structure
and dynamics of the penumbral field as a consequence of turbulent
magnetoconvection in a highly inclined, strong magnetic field,
which forms filamentary structures and has properties of traveling
convective wave. The model also shows that the appearance of the
sea-serpent magnetic field lines is closely related to high-speed
patches ("Evershed clouds") of the penumbra radial outflow.
---------------------------------------------------------
Title: Decaimiento de flujo magnético en el Sol: Manchas, MMFs
y ERs
---------------------------------------------------------
Title: Decaimiento de flujo magnético en el Sol: Manchas,
MMFs y ERs
---------------------------------------------------------
Title: Magnetic Flux Decay in the Sun: Spots, MMFs
[moving magnetic features] and ERs;
Authors: Sainz Dalda, Alberto
2009PhDT.......573S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Model Atmosphere from Inversion of Stokes Profiles
Authors: Wenzel, R.; Berdyugina, V. S.; Fluri, D. M.; Arnaud, J.;
Sainz Dalda, A.
2008ESPM...12.2.24W Altcode:
We present results of a spectropolarimetric analysis of sunspots. By
inversion of full Stokes spectra observed in serveral spectral regions
in the optical at the THEMIS facility we infer the height dependence of
physical quantities such as the temperature, LOS velocity and magnetic
field for different sunspot regions. The wide spectral range and
the use of TiO and MgH transitions, which are extremely temperature
sensitive and can be treated in LTE even in higher layers, allow us
to extend and improve a sunspot model atmosphere.
---------------------------------------------------------
Title: Comet McNaught C/2006 P1: observation of the sodium emission
by the solar telescope THEMIS
Authors: Leblanc, F.; Fulle, M.; López Ariste, A.; Cremonese, G.;
Doressoundiram, A.; Sainz Dalda, A.; Gelly, B.
2008A&A...482..293L Altcode:
Comet McNaught C/2006 P1 was the brightest comet of the last forty
years when reaching its perihelion at an heliocentric distance of
0.17Â AU. Two days before this perihelion, at an heliocentric distance
of 0.2Â AU, Themis, a French-Italian solar telescope in the Canary
Islands, Spain, observed the Comet sodium emission of McNaught. The
measured maximum sodium brightness of the D2Â emission line peaked
at 900Â Mega-Rayleigh. The spatial distribution of the sodium
emission with respect to the nucleus of the comet is in agreement
with previous observations. It displays a clear sunward-tailward
asymmetry that suggests a dichotomy of the sodium sources between
a source close to the nucleus and an extended source most probably
corresponding to the dust tail. The spatial distribution along the
slit of the width and speed of the Doppler Na distribution also
suggests such a dichotomy. The sodium ejection rate inferred from this
observation agrees with the value of the ejection rate extrapolated
from comet Hale-Bopp, taking into account the heliocentric distance
of comet McNaught and its significantly larger dust release. If
we suppose a similar concentration of sodium atoms in both comets,
this observation suggests that the sodium ejection rate from comets
McNaught and Hale-Bopp is proportional to the solar flux. Therefore
the most probable ejection mechanisms are photo-sputtering, solar wind
sputtering, or cometary ion sputtering, and not thermal desorption.
---------------------------------------------------------
Title: Detection of sea-serpent field lines in sunspot penumbrae
Authors: Sainz Dalda, A.; Bellot Rubio, L. R.
2008A&A...481L..21S Altcode: 2007arXiv0712.2983S
Aims:We investigate the spatial distribution of magnetic polarities
in the penumbra of a spot observed very close to disk center. <BR
/>Methods: High angular and temporal resolution magnetograms taken with
the Narrowband Filter Imager aboard Hinode are used in this study. They
provide continuous and stable measurements in the photospheric Fe I
630.25 line for long periods of time. <BR />Results: Our observations
show small-scale, elongated, bipolar magnetic structures that appear in
the mid penumbra and move radially outward. They occur in between the
more vertical fields of the penumbra, and can be associated with the
horizontal fields that harbor the Evershed flow. Many of them cross
the outer penumbral boundary, becoming moving magnetic features in
the sunspot moat. We determine the properties of these structures,
including their sizes, proper motions, footpoint separation, and
lifetimes. <BR />Conclusions: The bipolar patches can be interpreted
as being produced by sea-serpent field lines that originate in the mid
penumbra and eventually leave the spot in the form moving magnetic
features. The existence of such field lines has been inferred from
Stokes inversions of spectropolarimetric measurements at lower angular
resolution, but this is the first time they are imaged directly. Our
observations add another piece of evidence in favor of the uncombed
structure of penumbral magnetic fields. <P />A movie is only available
in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Chromospheric reversals in the emergence of an ephemeral region
Authors: Sainz Dalda, A.; López Ariste, A.
2007A&A...469..721S Altcode:
Context: The behaviour of both ephemeral regions and moving magnetic
features has been often described for the photospheric layer, but
not for the chromosphere. Both magnetic structures are related to the
decay of active regions, but their actual role is not yet clear. <BR
/>Aims: Our aim is to observe and understand the behaviour of these
structures in the chromosphere. <BR />Methods: We performed simultaneous
photospheric and chromospheric spectropolarimetric observations of an
ephemeral region and a moving magnetic feature. A new code developed
for the reduction of spectropolarimetric data of several wavelengths
observed simultaneously was used here for the first time and will be
described here for future reference. The resulting Stokes profiles are
analysed in detail. <BR />Results: The Stokes V profiles of Fe i 6301
and 6302 Å are reversed in polarity with respect to the chromospheric
Ca ii 8498 and 8542 Å in the cases shown. They reveal a reversed
magnetic field topology between these layers for both structures. The
time evolution of the ephemeral region results in a cancellation of
the chromospheric signal, while the ratio of Stokes V amplitudes of
Fe i 6301 and 6302 Å simultaneously informs us of a strengthening of
the photospheric field. A scenario of the evolution of the ephemeral
region is consequently suggested. <BR />Conclusions: The moving magnetic
feature reveals itself as an exclusively photospheric feature, similar
to the ephemeral region in the initial stages of its emergence. As
the loop emerges into the chromosphere it is slowed down and does not
reach the corona. Most probably, the opposite polarity background in
the chromosphere prevents ascent into corona.
---------------------------------------------------------
Title: Using reduction and inversion tools for THEMIS-MTR data:
chromospheric reversals of a moving magnetic feature and an ephemeral
region .
Authors: Sainz Dalda, A.; López Ariste, A.
2007MmSAI..78..154S Altcode:
New tools have been developed for THEMIS spectropolarimetric data. In
this paper we present how these tools work and can be used in order
to understand two interesting observed phenomena: a moving magnetic
feature and an ephemeral region.
---------------------------------------------------------
Title: First observation of bald patches in a filament channel and
at a barb endpoint
Authors: López Ariste, A.; Aulanier, G.; Schmieder, B.; Sainz
Dalda, A.
2006A&A...456..725L Altcode:
The 3D magnetic field topology of solar filaments/prominences is
strongly debated, because it is not directly measureable in the
corona. Among various prominence models, several are consistent
with many observations, but their related topologies are very
different. We conduct observations to address this paradigm. We
measure the photospheric vector magnetic field in several small
flux concentrations surrounding a filament observed far from disc
center. Our objective is to test for the presence/absence of magnetic
dips around/below the filament body/barb, which is a strong constraint
on prominence models, and that is still untested by observations. Our
observations are performed with the THEMIS/MTR instrument. The four
Stokes parameters are extracted, from which the vector magnetic fields
are calculated using a PCA inversion. The resulting vector fields
are then deprojected onto the photospheric plane. The 180° ambiguity
is then solved by selecting the only solution that matches filament
chirality rules. Considering the weakness of the resulting magnetic
fields, a careful analysis of the inversion procedure and its error
bars was performed, to avoid over-interpretation of noisy or ambiguous
Stokes profiles. Thanks to the simultaneous multi-wavelength THEMIS
observations, the vector field maps are coaligned with the Hα image of
the filament. By definition, photospheric dips are identifiable where
the horizontal component of the magnetic field points from a negative
toward a positive polarity. Among six bipolar regions analyzed in the
filament channel, four at least display photospheric magnetic dips,
i.e. bald patches. For barbs, the topology of the endpoint is that of
a bald patch located next to a parasitic polarity, not of an arcade
pointing within the polarity. The observed magnetic field topology in
the photosphere tends to support models of prominence based on magnetic
dips located within weakly twisted flux tubes. Their underlying and
lateral extensions form photospheric dips both within the channel and
below barbs.
---------------------------------------------------------
Title: Moving Magnetic Features as Prolongation of Penumbral Filaments
Authors: Sainz Dalda, A.; Martínez Pillet, V.
2005ApJ...632.1176S Altcode:
A sequence of 633 high spatial resolution magnetograms and continuum
images from SOHO MDI of NOAA AR 0330 is used to study moving magnetic
feature (MMF) activity in the moat surrounding a mature leader
sunspot. The time-averaged frame shows that the moat region is covered
by a magnetic field that exhibits the same polarity distribution as that
observed in the penumbra. The moat field displays the true polarity
of the spot in the sector where the penumbra displays it. Similarly,
on the side where the penumbra shows a polarity opposite the true one
(due to projection effects after the so-called apparent neutral line),
the moat field also displays a polarity opposite the true one. This is
only compatible with a moat field that is horizontal almost everywhere,
as in the outer penumbra. Indeed, this horizontal moat field is seen
to be physically connected with the penumbra. This connection is
made evident when analyzing the individual structures detected in the
averaged images, which we call moat filaments. The filaments stretch
out for 12" in the moat and can be traced back into the penumbra. The
observed polarity distribution along them is only compatible with mean
inclinations in the range of 80°-90°. Inside the spot, these filaments
are linked to the more horizontal magnetic field component that is
thought to carry a large part of the Evershed flow. Several bipolar
MMFs are seen to originate inside the penumbra and cross the sunspot
outer boundary to enter the moat region, following the paths outlined
by the moat filaments. These results are discussed in the frame of our
current theoretical understanding of the Evershed flow and MMF activity.
---------------------------------------------------------
Title: Flux Cancellation in a Decaying Active Region
Authors: Martinez Pillet, V.; Sainz Dalda, A.; van Driel-Gesztelyi, L.
2004cosp...35.1133M Altcode: 2004cosp.meet.1133M
Flux Cancellation in a Decaying Active Region Flux cancellation
is observed in many regions on the Sun as internetwork, network
and active regions fields. It clearly plays a crucial role in the
constant flux processing observed in the solar surface. During the
decay of an active region, we have observed the in-situ dissapearance
of 70 % of its flux (from SOHO/MDI). Active region flux decay is a
global, large-scale, process crucial to the solar cycle. But the
flux cancellations, where the flux actually disappears, do take
place in very small scale regions. There opposite polarities meet and
vanish. The process needs of observations with sufficient sensitivity
and angular resolution. In the example presented here, we show how
up to 4 of these cancellations are associated with outward moving
material in the Corona (as observed by TRACE), including a major
active region filament eruption. Solar Orbiter, profiting from the
advantage observing position and near-corotation can follow these
subtle, but crucial, processes with the necessary set of instruments:
Magnetographs, Coronal imagers and spectrographs. For those events
occurring in the spacecraft solar vertical, one should not exclude
the detection of the phenomena in the in-situ instruments.
