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Author name code: gosic
ADS astronomy entries on 2022-09-14
author:"Gosic, Milan"
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Title: Unipolar versus Bipolar Internetwork Flux Appearance
Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, L. R.; Del
Toro Iniesta, Jose Carlos; Cheung, Mark; Orozco Suárez, David
2022cosp...44.2513G Altcode:
Small-scale internetwork (IN) magnetic fields are considered to be
the main building blocks of the quiet Sun magnetism. It is therefore
of paramount importance to understand how these fields are generated
on the solar surface. To shed new light on this open question,
we studied the appearance modes and spatio-temporal evolution of
individual IN magnetic elements inside one supergranular cell. For
that purpose, we employed a high-resolution, high-sensitivity,
long-duration Hinode/NFI magnetogram sequence. From identification
of flux patches and magnetofrictional simulations, we show that there
are two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger, live longer
and carry more flux than unipolar features. About $70$% of the total
instantaneous IN flux detected inside the supergranule is in the form
of bipoles. Both types of flux concentrations are uniformly distributed
over the solar surface. However, bipolar features appear (randomly
oriented) at a faster rate than unipolar features (68 as opposed to
55~Mx~cm$^{-2}$~day$^{-1}$). Our results lend support to the idea that
bipolar features may be the signature of local dynamo action, while
unipolar features seem to be formed by coalescence of background flux.
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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: The Solar Internetwork. III. Unipolar versus Bipolar Flux
Appearance
Authors: Gošić, M.; Bellot Rubio, L. R.; Cheung, M. C. M.; Orozco
Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C.
2022ApJ...925..188G Altcode: 2021arXiv211103208G
Small-scale internetwork (IN) magnetic fields are considered to be the
main building blocks of quiet Sun magnetism. For this reason, it is
crucial to understand how they appear on the solar surface. Here,
we employ a high-resolution, high-sensitivity, long-duration
Hinode/NFI magnetogram sequence to analyze the appearance modes and
spatiotemporal evolution of individual IN magnetic elements inside a
supergranular cell at the disk center. From identification of flux
patches and magnetofrictional simulations, we show that there are
two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger and stronger
than unipolar features. They also live longer and carry more flux
per feature. Both types of flux concentrations appear uniformly over
the solar surface. However, we argue that bipolar features truly
represent the emergence of new flux on the solar surface, while
unipolar features seem to be formed by the coalescence of background
flux. Magnetic bipoles appear at a faster rate than unipolar features
(68 as opposed to 55 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>), and provide
about 70% of the total instantaneous IN flux detected in the interior
of the supergranule.
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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: 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: Lagrangian chaotic saddles and objective vortices in solar
plasmas
Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico L.;
Bellot Rubio, Luis R.; Gošić, Milan; Kusano, Kanya; Park, Sung-Hong
2020PhRvE.102f0201C Altcode:
We report observational evidence of Lagrangian chaotic saddles
in plasmas, given by the intersections of finite-time unstable and
stable manifolds, using an ≈22 h sequence of spacecraft images of the
horizontal velocity field of solar photosphere. A set of 29 persistent
objective vortices with lifetimes varying from 28.5 to 298.3 min are
detected by computing the Lagrangian averaged vorticity deviation. The
unstable manifold of the Lagrangian chaotic saddles computed for ≈11
h exhibits twisted folding motions indicative of recurring vortices in
a magnetic mixed-polarity region. We show that the persistent objective
vortices are formed in the gap regions of Lagrangian chaotic saddles
at supergranular junctions.
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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: Chromospheric and TR diagnostics in a large scale numerical
simulation of flux emergence: Synthetic vs Real observables
Authors: Hansteen, V. H.; De Pontieu, B.; Testa, P.; Gosic, M.;
Martinez-Sykora, J.
2020AGUFMSH0010021H Altcode:
Field stored just below or rising to the photosphere will break through
the surface and enter the upper atmosphere once the gradient of the
subphotospheric field strength becomes sufficiently large. Opposite
polarity flux bundles will reconnect in the photosphere and above,
to form steadily longer loops that expand into the outer solar
atmosphere, forming the corona. Some of the emerging flux is likely
due to a local dynamo, but also the direct emergence of large scale
magnetic structures from below is important, even in the quiet Sun. A
significant proportion of this field likely reaches the chromosphere
and may leave imprint on chromospheric dynamics and energetics. Using
large scale numerical models (72x72x60) Mm and the high resolution
spectra and slit jaw images from IRIS, as well as photospheric data
from Hinode/SOT, and SDO/HMI we study the interactions between the
magnetic flux caught in the granular flow field and the chromosphere
and chromospheric field above. We will compare synthetic observables
of the photospheric Fe I 617.3 nm line, the chromospheric Mg II h&k
lines, and the transition region Si IV lines, with their observational
counterparts. We will also generate synthetic ALMA band 3 images. The
comparison of synthetic observational data will let us draw conclusions
as to the validity of the numerical modeling and the importance of flux
emergence for the dynamics and energetics of the outer solar atmosphere.
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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: Erratum: Supergranular turbulence in the quiet Sun: Lagrangian
coherent structures
Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico
L.; Gošić; , Milan; Bellot Rubio, Luis R.; Kusano, Kanya; Miranda,
Rodrigo A.; Requerey, Iker S.
2019MNRAS.489..707C Altcode: 2019MNRAS.tmp.2225C
No abstract at ADS
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Title: Supergranular turbulence in the quiet Sun: Lagrangian coherent
structures
Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico
L.; Gošić; , Milan; Bellot Rubio, Luis R.; Kusano, Kanya; Miranda,
Rodrigo A.; Requerey, Iker S.
2019MNRAS.488.3076C Altcode: 2019MNRAS.tmp.1841C; 2019arXiv190408472C
The quiet Sun exhibits a wealth of magnetic activities that are
fundamental for our understanding of solar magnetism. The magnetic
fields in the quiet Sun are observed to evolve coherently, interacting
with each other to form prominent structures as they are advected by
photospheric flows. The aim of this paper is to study supergranular
turbulence by detecting Lagrangian coherent structures (LCS) based on
the horizontal velocity fields derived from Hinode intensity images at
disc centre of the quiet Sun on 2010 November 2. LCS act as transport
barriers and are responsible for attracting/repelling the fluid elements
and swirling motions in a finite time. Repelling/attracting LCS are
found by computing the forward/backward finite-time Lyapunov exponent
(FTLE), and vortices are found by the Lagrangian-averaged vorticity
deviation method. We show that the Lagrangian centres and boundaries
of supergranular cells are given by the local maximum of the forward
and backward FTLE, respectively. The attracting LCS expose the location
of the sinks of photospheric flows at supergranular junctions, whereas
the repelling LCS interconnect the Lagrangian centres of neighbouring
supergranular cells. Lagrangian transport barriers are found within a
supergranular cell and from one cell to other cells, which play a key
role in the dynamics of internetwork and network magnetic elements. Such
barriers favour the formation of vortices in supergranular junctions. In
particular, we show that the magnetic field distribution in the quiet
Sun is determined by the combined action of attracting/repelling LCS
and vortices.
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Title: Evolution of bipolar internetwork magnetic fields
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis Ramon
2019AAS...23431102G Altcode:
Internetwork (IN) magnetic fields can be found inside supergranular
cells all over the solar surface. Thanks to their abundance and
appearance rate, IN fields are considered to be an essential contributor
to the magnetic flux and energy budget of the solar photosphere, and
may also play a major role in the energy budget of the chromosphere
and transition region. Therefore, it is crucial to understand how
IN magnetic fields appear, evolve, interact with the preexisting
magnetic structures, and what impact they have on the upper solar
atmosphere. Here, we analyze spatio-temporal evolution of IN magnetic
bipolar structures, i.e, loops and clusters, employing multi-instrument
(IRIS and SST), multi-wavelength observations of IN regions with the
highest sensitivity and resolution possible. For the first time, our
observations allow us to describe in detail how IN bipoles emerge in
the photosphere and even reach the chromosphere. We estimate the field
strengths of these IN magnetic structures both in the photosphere and
the chromosphere, using full Stokes measurements in Fe I 6173 Å, Mg I
b<SUB>2</SUB> 5173 Å, and Ca II 8542 Å. Employing the IRIS FUV and
NUV spectra, we show that IN fields contribute to the chromospheric
and transition region heating through interaction with the preexisting
ambient fields.
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Title: On the Origin of the Magnetic Energy in the Quiet Solar
Chromosphere
Authors: Martínez-Sykora, Juan; Hansteen, Viggo H.; Gudiksen, Boris;
Carlsson, Mats; De Pontieu, Bart; Gošić, Milan
2019ApJ...878...40M Altcode: 2019arXiv190404464M
The presence of magnetic field is crucial in the transport of energy
through the solar atmosphere. Recent ground-based and space-borne
observations of the quiet Sun have revealed that magnetic field
accumulates at photospheric heights, via a local dynamo or from
small-scale flux emergence events. However, most of this small-scale
magnetic field may not expand into the chromosphere due to the entropy
drop with height at the photosphere. Here we present a study that uses
a high-resolution 3D radiative MHD simulation of the solar atmosphere
with non-gray and non-LTE radiative transfer and thermal conduction
along the magnetic field to reveal that (1) the net magnetic flux
from the simulated quiet photosphere is not sufficient to maintain a
chromospheric magnetic field (on average), (2) processes in the lower
chromosphere, in the region dominated by magnetoacoustic shocks,
are able to convert kinetic energy into magnetic energy, (3) the
magnetic energy in the chromosphere increases linearly in time until
the rms of the magnetic field strength saturates at roughly 4-30 G
(horizontal average) due to conversion from kinetic energy, (4) and
that the magnetic features formed in the chromosphere are localized
to this region.
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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: Convection-driven Generation of Ubiquitous Coronal Waves
Authors: Aschwanden, Markus J.; Gošic, Milan; Hurlburt, Neal E.;
Scullion, Eamon
2018ApJ...866...73A Altcode:
We develop a new method to measure the 3D kinematics of the
subphotospheric motion of magnetic elements, which is used to study
the coupling between the convection-driven vortex motion and the
generation of ubiquitous coronal waves. We use the method of decomposing
a line-of-sight magnetogram from MDI/SDO into unipolar magnetic charges,
which yields the (projected) 2D motion [x(t), y(t)] and the (half) width
evolution w(t) of an emerging magnetic element from an initial depth
of d ≲ 1500 km below the photosphere. A simple model of rotational
vortex motion with magnetic flux conservation during the emergence
process of a magnetic element predicts the width evolution, i.e.,
w(t)/w <SUB>0</SUB> = [B(t)/B <SUB>0</SUB>]<SUP>-1/2</SUP>, and an
upper limit of the depth variation d(t) ≤ 1.3 w(t). While previous
2D tracing of magnetic elements provided information on advection
and superdiffusion, our 3D tracing during the emergence process of a
magnetic element is consistent with a ballistic trajectory in the upward
direction. From the estimated Poynting flux and lifetimes of convective
cells, we conclude that the Coronal Multi-channel Polarimeter-detected
low-amplitude transverse magnetohydrodynamic waves are generated by
the convection-driven vortex motion. Our observational measurements
of magnetic elements appear to contradict the theoretical random-walk
braiding scenario of Parker.
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Title: Emergence of internetwork magnetic fields through the solar
atmosphere
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R.
2018cosp...42E1261G Altcode:
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 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
largely unknown. Here we use coordinated IRIS and SST observations
of IN regions at high spatial and temporal resolution. They give us
the opportunity to follow the evolution of IN magnetic loops as they
emerge into the photosphere. For the first time, our polarimetric
measurements provide a direct observational evidence of IN fields
reaching the chromosphere. Moreover, we show that IN magnetic loops
contribute to the chromospheric and transition region heating through
interaction with preexisting ambient fields.
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Title: Transport of Internetwork Magnetic Flux Elements in the Solar
Photosphere : Signatures of Large-Scale Flows and their Effect on
Transport Statistics
Authors: Agrawal, Piyush; Rast, Mark; Gosic, Milan; Rempel, Matthias;
Bellot Rubio, Luis
2018tess.conf21704A Altcode:
The motions of small-scale magnetic <span class="s1" flux elements
in the solar photosphere can provide some measure of the Lagrangian
properties of the convective <span class="s1" flow. Measurements of
these motions have been critical in estimating the turbulent diffusion
coef<span class="s1" ficient in <span class="s1" flux-transport
dynamo models and in determining the Alfvén wave excitation spectrum
for coronal heating models. We examine the motions of internetwork
<span class="s1" flux elements in Hinode<span class="s1"
/Narrowband Filter Imager magnetograms and study the scaling of
their mean squared displacement and the shape of their displacement
probability distribution as a function of time. We <span class="s1"
find that the mean squared displacement scales super-diffusively with
a slope of about 1.48. Super-diffusive scaling has been observed in
other studies for temporal increments as small as 5 s, increments over
which ballistic scaling would be expected. Using high-cadence MURaM
simulations, we show that the observed super-diffusive scaling at short
increments is a consequence of random changes in barycenter positions
due to <span class="s1" flux evolution. We also <span class="s1"
find that for long temporal increments, beyond granular lifetimes,
the observed displacement distribution deviates from that expected
for a diffusive process, evolving from Rayleigh to Gaussian. This
change in distribution can be modeled analytically by accounting for
supergranular advection along with granular motions. These results
complicate the interpretation of magnetic element motions as strictly
advective or diffusive on short and long timescales and suggest that
measurements of magnetic element motions must be used with caution
in turbulent diffusion or wave excitation models. We propose that
passive tracer motions in measured photospheric <span class="s1"
flows may yield more robust transport statistics.
---------------------------------------------------------
Title: Emergence of internetwork magnetic fields through the solar
atmosphere
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis
2018tess.conf21701G Altcode:
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 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
largely unknown. Here we use coordinated IRIS and SST observations
of IN regions at high spatial and temporal resolution. They give us
the opportunity to follow the evolution of IN magnetic loops as they
emerge into the photosphere. For the first time, our polarimetric
measurements provide a direct observational evidence of IN fields
reaching the chromosphere. Moreover, we show that IN magnetic loops
contribute to the chromospheric and transition region heating through
interaction with preexisting ambient fields.
---------------------------------------------------------
Title: Chromospheric Heating due to Cancellation of Quiet Sun
Internetwork Fields
Authors: Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot
Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V.
2018ApJ...857...48G Altcode: 2018arXiv180207392G
The heating of the solar chromosphere remains one of the most
important questions in solar physics. Our current understanding is that
small-scale internetwork (IN) magnetic fields play an important role
as a heating agent. Indeed, cancellations of IN magnetic elements in
the photosphere can produce transient brightenings in the chromosphere
and transition region. These bright structures might be the signature
of energy release and plasma heating, probably driven by the magnetic
reconnection of IN field lines. Although single events are not expected
to release large amounts of energy, their global contribution to the
chromosphere may be significant due to their ubiquitous presence
in quiet Sun regions. In this paper, we study cancellations of IN
elements and analyze their impact on the energetics and dynamics of
the quiet Sun atmosphere. We use high-resolution, multiwavelength,
coordinated observations obtained with the Interface Region Imaging
Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify
cancellations of IN magnetic flux patches and follow their evolution. We
find that, on average, these events live for ∼3 minutes in the
photosphere and ∼12 minutes in the chromosphere and/or transition
region. Employing multi-line inversions of the Mg II h and k lines,
we show that cancellations produce clear signatures of heating in the
upper atmospheric layers. However, at the resolution and sensitivity
accessible to the SST, their number density still seems to be one
order of magnitude too low to explain the global chromospheric heating.
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Title: Investigating the Response of Loop Plasma to Nanoflare Heating
Using RADYN Simulations
Authors: Polito, V.; Testa, P.; Allred, J.; De Pontieu, B.; Carlsson,
M.; Pereira, T. M. D.; Gošić, Milan; Reale, Fabio
2018ApJ...856..178P Altcode: 2018arXiv180405970P
We present the results of 1D hydrodynamic simulations of coronal
loops that are subject to nanoflares, caused by either in situ
thermal heating or nonthermal electron (NTE) beams. The synthesized
intensity and Doppler shifts can be directly compared with Interface
Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly
(AIA) observations of rapid variability in the transition region (TR)
of coronal loops, associated with transient coronal heating. We find
that NTEs with high enough low-energy cutoff ({E}<SUB>{{C</SUB>}})
deposit energy in the lower TR and chromosphere, causing blueshifts
(up to ∼20 km s<SUP>-1</SUP>) in the IRIS Si IV lines, which
thermal conduction cannot reproduce. The {E}<SUB>{{C</SUB>}} threshold
value for the blueshifts depends on the total energy of the events
(≈5 keV for 10<SUP>24</SUP> erg, up to 15 keV for 10<SUP>25</SUP>
erg). The observed footpoint emission intensity and flows, combined
with the simulations, can provide constraints on both the energy of the
heating event and {E}<SUB>{{C</SUB>}}. The response of the loop plasma
to nanoflares depends crucially on the electron density: significant
Si IV intensity enhancements and flows are observed only for initially
low-density loops (<10<SUP>9</SUP> cm<SUP>-3</SUP>). This provides
a possible explanation of the relative scarcity of observations of
significant moss variability. While the TR response to single heating
episodes can be clearly observed, the predicted coronal emission (AIA
94 Å) for single strands is below current detectability and can only
be observed when several strands are heated closely in time. Finally,
we show that the analysis of the IRIS Mg II chromospheric lines can
help further constrain the properties of the heating mechanisms.
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Title: Persistent magnetic vortex flow at a supergranular vertex
Authors: Requerey, Iker S.; Cobo, Basilio Ruiz; Gošić, Milan;
Bellot Rubio, Luis R.
2018A&A...610A..84R Altcode: 2017arXiv171201510R
Context. Photospheric vortex flows are thought to play a key role
in the evolution of magnetic fields. Recent studies show that these
swirling motions are ubiquitous in the solar surface convection and
occur in a wide range of temporal and spatial scales. Their interplay
with magnetic fields is poorly characterized, however. <BR /> Aims:
We study the relation between a persistent photospheric vortex flow
and the evolution of a network magnetic element at a supergranular
vertex. <BR /> Methods: We used long-duration sequences of continuum
intensity images acquired with Hinode and the local correlation-tracking
method to derive the horizontal photospheric flows. Supergranular
cells are detected as large-scale divergence structures in the flow
maps. At their vertices, and cospatial with network magnetic elements,
the velocity flows converge on a central point. <BR /> Results: One
of these converging flows is observed as a vortex during the whole
24 h time series. It consists of three consecutive vortices that
appear nearly at the same location. At their core, a network magnetic
element is also detected. Its evolution is strongly correlated to
that of the vortices. The magnetic feature is concentrated and
evacuated when it is caught by the vortices and is weakened and
fragmented after the whirls disappear. <BR /> Conclusions: This
evolutionary behavior supports the picture presented previously,
where a small flux tube becomes stable when it is surrounded by
a vortex flow. <P />A movie attached to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201731842/olm">https://www.aanda.org</A>
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Title: Occurrence and persistence of magnetic elements in the
quiet Sun
Authors: Giannattasio, F.; Berrilli, F.; Consolini, G.; Del Moro,
D.; Gošić, M.; Bellot Rubio, L.
2018A&A...611A..56G Altcode: 2018arXiv180103871G
Context. Turbulent convection efficiently transports energy up to the
solar photosphere, but its multi-scale nature and dynamic properties
are still not fully understood. Several works in the literature have
investigated the emergence of patterns of convective and magnetic
nature in the quiet Sun at spatial and temporal scales from granular
to global. <BR /> Aims: To shed light on the scales of organisation
at which turbulent convection operates, and its relationship with
the magnetic flux therein, we studied characteristic spatial and
temporal scales of magnetic features in the quiet Sun. <BR /> Methods:
Thanks to an unprecedented data set entirely enclosing a supergranule,
occurrence and persistence analysis of magnetogram time series were
used to detect spatial and long-lived temporal correlations in the
quiet Sun and to investigate their nature. <BR /> Results: A relation
between occurrence and persistence representative for the quiet Sun was
found. In particular, highly recurrent and persistent patterns were
detected especially in the boundary of the supergranular cell. These
are due to moving magnetic elements undergoing motion that behaves
like a random walk together with longer decorrelations ( 2 h) with
respect to regions inside the supergranule. In the vertices of the
supegranular cell the maximum observed occurrence is not associated
with the maximum persistence, suggesting that there are different
dynamic regimes affecting the magnetic elements.
---------------------------------------------------------
Title: Transport of Internetwork Magnetic Flux Elements in the
Solar Photosphere
Authors: Agrawal, Piyush; Rast, Mark P.; Gošić, Milan; Bellot Rubio,
Luis R.; Rempel, Matthias
2018ApJ...854..118A Altcode: 2017arXiv171101290A
The motions of small-scale magnetic flux elements in the solar
photosphere can provide some measure of the Lagrangian properties of
the convective flow. Measurements of these motions have been critical
in estimating the turbulent diffusion coefficient in flux-transport
dynamo models and in determining the Alfvén wave excitation spectrum
for coronal heating models. We examine the motions of internetwork
flux elements in Hinode/Narrowband Filter Imager magnetograms and
study the scaling of their mean squared displacement and the shape of
their displacement probability distribution as a function of time. We
find that the mean squared displacement scales super-diffusively with
a slope of about 1.48. Super-diffusive scaling has been observed in
other studies for temporal increments as small as 5 s, increments
over which ballistic scaling would be expected. Using high-cadence
MURaM simulations, we show that the observed super-diffusive scaling
at short increments is a consequence of random changes in barycenter
positions due to flux evolution. We also find that for long temporal
increments, beyond granular lifetimes, the observed displacement
distribution deviates from that expected for a diffusive process,
evolving from Rayleigh to Gaussian. This change in distribution can be
modeled analytically by accounting for supergranular advection along
with granular motions. These results complicate the interpretation
of magnetic element motions as strictly advective or diffusive on
short and long timescales and suggest that measurements of magnetic
element motions must be used with caution in turbulent diffusion or
wave excitation models. We propose that passive tracer motions in
measured photospheric flows may yield more robust transport statistics.
---------------------------------------------------------
Title: Chromospheric Heating Driven by Cancellations of Internetwork
Magnetic Flux
Authors: Gosic, M.; de la Cruz Rodriguez, J.; De Pontieu, B.; Bellot
Rubio, L.; Esteban Pozuelo, S.; Ortiz-Carbonell, A. N.
2017AGUFMSH41C..02G Altcode:
The heating of the solar chromosphere remains to be one of the
most important questions in solar physics. It is believed that this
phenomenon may significantly be supported by small-scale internetwork
(IN) magnetic fields. Indeed, cancellations of IN magnetic flux can
generate transient brightenings in the chromosphere and transition
region. These bright structures might be the signature of energy release
and plasma heating, probably driven by magnetic reconnection of IN field
lines. Using high resolution, multiwavelength, coordinated observations
recorded with the Interface Region Imaging Spectrograph (IRIS) and
the Swedish 1-m Solar Telescope (SST), we analyzed cancellations of IN
flux and their impact on the energetics and dynamics of the quiet Sun
atmosphere. From their temporal and spatial evolution, we determine that
these events can heat locally the upper atmospheric layers. However,
employing multi-line inversions of the Mg II h & k lines, we show
that cancellations, although occurring ubiquitously over IN regions,
are not capable of sustaining the total radiative losses of the quiet
Sun chromosphere.
---------------------------------------------------------
Title: Chromospheric heating due to internetwork magnetic flux
cancellations
Authors: Gosic, Milan; de la Cruz Rodriguez, Jaime; De Pontieu, Bart;
Bellot Rubio, Luis; Ortiz, Ada; Esteban Pozuelo, Sara
2017SPD....4810404G Altcode:
The heating of the solar chromosphere is one of the most intriguing
unanswered problems in solar physics. It is believed that this
phenomenon may significantly be supported by small-scale internetwork
(IN) magnetic fields. Indeed, cancellations of IN magnetic flux
patches might be an efficient way to transport flux and energy from
the photosphere to the chromosphere. Because of this, it is essential
to determine where they occur, the rates at which they proceed, and
understand their influence on the chromosphere. Here we study the
spatial and temporal evolution of IN cancelling patches using high
resolution, multiwavelength, coordinated observations obtained with
the Interface Region Imaging Spectrograph (IRIS) and the Swedish
1-m Solar Telescope (SST). Employing multi-line inversions of the
Mg II h&k lines we show that cancelling events, while occurring
ubiquitously over IN regions, produce clear signatures of heating in
the upper atmospheric layers. Using the RADYN code we determine the
energy released due to cancellations of IN elements and discuss about
their impact on the dynamics and energetics of the solar chromosphere.
---------------------------------------------------------
Title: Flux appearance and disappearance rates in the solar
internetwork
Authors: Gosic, Milan; Bellot Rubio, Luis; Del Toro Iniesta, Jose
Carlos; Orozco Suarez, David; Katsukawa, Yukio
2016SPD....4740105G Altcode:
The solar internetwork contains weak and highly dynamic magnetic
fields that are essential to understanding the solar magnetism at small
spatial and temporal scales. Therefore, it is important to determine
how these fields are maintained on the solar surface. Using unique
Hinode observations, we follow the evolution of individual magnetic
elements in the interior of two supergranular cells at the disk
center. From up to 38 hr of continuous measurements, we show that
magnetic flux appears in internetwork regions at a rate of 120±3
Mx cm<SUP>-2</SUP> day<SUP>-1</SUP> (3.7±0.4 × 10<SUP>24</SUP> Mx
day<SUP>-1</SUP> over the entire solar surface). Flux disappears from
the internetwork at a rate of 125±6 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>
(3.9±0.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>) through fading of
magnetic elements, cancellation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. The removal of flux from supergranules
occurs mainly through fading and interactions with network, at nearly
the same rate of about 50 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>. Our
results demonstrate that the sources and sinks of internetwork magnetic
flux are well balanced, reflecting the steady-state nature of the quiet
Sun. Using the instantaneous flux appearance and disappearance rates,
we successfully reproduce, for the first time, the temporal evolution
of the total unsigned flux in the interior of supergranular cells.
---------------------------------------------------------
Title: The Solar Internetwork. II. Flux Appearance and Disappearance
Rates
Authors: Gošić, M.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.;
Orozco Suárez, D.; Katsukawa, Y.
2016ApJ...820...35G Altcode: 2016arXiv160205892G
Small-scale internetwork magnetic fields are important ingredients of
the quiet Sun. In this paper we analyze how they appear and disappear
on the solar surface. Using high resolution Hinode magnetograms,
we follow the evolution of individual magnetic elements in the
interior of two supergranular cells at the disk center. From up to
38 hr of continuous measurements, we show that magnetic flux appears
in internetwork regions at a rate of 120 ± 3 Mx cm<SUP>-2</SUP>
day<SUP>-1</SUP> (3.7 ± 0.4 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>
over the entire solar surface). Flux disappears from the internetwork
at a rate of 125 ± 6 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP> (3.9
± 0.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP>) through fading of
magnetic elements, cancelation between opposite-polarity features,
and interactions with network patches, which converts internetwork
elements into network features. Most of the flux is lost through
fading and interactions with the network, at nearly the same rate of
about 50 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>. Our results demonstrate
that the sources and sinks of internetwork magnetic flux are well
balanced. Using the instantaneous flux appearance and disappearance
rates, we successfully reproduce the time evolution of the total
unsigned flux in the two supergranular cells.
---------------------------------------------------------
Title: Super-diffusion versus competitive advection: a simulation
Authors: Del Moro, D.; Giannattasio, F.; Berrilli, F.; Consolini,
G.; Lepreti, F.; Gošić, M.
2015A&A...576A..47D Altcode: 2015arXiv150105444D
Context. Magnetic element tracking is often used to study the transport
and diffusion of the magnetic field on the solar photosphere. From the
analysis of the displacement spectrum of these tracers, it has recently
been agreed that a regime of super-diffusivity dominates the solar
surface. Quite habitually this result is discussed in the framework of
fully developed turbulence. <BR /> Aims: However, the debate whether
the super-diffusivity is generated by a turbulent dispersion process,
by the advection due to the convective pattern, or even by another
process is still open, as is the question of the amount of diffusivity
at the scales relevant to the local dynamo process. <BR /> Methods:
To understand how such peculiar diffusion in the solar atmosphere
takes place, we compared the results from two different data sets
(ground-based and space-borne) and developed a simulation of passive
tracers advection by the deformation of a Voronoi network. <BR />
Results: The displacement spectra of the magnetic elements obtained by
the data sets are consistent in retrieving a super-diffusive regime for
the solar photosphere, but the simulation also shows a super-diffusive
displacement spectrum: its competitive advection process can reproduce
the signature of super-diffusion. <BR /> Conclusions: Therefore, it
is not necessary to hypothesize a totally developed turbulence regime
to explain the motion of the magnetic elements on the solar surface.
---------------------------------------------------------
Title: The solar internetwork
Authors: Gosic, Milan
2015PhDT.......305G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Solar Internetwork. I. Contribution to the Network
Magnetic Flux
Authors: Gošić, M.; Bellot Rubio, L. R.; Orozco Suárez, D.;
Katsukawa, Y.; del Toro Iniesta, J. C.
2014ApJ...797...49G Altcode: 2014arXiv1408.2369G
The magnetic network (NE) observed on the solar surface harbors a
sizable fraction of the total quiet Sun flux. However, its origin and
maintenance are not well known. Here we investigate the contribution
of internetwork (IN) magnetic fields to the NE flux. IN fields permeate
the interior of supergranular cells and show large emergence rates. We
use long-duration sequences of magnetograms acquired by Hinode and
an automatic feature tracking algorithm to follow the evolution of NE
and IN flux elements. We find that 14% of the quiet Sun (QS) flux is
in the form of IN fields with little temporal variations. IN elements
interact with NE patches and modify the flux budget of the NE either
by adding flux (through merging processes) or by removing it (through
cancellation events). Mergings appear to be dominant, so the net flux
contribution of the IN is positive. The observed rate of flux transfer
to the NE is 1.5 × 10<SUP>24</SUP> Mx day<SUP>-1</SUP> over the entire
solar surface. Thus, the IN supplies as much flux as is present in the
NE in only 9-13 hr. Taking into account that not all the transferred
flux is incorporated into the NE, we find that the IN would be able
to replace the entire NE flux in approximately 18-24 hr. This renders
the IN the most important contributor to the NE, challenging the view
that ephemeral regions are the main source of flux in the QS. About 40%
of the total IN flux eventually ends up in the NE.
---------------------------------------------------------
Title: Pair separation of magnetic elements in the quiet Sun
Authors: Giannattasio, F.; Berrilli, F.; Biferale, L.; Del Moro, D.;
Sbragaglia, M.; Bellot Rubio, L.; Gošić, M.; Orozco Suárez, D.
2014A&A...569A.121G Altcode: 2014arXiv1409.1010G
The dynamic properties of the quiet Sun photosphere can be investigated
by analyzing the pair dispersion of small-scale magnetic fields
(i.e., magnetic elements). By using 25 h-long Hinode magnetograms
at high spatial resolution (0.3 arcsec), we tracked 68 490 magnetic
element pairs within a supergranular cell near the disk center. The
computed pair separation spectrum, calculated on the whole set of
particle pairs independently of their initial separation, points
out what is known as a super-diffusive regime with spectral index
γ = 1.55 ± 0.05, in agreement with the most recent literature, but
extended to unprecedented spatial and temporal scales (from granular
to supergranular). Furthermore, for the first time, we investigated
here the spectrum of the mean square displacement of pairs of magnetic
elements, depending on their initial separation r<SUB>0</SUB>. We found
that there is a typical initial distance above (below) which the pair
separation is faster (slower) than the average. A possible physical
interpretation of such a typical spatial scale is also provided.
---------------------------------------------------------
Title: Flux emergence in the solar internetwork and its contribution
to the network
Authors: Gosic, Milan; Katsukawa, Yukio; Orozco Suarez, David; Bellot
Rubio, L. R.
2014cosp...40E1055G Altcode:
Network and internetwork magnetic fields are believed to play a
crucial role in the energy budget of the solar atmosphere. Therefore,
it is essential to understand how they are maintained on the
solar surface. Using high resolution Hinode/NFI magnetograms at
disk center, we automatically follow quiet Sun magnetic elements
from their appearance to disappearance. From up to 40 hours of
continuous measurements, we derive the flux emergence rate in the
solar internetwork to be around 40 Mx cm(-2) day(-1) . We show
that internetwork fields appearing in the interior of individual
supergranular cells contribute flux to the surrounding network at
a rate of 2×10(19) Mx h(-1) . In only 10-20 hours, internetwork
elements can transfer as much flux as resides in network features,
establishing them as the most important source of flux for the network
and the quiet Sun flux budget.
---------------------------------------------------------
Title: Diffusion of Solar Magnetic Elements up to Supergranular
Spatial and Temporal Scales
Authors: Giannattasio, F.; Del Moro, D.; Berrilli, F.; Bellot Rubio,
L.; Gošić, M.; Orozco Suárez, D.
2013ApJ...770L..36G Altcode: 2013arXiv1305.4006G
The study of spatial and temporal scales on which small magnetic
structures (magnetic elements) are organized in the quiet Sun
may be approached by determining how they are transported on the
solar photosphere by convective motions. The process involved
is diffusion. Taking advantage of Hinode high spatial resolution
magnetograms of a quiet-Sun region at the disk center, we tracked
20,145 magnetic elements. The large field of view (~50 Mm) and the
long duration of the observations (over 25 hr without interruption at
a cadence of 90 s) allowed us to investigate the turbulent flows at
unprecedented large spatial and temporal scales. In the field of view
an entire supergranule is clearly recognizable. The magnetic element
displacement spectrum shows a double-regime behavior: superdiffusive
(γ = 1.34 ± 0.02) up to granular spatial scales (~1500 km) and
slightly superdiffusive (γ = 1.20 ± 0.05) up to supergranular scales.
---------------------------------------------------------
Title: Turbulent diffusion on the solar photosphere through 24-hour
continuous observations of magnetic elements
Authors: Giannattasio, F.; Berrilli, F.; Del Moro, D.; Bellot Rubio,
L.; Orozco Suarez, D.; Gosic, M.
2012AGUFMSH13A2242G Altcode:
Solar atmosphere is a unique laboratory for the study of turbulent
flows under extreme conditions (e.g. very high Reynolds numbers). The
turbulent nature of the flow may be approached by determining how
magnetic flux elements are transported on the solar surface, and
measuring the spatio-temporal scales on which these small magnetic
structures are organized. The process involved is diffusion. Several
works explored this topic, both by simulations and observations,
and the results are often contradictory, ranging from fully-developed
turbulent scenarios to normal-diffusive motions. We analyze 24-hour
continuous Hinode SOT observations of a supergranular region (for the
first time these long scales are explored), studying the evolution of
the mutual distance between magnetic element pairs and its scaling laws,
in order to investigate the diffusion process. We find a super-diffusive
behavior, with a gamma index depending on the spatial scale selected.
---------------------------------------------------------
Title: Evolution of internetwork magnetic fields inside supergranular
cells
Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, Luis; Orozco
Suarez, David
2012cosp...39..657G Altcode: 2012cosp.meet..657G
To understand the formation of small-scale magnetic fields in the quiet
Sun and their contribution to the solar activity, it is essential to
investigate the properties of internetwork magnetic fields. Using
Hinode/NFI magnetograms of very high sensitivity (7 Mx/cm^{2}),
spatial resolution (0.16 arcsec/pixel), and cadence (90 s), we
follow the evolution of magnetic fields inside of a supergranular
cell located at disk center. In 5 hours of continuous measurements
covering an area of 20.8 × 23.2 arcsec^{2}, we manually track 2415
magnetic elements from appearance to disappearance and derive their
physical properties. The average values of the magnetic flux, effective
diameter, lifetime, and horizontal velocity are 3 × 10^{17} Mx, 0.5 Mm,
17 min, and 2 km/s, respectively. We also investigate how the physical
parameters of the individual elements vary as a function of time,
flux, and spatial position. Using this unique data set, we determine
with unprecedented accuracy the flux emergence and disappearance rate
in the solar internetwork.
---------------------------------------------------------
Title: On the solar abundance of indium
Authors: Vitas, N.; Vince, I.; Lugaro, M.; Andriyenko, O.; Gošić,
M.; Rutten, R. J.
2008MNRAS.384..370V Altcode: 2008MNRAS.tmp...25V; 2007arXiv0711.2166V
The generally adopted value for the solar abundance of indium is over
six times higher than the meteoritic value. We address this discrepancy
through numerical synthesis of the 451.13-nm line on which all indium
abundance studies are based, both for the quiet Sun and the sunspot
umbra spectrum, employing standard atmosphere models and accounting
for hyperfine structure and Zeeman splitting in detail. The results,
as well as a re-appraisal of indium nucleosynthesis, suggest that
the solar indium abundance is close to the meteoritic value, and
that some unidentified ion line causes the 451.13-nm feature in the
quiet-Sun spectrum.
---------------------------------------------------------
Title: Program of Telluric Lines Monitoring
Authors: Vince, I.; Kos, P.; Latkovic, O.; Martinovic, N.; Gosic,
M.; Stojadinovic, J.
2006SerAJ.173..101V Altcode:
A new observational program of telluric lines monitoring was introduced
at Belgrade Astronomical Observatory. The ultimate goal of this program
is to investigate the properties of Earth's atmosphere through modeling
the observed profiles of telluric lines. The program is intend to
observe infrared molecular oxygen lines that were selected according to
spectral sensitivity of the available CCD camera. In this paper we give
the initial and the final selection criteria for spectral lines included
in the program, the description of equipment and procedures used for
observations and reduction, a review of preliminary observational
results with the estimated precision, and a short discussion on the
comparison of the theoretical predictions and the measurements.
