explanation blue bibcodes open ADS page with paths to full text
Author name code: malanushenko-anna
ADS astronomy entries on 2022-09-14
author:"Malanushenko, Anna V."
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Title: Derivation of Boundary Conditions for Data-Driven Simulations
of Active Regions and their Emission
Authors: Tremblay, Benoit; Malanushenko, Anna; Rempel, Matthias;
Kazachenko, Maria
2022cosp...44.2472T Altcode:
Coronal heating remains a major area of research in solar physics. In
particular, the spatial dimensions and the structuring of heating
processes have yet to be fully understood. Whereas observations suggest
that plasma is heated in bundles of thin flux tubes, it's been theorized
from simulations that emission in active regions can be structured
in larger flux tubes with irregular boundaries. In the latter case,
the emission can appear like the emission from loop bundles, with
variations of the column depth at their boundaries causing an impression
of individual loops. These scenarios have distinct implications for
coronal heating and the study of coronal loops and thus need to be
confirmed observationally. Our objective is to develop insight into
the spatial properties of solar coronal heating using a statistical
analysis of the emission from observed and simulated active regions. To
this end, we perform data-driven MHD simulations of active regions. The
MURaM simulation is being modified to work with photospheric inputs
as boundary conditions, including observed vector magnetograms, and
electric field maps and flow maps inferred from observations. We
focus on electric field maps derived using the PDFI\_SS inversion
technique and flow maps derived through supervised deep learning. More
specifically, we train a convolutional neural network to emulate the
MURaM simulation and infer MURaM-like flows from observational data,
including large-scale flows in the granulation surrounding active
regions. We present derivations of boundary conditions (i.e., electric
field maps, flows maps) from SDO/HMI observations of selected active
regions, and discuss the limitations and challenges associated with
the methods. We detail ongoing efforts in driving the MURaM simulation
from derived boundary conditions. Finally, we illustrate how these
data-driven simulations will be used to study the structuring of the
emission of active regions statistically and identify which scenario
of coronal heating best matches observations.
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Title: A Statistical Approach to Study Fine Structure of EUV Emission
in Active Regions
Authors: Malanushenko, Anna; Rempel, Matthias; Tremblay, Benoit;
Kazachenko, Maria
2022cosp...44.2526M Altcode:
Heating of the solar corona is one of the major problems in solar
physics, and spatial dimension and structuring of the processes involved
in heating are yet to be understood. Observations of the numerous
thin coronal loops above active regions (ARs) suggest that coronal
heating itself is highly variable on small scales, heating plasma in
collections of thin flux tubes. It has recently been theorized, based
on simulations, that emitting plasma in ARs can also be structured in
larger flux tubes with irregular boundaries. The emission of these large
flux tubes can appear like emission of loop bundles, with variations of
the column depth at their boundaries causing an impression of individual
loops. This "coronal veil" theory was argued to be a more general
scenario, which better explains AR emission properties than previous
models. If confirmed observationally, it will have a large impact
on coronal heating studies, suggesting that existing measurements of
temperature and density in coronal loops may need to be reevaluated. The
observational validation of this hypothesis is as important as it is
difficult. For a given coronal loop, it is difficult to tell whether it
is a compact feature or a projection artifact. In this talk, we propose
a new statistical approach to address this problem. Instead of trying
to analyze each loop individually, we focus on scaling relationship
between a number of loops in a given AR and the AR's total brightness in
a given wavelength. We argue that these two quantities are related by a
power law. We demonstrate in theoretical calculations how the power law
coefficients will differ depending on whether the emission is structured
into (a) compact features, (b) large features with irregular boundaries,
or (c) extended and thin veil-like features. We demonstrate that these
power laws exist in observations and discuss numerical experiments
which may help us to determine which of these scenarios, if any,
best describes observations. We further describe the observational
statistics that can, in conjunction with numerical experiments, help
us understand which of these scenarios take place in the Sun. We also
present the first results from our project to collect these data.
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Title: Extracting characteristics of interplanetary CMEs from database
of synthetic white-light images based on ensemble MHD simulations
Authors: Provornikova, Elena; Gibson, Sarah; Wiltberger, Michael;
Dalmasse, Kévin; Merkin, Viacheslav; Malanushenko, Anna; Vourlidas,
Angelos; Arge, Charles
2022cosp...44.2433P Altcode:
In this work, we investigate to what extent properties of CMEs
determined from synthetic white light images represent properties of
simulated interplanetary CMEs. The propagation of an interplanetary CME
with an internal flux rope is modeled with the GAMERA global model of
the inner heliosphere (0.1- 1 AU) coupled with the Gibson-Low (G&L)
model of a self-similarly expanding CME with an internal magnetic
field. The solar wind background in the inner heliosphere is driven
by the Wang-Sheeley-Arge (WSA)-ADAPT corona solution. An ensemble of
CME simulations is created by setting different input parameters of a
CME flux rope in the G&L model (e.g., magnetic field topology and
magnetic field strength, angular width, speed, orientation, latitude,
and longitude). A set of values for each of the defining G&L
parameters are taken from statistical distributions obtained from
an analysis of white light CME imagery near the Sun. To set the CME
magnetic structure we choose four topologies allowed by the G&L
model: spheromak, tethered spheromak, flux rope, and magnetic arcade. We
run an ensemble of a few hundred MHD simulations of interplanetary CMEs
with internal flux rope. The ensemble is used to produce a database of
synthetic CME images in white-light total brightness. We use the CACTUS
package to autonomously detect CMEs in synthetic white light images and
determine CME angular width and variations of CME velocity, mass, and
trajectory during the interplanetary CME propagation. We then compare
results from CACTUS with the ground truth data extracted directly from
MHD simulation output. We analyze cases showing a disagreement between
the true and inferred properties in more detail.
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Title: Exploring Structures and Flows with NASA's under-construction
PUNCH mission
Authors: DeForest, Craig; Gibson, Sarah; Thompson, Barbara;
Malanushenko, Anna; Desai, Mihir; Elliott, Heather; Viall, Nicholeen;
Cranmer, Steven; de Koning, Curt
2022cosp...44.1077D Altcode:
The Polarimeter to UNify the Corona and Heliosphere is a NASA Small
Explorer to image the corona and heliosphere as parts of a single
system. PUNCH comprises four ~50kg smallsats, each carrying one imaging
instrument, that work together to form a single "virtual coronagraph"
with a 90° field of view, centered on the Sun. Scheduled for joint
launch with NASA's SPHEREx mission, PUNCH starts its two-year prime
science phase in 2025. PUNCH will generate full polarized image
sequences of Thomson-scattered light from free electrons in the corona
and young solar wind, once every four minutes continuously. This
enables tracking the young solar wind and turbulent structures within
it as they disconnect from the Sun itself, as well as large transients
such as CMEs, CIRs, and other shocks within the young solar wind. A
student-contributed X-ray spectrometer (STEAM) will address questions
of coronal heating and flare physics. We present motivating science,
expected advances, mission status, and how to get involved with PUNCH
science now.
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Title: Expected results for the cradle of the Solar Wind with the
Polarimeter to UNify the Corona and Heliosphere (PUNCH)
Authors: DeForest, Craig; Gibson, Sarah; De Koning, Curt A.; Thompson,
Barbara; Malanushenko, Anna; Desai, Mihir; Elliott, Heather; Viall,
Nicholeen; Cranmer, Steven
2022cosp...44.1324D Altcode:
The Polarimeter to UNify the Corona and Heliosphere is a NASA Small
Explorer to image the corona and heliosphere as parts of a single
system. Imaging the corona and heliosphere together from a constellation
of four synchronized smallsats, PUNCH will — starting in 2025 —
provide a unique window on global structure and cross-scale processes
in the outer corona and young solar wind. PUNCH science is informed
by, and complements, the results of PSP and Solar Orbiter; and will
synergize with PROBA3/ASPIICS. We present early prototype results from
STEREO/SECCHI and current preparation work to enable PUNCH science
when data arrive, discuss anticipated results from the deeper-field,
higher time resolution imaging that PUNCH will provide, and describe
how to get involved with PUNCH science now.
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Title: The Coronal Veil
Authors: Malanushenko, A.; Cheung, M. C. M.; DeForest, C. E.; Klimchuk,
J. A.; Rempel, M.
2022ApJ...927....1M Altcode: 2021arXiv210614877M
Coronal loops, seen in solar coronal images, are believed to
represent emission from magnetic flux tubes with compact cross
sections. We examine the 3D structure of plasma above an active
region in a radiative magnetohydrodynamic simulation to locate volume
counterparts for coronal loops. In many cases, a loop cannot be linked
to an individual thin strand in the volume. While many thin loops are
present in the synthetic images, the bright structures in the volume
are fewer and of complex shape. We demonstrate that this complexity
can form impressions of thin bright loops, even in the absence of thin
bright plasma strands. We demonstrate the difficulty of discerning
from observations whether a particular loop corresponds to a strand in
the volume, or a projection artifact. We demonstrate how apparently
isolated loops could deceive observers, even when observations from
multiple viewing angles are available. While we base our analysis
on a simulation, the main findings are independent from a particular
simulation setup and illustrate the intrinsic complexity involved in
interpreting observations resulting from line-of-sight integration
in an optically thin plasma. We propose alternative interpretation
for strands seen in Extreme Ultraviolet images of the corona. The
"coronal veil" hypothesis is mathematically more generic, and
naturally explains properties of loops that are difficult to address
otherwise-such as their constant cross section and anomalously high
density scale height. We challenge the paradigm of coronal loops as
thin magnetic flux tubes, offering new understanding of solar corona,
and by extension, of other magnetically confined bright hot plasmas.
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Title: Establishing flux rope chirality using white light polarization
data from the PUNCH mission
Authors: Gibson, Sarah; Morgan, Huw; Provornikova, Elena; Malanushenko,
Anna; DeForest, Craig; de Koning, Curt; Fan, Yuhong; Merkin,
Viacheslav; Webb, David
2021AGUFMSH32A..03G Altcode:
Interplanetary Coronal Mass Ejections (ICMEs) are generally expected
to incorporate coherently-twisted magnetic fields, i.e., magnetic
flux ropes. We expect and have observed to some extent evolution
and interactions between flux ropes and the background corona and
solar wind, including rotation, deflection, and potentially continued
topological changes. The upcoming PUNCH mission will provide a full
field of view from pole to pole and fill existing gaps between
coronagraphs and heliospheric imagers, and will obtain polarized
brightness measurements which may be used along with brightness
measurements as a powerful tool for imaging and localizing CME
substructure evolution in transit. Further analysis of these
substructures may then lead to information about the chirality, or
handedness of magnetic twist of the flux rope. In order to demonstrate
these capabilities, we present synthetic polarization from forward
modeled simulations of flux rope CMEs. We compare the 3D position
of substructure that can be extracted from these data to the ground
truth simulation knowledge of the position of mass along the line
of sight. We further consider the implications for chirality and the
robustness of the method to topological variation of the flux rope at
the heart of the ICME.
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Title: Analyzing the Structure of Coronal Loops in MURaM Radiation
MHD Simulations
Authors: David, Mia; Rempel, Matthias; Malanushenko, Anna
2021AGUFMSH45B2377D Altcode:
Coronal loops are emission features that trace out parts of the solar
magnetic field in the corona, and as such they provide important
information about the magnetic and plasma structure of the solar
corona. Their thermal substructure is still an open question: their
thickness is at the limit of resolution of the instruments observing
them, and higher resolution instruments tend to find finer strands. This
raises the question whether the finest strands are resolved with the
currently available highest resolution instruments. In this project,
we address this from a modeling perspective and look to answer the
following questions. Does the number of strands identified in synthetic
observations depend on the resolution of the numerical simulation? How
many strands remain hidden in current observations that may otherwise
be evident in future higher resolution observations? We look at
simulations done with MURaM code of a bipolar active region that
are available at three different numerical resolutions. We emulate
observables at various resolutions, including one which exceeds that of
current instruments. We synthesize data in resolution of Atmospheric
Imaging Assembly onboard Solar Dynamics Observatory (SDO/AIA) and
High-Resolution Coronal Imager (HiC). We find that the number of
strands found in synthetic AIA does not depend on the resolution of
the simulation, and that it is a small fraction of the strands found
in the native resolution of the simulation. The number of strands
seen in synthetic HiC data is a factor of 2-4 higher than that in
synthetic AIA, and increases moderately with the resolution of the
simulation. We compare the results with observations by studying an
active region observed by AIA. We study the dependence of the number
of loops counted on the viewing angle in both synthetic and observable
data. We also report statistical properties of these strands.
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Title: A Statistical Approach to Study Spatial Characteristics of
EUV Emission in Active Regions
Authors: Malanushenko, Anna; Egeland, Ricky; Kazachenko, Maria;
Rempel, Matthias; Tremblay, Benoit
2021AGUFMSH45B2360M Altcode:
Heating of the solar corona is one of the major problems in solar
physics, and spatial dimension and structuring of the processes involved
in heating are yet to be understood. Observations of the numerous
thin coronal loops above active regions (ARs) suggest that coronal
heating itself is highly variable on small scales, heating plasma in
collections of thin flux tubes. It has recently been theorized, based
on simulations, that emitting plasma in ARs can also be structured in
larger flux tubes with irregular boundaries. The emission of these large
flux tubes can appear like emission of loop bundles, with variations
of the column depth at their boundaries causing an impression of
individual loops. This "coronal veil" theory was argued to be a
more general scenario, which better explains AR emission properties
than previous models. If confirmed observationally, it will have a
large impact on coronal heating studies, suggesting that existing
measurements of temperature and density in coronal loops may need to
be reevaluated. The observational validation of this hypothesis is as
important as it is difficult. For a given coronal loop, it is difficult
to tell whether it is a compact feature or a projection artifact. In
this talk, we propose a new statistical approach to address this
problem. Instead of trying to analyze each loop individually, we focus
on scaling relationship between a number of loops in a given AR and the
AR's total brightness in a given wavelength. We argue that these two
quantities are related by a power law. We demonstrate in theoretical
calculations how the power law coefficients will differ depending on
whether the emission is structured into (a) compact features, (b)
large features with irregular boundaries, or (c) extended and thin
veil-like features. We demonstrate that these power laws exist in
observations and discuss numerical experiments which may help us to
determine which of these scenarios, if any, best describes observations.
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Title: Visualizing the Solar Corona in Virtual Reality
Authors: Wolff, Milana; Dima, Gabriel; Rempel, Matthias; Lacatus,
Daniela; Paraschiv, Alin; Lecinski, Alice; Malanushenko, Anna
2021AGUFMSH45B2365W Altcode:
This work presents novel visualizations of the optically thin solar
corona in a virtual reality environment created using the Unity
development platform. Unity enables fast rendering and interaction
with three dimensional datasets in an immersive setting. We depict
data derived from coronal simulations generated by radiative
magnetohydrodynamic MURaM. These visualizations represent synthetic
emissivity values computed for a variety of coronal emission lines
using high-resolution, time-dependent thermodynamic and magnetic
datasets. Users can enter the virtual environment, accessible on desktop
and mobile devices or with a virtual reality head-mounted display
(such as Oculus or Vive headsets) and observe and interact with both
static and dynamic structures in the solar corona from arbitrary
vantage points. These types of direct interaction techniques with
simulated large-scale structures enhance intuitive understanding of
solar dynamics. We welcome ideas from the community on how to further
leverage this technology.
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Title: Large ensemble simulations of CMEs in the inner heliosphere:
toward constraining distributions of CME parameters near the Sun
Authors: Provornikova, Elena; Merkin, Viacheslav; Malanushenko, Anna;
Gibson, Sarah; Vourlidas, Angelos; Arge, Charles; Dalmasse, Kevin
2021AGUFMSH32A..01P Altcode:
In this work, we take a comprehensive approach which combines
physics-based simulations, observations and statistical methods
toward understanding the evolution of coronal mass ejections in
the inner heliosphere and linking characteristics of CMEs near the
Sun and their plasma and magnetic field properties as they would be
observed at 1 AU. We simulate the propagation of ICMEs using a global
model of the inner heliosphere driven at the coronal boundary by
the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs are initiated at 21.5
solar radii using an MHD analytical Gibson-Low (G&L) model of a
self-similarly expanding magnetic bubble with defining parameters (e.g.,
latitude and longitude, magnetic field topology and strength, angular
width, speed, orientation). The ICME propagation is simulated using
the inner heliosphere version of the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a reinvention of the
high-heritage Lyon-Fedder-Mobarry (LFM) code. A set of values for each
of the defining G&L parameters was constrained by the statistical
representation of CME images near the Sun. Intending to span the solar
cycle, we model ICME propagation in different solar wind backgrounds
corresponding to rising, declining, and minimum solar cycle phases. A
grid of CME parameters and three solar wind backgrounds constitute
a parameter space for 50,000 ICME simulations. We describe types and
a structure of the output data from simulations and an algorithm of
automatic performance of many thousands of runs. We discuss methods to
incorporate CME data from both solar observations and in-situ at 1 AU
in a statistical study to construct posterior predictive distributions
of CME model input parameters.
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Title: Multi-spacecraft Observations Of Coronal Loops To Verify A
Force-free Field Reconstruction And Infer Loop Cross Sections
Authors: McCarthy, M.; Longcope, D.; Malanushenko, A.
2021AAS...23820501M Altcode:
Active region EUV loops are believed to trace a subset of magnetic
field lines through the corona. Malanushenko et al. (2009) proposed a
method, using loop images and line-of-sight photospheric magnetograms,
to infer the three-dimensional shape and field strength along each
loop. McCarthy et al. (2019) used this novel method to compute the
total magnetic flux interconnecting a pair of active regions observed
by SDO/AIA. They adopted the common assumption that each loop had a
circular cross section. The accuracy of inferred shape and circularity
of cross sections can both be tested using observations of the same
loops from additional vantage points as provided by STEREO/EUVI. Here,
we use multiple viewing angles to confirm the three-dimensional
structure of loops. Of 151 viable cases, 105 (69.5%) matched some
form of visible coronal structure when viewed approximately in
quadrature. A loop with a circular cross-section should appear of
a similar width in different perspectives. In contradiction to this,
we find a puzzling lack of correlation between loop diameters seen from
different perspectives, even an anti-correlation in some cases. Features
identified as monolithic loops in AIA may, in fact, be more complex
density enhancements. The 30.5% of reconstructions from AIA which did
not match any feature in EUVI might be such enhancements. Others may be
genuine loop structures, but with elliptical cross sections. We observe
an anti-correlation between diameter and brightness, lending support
to the latter hypothesis. Four loops are consistent with non-circular
cross sections, where we find anti-correlation in both comparisons.
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Title: Identifying Non-potential Energy Hot Spots In A Global
Coronal Simulation
Authors: Corchado Albelo, M. F.; Gibson, S. E.; Linker, J.; Mackay,
D. H.; Dalmasse, K.; Malanushenko, A.
2021AAS...23832803C Altcode:
Observing the global coronal magnetic field remains a difficult task;
limiting our understanding of the evolution of global phenomena in these
external layers of the solar atmosphere. Therefore, we rely on models to
get the solar exterior global field. While models can extrapolate the
magnetic field from surface flux and vector magnetogram observations,
e.g. by assuming a current-free corona, other techniques are used
to simulate the current-carrying field via magnetohydrodynamic (MHD)
evolution or surface flux transport of large scale field, and inserting
current-carrying small scale field structures like twisted flux ropes
into the corona. These current-carrying fields are of interest for
studying solar energetic eruptions like coronal mass ejections and
flares because they provide the energy reservoir needed to drive these
events. Previous studies suggest that ground-based infrared polarimetric
measurements of Fe XIII (1074.7 nm) line correlate with the energy
of the current-carrying field. In this study we generated synthetic
polarimetric observations from a fully-resolved magnetohydrodynamics
model of the August 21, 2017 eclipse. The synthetic observations
were used as input to a diagnostic we developed to identify regions
where the modeling team inserted twisted flux ropes. The diagnostic
evaluated linearly and circularly polarized synthetic observations
of the corona as a means to identify the current-carrying magnetic
energy density. We found that the diagnostic does identify the
distribution of flux ropes in the corona. Thus, our findings motivate
the implementation of polarimetric measurements to identify "hot spots"
in which we can insert flux ropes and a degree of the twist/shear in
the current-carrying field.
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Title: Multispacecraft Observations of Coronal Loops to Verify a
Force-free Field Reconstruction and Infer Loop Cross Sections
Authors: McCarthy, Marika I.; Longcope, Dana W.; Malanushenko, Anna
2021ApJ...913...56M Altcode: 2021arXiv210402722M
Active region EUV loops are believed to trace a subset of magnetic
field lines through the corona. Malanushenko et al. proposed a method,
using loop images and line-of-sight photospheric magnetograms, to infer
the 3D shape and field strength along each loop. McCarthy et al. used
this novel method to compute the total magnetic flux interconnecting
a pair of active regions observed by SDO/AIA. They adopted the common
assumption that each loop had a circular cross section. The accuracy
of inferred shape and circularity of cross sections can both be tested
using observations of the same loops from additional vantage points
as provided by STEREO/EUVI. Here we use multiple viewing angles to
confirm the 3D structure of loops. Of 151 viable cases, 105 (69.5%)
matched some form of visible coronal structure when viewed approximately
in quadrature. A loop with a circular cross section should appear of
a similar width in different perspectives. In contradiction to this,
we find a puzzling lack of correlation between loop diameters seen from
different perspectives, even an anticorrelation in some cases. Features
identified as monolithic loops in AIA may, in fact, be more complex
density enhancements. The 30.5% of reconstructions from AIA that did
not match any feature in EUVI might be such enhancements. Others may
be genuine loop structures, but with elliptical cross sections. We
observe an anticorrelation between diameter and brightness, lending
support to the latter hypothesis. Of 13 loops suitable for width
analysis, 4 are consistent with noncircular cross sections, where we
find anticorrelation in both comparisons.
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Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, Anna; Gibson, Sarah; Provornikova, Elena;
Dalmasse, Kévin; Merkin, Viacheslav; Vourlidas, Angelos; Nychka,
Doug; Flyer, Natasha; Arge, Charles
2021cosp...43E1736M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson \& Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different congurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson \& Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic congurations within this
analytic solution is of great value to such simulations, as well as
for the studies of the flux ropes forming in the solar corona.
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Title: Designing a New Coronal Magnetic Field Energy Diagnostic
Authors: Corchado-Albelo, Marcel F.; Dalmasse, Kévin; Gibson, Sarah;
Fan, Yuhong; Malanushenko, Anna
2021ApJ...907...23C Altcode:
In the solar corona, the free energy, i.e., the excess in magnetic
energy over a ground-state potential field, forms the reservoir of
energy that can be released during solar flares and coronal mass
ejections. Such free energy provides a measure of the magnetic field
nonpotentiality. Recent theoretical and observational studies indicate
that the presence of nonpotential magnetic fields is imprinted into
the structures of infrared, off-limb, coronal polarization. In this
paper, we investigate the possibility of exploiting such observations
for mapping and studying the accumulation and release of coronal free
magnetic energy, with the goal of developing a new tool for identifying
"hot spots" of coronal free energy such as those associated with
twisted and/or sheared coronal magnetic fields. We applied forward
modeling of infrared coronal polarimetry to three-dimensional models
of nonpotential and potential magnetic fields. From these we defined a
quantitative diagnostic of nonpotentiality that in the future could be
calculated from a comparison of infrared, off-limb, coronal polarization
observations from, e.g., the Coronal Multi-channel Polarimeter or the
Daniel K. Inouye Solar Telescope, and the corresponding polarization
signal forward-modeled from a potential field extrapolated from
photospheric magnetograms. We considered the relative diagnostic
potential of linear and circular polarization, and the sensitivities
of these diagnostics to coronal density distributions and assumed
boundary conditions of the potential field. Our work confirms the
capacity of polarization measurements for diagnosing nonpotentiality
and free energy in the solar corona.
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Title: The Magnetic Skeleton of the Solar Corona Over Several Solar
Rotations: Features, Analysis, and Community Availability
Authors: Malanushenko, A. V.; Gibson, S. E.; Kucera, T. A.; McKenzie,
D. E.
2020AGUFMSH041..02M Altcode:
The magnetic field in the solar corona is thought to be the main
driver for solar eruptive events, such as flares and coronal mass
ejections. The coronal magnetic field is therefore important to study,
but it is difficult to measure directly. Usually, it is studied through
extrapolations based on photospheric magnetograms. As the corona is
thought to be mostly in a state of equilibrium, equations of low-beta
equilibria are often used in order to study the structure of the
field, or to estimate the magnetic energy. One of the complications
that arise from this approach is that the solar photosphere itself is
not a low-beta equilibrium. <P />Images of the solar corona in extreme
ultraviolet (EUV) do not directly measure the magnetic field; however,
they do reveal structures from which information about magnetic field
can be inferred. For example, coronal loops are thought to trace
out magnetic field lines, coronal cavities are bounded by magnetic
surfaces, coronal holes are areas of magnetic flux that is open to
the heliosphere, and plasma flows are also thought to follow lines
of magnetic field. In other wavelengths, coronal spectropolarimetry
(SP) can provide us with proxies for magnetic field strength and
reveal plasma flows along the line of sight, off the limb. The EUV
images and SP data are frequently used to validate magnetic field
models. Additionally, new models are emerging which can use these data
directly as additional constraints. <P />We aggregate available relevant
features seen in EUV and SP data for several solar rotations. We
apply existing techniques to infer 3D constraints on the magnetic
field from these data. The result is an interactive 3D model based on
these constraints for a full rotation, or a "magnetic skeleton". It
is modular, so individual constraints can be easily added, or only
selected constraints can be used. The features could be exported in
either graphical or numerical form. The possible uses of our approach
include validation of magnetic models that are based on extrapolations
alone. Some models allow for using additional coronal constraints
directly. These 'skeletons' can also be used in non-magnetic-modeling
applications, as a simple, interactive reference for features seen in
a given rotation. We make the models available to the community and
show how to obtain and use them.
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Title: Tracking CME substructure evolution through the solar wind
Authors: Gibson, S. E.; DeForest, C.; de Koning, C. A.; Fan, Y.;
Malanushenko, A. V.; Merkin, V. G.; Provornikova, E.; Thompson, B. J.;
Webb, D. F.
2020AGUFMSH0280005G Altcode:
Future coronagraphs and heliospheric imagers, in particular those
to be launched on the PUNCH mission, will have the capability to
track the evolution of CME substructures as the CME moves through and
interacts with the solar wind. We present analysis using polarization
data obtained from forward modeling simulations of CMEs in the corona
and inner heliosphere. We use these data to track the evolution
of substructures in three dimensions, and consider the diagnostic
potential of internal substructure vs structure at the front of the
CME. In particular, we develop methods for extracting information
about chirality of CME magnetic flux ropes from polarization data.
---------------------------------------------------------
Title: Ensemble modeling of interplanetary CMEs with data-constrained
internal magnetic flux rope
Authors: Provornikova, E.; Merkin, V. G.; Malanushenko, A. V.; Gibson,
S. E.; Vourlidas, A.; Arge, C. N.
2020AGUFMSH0030016P Altcode:
Understanding the evolution of the CME magnetic structure as it
propagates through the interplanetary space is a key aspect in the
development of forecasting of magnetic properties of a CME arriving
at Earth and thus its impact on space weather. To analyze processes
of interplanetary CME (ICME)/solar-wind interactions and the role of
CME flux rope specification and solar wind background structure, we
take a statistical approach and perform thousands of data-driven MHD
simulations of ICME propagation in the inner heliosphere. Data-driven
modeling of ICMEs in the inner heliosphere (starting beyond the critical
surface in the corona) presents an attractive and computationally
feasible approach, since it bypasses the complex problem of CME
initiation and eruption in the corona. We simulate the propagation
of ICMEs in the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 21.5 solar radii using an MHD analytical Gibson-Low
(G&L) model of a self-similarly expanding magnetic flux rope
with defining parameters (e.g., location, magnetic topology, width,
magnetic field strength, speed, orientation). The ICME propagation
is simulated using the inner heliosphere version of the Grid Agnostic
MHD for Extended Research Applications (GAMERA) MHD model, which is a
reinvention of the high-heritage Lyon-Fedder-Mobarry (LFM) code. A set
of values for each of the defining G&L parameters was constrained
by statistical representation of solar CME observations. With the
aim to span the solar cycle, we model ICME propagation in different
solar wind backgrounds corresponding to rising, maximum, declining and
minimum solar cycle phases. A grid of G&L parameters and four solar
wind backgrounds constitute a parameter space for thousands of MHD
ICME runs. For each of the simulations we extract synthetic in-situ
observations of ICME as it passes Earth and synthetic white-light
images of an ICME as it propagates in the interplanetary space. We
present an analysis of produced distributions of ICME parameters and
characteristics.
---------------------------------------------------------
Title: Untangling the global coronal magnetic field with
multiwavelength observations
Authors: Gibson, S. E.; Malanushenko, A.; de Toma, G.; Tomczyk, S.;
Reeves, K.; Tian, H.; Yang, Z.; Chen, B.; Fleishman, G.; Gary, D.;
Nita, G.; Pillet, V. M.; White, S.; Bąk-Stęślicka, U.; Dalmasse,
K.; Kucera, T.; Rachmeler, L. A.; Raouafi, N. E.; Zhao, J.
2020arXiv201209992G Altcode:
Magnetism defines the complex and dynamic solar corona. Coronal
mass ejections (CMEs) are thought to be caused by stresses, twists,
and tangles in coronal magnetic fields that build up energy and
ultimately erupt, hurling plasma into interplanetary space. Even the
ever-present solar wind possesses a three-dimensional morphology shaped
by the global coronal magnetic field, forming geoeffective corotating
interaction regions. CME evolution and the structure of the solar
wind depend intimately on the coronal magnetic field, so comprehensive
observations of the global magnetothermal atmosphere are crucial both
for scientific progress and space weather predictions. Although some
advances have been made in measuring coronal magnetic fields locally,
synoptic measurements of the global coronal magnetic field are not yet
available. We conclude that a key goal for 2050 should be comprehensive,
ongoing 3D synoptic maps of the global coronal magnetic field. This will
require the construction of new telescopes, ground and space-based,
to obtain complementary, multiwavelength observations sensitive
to the coronal magnetic field. It will also require development of
inversion frameworks capable of incorporating multi-wavelength data,
and forward analysis tools and simulation testbeds to prioritize and
establish observational requirements on the proposed telescopes.
---------------------------------------------------------
Title: Localized Reconnection Heating Inferred from the
Three-dimensional Locations of Bright Active Region Coronal Loops
Authors: Longcope, Dana; McCarthy, Marika; Malanushenko, Anna
2020ApJ...901..147L Altcode:
Coronal loops observed in soft X-rays and extreme ultraviolet
imaging data offer direct evidence that coronal plasma is heated
by some mechanism. That mechanism appears to energize a particular
bundle of field lines somehow selected from the magnetized coronal
volume. Magnetic reconnection localized to a patch within a coronal
current sheet is one mechanism that would select a flux bundle at
the same time it energized it. Since magnetic reconnection occurs
preferentially at topological boundaries, we would expect to find
coronal loops concentrated there if it were at work. We explore this
hypothesis using a data set, previously compiled by McCarthy et al.,
consisting of 301 coronal loops interconnecting a pair of active
regions over a 48 hr period. That work computed the three-dimensional
geometries and magnetic field strengths for most of the loops. This
revealed many bright loops lying at the periphery of the interconnecting
flux domain, possibly created and energized by the reconnection that
created the interconnecting flux. There were, however, many loops
well inside the domain which would be difficult to attribute to that
mode of reconnection. Here we use detailed magnetic models of the
interconnecting domain to show that these internal loops tend to occur
along internal boundaries: separatrices. This offers a novel form of
evidence that coronal loops are the products of patchy reconnection
even under quiescent conditions.
---------------------------------------------------------
Title: Convolutional Neural Networks for Predicting the strength
of the Near-Earth Magnetic Field Caused by Interplanetary Coronal
Mass Ejections
Authors: Malanushenko, Anna; Flyer, Natasha; Gibson, Sarah
2020FrASS...7...62M Altcode:
In this paper, we explore the potential of neural networks for
making space weather predictions based on near-Sun observations. Our
second goal is to determine the extent to which coronal polarimetric
observations of erupting structures near the Sun encode sufficient
information to predict the impact these structures will have on
Earth. We focus on predicting the maximal southward component of the
magnetic field ("-Bz") inside an interplanetary coronal mass ejection
(ICME) as it impacts the Earth. We use Gibson&Low (G&L)
self-similarly expanding flux rope model (Gibson&Low 1998), which
allows to consider CMEs with varying location, orientation, size,
and morphology. We vary 5 parameters of the model to alter these CME
properties, and generate a large database of synthetic CMEs (over
36k synthetic events). For each model CME, we synthesize near-Sun
observations, as seen from an observer in quadrature (assuming the
CME is directed Earthwards), of either three components of the vector
magnetic field ("Experiment 1"), or of synthetic Stokes images,
("Experiment 2"). We then allow the flux rope to expand and record
max(-Bz) as the ICME passes 1AU. We further conduct two separate machine
learning experiments and develop two different regression-based deep
convolutional neural networks (CNNs) to predict max(-Bz) based on
these two kinds of the near-Sun input data. Experiment 1 is a proof
of concept, to see if a 3-channel CNN (hereafter CNN1), similar
to those used in RGB image recognition, can reproduce the results
of the self-similar (i.e. scale-invariant) expansion of the G&L
model. Experiment 2 is less trivial, as Stokes vector is not linearly
related to B, and the line-of-sight integration in the optically
thin corona presents additional difficulties for interpreting the
signal. This second CNN (hereafter CNN2), although resembling CNN1
in Experiment 1, will have a different number of layers and set of
hyperparameters due to a much more complicated mapping between the input
and output data. We find that, given vector B, CNN1 can predict max(-Bz)
with 97% accuracy, and for the Stokes vector as input, CNN2 can predict
max(-Bz) with 95%, both measured in the relative root square error.
---------------------------------------------------------
Title: Evolution of the geoeffective April 5, 2010 CME in the inner
heliosphere: A global MHD model with a data-constrained magnetic
flux rope specification.
Authors: Provornikova, E.; Merkin, V. G.; Gibson, S. E.; Malanushenko,
A. V.; Arge, C. N.; Vourlidas, A.
2019AGUFMSH42A..03P Altcode:
Modeling the evolution of internal magnetic structure of interplanetary
coronal mass ejections (ICMEs) is important both for space weather
prediction and for basic understanding of magnetized space plasma
interactions. Data-driven modeling of ICMEs in the inner heliosphere
(starting beyond the critical surface in the corona) presents
an attractive and computationally feasible approach, since it
bypasses the complex problem of CME initiation and eruption in the
corona. Using this approach, we simulate the propagation of ICMEs
through the inner heliosphere using a global model driven at the
coronal boundary by the Wang-Sheeley-Arge (WSA)-ADAPT model. ICMEs
are initiated at 20 solar radii (Rs) using a magnetohydrodynamic
(MHD) analytical Gibson-Low (GL) model of a self-similarly expanding
magnetic flux rope with parameters (e.g., location, geometry, speed,
orientation) constrained by white-light coronograph observations. The
ICME propagation is simulated using the Grid Agnostic MHD for Extended
Research Applications (GAMERA) MHD model, which is a recent reinvention
of the high-heritage Lyon-Fedder-Mobarry (LFM) code. We apply this
approach to the study of a geoeffective ICME which arrived at Earth
on April 5, 2010. This ICME appeared bright in SOHO/LASCO and STEREO
coronagraphs allowing derivation of its parameters near the Sun thus
constraining its properties in our model. However, the orientation of
the flux rope was not determined uniquely from the observations. It was
also not clear which part of the ICME hit Earth and caused the severe
geomagnetic storm. By comparing synthetic white-light images derived
from our MHD modeling with images from SOHO/LASCO and STEREO/HI1 and
HI2, we shed light on the ICME initial orientation and it evolution due
to the interaction with the background solar wind. We further compare
the modeling results with ACE observations at 1 AU and discuss which
part of the CME was probed by the spacecraft.
---------------------------------------------------------
Title: Gibson & Low Flux Rope Model: More Than a Spheromak!
Authors: Malanushenko, A. V.; Gibson, S. E.; Provornikova, E.;
Merkin, V. G.; Vourlidas, A.; Arge, C. N.; Dalmasse, K.; Nychka,
D. W.; Flyer, N.
2019AGUFMSH11C3397M Altcode:
Modeling solar coronal mass ejections (CMEs) is very important for
both understanding coronal physics and for improving the accuracy of
space weather forecasts. While it is generally accepted that CMEs
are primarily magnetic structures, the exact properties of these
structures could differ in different models and events. A structure
often considered is a spheromak, a toroidal twisted flux rope, which
is ejected as a CME bubble. Another commonly considered structure is a
twisted magnetic flux rope, which is anchored to the solar surface while
its upper portion is ejected into interplanetary space. In this talk
we will show how a well-known analytical magnetohydrodynamic CME model
(Gibson&Low, 1998), generally considered a spheromak-like model,
can be extended to represent both standard spheromak and twisted flux
tube configurations, as well as other topologically distinct magnetic
structures. We will begin with the general parameters of the flux rope
in this model (such as size and stretching parameters), and explore
topologically different configurations possible with their variation. We
then present several dimensionless parameters which can be varied to
achieve these different configurations and consider how they relate
to directly observable quantities. This work is particularly timely,
as the Gibson&Low model is been increasingly used as input to
numerical models of the solar corona and the heliosphere. The ability
to generate topologically different magnetic configurations within
this analytic solution is of great value to such simulations, as well
as for the studies of the flux ropes forming in the solar corona.
---------------------------------------------------------
Title: Measuring and Modeling the Rate of Separator Reconnection
between an Emerging and an Existing Active Region
Authors: McCarthy, Marika I.; Longcope, Dana W.; Malanushenko, Anna;
McKenzie, David E.
2019ApJ...887..140M Altcode: 2019arXiv191106340M
Magnetic reconnection occurs when new flux emerges into the corona
and becomes incorporated into the existing coronal field. A new
active region (AR) emerging in the vicinity of an existing AR
provides a convenient laboratory in which reconnection of this kind
can be quantified. We use high time-cadence 171 Å data from Solar
Dynamics Observatory (SDO)/AIA, focused on new/old active region
pair 11147/11149, to quantify reconnection. We identify new loops
as brightenings within a strip of pixels between the regions. This
strategy is premised on the assumption that the energy responsible for
brightening a loop originates in magnetic reconnection. We catalog 301
loops observed in the 48 hr time period beginning with the emergence of
AR 11149. The rate at which these loops appear between the two ARs is
used to calculate the reconnection rate between them. We then fit these
loops with magnetic field, solving for each loop’s field strength,
geometry, and twist (via its proxy, coronal α). We find the rate of
newly brightened flux overestimates the flux that could be undergoing
reconnection. This excess can be explained by our finding that the
interconnecting region is not at its lowest energy (constant-α)
state; the extrapolations exhibit loop-to-loop variation in α. This
flux overestimate may result from the slow emergence of AR 11149,
which allows time for Taylor relaxation internal to the domain of the
reconnected flux to bring the α distribution toward a single value,
providing another mechanism for brightening loops after they are
first created.
---------------------------------------------------------
Title: A correlation Study of Coronal EUV Brightenings and Radio
Emission Observed by Parker Solar Probe
Authors: Martinez Oliveros, J. C.; Pulupa, M.; Malanushenko, A. V.;
Guevara Gómez, J. C.; Bale, S.; Bonnell, J. W.; Dudok de Wit, T.;
Goetz, K.; Harvey, P.; MacDowall, R. J.; Malaspina, D.
2019AGUFMSH13C3433M Altcode:
The dynamic nature of our host star is clearly observable in the
solar corona. Different structures are visible in it (coronal loops,
streamers, coronal holes), which have a direct relationship with changes
that the Sun is experiencing in its interior and photosphere. The
morphology of these coronal structures is governed by the magnetic
field, but what is more important, the dynamic changes that occur
in them are also the product of the magnetic field. One of the
consequences of these dynamic changes are solar flares, accompanied
by all their manifestations (hard X-ray, EUV, UV, white-light, and
radio emissions). Here we present a simple correlation study between
EUV brightening observed by the STEREO/EUVI and SDO/AIA instruments
and type III radio bursts detected by the FIELDS instrument on-board
Parker Solar Probe. We study their possible magnetic connection to the
spacecraft and determine the most likely region on the solar corona
and photosphere that can be associated with the observed radio emission.
---------------------------------------------------------
Title: Examination of Separator Reconnection Rates in a Series of
Adjacent Emerging/Existing Active Region Pairs
Authors: McCarthy, M.; Longcope, D. W.; Malanushenko, A. V.; McKenzie,
D. E.
2019AGUFMSH11D3387M Altcode:
Changes in magnetic field line topology must be occurring when new flux
emerges in the solar corona in order for it to become incorporated
in the existing coronal field. Magnetic reconnection is the process
responsible for this incorporation. We have previously quantified
this process using a system in which a new active region (AR) emerges
in the vicinity of an existing one by cataloging the loops formed
between them. We make a spatial/temporal stack plot of the region
between the ARs by extracting the pixels along a virtual slit. A
persistent, bright streak in such a plot indicates a coronal loop
connecting the newly emerging flux to the existing AR. We assert that
loops formed post-emergence between the ARs are initially the result of
reconnection. This work presents an extension of our data set to include
12 new emergence events using high time-cadence data from SDO/AIA. Our
data set includes several events in which no reconnected loops seem
to form between the two ARs. We present an improved method of our loop
cataloging procedure. Previous studies of such events have both under
and over-sampled the expected reconnected flux formed between the two
regions, and included a variety of delays between the emergence of the
new AR and the onset of reconnection. To elucidate such discrepancies,
we fit loops using a linear force-free field (LFFF) model which we
then use to construct a full, non-linear force-free field (NLFFF)
model of the system. <P />This work was supported by NASA's HGI program.
---------------------------------------------------------
Title: Convolutional Neural Networks for Predicting The Impact of
Interplanetary Coronal Mass Ejections on The Near-Earth Magnetic Field
Authors: Flyer, N.; Malanushenko, A. V.; Gibson, S. E.
2019AGUFMSH34B..07F Altcode:
We present a convolutional neural network (CNN) for predicting the
maximal amplitude of southward component of the near-Earth magnetic
field near from a passing interplanetary coronal mass ejection
(iCME). The input to the CNN is the Gibson & Low (GLOW) flux rope
model (1998) that describes the coronal properties of a CME, where its
morphology and position are controlled by 6 parameters. Our ultimate
goal is to assess the ability of using a CNN architecture (2D or 3D)
as an emulator of the physical processes operating on the CME between
the Sun and Earth. The GLOW model is used as a first, simple test of
a self-similarly expanding flux rope. It is the input to numerical
simulations of CMEs propagating in the solar wind, in particular APL's
Gamera code which uses GLOW as an input. The CNN problem is set up in
two phases: 1) given input data near Sun, sets of three 2D images in
the meridional plane, of the components magnetic field B: Bx, By, Bz,
predict the maximal southward amplitude of the measured Bz at the Earth;
2) given line-of-sight integrated images of the Stokes parameters, U/I,
V/I, Q/I, corresponding to the physical configuration in part 1, predict
the maximal southward amplitude of the measured Bz at the Earth. Results
will be presented for these two different CNN configurations.
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Measuring and modeling the rate of separator reconnection
between an emerging and existing active region
Authors: McCarthy, Marika; Longcope, Dana; Malanushenko, Anna;
McKenzie, David Eugene
2019AAS...23411705M Altcode:
Magnetic reconnection must occur when new flux emerges into the corona
and becomes incorporated into the existing coronal field. A new active
region (AR) emerging in the vicinity of an existing AR provides
a convenient laboratory in which reconnection of this kind can be
quantified. We perform such a measurement using high time-cadence
171 Å data from SDO/AIA of active region NOAA AR11149 which emerged
in the vicinity of AR11147 beginning on 20 January 2011. We make a
spatial/temporal stack plot of the region between the ARs by extracting
the pixels along a virtual slit. A persistent, bright streak in such
a plot indicates a bright coronal loop connecting the newly emerging
flux to the existing AR. This loop must have been formed through a
process of coronal reconnection across the separator separating the
four topologically distinct flux systems. We assume further that energy
released during that reconnection is responsible for its brightening. We
catalog 205 loops observed in the a 48-hour time period beginning
with the emergence of AR 11149. The rate at which new magnetic flux
appears is used to calculate the rate of separator reconnection. We
can further fit these cataloged field lines using a linear force-free
field (LFFF) extrapolation, solving for an individual loop's field
strength and twist. Ultimately, we find the rate of newly-brightened
flux overestimates the flux which could be undergoing reconnection. This
excess can be explained by our finding that the interconnecting region
is not at its lowest energy (constant-α) state; the LFFF modeling
shows a variation in values of α. This overestimate might be the result
of the region's unusually slow emergence, providing time for internal
Taylor-relaxation reconnection of the interconnecting flux following
its initial formation by reconnection. We support this hypothesis by
computing the rates of brightening within the plane of the virtual
slit. This work was supported by NASA's HGI program.
---------------------------------------------------------
Title: MHD modeling of evolving ICME magnetic structure in the
inner heliosphere
Authors: Provornikova, Elena; Merkin, Vyacheslav; Malanushenko, Anna;
Gibson, Sarah; Arge, Nick; Vourlidas, Angelos
2019shin.confE.230P Altcode:
As CME propagates through the inner heliosphere, evolution of its
structure is influenced by the interaction with the solar wind
streams. I will present our recent simulations with GAMERA code
of propagating flux rope-CME from 0.1 to 1 AU in the background
solar wind. We evaluate self-similarly an erupting CME at 0.1 AU
based on the Gibson-Low model and insert it into our global inner
heliosphere model driven by the Wang-Sheeley-Arge (WSA) model of the
corona, while WSA, in turn, is driven by ADAPT global photospheric
magnetic field maps. To simulate the ICME propagation in the inner
heliosphere, we use the GAMERA (Grid Agnostic MHD for Extended Research
Applications) magnetohydrodynamic (MHD) code which is a reinvention of
the high-heritage Lyon-Fedder-Mobarry (LFM) code. We present modeling
results and focus on the evolution of the large-scale structure of
the CME from the outer solar corona to Earth. In particular I will
present a simulation of the April 3, 2010 CME event.
---------------------------------------------------------
Title: Coronal Mass Ejections from Sun to Earth: Recent Advances in
Modeling and Statistical Approaches
Authors: Malanushenko, Anna; Gibson, S.; Dalmasse, K.; Merkin, V.;
Provornikova, E.; Vourlidas, A.; Arge, C.; Nychka, D.; Wiltberger,
M.; Flyer, N.
2019shin.confE.206M Altcode:
Solar coronal mass ejections (CMEs) are violent eruptive phenomena
which originate on the Sun; their heliospheric extensions, called
interplanetary CMEs, are known for their potential to impact the
whole heliosphere and, in particular, the Earth. While not all CMEs
are launched in such a way as to hit the Earth, those that do can
have big impacts on Earth's magnetosphere. The magnitude of such
impact depends upon many factors such as the CME launch location and
velocity, its positioning within the background solar wind, its mass,
and its magnetic properties such as the orientation of its front with
respect to the Earth's magnetic field. <P />Case studies of how iCMEs
propagate through the heliosphere are complicated by many factors,
including often incomplete input for models. We present and discuss
a different approach. Rather than focusing on modeling a particular
event, we intend to carry out a large statistical study in the event
parameter space. Further, Bayesian statistics will be used along with
large statistical databases of near-Sun and near-Earth observables,
to infer statistical distributions of relevant CME input parameters,
which are capable of yielding given distributions of observables,
for a given stage of the the solar cycle. <P />We use a analytical
flux rope model (Gibson&Low model) and a background solar wind
boundary (Wang-Sheeley-Arge model) as inputs for a new MHD heliospheric
simulation code (Gamera). We give an overview and update of the project
and show first modeling results.
---------------------------------------------------------
Title: "Building a Magnetic Skeleton of the Solar Corona: Towards
Better 3-D Constraints on the Coronal Magnetic Field
Authors: Malanushenko, Anna; Gibson, Sarah; Kucera, Therese; McKenzie,
David
2018cosp...42E2139M Altcode:
The energy stored in the solar magnetic field is what is powering many
violent explosive events in the solar atmosphere, or the corona. Some
of these events result in the coronal mass ejections (CME's) released
into the interplanetary space. The magnetic field in the solar corona
is therefore very important to know, yet it is very difficult to
measure. Most of the time it is modeled with the magnetic maps at
the solar surface used as boundary conditions. The magnetic maps on
the surface are therefore also important to know, yet the full vector
of the field on the surface is also difficult to measure. Once such
measurements are made, constructing a model capable of predicting
eruptive potential of a given region is on its own a complicated
task. One of the problems arising is that that the equations for
low-beta equilibria, which are often used to describe the coronal
field, do not, strictly speaking, work for the solar surface. In
short, we need better inputs to model the solar corona. The use of
non-magnetic and non-surface constraints on the magnetic field becomes
increasingly popular. For example, the paths of filaments can be used
to guide flux rope trajectories; the loops of active regions, seen
in extreme ultraviolet (EUV) can be used to obtain 3-D trajectories
of magnetic field lines and estimate electric currents flowing along
them. We are currently exploring ways to use other sources of data,
such as flows in prominences and coronal spectropolarimetric data, in a
similar fashion. I will talk about this work, and about our project of
aggregating many different sources of non-magnetic 3-D constraints on
the magnetic field. The resulting 'skeleton' can be used to constraint
global field models, or to validate models obtained in traditional
ways. We intend to develop a pipeline and assemble several skeletons
for several instances in time of the Sun, which we will then release
to community.
---------------------------------------------------------
Title: Global Solar Magnetic Field Evolution Over 4 Solar Cycles:
Use of the McIntosh Archive
Authors: Webb, David F.; Gibson, Sarah E.; Hewins, Ian M.; McFadden,
Robert H.; Emery, Barbara A.; Malanushenko, Anna; Kuchar, Thomas A.
2018FrASS...5...23W Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly Hα, He-I 10830Å and photospheric magnetic measurements from
both ground-based and NASA satellite observations. With these he traced
polarity inversion lines (PILs), filaments, sunspots and plage and,
later, coronal holes over a 45-year period. This yielded a unique
record of synoptic maps of features associated with the large-scale
solar magnetic field over four complete solar cycles. We first discuss
how these and similar maps have been used in the past to investigate
long-term solar variability. Then we describe our work in preserving
and digitizing this archive, developing a digital, searchable format,
and creating a website and an archival repository at NOAA's National
Centers for Environmental Information (NCEI). Next we show examples of
how the data base can be utilized for scientific applications. Finally,
we present some preliminary results on the solar-cycle evolution of
the solar magnetic field, including the polar field reversal process,
the evolution of active longitudes, and the role of differential
solar rotation.
---------------------------------------------------------
Title: Vector Magnetograms - From Photosphere to the Base of the
Solar Corona
Authors: Malanushenko, Anna V.; Rempel, Matthias; Cheung, Chun
Ming Mark
2018tess.conf20234M Altcode:
The magnetic field in solar active regions is currently a major
topic of research in solar physics. While hard to measure directly,
it is commonly modeled with the use of photospheric magnetograms. An
assumption that is often made in such modeling is that the plasma
beta is small in the rarefied corona and therefore an equilibrium
configuration requires that the Lorentz force vanishes through
the volume. While this assumption greatly simplifies the modeling,
it also complicates the use of the photospheric magnetic field as a
boundary condition, as the photosphere is not in general a low-beta
environment. While vector magnetograms at the base of the low-beta
corona are not routinely available, the photospheric magnetograms
continue to be widely used for coronal modeling. Additional steps,
such as pre-processing, can be taken during the modeling to make these
data as consistent with the low-beta equilibria as possible. In this
work, we attempt to analyze how much do magnetograms of the coronal
base differ from those of the photosphere, analyze their morphology,
magnitude and how they change with height. For this, we analyze some
of the most realistic full-MHD simulations of active regions made
with MURaM code. They simulation volume includes upper convection
zone, photosphere, transition region, and the corona. While they are
not simulations of a specific active region, they appear extremely
realistic in wide range of diagnostics, from the magnetic field in the
photosphere, to the coronal morphology, to evolution typically observed
in active regions. We study these simulations and the synthetic data
they produce, focusing on the applicability of vector magnetograms to
low-beta coronal magnetic modeling. We also describe some alternative
methods of gathering vector magnetograms of the chromosphere from
the coronal morphology, and compare them to the actual structures of
the simulations.
---------------------------------------------------------
Title: Measuring separator reconnection between emerging and existing
active regions using extreme ultraviolet imaging observations
Authors: McCarthy, Marika; Longcope, Dana; McKenzie, David E.;
Malanushenko, Anna V.
2018tess.conf20545M Altcode:
Magnetic reconnection must be occurring when new flux emerges into the
corona, in order that the flux become incorporated into the existing
corona. The most evident, and easily quantified, example of this
occurs when a new active region (AR) emerges in the vicinity of an
existing AR. In a study of such emergence observed by TRACE, Longcope et
al. (2005) found a delay of approximately 24 hours between the new AR
emerging and its reconnection with the field of the existing AR. This
turned out to be the only suitable event in the TRACE archive. Here
we apply the same method to events observed by SDO/AIA. Using high
time-cadence images in one EUV wavelength, such as 171 A, we make
a spatial/temporal stack plot of the region between the ARs by
extracting the pixel in a virtual slit. A persistent, bright streak
indicates a bright coronal loop connecting the newly emerging flux
to the existing AR. This loop must have been formed through a process
of coronal reconnection across the separator separating the two flux
systems. The rate at which new loops appear is used to compute the
rate of separator reconnection. The continuous, high-cadence data from
AIA permits flux transfer to be quantified for intervals exceeding 48
hours. <P />This work was supported by NASA's HGI program.
---------------------------------------------------------
Title: Studies of Global Solar Magnetic Field Patterns Using a Newly
Digitized Archive
Authors: Hewins, I.; Webb, D. F.; Gibson, S. E.; McFadden, R.; Emery,
B. A.; Malanushenko, A. V.
2017AGUFMSH54A..01H Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly Ha, He 10830Å and photospheric magnetic measurements from both
ground-based and NASA satellite observations. With these he traced
polarity inversion lines (PILs), filaments, sunspots and plage and,
later, coronal holes, yielding a unique 45-year record of features
associated with the large-scale organization of the solar magnetic
field. We discuss our efforts to preserve and digitize this archive;
the original hand-drawn maps have been scanned, a method for processing
these scans into digital, searchable format has been developed,
and a website and an archival repository at NOAA's National Centers
for Environmental Information (NCEI) has been created. The archive
is complete for SC 23 and partially complete for SCs 21 and 22. In
this paper we show examples of how the data base can be utilized for
scientific applications. We compare the evolution of the areas and
boundaries of CHs with other recent results, and we use the maps to
track the global, SC-evolution of filaments, large-scale positive and
negative polarity regions, PILs and sunspots.
---------------------------------------------------------
Title: The McIntosh Archive: A solar feature database spanning four
solar cycles
Authors: Gibson, S. E.; Malanushenko, A. V.; Hewins, I.; McFadden,
R.; Emery, B.; Webb, D. F.; Denig, W. F.
2016AGUFMSH11A2220G Altcode:
The McIntosh Archive consists of a set of hand-drawn solar Carrington
maps created by Patrick McIntosh from 1964 to 2009. McIntosh used
mainly H-alpha, He-1 10830 and photospheric magnetic measurements
from both ground-based and NASA satellite observations. With these he
traced coronal holes, polarity inversion lines, filaments, sunspots
and plage, yielding a unique 45-year record of the features associated
with the large-scale solar magnetic field. We will present the results
of recent efforts to preserve and digitize this archive. Most of the
original hand-drawn maps have been scanned, a method for processing
these scans into digital, searchable format has been developed and
streamlined, and an archival repository at NOAA's National Centers for
Environmental Information (NCEI) has been created. We will demonstrate
how Solar Cycle 23 data may now be accessed and how it may be utilized
for scientific applications. In addition, we will discuss how this
database of human-recognized features, which overlaps with the onset
of high-resolution, continuous modern solar data, may act as a training
set for computer feature recognition algorithms.
---------------------------------------------------------
Title: Distortions of Magnetic Flux Tubes in the Presence of Electric
Currents
Authors: Malanushenko, Anna; Rempel, Matthias; Cheung, Mark
2016SPD....47.0322M Altcode:
Solar coronal loops possess several peculiar properties, which
have been a subject of intensive research for a long time. These in
particular include the lack of apparent expansion of coronal loops
and the increased pressure scale height in loops compared to the
diffuse background. Previously, Malanushenko & Schrijver (2013)
proposed that these could be explained by the fact that magnetic
flux tubes expand with height in a highly anisotropic manner. They
used potential field models to demonstrate that flux tubes that have
circular cross section at the photosphere, in the corona turn into
a highly elongates structures, more resembling thick ribbons. Such
ribbons, viewed along the expanding edge, would appear as thin, crisp
structures of a constant cross-section with an increased pressure scale
height, and when viewed along the non-expanding side, would appear
as faint, wide and underdense features. This may also introduce a
selection bias,when a set of loops is collected for a further study,
towards those viewed along the expanding edge.However, some of the
past studies have indicated that strong electric currents flowing in a
given flux tube may result in the tube maintaining a relatively constant
cross-sectional shape along its length. Given that Malanushenko &
Schrijver (2013) focused on a potential, or current-free, field model of
an active region, the extend to which their analysis could be applied
to the real solar fields, was unclear.In the present study, we use a
magnetic field created by MURaM, a highly realistic state-of-the-art
radiative MHD code (Vogler et al, 2005; Rempel et al, 2009b). MURaM was
shown to reproduce a wide variety of observed features of the solar
corona (e.g., Hansteen et al, 2010; Cheung et al. 2007, 2008; Rempel
2009a,b). We analyze the distortions of magnetic flux tubes in a MURaM
simulation of an active region corona. We quantify such distortions and
correlate them with a number of relevant parameters of flux tubes, with
a particular emphasis on the electric currents in the simulated corona.
---------------------------------------------------------
Title: Coronal Heating: Testing Models of Coronal Heating by
Forward-Modeling the AIA Emission of the Ansample of Coronal Loops
Authors: Malanushenko, A. V.
2015AGUFMSH31B2423M Altcode:
We present a systemic exploration of the properties of coronal heating,
by forward-modeling the emission of the ensemble of 1D quasi-steady
loops. This approximations were used in many theoretical models of
the coronal heating. The latter is described in many such models in
the form of power laws, relating heat flux through the photosphere or
volumetric heating to the strength of the magnetic field and length
of a given field line. We perform a large search in the parameter
space of these power laws, amongst other variables, and compare the
resulting emission of the active region to that observed by AIA. We
use a recently developed magnetic field model which uses shapes of
coronal loops to guide the magnetic model; the result closely resembles
observed structures by design. We take advantage of this, by comparing,
in individual sub-regions of the active region, the emission of the
active region and its synthetic model. This study allows us to rule
out many theoretical models and formulate predictions for the heating
models to come.
---------------------------------------------------------
Title: The Influence of Spatial resolution on Nonlinear Force-free
Modeling
Authors: DeRosa, M. L.; Wheatland, M. S.; Leka, K. D.; Barnes, G.;
Amari, T.; Canou, A.; Gilchrist, S. A.; Thalmann, J. K.; Valori,
G.; Wiegelmann, T.; Schrijver, C. J.; Malanushenko, A.; Sun, X.;
Régnier, S.
2015ApJ...811..107D Altcode: 2015arXiv150805455D
The nonlinear force-free field (NLFFF) model is often used to
describe the solar coronal magnetic field, however a series of
earlier studies revealed difficulties in the numerical solution of the
model in application to photospheric boundary data. We investigate
the sensitivity of the modeling to the spatial resolution of the
boundary data, by applying multiple codes that numerically solve the
NLFFF model to a sequence of vector magnetogram data at different
resolutions, prepared from a single Hinode/Solar Optical Telescope
Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December
13. We analyze the resulting energies and relative magnetic helicities,
employ a Helmholtz decomposition to characterize divergence errors, and
quantify changes made by the codes to the vector magnetogram boundary
data in order to be compatible with the force-free model. This study
shows that NLFFF modeling results depend quantitatively on the spatial
resolution of the input boundary data, and that using more highly
resolved boundary data yields more self-consistent results. The
free energies of the resulting solutions generally trend higher
with increasing resolution, while relative magnetic helicity values
vary significantly between resolutions for all methods. All methods
require changing the horizontal components, and for some methods also
the vertical components, of the vector magnetogram boundary field in
excess of nominal uncertainties in the data. The solutions produced
by the various methods are significantly different at each resolution
level. We continue to recommend verifying agreement between the modeled
field lines and corresponding coronal loop images before any NLFFF
model is used in a scientific setting.
---------------------------------------------------------
Title: Blind Stereoscopy of the Coronal Magnetic Field
Authors: Aschwanden, Markus J.; Schrijver, Carolus J.; Malanushenko,
Anna
2015SoPh..290.2765A Altcode: 2015SoPh..tmp..147A; 2015arXiv150604713A
We test the feasibility of 3D coronal-loop tracing in stereoscopic
EUV image pairs, with the ultimate goal of enabling efficient 3D
reconstruction of the coronal magnetic field that drives flares and
coronal mass ejections (CMEs). We developed an automated code designed
to perform triangulation of coronal loops in pairs (or triplets) of EUV
images recorded from different perspectives. The automated (or blind)
stereoscopy code includes three major tasks: i) automated pattern
recognition of coronal loops in EUV images, ii) automated pairing of
corresponding loop patterns from two different aspect angles, and iii)
stereoscopic triangulation of 3D loop coordinates. We perform tests
with simulated stereoscopic EUV images and quantify the accuracy of
all three procedures. In addition we test the performance of the
blind-stereoscopy code as a function of the spacecraft-separation
angle and as a function of the spatial resolution. We also test the
sensitivity to magnetic non-potentiality. The automated code developed
here can be used for analysis of existing Solar TErrestrial RElationship
Observatory (STEREO) data, but primarily serves for a design study
of a future mission with dedicated diagnostics of non-potential
magnetic fields. For a pixel size of 0.6<SUP>″</SUP> (corresponding
to the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
(AIA) spatial resolution of 1.4<SUP>″</SUP>), we find an optimum
spacecraft-separation angle of α<SUB>s</SUB>≈5<SUP>∘</SUP>.
---------------------------------------------------------
Title: Thermal Diagnostics with the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory: A Validated Method for
Differential Emission Measure Inversions
Authors: Cheung, Mark C. M.; Boerner, P.; Schrijver, C. J.; Testa,
P.; Chen, F.; Peter, H.; Malanushenko, A.
2015ApJ...807..143C Altcode: 2015arXiv150403258C
We present a new method for performing differential emission measure
(DEM) inversions on narrow-band EUV images from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The
method yields positive definite DEM solutions by solving a linear
program. This method has been validated against a diverse set of
thermal models of varying complexity and realism. These include
(1) idealized Gaussian DEM distributions, (2) 3D models of NOAA
Active Region 11158 comprising quasi-steady loop atmospheres in a
nonlinear force-free field, and (3) thermodynamic models from a fully
compressible, 3D MHD simulation of active region (AR) corona formation
following magnetic flux emergence. We then present results from the
application of the method to AIA observations of Active Region 11158,
comparing the region's thermal structure on two successive solar
rotations. Additionally, we show how the DEM inversion method can be
adapted to simultaneously invert AIA and Hinode X-ray Telescope data,
and how supplementing AIA data with the latter improves the inversion
result. The speed of the method allows for routine production of DEM
maps, thus facilitating science studies that require tracking of the
thermal structure of the solar corona in time and space.
---------------------------------------------------------
Title: MHD Simulations of the Evolution of the Coronal Magnetic Field:
First Steps in Using the Realistic Initial State Model
Authors: Malanushenko, Anna V.; Fan, Yuhong
2015TESS....120312M Altcode:
We present the first results of simulations of a realistic coronal
magnetic field evolution. The initial state of the field is a non-linear
force-free model (NLFFF) which matches the observed coronal features
by design (see Malanushenko et al, 2012). We evolve this field model
using an ideal MHD code (see Fan, 2009). We use the model of AR 11158
shortly before X2.2 class flare on February 15th. This model was shown
by Malanushenko et al (2014) to possess both the correct morphology of
the coronal field (compared to the EUV images), and free magnetic energy
sufficient for a flare of this class. We demonstrate stability of the
twisted current bundle in the core of the region when no photospheric
driving is present, and the first results of the evolution of the
model corona when the photospheric driving roughly corresponds to that
observed at the photosphere.
---------------------------------------------------------
Title: Time Evolution of Force-Free Parameter and Free Magnetic
Energy in Active Region NOAA 10365
Authors: Valori, G.; Romano, P.; Malanushenko, A.; Ermolli, I.;
Giorgi, F.; Steed, K.; van Driel-Gesztelyi, L.; Zuccarello, F.;
Malherbe, J. -M.
2015SoPh..290..491V Altcode:
We describe the variation of the accumulated coronal helicity derived
from the magnetic helicity flux through the photosphere in active region
(AR) NOAA 10365, where several large flares and coronal mass ejections
(CMEs) occurred. We used SOHO/MDI full-disk line-of-sight magnetograms
to measure the helicity flux, and the integral of GOES X-ray flux as a
proxy of the coronal energy variations due to flares or CMEs. Using the
linear force-free field model, we transformed the accumulated helicity
flux into a time sequence of the force-free parameter α accounting for
flares or CMEs via the proxy derived from GOES observations. This method
can be used to derive the value of α at different times during the
AR evolution, and is a partial alternative to the commonly used match
of field lines with EUV loops. By combining the accumulated helicity
obtained from the observations with the linear force-free theory, we
describe the main phases of the emergence process of the AR, and relate
them temporally with the occurrence of flares or CMEs. Additionally,
a comparison with the loop-matching method of fixing alpha at each time
independently shows that the proposed method may be helpful in avoiding
unrealistic or undetermined values of alpha that may originate from
an insufficient quality of the image used to identify coronal loops
at a given time. For the relative intensity of the considered events,
the linear force-free field theory implies that there is a direct
correlation between the released energy on the one hand and the product
of the coronal helicity with the variation of α due to the event on
the other. Therefore, the higher the value of the accumulated coronal
helicity, the smaller the force-free parameter variation required to
produce the same decrease in the free energy during the CMEs.
---------------------------------------------------------
Title: Deciphering Solar Magnetic Activity. I. On the Relationship
between the Sunspot Cycle and the Evolution of Small Magnetic Features
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Davey,
Alisdair R.; Howe, Rachel; Krista, Larisza D.; Malanushenko, Anna V.;
Markel, Robert S.; Cirtain, Jonathan W.; Gurman, Joseph B.; Pesnell,
William D.; Thompson, Michael J.
2014ApJ...792...12M Altcode: 2014arXiv1403.3071M
Sunspots are a canonical marker of the Sun's internal magnetic
field which flips polarity every ~22 yr. The principal variation of
sunspots, an ~11 yr variation, modulates the amount of the magnetic
field that pierces the solar surface and drives significant variations
in our star's radiative, particulate, and eruptive output over that
period. This paper presents observations from the Solar and Heliospheric
Observatory and Solar Dynamics Observatory indicating that the 11
yr sunspot variation is intrinsically tied to the spatio-temporal
overlap of the activity bands belonging to the 22 yr magnetic activity
cycle. Using a systematic analysis of ubiquitous coronal brightpoints
and the magnetic scale on which they appear to form, we show that the
landmarks of sunspot cycle 23 can be explained by considering the
evolution and interaction of the overlapping activity bands of the
longer-scale variability.
---------------------------------------------------------
Title: Forward Modeling of Coronal Emission
Authors: Malanushenko, Anna; Schrijver, Carolus J.; Van Ballegooijen,
Adriaan A.
2014AAS...22432102M Altcode:
In this work, we present simulations of the coronal emission in
Extreme Ultraviolet wavelengths, subject to the possible physical
models of how the solar corona is heated. In order to maximize the
match of the simulations with the observations, we also use models
of coronal magnetic field which are constructed to match the observed
coronal features (see Malanushenko et al, 2014). While we utilize the 1D
quasi-steady atmosphere approach (as in Schrijver & van Ballegoijen,
2005), we take a step away from the commonly used assumption about
circular cross-sections of magnetic flux tubes, as our previous research
(Malanushenko & Schrijver, 2013) suggests that this assumption might
lead to substantial artefacts when comparing the simulations to the
observations. In this work, we explore how such treatment of magnetic
flux tubes is capable of producing realistic coronal features. Using
these two major advances, the realistic field model and the realistic
treatment of the cross-section of flux tubes, we test a wide range
of possible heating scenarios, ruling out possibilities by comparing
the simulations with data from a wide range of EUV channels onboard
SDO/AIA spacecraft.
---------------------------------------------------------
Title: Active region 11748: Recurring X-class flares, large scale
dimmings and waves.
Authors: Davey, Alisdair R.; Malanushenko, Anna; McIntosh, Scott W.
2014AAS...22421818D Altcode:
AR 11748 was a relatively compact active region that crossed the solar
disk between 05/14/2013 and 05/26/2013. Despite its size it produced
a number X-class flares, and global scale eruptive events that were
captured by the SDO Feature Finding Team's (FFT) Dimming Region
Detector. Using the results of this module and other FFT modules,
we present an analysis of the this AR region and investigate why it
was so globally impactful.
---------------------------------------------------------
Title: Active Region Magnetic Field Modeling Guided by Coronal Loops
and Surface Fields
Authors: DeRosa, Marc L.; Malanushenko, Anna; Schrijver, Carolus J.;
Wheatland, Michael S
2014AAS...22432319D Altcode:
Dynamic events such as solar flares, filament eruptions, and mass
ejections are powered by the evolving coronal magnetic field. However,
the ways in which energy is stored in, and released from, the coronal
magnetic field are poorly understood, in large part because the field
configuration cannot be determined directly from observations and has
eluded the successful application of routine modeling based on surface
magnetograms. Recently, we have demonstrated that the Quasi-Grad-Rubin
(QGR) method for modeling the current-carrying field associated with
active regions shows promise. In Malanushenko et al. (2014, ApJ 783:102)
we have used the QGR method to construct the magnetic field at several
times during the evolution of AR11158 during February 2011. The QGR
method does not require vector magnetograms, and instead uses the
trajectories of observed coronal loops to constrain the locations
of electric currents within the modeling domain. In this study,
we continue to assess the utility of QGR by applying this method to
additional active regions from the current activity cycle, making use
of SDO/HMI line-of-sight magnetograms and imagery from the extreme
ultraviolet channels of SDO/AIA.
---------------------------------------------------------
Title: Using Coronal Loops to Reconstruct the Magnetic Field of an
Active Region before and after a Major Flare
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
M. S.
2014ApJ...783..102M Altcode: 2013arXiv1312.5389M
The shapes of solar coronal loops are sensitive to the presence
of electrical currents that are the carriers of the non-potential
energy available for impulsive activity. We use this information in
a new method for modeling the coronal magnetic field of active region
(AR) 11158 as a nonlinear force-free field (NLFFF). The observations
used are coronal images around the time of major flare activity on
2011 February 15, together with the surface line-of-sight magnetic
field measurements. The data are from the Helioseismic and Magnetic
Imager and Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory. The model fields are constrained to approximate the coronal
loop configurations as closely as possible, while also being subject
to the force-free constraints. The method does not use transverse
photospheric magnetic field components as input and is thereby
distinct from methods for modeling NLFFFs based on photospheric vector
magnetograms. We validate the method using observations of AR 11158
at a time well before major flaring and subsequently review the field
evolution just prior to and following an X2.2 flare and associated
eruption. The models indicate that the energy released during the
instability is about 1 × 10<SUP>32</SUP> erg, consistent with what
is needed to power such a large eruptive flare. Immediately prior to
the eruption, the model field contains a compact sigmoid bundle of
twisted flux that is not present in the post-eruption models, which
is consistent with the observations. The core of that model structure
is twisted by ≈0.9 full turns about its axis.
---------------------------------------------------------
Title: Using coronal loops to model the coronal magnetic field before
and after major eruptive events
Authors: Malanushenko, Anna; Schrijver, Carolus; Wheatland, M. S.;
DeRosa, Marc
2014cosp...40E1960M Altcode:
Solar flares are believed to be a manifestation of major release of
magnetic energy stored in active region field. Modeling the coronal
magnetic field may enable us to evaluate the energy available for
release, as well as possible sites of the reconnection and other
relevant properties of the field. We use a new method to aid this
problem by including the observed structure of the field (manifested
in coronal loops) as additional constraints. We verify that the method
(previously shown to work on synthetic data in Malanushenko et. al.,
ApJ, 756, 153, 2012) is generally acceptable for the solar data, as
it gives self-consistent, slowly changing results for slowly evolving
structures. We further develop the potential of this method to access
changes in the coronal magnetic field triggered by major eruptive
events, and compare the results with observations.
---------------------------------------------------------
Title: On the Anisotropy in Expansion of Magnetic Flux Tubes in the
Solar Corona
Authors: Malanushenko, A.; Schrijver, C. J.
2013ApJ...775..120M Altcode: 2013arXiv1307.3440M
Most one-dimensional hydrodynamic models of plasma confined to magnetic
flux tubes assume circular tube cross sections. We use potential field
models to show that flux tubes in circumstances relevant to the solar
corona do not, in general, maintain the same cross-sectional shape
through their length and therefore the assumption of a circular cross
section is rarely true. We support our hypothesis with mathematical
reasoning and numerical experiments. We demonstrate that lifting this
assumption in favor of realistic, non-circular loops makes the apparent
expansion of magnetic flux tubes consistent with that of observed
coronal loops. We propose that in a bundle of ribbon-like loops, those
that are viewed along the wide direction would stand out against those
that are viewed across the wide direction due to the difference in
their column depths. That result would impose a bias toward selecting
loops that appear not to be expanding, seen projected in the plane of
sky. An implication of this selection bias is that the preferentially
selected non-circular loops would appear to have increased pressure
scale heights even if they are resolved by current instruments.
---------------------------------------------------------
Title: A Nonlinear Force-Free Magnetic Field Approximation Suitable
for Fast Forward-Fitting to Coronal Loops. II. Numeric Code and Tests
Authors: Aschwanden, Markus J.; Malanushenko, Anna
2013SoPh..287..345A Altcode: 2012arXiv1207.2783A; 2012SoPh..tmp..182A
Based on a second-order approximation of nonlinear force-free
magnetic field solutions in terms of uniformly twisted field lines
derived in Paper I, we develop here a numeric code that is capable
to forward-fit such analytical solutions to arbitrary magnetogram (or
vector magnetograph) data combined with (stereoscopically triangulated)
coronal loop 3D coordinates. We test the code here by forward-fitting to
six potential field and six nonpotential field cases simulated with our
analytical model, as well as by forward-fitting to an exactly force-free
solution of the Low and Lou (Astrophys. J.352, 343, 1990) model. The
forward-fitting tests demonstrate: i) a satisfactory convergence
behavior (with typical misalignment angles of μ≈1<SUP>∘</SUP> -
10<SUP>∘</SUP>), ii) relatively fast computation times (from seconds
to a few minutes), and iii) the high fidelity of retrieved force-free
α-parameters (α<SUB>fit</SUB>/α<SUB>model</SUB>≈0.9 - 1.0 for
simulations and α<SUB>fit</SUB>/α<SUB>model</SUB>≈0.7±0.3 for
the Low and Lou model). The salient feature of this numeric code is
the relatively fast computation of a quasi-force-free magnetic field,
which closely matches the geometry of coronal loops in active regions,
and complements the existing nonlinear force-free field (NLFFF) codes
based on photospheric magnetograms without coronal constraints.
---------------------------------------------------------
Title: On Cross-Sectional Properties of Coronal Loops
Authors: Malanushenko, Anna; Schrijver, C. J.
2013SPD....4420105M Altcode:
Coronal loops have been observed for several decades, yet some of their
properties remain a mystery. These in particular include the lack of
apparent expansion of coronal loops and the increased pressure scale
height in loops compared to the diffuse background. We approach these
problems in an entirely new way. We demonstrate that solely lifting
the assumption about circular cross-sectional shape of flux tubes is
alone sufficient to explain lack of expansion and increased pressure
scale height. While magnetic flux tubes expand in the corona, they do
so in a highly anisotropic manner, which we examine in details for
several model fields and quantify for a potential field model based
on HMI data. We demonstrate how, and why, this leads towards (1)
selection bias which might make some loops stand out if they expand
mostly along the line of sight, due to their increased column depth;
(2) principal limitations on measuring expansion of coronal loops,
even if they are resolved and (3) the apparent increased pressure scale
height. We also address the existing studies which seemingly concluded
the opposite. The latter was based on several properties of the loops'
emission which, as we show, are also reproduced when loops are oblate
in cross-section.
---------------------------------------------------------
Title: Modeling coronal loop oscillations in realistic magnetic and
density structures
Authors: Ofman, Leon; Wang, T.; Malanushenko, A.; Davila, J. M.
2013SPD....4410404O Altcode:
Recently, ubiquitous coronal loop oscillations were detected in
active region loops by SDO/AIA. Hinode/EIS observations indicate that
quasi-periodic flows are present at footpoints of loops in active
regions, and related propagating disturbances (PD's) were detected in
open and closed loop structures. Recent 3D MHD models in idealized
(bipolar) active regions (Ofman et al. 2012; Wang et al. 2013,
this meeting) have demonstrated that the flows can produce slow
magnetosonic waves in loops, as well as transverse oscillations. We
extend the idealized studies by considering more realistic magnetic
field structures modeled by including photospheric magnetic field
extrapolated to the corona as boundary and initial conditions for
the 3D MHD modeling. We use potential and nonlinear magnetic field
extrapolations combined with gravitationally stratified density and
introduce flows at the corona-transition region boundary in our 3D MHD
model. We apply coronal seismology to the resulting loop oscillations
and compare to oscillation events detected by SDO/AIA. We aim to
improve the accuracy of coronal seismology by modeling coronal loop
oscillations in realistic magnetic geometry and density structures.
---------------------------------------------------------
Title: Automated Temperature and Emission Measure Analysis of
Coronal Loops and Active Regions Observed with the Atmospheric
Imaging Assembly on the Solar Dynamics Observatory (SDO/AIA)
Authors: Aschwanden, Markus J.; Boerner, Paul; Schrijver, Carolus J.;
Malanushenko, Anna
2013SoPh..283....5A Altcode: 2011SoPh..tmp..384A
We developed numerical codes designed for automated analysis of
SDO/AIA image datasets in the six coronal filters, including: i)
coalignment test between different wavelengths with measurements of
the altitude of the EUV-absorbing chromosphere, ii) self-calibration by
empirical correction of instrumental response functions, iii) automated
generation of differential emission measure [DEM] distributions
with peak-temperature maps [T<SUB>p</SUB>(x,y)] and emission measure
maps [EM<SUB>p</SUB>(x,y)] of the full Sun or active region areas,
iv) composite DEM distributions [dEM(T)/dT] of active regions or
subareas, v) automated detection of coronal loops, and vi) automated
background subtraction and thermal analysis of coronal loops, which
yields statistics of loop temperatures [T<SUB>e</SUB>], temperature
widths [σ<SUB>T</SUB>], emission measures [EM], electron densities
[n<SUB>e</SUB>], and loop widths [w]. The combination of these
numerical codes allows for automated and objective processing of
numerous coronal loops. As an example, we present the results of an
application to the active region NOAA 11158, observed on 15 February
2011, shortly before it produced the largest (X2.2) flare during the
current solar cycle. We detect 570 loop segments at temperatures in the
entire range of log(T<SUB>e</SUB>)=5.7 - 7.0 K and corroborate previous
TRACE and AIA results on their near-isothermality and the validity of
the Rosner-Tucker-Vaiana (RTV) law at soft X-ray temperatures (T≳2
MK) and its failure at lower EUV temperatures.
---------------------------------------------------------
Title: First Three-dimensional Reconstructions of Coronal Loops
with the STEREO A+B Spacecraft. IV. Magnetic Modeling with Twisted
Force-free Fields
Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.; DeRosa, Marc L.; Malanushenko, Anna
2012ApJ...756..124A Altcode: 2012arXiv1207.2790A
The three-dimensional coordinates of stereoscopically triangulated
loops provide strong constraints for magnetic field models of active
regions in the solar corona. Here, we use STEREO/A and B data from some
500 stereoscopically triangulated loops observed in four active regions
(2007 April 30, May 9, May 19, and December 11), together with SOHO/MDI
line-of-sight magnetograms. We measure the average misalignment angle
between the stereoscopic loops and theoretical magnetic field models,
finding a mismatch of μ = 19°-46° for a potential field model,
which is reduced to μ = 14°-19° for a non-potential field model
parameterized by twist parameters. The residual error is commensurable
with stereoscopic measurement errors (μ<SUB>SE</SUB> ≈ 8°-12°). We
developed a potential field code that deconvolves a line-of-sight
magnetogram into three magnetic field components (B<SUB>x</SUB> ,
B<SUB>y</SUB> , B<SUB>z</SUB> ), as well as a non-potential field
forward-fitting code that determines the full length of twisted loops
(L ≈ 50-300 Mm), the number of twist turns (median N <SUB>twist</SUB>
= 0.06), the nonlinear force-free α-parameter (median α ≈ 4 ×
10<SUP>-11</SUP> cm<SUP>-1</SUP>), and the current density (median
j<SUB>z</SUB> ≈ 1500 Mx cm<SUP>-2</SUP> s<SUP>-1</SUP>). All twisted
loops are found to be far below the critical value for kink instability,
and Joule dissipation of their currents is found to be far below the
coronal heating requirement. The algorithm developed here, based on an
analytical solution of nonlinear force-free fields that is accurate to
second order (in the force-free parameter α), represents the first
code that enables fast forward fitting to photospheric magnetograms
and stereoscopically triangulated loops in the solar corona.
---------------------------------------------------------
Title: Guiding Nonlinear Force-free Modeling Using Coronal
Observations: First Results Using a Quasi-Grad-Rubin Scheme
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
M. S.; Gilchrist, S. A.
2012ApJ...756..153M Altcode: 2012arXiv1202.5420M
At present, many models of the coronal magnetic field rely on
photospheric vector magnetograms, but these data have been shown
to be problematic as the sole boundary information for nonlinear
force-free field extrapolations. Magnetic fields in the corona
manifest themselves in high-energy images (X-rays and EUV) in the
shapes of coronal loops, providing an additional constraint that
is not at present used as constraints in the computational domain,
directly influencing the evolution of the model. This is in part due
to the mathematical complications of incorporating such input into
numerical models. Projection effects, confusion due to overlapping
loops (the coronal plasma is optically thin), and the limited number
of usable loops further complicate the use of information from
coronal images. We develop and test a new algorithm to use images of
coronal loops in the modeling of the solar coronal magnetic field. We
first fit projected field lines with those of constant-α force-free
fields to approximate the three-dimensional distribution of currents
in the corona along a sparse set of trajectories. We then apply a
Grad-Rubin-like iterative technique, which uses these trajectories as
volume constraints on the values of α, to obtain a volume-filling
nonlinear force-free model of the magnetic field, modifying a code
and method presented by Wheatland. We thoroughly test the technique
on known analytical and solar-like model magnetic fields previously
used for comparing different extrapolation techniques and compare the
results with those obtained by currently available methods relying
only on the photospheric data. We conclude that we have developed a
functioning method of modeling the coronal magnetic field by combining
the line-of-sight component of the photospheric magnetic field with
information from coronal images. Whereas we focus on the use of coronal
loop information in combination with line-of-sight magnetograms, the
method is readily extended to incorporate vector-magnetic data over
any part of the photospheric boundary.
---------------------------------------------------------
Title: Estimate of Energy Release In a Major Flare Using Coronal
Loops Data
Authors: Malanushenko, Anna; Schrijver, C. J.; DeRosa, M. L.
2012AAS...22052115M Altcode:
Coronal loops provide with valuable source of information about coronal
magnetic field. In particular, they allow one to observe reconfiguration
of the coronal magnetic field during eruptive episodes. The changes
in the coronal field, as observed in X-rays and extreme ultraviolet,
are often dramatic in even minor eruptions. Therefore, models of
magnetic field which take coronal loops into account might provide
for new insight at changes of the field during eruptions. We use
coronal loops data (gathered from SDO/AIA images) along with the
line-of-sight magnetograms (by SDO/HMI) to model magnetic field in
AR 11158 before and after the so-called Valentine's Flare, an X-class
flare in Feb 15, 2011. This is done using the recently developed Quasi
Grad-Rubin algorithm (QGR), which allows a reconstruction of non-linear
force-free field based on information about electric currents along
a set of arbitrary tracks in the computational domain. Tests of QGR
on solar-like fields demonstrate its ability to recover over 50% of
the free energy, as well as the large-scale structure of currents and
overall shape of field lines. We analyze model magnetic fields of AR
11158 before and after the flare, demonstrate their resemblance with
the observed structure of coronal loops and analyze the changes in
the structure of currents caused by the flare, and compare our results
with existing studies of the same event.
---------------------------------------------------------
Title: Force-Free Magneto-Stereoscopy of Coronal Loops
Authors: Aschwanden, Markus J.; Malanushenko, A.; Wuelser, J.; Nitta,
N.; Lemen, J. R.; DeRosa, M.
2012AAS...22041103A Altcode:
We derive an analytical approximation of nonlinear force-free
magnetic field solutions (NLFFF) that can efficiently be used for
fast forward-fitting to solar magnetic data, constrained either by
observed line-of-sight magnetograms and stereoscopically triangulated
coronal loops, or by 3D vector-magnetograph data. We test the code by
forward-fitting to simulated data, to force-free solutions derived by
Low and Lou (1990), and to active regions observed with STEREO/EUVI and
SOHO/MDI. The forward-fitting tests demonstrate: (i) a satisfactory
convergence behavior (with typical misalignment angles of 1-10 deg),
(ii) a high fidelity of retrieved force-free alpha-parameters, and
(iii) relatively fast computation times (from seconds to minutes). The
novel feature of this NLFFF code is the derivation of a quasi-forcefree
field based on coronal constraints, which bypasses the non-forcefree
photosphere of standard magnetograms. Applications range from magnetic
modeling of loops to the determnination of electric currents, twist,
helicity, and free (non-potential) energy in active regions.
---------------------------------------------------------
Title: Physics of Transient Seismic Emission from Flares
Authors: Lindsey, Charles A.; Donea, A.; Malanushenko, A.
2012AAS...22020409L Altcode:
We consider the physics of seismic activity in solar flares, i.e., the
release of powerful seismic transients into the solar interior during
the impulsive phases of some flares. Recent work by Hudson, Fisher,
Welsch and Bercik has attracted a great deal of positive attention
to the possible role of Lorentz-force transients in driving seismic
transient emission in flares. The implications of direct involvement
by magnetic forces in seismic transient emission, if this could be
confirmed, would be major, since magnetic fields are thought to hold
the energy source of the flares themselves. The energy invested into
acoustic transients is a small fraction of the total released by the
flare, but requires a massive impulse many times that required to
accelerate high-energy electrons into which the energy is initially
thought to be invested. What does this say about a flare mechanism that
sometimes does both? We discuss some of the outstanding diagnostic
questions that confront the recognition of magnetic-field transients
associated with Lorentz force transients based on resources HMI,
Hinode, AIA and other facilities offer us.
---------------------------------------------------------
Title: Force-free Magnetic Fields and Electric Currents inferred
from Coronal Loops and Stereoscopy
Authors: Aschwanden, Markus J.; Boerner, P.; Schrijver, C. J.;
Malanushenko, A.
2012decs.confE.105A Altcode:
Force-free magnetic fields are considered to be a natural state of the
low plasma-beta corona. There exist about a dozen of numerical nonlinear
force-free field (NLFFF) computation codes that are able to caclulate
a divergence-free and force-free solution of the magnetic field, by
extrapolation from a lower boundary condition that is specified with
3D vector magnetograph data. However, significant differences in the
solutions have been found among the different NLFFF codes, as well as in
comparison with stereoscopically triangulated 3D coordinates of coronal
loops, exhibiting field misalignment angles of 20-40 degrees. Each
calculation of a NLFFF solution is computing-intensive and no code is
fast enough to enable forward-fitting to observations. Here we derive
an analytical approximation of NLFFF solutions that is accurate to
second order and can efficiently be used for forward-fitting to coronal
loops. We demonstrate the accurcay of the NLFFF forward-fitting code by
reproducing the Low and Lou (1990) analytical model withg an accuracy
of <5 degres. Further, we show examples of fitted NLFFF solutions to
STEREO observations of coronal loops. Future NLFFF fits are expected
based on line-of-sight magnetograms and automated loop tracings only,
without requiring vector field and STEREO data.
---------------------------------------------------------
Title: Non-Linear Force-Free Modeling of Solar Corona With The Aid
of Coronal Loops
Authors: Malanushenko, A.; DeRosa, M.; Schrijver, C.; Wheatland,
M. S.; Gilchrist, S.
2012decs.confE.113M Altcode:
Accurate models of the coronal magnetic field are vital for
understanding and predicting solar activity and are therefore of the
greatest interest for solar physics. As no reliable measurements of the
coronal magnetic field exists at present, the problem of constructing
field models is typically viewed as a boundary value problem. The
construction of realistic field models requires knowledge of the full
vector of magnetic field at the boundaries of the model domain; vector
magnetograms are, however, measured in the non force-free photosphere
and their horizontal components are subject to large uncertainties. Even
if an uncertainty-free vector magnetogram at the top layer of the
chromosphere was known, the problem remains an extremely challenging
non-linear problem. There are various methods for pre-processing
vector magnetograms and using them to construct models of the coronal
field. The success of these models is often judged based on how close
its field lines correspond to the observed coronal loops, which are
believed to follow lines of the coronal magnetic field. At present,
the correspondence between coronal loops and magnetic field lines
of many models based on the vector magnetograms is far from perfect
(DeRosa et. al., 2009). The estimates of free energy in the field as
well as distribution of the magnetic currents through the volume could
be dramatically different for different models used (Schrijver et. al.,
2008). This testifies to the need of a completely new approach to this
problem. We present such an approach and demonstrate its results based
on AIA and HMI data. We have developed a way to use coronal loops as a
constraint for magnetic modelling; the field is therefore constructed to
match coronal loops. We found that when tested on known magnetic fields
the new method is able to reproduce overall shape of the field lines,
large-scale spatial distribution of the electric currents and measure
up to 60% of the free energy stored in the field. This was achieved
with as little as line-of-sight magnetogram and less than hundred of
synthetic "loops", that is, lines of magnetic fields projected onto
a plane of the sky. We found that line-of-sight HMI magnetograms and
spatial resolution of the AIA instrument combined with the amount of
filters available are more than sufficient for obtaining such data. We
briefly describe this new method and demonstrate reconstructions of the
coronal magnetic field obtained using AIA and HMI data. We evaluate how
well it reproduces coronal features and how much energy and helicity
estimates fluctuate with time for a stable non-flaring active region,
thus establishing the reliability of the new method.
---------------------------------------------------------
Title: Non-Linear Force-Free Modeling With The Aid of Coronal
Observations
Authors: Malanushenko, A. V.; DeRosa, M. L.; Schrijver, C. J.;
Gilchrist, S. A.; Wheatland, M. S.
2011AGUFMSH43B1956M Altcode:
Currently many models of coronal magnetic field rely on vector
magnetograms and other kinds of information drawn from the
photosphere. Magnetic fields in the corona, however, manifest themselves
in the shapes of coronal loops, providing a constraint that at the
present stage receives little use due to mathematical complications of
incorporating such input into the numeric models. Projection effects
and the limited number of usable loops further complicate their
use. We present a possible way to account for coronal loops in the
models of magnetic field. We first fit the observed loops with lines
of constant-alpha fields and thus approximate three-dimensional
distribution of currents in the corona along a sparse set of
trajectories. We then apply a Grad-Rubin-like averaging technique
to obtain a volume-filling non-linear force-free model of magnetic
field, modified from the method presented in Wheatland & Regnier
(2009). We present thorough tests of this technique on several known
magnetic fields that were previously used for comparing different
extrapolation techniques (Schrijver et. al., 2006; Metcalf et. al.,
2008; Schrijver et. al., 2008; DeRosa et. al., 2009), as well as on
solar data and compare the results with those obtained by the currently
developed methods that rely completely on the photospheric data.
---------------------------------------------------------
Title: Direct Measurements of Magnetic Twist in the Solar Corona
Authors: Malanushenko, A.; Yusuf, M. H.; Longcope, D. W.
2011ApJ...736...97M Altcode: 2012arXiv1202.5421M
In the present work, we study the evolution of magnetic helicity in the
solar corona. We compare the rate of change of a quantity related to
the magnetic helicity in the corona to the flux of magnetic helicity
through the photosphere and find that the two rates are similar. This
gives observational evidence that helicity flux across the photosphere
is indeed what drives helicity changes in the solar corona during
emergence. For the purposes of estimating coronal helicity, we neither
assume a strictly linear force-free field nor attempt to construct a
nonlinear force-free field. For each coronal loop evident in extreme
ultraviolet, we find a best-matching line of a linear force-free field
and allow the twist parameter α to be different for each line. This
method was introduced and its applicability discussed in Malanushenko
et al. The object of this study is emerging and rapidly rotating AR
9004 over about 80 hr. As a proxy for coronal helicity, we use the
quantity langα<SUB> i </SUB> L<SUB>i</SUB> /2rang averaged over many
reconstructed lines of magnetic field. We argue that it is approximately
proportional to the "flux-normalized" helicity H/Φ<SUP>2</SUP>,
where H is the helicity and Φ is the total enclosed magnetic flux
of the active region. The time rate of change of such a quantity in
the corona is found to be about 0.021 rad hr<SUP>-1</SUP>, which is
comparable with the estimates for the same region obtained using other
methods, which estimated the flux of normalized helicity to be about
0.016 rad hr<SUP>-1</SUP>.
---------------------------------------------------------
Title: Computing Magnetic Energy From Aia Images And Hmi Line-of-sight
Magnetograms
Authors: Longcope, Dana; Malanushenko, A.; Tarr, L.
2011SPD....42.2118L Altcode: 2011BAAS..43S.2118L
The state of the art for computing the magnetic energy in an active
region's corona is to extrapolate a non-linear force-free field from
vector magnetic field data. This method infers coronal properties from
photospheric data without direct use of any coronal information. We
present here an alternative which uses the shapes of loops visible
in EUV or soft X-ray images to infer coronal currents. The method of
Malanushenko et al. (2009) is used to infer magnetic field strength
along each coronal loop. This sparse sampling of magnetic information is
used in a Monte Carlo integral to compute the total magnetic energy. We
also present a method for computing the free energy (the difference
between the energy of the actual field and the corresponding potential
field) directly as a single Monte Carlo integral. Both integrals are
estimates with known statistical uncertainties which are reasonably
small for samples as small as 25 loops. We demonstrate the method using
a test field and then apply it to observations of an active region.
---------------------------------------------------------
Title: Simulating Coronal Emission in Six AIA Channels Using
Quasi-Static Atmosphere Models and Non-Linear Magnetic Field Models
Authors: Malanushenko, Anna; Schrijver, C.; DeRosa, M.; Aschwanden,
M.; Wheatland, M. S.; van Ballegooijen, A. A.
2011SPD....42.2116M Altcode: 2011BAAS..43S.2116M
We present the results of simulations of the EUV coronal emission in
AIA channels. We use a non-linear force-free model of magnetic field
constructed in such a way that its field lines resemble the observed
coronal loops in EUV. We then solve one-dimensional quasi-steady
atmosphere model along the magnetic field lines (Schrijver &
Ballegooijen, 2005). Using coronal abundances from CHIANTI and AIA
response functions we then simulate the emission that would be observed
in AIA EUV channels. The resulting intensities are compared against the
real observations in a manner similar to that in Aschwanden et. al.,
2011. The study is similar to those by Lindquist et. al., 2008, with a
few important differences. We use a model of the coronal magnetic field
that resembles the topology observed in EUV, we study EUV emission of
cool loops (rather than SXR) and we make use of high resolution and
cadence AIA and HMI data.
---------------------------------------------------------
Title: Quantifying Separator Reconnection Between Emerging and
Existing Active Regions
Authors: Malanushenko, Anna; Longcope, D. W.; McKenzie, D. E.; Yusuf,
M. H.
2010AAS...21640507M Altcode: 2010BAAS...41..890M
When one active region emerges close to an older active region,
coronal loops connecting the two regions are often observed in
extreme ultraviolet (EUV). This signifies the occurrence of magnetic
reconnection, an important mechanism in other contexts, such as solar
flares and coronal mass ejections. We measure the rate of the magnetic
reconnection by identifying each coronal loop observed in EUV that
connects the existing and the emerging active regions. For each loop we
estimate amount of magnetic flux it carries by measuring its apparent
width in EUV and the magnetic field strength in the same location using
(non)-linear force-free field reconstruction (Malanushenko et. al.,
2009). We find that the amount of reconnected flux apparent on EUV
is smaller than the flux through the separator surface in the point
charge magnetic model (Longcope, 2005). This discrepancy provides a
means to estimate the fraction of reconnecting loops that would appear
in the EUV bandpass. We measure the delay time between the noticeable
beginning of the emergence and the reconnection apparent in EUV. We
apply this analysis to five emergence events. This work expands and
improves the method described by Longcope et. al. (2005).
---------------------------------------------------------
Title: Twist in coronal magnetic fields
Authors: Malanushenko, Anna Viktorovna
2010PhDT........68M Altcode:
Twist of magnetic field is believed to play important role in driving
instabilities that result in eruptive events on the Sun. This thesis
provides different methods to measure twist in the solar corona. First,
given a model of coronal field, twist of a magnetic domain (i.e.,
a volume that contains all field lines connecting two regions of
interest in the photosphere) is well studied for cases when the
domain is a thin cylinder. For cases when such approximation is
inapplicable a generalization of twist can be derived from a quantity
called additive self-helicity. I develop explicit numerical methods to
compute generalized twist. I also demonstrate that such a quantity sets
a threshold on kink instability like the traditional twist does for thin
cylinders. In a more realistic scenario, coronal magnetic field is not
known and so neither is its helicity. There are two principal methods to
overcome this problem. The first is to integrate helicity flux across
the photosphere (as helicity is believed to be approximately conserved
in the corona) using magnetic field on Sun's surface. There is little
published evidence as yet that coronal helicity indeed corresponds
to its integrated photospheric flux. The second is to extrapolate the
coronal magnetic field using surface measurements as boundary conditions
and use this extrapolation for helicity computation; for fields with
complicated structure such extrapolations are extremely challenging
and suffer from major drawbacks. I develop a method to estimate twist
of coronal fields without attempting complicated extrapolations or
studying helicity flux. The method builds a simple uniformly-twisted
magnetic field and adjusts its properties until there is one line
in this field that matches one coronal loop; this is repeated for
all evident coronal loops resulting in twist measurements for each
individual loop. I use this method to demonstrate that the rate of
change of twist in the solar corona is indeed approximately equal to
the one derived from photospheric helicity flux. The results of this
dissertation are useful for better understanding of magnetic topology
in general. They are also extremely promising for extrapolating coronal
magnetic fields. Measurements of coronal twist might aid in predicting
magnetic instabilities.
---------------------------------------------------------
Title: Reconstructing the Local Twist of Coronal Magnetic Fields and
the Three-Dimensional Shape of the Field Lines from Coronal Loops
in Extreme-Ultraviolet and X-Ray Images
Authors: Malanushenko, A.; Longcope, D. W.; McKenzie, D. E.
2009ApJ...707.1044M Altcode: 2009arXiv0909.5141M
Nonlinear force-free fields are the most general case of force-free
fields, but the hardest to model as well. There are numerous methods
of computing such fields by extrapolating vector magnetograms from the
photosphere, but very few attempts have so far made quantitative use of
coronal morphology. We present a method to make such quantitative use
of X-ray and EUV images of coronal loops. Each individual loop is fit
to a field line of a linear force-free field, allowing the estimation
of the field line's twist, three-dimensional geometry, and the field
strength along it. We assess the validity of such a reconstruction
since the actual corona is probably not a linear force-free field,
and that the superposition of linear force-free fields is generally
not itself a force-free field. To do so, we perform a series of tests
on nonlinear force-free fields, described in Low & Lou. For model
loops we project field lines onto the photosphere. We compare several
results of the method with the original field, in particular the
three-dimensional loop shapes, local twist (coronal α), distribution
of twist in the model photosphere, and strength of the magnetic
field. We find that (1) for these trial fields, the method reconstructs
twist with a mean absolute deviation of at most 15% of the range of
photospheric twist, (2) heights of the loops are reconstructed with a
mean absolute deviation of at most 5% of the range of trial heights,
and (3) the magnitude of non-potential contribution to a photospheric
field is reconstructed with a mean absolute deviation of at most 10%
of the maximal value.
---------------------------------------------------------
Title: Measuring Coronal Magnetic Twist Injected by Photospheric
Rotation
Authors: Malanushenko, A.; Yusuf, M.; Longcope, D. W.
2009AGUFMSH23B1537M Altcode:
Measuring the twist of the coronal magnetic field is important for
understanding and predicting solar flares. The studies of instabilities
in the past decades suggest a relation between solar flares and
instabilities, such as the external kink mode, driven by excessive
twist. We study the buildup of twist in an emerging and rapidly
rotating active region (AR 9002) using the technique developed by
Malanushenko et al. (2009). This uses EUV coronal images, from TRACE,
and line-of-sight magnetograms, from MDI, to infer properties of the
coronal magnetic field, including its local twist parameter alpha. We
find that the twist of AR 9002 does not change with time, while twist
of emerging AR 9004 starts left handed and becomes, after 80 hours,
right handed. We compare the change rate of twist for AR 9004 to the
predicted rate given the simple model of braiding and spinning flux tube
and demonstrate the general agreement of the two. We also characterize
the coronal twist of the flux interconnecting the two regions which is
produced through reconnection. This work was supported by NASA and NSF.
---------------------------------------------------------
Title: Additive Self-helicity as a Kink Mode Threshold
Authors: Malanushenko, A.; Longcope, D. W.; Fan, Y.; Gibson, S. E.
2009ApJ...702..580M Altcode: 2009arXiv0909.4959M
In this paper, we propose that additive self-helicity, introduced
by Longcope and Malanushenko, plays a role in the kink instability
for complex equilibria, similar to twist helicity for thin flux
tubes. We support this hypothesis by a calculation of additive
self-helicity of a twisted flux tube from the simulation of Fan and
Gibson. As more twist gets introduced, the additive self-helicity
increases, and the kink instability of the tube coincides with the
drop of additive self-helicity, after the latter reaches the value
of H<SUB>A</SUB> /Φ<SUP>2</SUP> ≈ 1.5 (where Φ is the flux of the
tube and H<SUB>A</SUB> is the additive self-helicity). We compare the
additive self-helicity to twist for a thin subportion of the tube
to illustrate that H<SUB>A</SUB> /Φ<SUP>2</SUP> is equal to the
twist number, studied by Berger and Field, when the thin flux tube
approximation is applicable. We suggest that the quantity H<SUB>A</SUB>
/Φ<SUP>2</SUP> could be treated as a generalization of a twist number,
when the thin flux tube approximation is not applicable. A threshold on
a generalized twist number might prove extremely useful studying complex
equilibria, just as the twist number itself has proven useful studying
idealized thin flux tubes. We explicitly describe a numerical method
for calculating additive self-helicity, which includes an algorithm
for identifying a domain occupied by a flux bundle and a method of
calculating potential magnetic field confined to this domain. We also
describe a numerical method to calculate twist of a thin flux tube,
using a frame parallelly transported along the axis of the tube.
---------------------------------------------------------
Title: Inferring Local Twist of the Coronal Magnetic Field from
Coronal Loops in EUV and X-ray Images
Authors: Malanushenko, Anna; Longcope, D. W.; McKenzie, D. E.
2009SPD....40.2902M Altcode:
Non-linear force-free fields are the most general case of force-free
fields, but the hardest to model as well. There are numerous methods
of computing such fields by extrapolating vector magnetograms from
the photosphere, but very few attempts have so far made quantitative
use of coronal morphology. We present an improved method which infers
properties of the force-free field from X-Ray and EUV images of active
region coronal loops. Each loop evident in an image is fit to field
lines from constant-alpha fields. Our algorithm thereby estimates
the three-dimensional geometry of each loop as well its local twist
(alpha) and the magnetic field strength over its length. We assess
the performance of this method by applying it to known examples of
3D non-linear force free fields. We demonstrate that at least some
features of the local twist distribution could be reconstructed using
this method.
---------------------------------------------------------
Title: Modeling the Evolving Magnetic Field in a Coronal Sigmoid
Authors: McKenzie, David Eugene; Malanushenko, A.; Longcope, D.
2009SPD....40.1203M Altcode:
The importance of coronal sigmoids as progenitors of eruptions and
mass ejections is well established. However, the storage of magnetic
energy prior to a sigmoid's eruption is difficult to quantify. While
the non-potentiality of the coronal force-free fields is clearly
responsible for the free energy, models of the field are difficult to
verify. We utilize a method, developed at Montana State University and
described at this meeting by A. Malanushenko, to model the force-free
field within a coronal sigmoid observed by TRACE and Hinode/XRT. By
modeling the twist in the sigmoid's field over the span of a few days
leading up to its eruption, it is hoped that such a model can yield
insight to the buildup of energy. This work is supported by NASA
contract NNX07AI01G, and by SAO contract SV7-77003.
---------------------------------------------------------
Title: Defining and Calculating Self-Helicity in Coronal Magnetic
Fields
Authors: Longcope, D. W.; Malanushenko, A.
2008ApJ...674.1130L Altcode:
We introduce two different generalizations of relative helicity which
may be applied to a portion of the coronal volume. Such a quantity is
generally referred to as the self-helicity of the field occupying the
subvolume. Each definition is a natural application of the traditional
relative helicity but relative to a different reference field. One
of the generalizations, which we term additive self-helicity, can be
considered a generalization of twist helicity to volumes which are
neither closed nor thin. It shares with twist the property of being
identically zero for any portion of a potential magnetic field. The
other helicity, unconfined self-helicity, is independent of the shape
of the volume occupied by the field portion and is therefore akin to
the sum of twist and writhe helicity. We demonstrate how each kind
of self-helicity may be evaluated in practice. The set of additive
self-helicities may be used as a constraint in the minimization of
magnetic energy to produce a piecewise constant-α equilibrium. This
class of fields falls into a hierarchy, along with the flux-constrained
equilibria and potential fields, of fields with monotonically decreasing
magnetic energies. Piecewise constant-α fields generally have fewer
unphysical properties than genuinely constant-α fields, whose twist
α is uniform throughout the entire corona.
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Title: Quantifying The Self-helicity Of A Flux Tubes
Authors: Malanushenko, Anna; Longcope, D.
2007AAS...210.9110M Altcode: 2007BAAS...39..205M
Magnetic helicity has proven to be a powerful tool for understanding
energetics of the solar corona. As it is usually defined, relative
helicity is an integral over the entire coronal volume. In this work
we consider two different generalizations by which relative helicity
of a portion of the entire coronal volume may be calculated. Such a
quantity is generally called the self helicity of the sub-volume. Each
definition is a natural application of the traditional helicity formula
but relative to different fields. One of the generalizations, which we
term "additive self-helicity", has particularly desirable properties,
such as being identically zero for any portion of a potential magnetic
field. During a flare it is believed that the total helicity of
the volume is conserved, but as reconnection transfers flux between
domains, this will change the self-helicity of those. We demonstrate
how "additive self-helicity" may be evaluated in practice to find the
self-helicities for flux systems, or domains, composed of all field
lines connecting a designated pair of photospheric source regions. It
is then possible to quantify the transfer of self-helicity which would
occur when reconnection transfers flux between flux systems.
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Title: Quantifying The Relationship Between Reconnection Rate And
Energy Release In A Survey Of Coronal Bright Points
Authors: Malanushenko, Anna V.; Longcope, D.; Aver, E.; Kankelborg, C.
2006SPD....37.1001M Altcode: 2006BAAS...38Q.237M
This is an observational study of coronal bright points aimed at
quantifying the relationship between reconnection rate and dissipated
power. We assemble surveys of 733 bright from archival SOHO data. Bright
points are found in two channels of EIT (EUV Imaging Telescope)
data. We match these features to magnetic bipoles found in photospheric
magnetic field observations of MDI. From the MDI magnetograms we extract
measurements of each quantity relevant to simple three-dimensional
reconnection model including the relative velocities of the magnetic
poles. The study reveals temporal and spatial properties of X-ray bright
points and compares them to the simple models of spatial distribution
over the disk. The temporal evolution of the poles is used to test the
hypothesis that coronal heating is due to magnetic reconnection and
furthermore to quantify the relationship between reconnection rate and
heating power.This work was supported by NASA under grant NAG5-10489.
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Title: The GONG Farside Project
Authors: Leibacher, J. W.; Braun, D.; González Hernández, I.;
Goodrich, J.; Kholikov, S.; Lindsey, C.; Malanushenko, A.; Scherrer, P.
2005AGUSMSP11B..14L Altcode:
The GONG program is currently providing near-real-time helioseismic
images of the farside of the Sun. The continuous stream of low
resolution images, obtained from the 6 earth based GONG stations, are
merged into a single data series that are the input to the farside
pipeline. In order to validate the farside images, it is crucial
to compare the results obtained from different instruments. We show
comparisons between the farside images provided by the MDI instrument
and the GONG ones. New aditions to the pipeline will allow us to create
full-hemisphere farside images, examples of the latest are shown in
this poster. Our efforts are now concentrated in calibrating the
farside signal so it became a reliable solar activity forecasting
tool. We are also testing single-skip acoustic power holography
at 5-7 mHz as a prospective means of reinforcing the signatures of
active regions crossing the the east and west limb and monitoring
acoustic emission in the neighborhoods of Sun's the poles. This work
utilizes data obtained by the Global Oscillation Network Group (GONG)
Program, managed by the National Solar Observatory, which is operated
by AURA, Inc. under a cooperative agreement with the National Science
Foundation. The data were acquired by instruments operated by the Big
Bear Solar Observatory, High Altitude Observatory, Learmonth Solar
Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de
Canarias, and Cerro Tololo Interamerican Observatory, as well as
the Michaelson Doppler Imager on SoHO, a mission of international
cooperation between ESA and NASA. This work has been supported by the
NASA Living with a Star - Targeted Research and Technology program.
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Title: Remote distributed pipeline processing of GONG helioseismic
data: experience and lessons learned
Authors: Goodrich, Jean N.; Kholikov, Shukur; Lindsey, Charles;
Malanushenko, Anna; Shroff, Chirag; Toner, Clifford
2004SPIE.5493..538G Altcode:
The Global Oscillation Network Group (GONG) helioseismic network
can create images of the farside of the Sun which frequently show the
presence of large active regions that would be otherwise invisible. This
ability to "see" through the sun is of potential benefit to the
prediction of solar influences on the Earth, provided that the data can
be obtained and reduced in a timely fashion. Thus, GONG is developing a
system to A) perform initial data analysis steps at six geographically
distributed sites, B) transmit the reduced data to a home station, C)
perform the final steps in the analysis, and D) distribute the science
products to space weather forecasters. The essential requirements are
that the system operate automatically around the clock with little human
intervention, and that the science products be available no more than 48
hours after the observations are obtained. We will discuss the design,
implementation, testing, and current status of the system.
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Title: Acoustic Holographic Studies of Solar Active Regions
Authors: Malanushenko, A.; Braun, D.; Kholikov, S.; Leibacher, J.;
Lindsey, C.
2004IAUS..223..283M Altcode: 2005IAUS..223..283M
We present results of a study of the morphology and evolution of
active regions using solar acoustic holography. These include acoustic
signatures of large far-side active regions and their relationship to
near-side activity indices a half rotation before and after the farside
image, and the direct comparison of near-side acoustic signatures with
the standard activity indicators, not only in their own right but also
to calibrate the farside acoustic signature.
