Author name code: cheung
ADS astronomy entries on 2022-09-14
author:"Cheung, Mark C.M."
------------------------------------------------------------------------
Title: ML pipeline for Solar Dynamics Observatory (SDO) data
Authors: Salvatelli, Valentina; Neuberg, Brad; Dos Santos, Luiz F. G.;
Bose, Souvik; Cheung, Mark C. M; Janvier, Miho; Jin, Meng; Gal, Yarin;
Güneş Baydın, Atılım
Bibcode: 2022zndo...6954828S
Altcode:
This software has been developed from the [FDL SDO
Team](https://frontierdevelopmentlab.org/2019-sdo). The
package contains: a configurable pipeline to train and
test ML models on data from the Solar Dynamics Observatory
some notebooks for data exploration and results analysis. It
contains all the code supporting the publications: [Multi-Channel
Auto-Calibration for the Atmospheric Imaging Assembly using Machine
Learning](https://arxiv.org/abs/2012.14023) "Exploring the Limits of
Synthetic Creation of Solar EUV Images via Image-to-Image Translation"
Accepted for publication on ApJ (July 2022)
Title: Exploring the Limits of Synthetic Creation of Solar EUV Images
via Image-to-Image Translation
Authors: Salvatelli, Valentina; dos Santos, Luiz F. G.; Bose, Souvik;
Neuberg, Brad; Cheung, Mark C. M.; Janvier, Miho; Jin, Meng; Gal,
Yarin; Gunes Baydin, Atilim
Bibcode: 2022arXiv220809512S
Altcode:
The Solar Dynamics Observatory (SDO), a NASA multi-spectral decade-long
mission that has been daily producing terabytes of observational data
from the Sun, has been recently used as a use-case to demonstrate the
potential of machine learning methodologies and to pave the way for
future deep-space mission planning. In particular, the idea of using
image-to-image translation to virtually produce extreme ultra-violet
channels has been proposed in several recent studies, as a way to
both enhance missions with less available channels and to alleviate
the challenges due to the low downlink rate in deep space. This
paper investigates the potential and the limitations of such a deep
learning approach by focusing on the permutation of four channels and
an encoder--decoder based architecture, with particular attention to
how morphological traits and brightness of the solar surface affect the
neural network predictions. In this work we want to answer the question:
can synthetic images of the solar corona produced via image-to-image
translation be used for scientific studies of the Sun? The analysis
highlights that the neural network produces high-quality images
over three orders of magnitude in count rate (pixel intensity)
and can generally reproduce the covariance across channels within
a 1% error. However the model performance drastically diminishes in
correspondence of extremely high energetic events like flares, and we
argue that the reason is related to the rareness of such events posing
a challenge to model training.
Title: Predicted appearance of Magnetic Flux Rope and Sheared Magnetic
Arcade Structures before a Coronal Mass Ejection via three-dimensional
radiative Magnetohydrodynamic Modeling
Authors: Chintzoglou, Georgios; Cheung, Mark; Rempel, Matthias
Bibcode: 2022cosp...44.2406C
Altcode:
Magnetic Flux Ropes (MFRs) are free-energy-carrying, three-dimensional
magnetized plasma structures characterized by twisted magnetic field
lines and are widely considered the core structure of Coronal Mass
Ejections (CMEs) propagating in the interplanetary space. The way MFRs
form remains unclear as different theories predict that either MFRs
form during the initiation of the CME or pre-exist the onset of the
CME. The term "pre-existing structure" is synonymous with "filament
channels." On the one hand, the theories predicting on-the-fly MFR
formation require Sheared Magnetic Arcades (SMAs; low twist but
stressed magnetic structures) for the filament channel/pre-existing
magnetic structure of CMEs. On the other hand, a growing number of
works using SDO/AIA observations (combined with non-linear force-free
extrapolations; NLFFF) suggest that MFRs may be the form of filament
channels, therefore pre-existing the CME eruption. However, due to
the inability to routinely measure the 3D magnetic field in the solar
atmosphere, we cannot unambiguously interpret optical and EUV imaging
observations as projected on the plane of the sky. Therefore, a raging
debate on the nature of the pre-eruptive structure continues. It is
also possible that the filament channel/pre-eruptive structure evolves
from SMA to MFR slowly, further complicating the distinction between
these two types of structures in the solar observations. This work
presents realistic simulated optical and EUV observations synthesized
on a time-evolving radiative MURaM MHD model at different times
along the slow evolution of an SMA converting to an MFR. We discuss
the implications of our results in the context of filament channel
formation and CME initiation theory.
Title: The Physics of Magnetic Flux Emergence
Authors: Cheung, Mark
Bibcode: 2022cosp...44.2403C
Altcode:
We discuss the physical processes governing how magnetic flux emerges
from the solar interior into the overlying atmosphere. Key concepts
include stratification, magnetic buoyancy, magnetoconvection, twist /
helicity, interaction of emerged fields with pre-existing fields,
magnetic reconnection, emergence-driven shearing, and flux rope
formation and eruption. We consider how these concepts can be applied
to model the evolution of flux ropes in other stellar environments,
and consider potential observational diagnostics such as stellar flares
and coronal dimmings.
Title: The Magnetic Origin of Solar Campfires: Observations by Solar
Orbiter and SDO
Authors: Panesar, Navdeep Kaur; Zhukov, Andrei; Berghmans, David;
Auchere, Frederic; Müller, Daniel; Tiwari, Sanjiv Kumar; Cheung, Mark
Bibcode: 2022cosp...44.2564P
Altcode:
Solar campfires are small-scale, short-lived coronal brightenings,
recently observed in 174 Å images by Extreme Ultraviolet Imager (EUI)
on board Solar Orbiter (SolO). Here we investigate the magnetic origin
of 52 campfires, in quiet-Sun, using line-of-sight magnetograms from
Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager
(HMI) together with extreme ultraviolet images from SolO /EUI and
SDO/Atmospheric Imaging Assembly (AIA). We find that the campfires
are rooted at the edges of photospheric magnetic network lanes; (ii)
most of the campfires reside above neutral lines and 77% of them appear
at sites of magnetic flux cancelation between the majority-polarity
magnetic flux patch and a merging minority-polarity flux patch, with
a flux cancelation rate of ∼1018 Mx hr‑1; some of the smallest
campfires come from the sites where magnetic flux elements were barely
discernible in HMI; (iii) some of the campfires occur repeatedly
from the same neutral line; (iv) in the large majority of instances
(79%), campfires are preceded by a cool-plasma structure, analogous to
minifilaments in coronal jets; and (v) although many campfires have
"complex" structure, most campfires resemble small-scale jets, dots,
or loops. Thus, "campfire" is a general term that includes different
types of small-scale solar dynamic features. They contain sufficient
magnetic energy (∼1026-1027 erg) to heat the solar atmosphere
locally to 0.5-2.5 MK. Their lifetimes range from about 1 minute to
over 1 hour, with most of the campfires having a lifetime of <10
minutes. The average lengths and widths of the campfires are 5400 ±
2500 km and 1600 ± 640 km, respectively. Our observations suggest that
(a) the presence of magnetic flux ropes may be ubiquitous in the solar
atmosphere and not limited to coronal jets and larger-scale eruptions
that make CMEs, and (b) magnetic flux cancelation, most likely driven
by magnetic reconnection in the lower atmosphere, is the fundamental
process for the formation and triggering of most campfires.
Title: Unipolar versus Bipolar Internetwork Flux Appearance
Authors: Gosic, Milan; Katsukawa, Yukio; Bellot Rubio, L. R.; Del
Toro Iniesta, Jose Carlos; Cheung, Mark; Orozco Suárez, David
Bibcode: 2022cosp...44.2513G
Altcode:
Small-scale internetwork (IN) magnetic fields are considered to be
the main building blocks of the quiet Sun magnetism. It is therefore
of paramount importance to understand how these fields are generated
on the solar surface. To shed new light on this open question,
we studied the appearance modes and spatio-temporal evolution of
individual IN magnetic elements inside one supergranular cell. For
that purpose, we employed a high-resolution, high-sensitivity,
long-duration Hinode/NFI magnetogram sequence. From identification
of flux patches and magnetofrictional simulations, we show that there
are two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger, live longer
and carry more flux than unipolar features. About $70$% of the total
instantaneous IN flux detected inside the supergranule is in the form
of bipoles. Both types of flux concentrations are uniformly distributed
over the solar surface. However, bipolar features appear (randomly
oriented) at a faster rate than unipolar features (68 as opposed to
55~Mx~cm$^{-2}$~day$^{-1}$). Our results lend support to the idea that
bipolar features may be the signature of local dynamo action, while
unipolar features seem to be formed by coalescence of background flux.
Title: Coronal Dimming as a Proxy for Solar and Stellar Coronal
Mass Ejections
Authors: Jin, Meng; Nitta, Nariaki; Derosa, Marc; Cheung, Mark; Osten,
Rachel; France, Kevin; Mason, James; Kowalski, Adam; Schrijver, Carolus
Bibcode: 2022cosp...44.1404J
Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings as well as their relationship
with CMEs. Recent study (e.g., Veronig et al. 2021) also shows promising
dimming signals from distant stars, which suggest the possibility of
using coronal dimming as a proxy to diagnose stellar CMEs. In this
study, we first conduct a comparative study of solar coronal dimming
using MHD simulations and SDO observations. A detailed analysis of
the simulation and observation data reveals how transient dimming
/ brightening are related to plasma heating processes, while the
long-lasting core and remote dimmings are caused by mass loss process
induced by the CME. Using metrics such as dimming depth and dimming
slope, we uncover a relationship between dimmings and CME properties
(e.g., CME mass, CME speed) in the simulation. We further extend the
model for simulating the stellar CMEs and dimmings and compare with
solar cases. Our result suggests that coronal dimmings encode important
information about the associated CMEs, which provides a physical basis
for detecting stellar CMEs from distant solar-like stars.
Title: How could we use observations to constrain and validate
data-driven models of solar eruptions?
Authors: Kazachenko, Maria; Fan, Yuhong; Fisher, George; Cheung,
Mark; Afanasev, Andrei; Tremblay, Benoit; Kazachenko, Maria
Bibcode: 2022cosp...44.2464K
Altcode:
Observations of vector magnetic fields, coronal loops, flare ribbons and
coronal dimmings provide observational constraints for data-constrained
and data-driven models of solar eruptions. In this talk I will review
specific observational properties that we could use to evaluate the
realism of these models: photospheric energy fluxes, reconnection
fluxes, inferred flux rope properties and future coronal field
measurements. I will also discuss possible ways to improve current
models using more realistic photospheric boundary conditions.
Title: Synergetic data-driven magnetofrictional and MHD simulations
of an eruptive solar active region
Authors: Afanasev, Andrei; Fan, Yuhong; Cheung, Mark; Kazachenko, Maria
Bibcode: 2022cosp...44.2470A
Altcode:
One of the most informative and precise ways to study solar eruptions
is MHD simulations. However, full-MHD simulations of eruptions with
time-dependent observation-based boundaries (the so-called data-driven
simulations) can be computationally expensive. We combine the
data-driven magnetofrictional approach and MHD simulations to analyse
the evolution of active region NOAA 11158 that produced an X-class flare
and coronal mass ejection on Feb 15, 2011. We use the magnetofrictional
code within the Coronal Global Evolutionary Model (CGEM) framework
to simulate the evolution of the active region from the magnetic
flux emergence on the photosphere until the formation of a magnetic
flux rope at coronal heights before the eruption, with the boundary
conditions determined with the PDFISS method. After that, we use the
Magnetic Flux Eruption code to calculate the subsequent MHD evolution
of the obtained pre-eruptive coronal magnetic configuration. We present
details of these combined simulations and discuss the results. In our
simulations, we obtain the eruption of the magnetic flux rope and find
good agreement of the simulated flare ribbons with SDO/AIA observations.
Title: Ultraviolet Spectropolarimetry With Polstar: Using Polstar
to test Magnetospheric Mass-loss Quenching
Authors: Shultz, M. E.; Casini, R.; Cheung, M. C. M.; David-Uraz, A.;
del Pino Alemán, T.; Erba, C.; Folsom, C. P.; Gayley, K.; Ignace,
R.; Keszthelyi, Z.; Kochukhov, O.; Nazé, Y.; Neiner, C.; Oksala,
M.; Petit, V.; Scowen, P. A.; Sudnik, N.; ud-Doula, A.; Vink, J. S.;
Wade, G. A.
Bibcode: 2022arXiv220712970S
Altcode:
Polstar is a proposed NASA MIDEX space telescope that will provide
high-resolution, simultaneous full-Stokes spectropolarimetry in the
far ultraviolet, together with low-resolution linear polarimetry in the
near ultraviolet. This observatory offers unprecedented capabilities to
obtain unique information on the magnetic and plasma properties of the
magnetospheres of hot stars. We describe an observing program making use
of the known population of magnetic hot stars to test the fundamental
hypothesis that magnetospheres should act to rapidly drain angular
momentum, thereby spinning the star down, whilst simultaneously reducing
the net mass-loss rate. Both effects are expected to lead to dramatic
differences in the evolution of magnetic vs. non-magnetic stars.
Title: Ultraviolet Spectropolarimetric Diagnostics of Hot Star
Magnetospheres
Authors: ud-Doula, Asif; Cheung, M. C. M.; David-Uraz, A.; Erba, C.;
Folsom, C. P.; Gayley, K.; Naze, Y.; Neiner, C.; Petit, V.; Prinja,
R.; Shultz, M. E.; Sudnik, N.; Vink, J. S.; Wade, G. A.
Bibcode: 2022arXiv220612838U
Altcode:
Several space missions and instruments for UV spectropolarimetry
are in preparation, such as the proposed NASA MIDEX Polstar project,
the proposed ESA M mission Arago, and the Pollux instrument on the
future LUVOIR-like NASA flagship mission. In the frame of Polstar,
we have studied the capabilities these observatories would offer
to gain information on the magnetic and plasma properties of the
magnetospheres of hot stars, helping us test the fundamental hypothesis
that magnetospheres should act to rapidly drain angular momentum,
thereby spinning the star down, whilst simultaneously reducing the
net mass-loss rate. Both effects are expected to lead to dramatic
differences in the evolution of magnetic vs. non-magnetic stars.
Title: Global Geomagnetic Perturbation Forecasting Using Deep Learning
Authors: Upendran, Vishal; Tigas, Panagiotis; Ferdousi, Banafsheh;
Bloch, Téo.; Cheung, Mark C. M.; Ganju, Siddha; Bhatt, Asti;
McGranaghan, Ryan M.; Gal, Yarin
Bibcode: 2022SpWea..2003045U
Altcode: 2022arXiv220512734U
Geomagnetically Induced Currents (GICs) arise from spatio-temporal
changes to Earth's magnetic field, which arise from the interaction
of the solar wind with Earth's magnetosphere, and drive catastrophic
destruction to our technologically dependent society. Hence,
computational models to forecast GICs globally with large forecast
horizon, high spatial resolution and temporal cadence are of increasing
importance to perform prompt necessary mitigation. Since GIC data is
proprietary, the time variability of the horizontal component of the
magnetic field perturbation (dB/dt) is used as a proxy for GICs. In
this work, we develop a fast, global dB/dt forecasting model, which
forecasts 30 min into the future using only solar wind measurements
as input. The model summarizes 2 hr of solar wind measurement using
a Gated Recurrent Unit and generates forecasts of coefficients
that are folded with a spherical harmonic basis to enable global
forecasts. When deployed, our model produces results in under a second,
and generates global forecasts for horizontal magnetic perturbation
components at 1 min cadence. We evaluate our model across models
in literature for two specific storms of 5 August 2011 and 17 March
2015, while having a self-consistent benchmark model set. Our model
outperforms, or has consistent performance with state-of-the-practice
high time cadence local and low time cadence global models, while
also outperforming/having comparable performance with the benchmark
models. Such quick inferences at high temporal cadence and arbitrary
spatial resolutions may ultimately enable accurate forewarning of
dB/dt for any place on Earth, resulting in precautionary measures to
be taken in an informed manner.
Title: Vishal-Upendran/geoeffectivenet-1: DAGGER model
Authors: Upendran, Vishal; Tigas, Panagiotis; Ferdousi, Banafsheh;
Bloch, Teo; Cheung, Mark C. M.; Ganju, Siddha; Bhatt, Asti;
McGranaghan, Ryan M.; Gal, Yarin
Bibcode: 2022zndo...6410499U
Altcode:
This is the first release of a Deep learning model to forecast
geomagnetic perturbations, given changing conditions in the solar wind.
Title: Coronal Mass Ejections and Dimmings: A Comparative Study
Using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark C. M.; DeRosa, Marc L.; Nitta,
Nariaki V.; Schrijver, Carolus J.
Bibcode: 2022ApJ...928..154J
Altcode: 2022arXiv220213034J
Solar coronal dimmings have been observed extensively in recent
years. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings as well as their relationship
with CMEs. In this study, we investigate coronal dimmings by combining
simulation and observational efforts. By utilizing a data-constrained
global magnetohydrodynamics model (Alfvén-wave solar model), we
simulate coronal dimmings resulting from different CME energetics and
flux rope configurations. We synthesize the emissions of different EUV
spectral bands/lines and compare with SDO/AIA and EVE observations. A
detailed analysis of the simulation and observation data suggests
that the transient dimming/brightening are related to plasma heating
processes, while the long-lasting core and remote dimmings are caused
by mass-loss process induced by the CME. Moreover, the interaction
between the erupting flux rope with different orientations and the
global solar corona could significantly influence the coronal dimming
patterns. Using metrics such as dimming depth and dimming slope,
we investigate the relationship between dimmings and CME properties
(e.g., CME mass, CME speed) in the simulation. Our result suggests
that coronal dimmings encode important information about the associated
CMEs, which provides a physical basis for detecting stellar CMEs from
distant solar-like stars.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Stansby, David; Shih, Albert Y.; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Barnes, Will; Hamilton, Alex; Manhas,
Abhijeet; Panda, Asish; Earnshaw, Matt; Choudhary, Nitin; Kumar, Ankit;
Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael S;
Mueller, Michael; Konge, Sudarshan; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Maloney, Shane;
Charlton, Michael; Mishra, Sashank; Paul, Jeffrey Aaron; MacBride,
Conor; Chorley, Nicky; Himanshu; Chouhan, Aryan; Modi, Sanskar;
Sharma, Yash; Mason, James Paul; Naman9639; Zivadinovic, Lazar; Bobra,
Monica G.; Campos Rozo, Jose Ivan; Manley, Larry; Ivashkiv, Kateryna;
Chatterjee, Agneet; Von Forstner, Johan Freiherr; Bazán, Juanjo;
Akira Stern, Kris; Evans, John; Jain, Sarthak; Malocha, Michael;
Ghosh, Sourav; Stańczak, Dominik; SophieLemos; Ranjan Singh, Rajiv;
De Visscher, Ruben; Verma, Shresth; Airmansmith97; Buddhika, Dumindu;
Sharma, Swapnil; Pathak, Himanshu; Rideout, Jai Ram; Agrawal, Ankit;
Alam, Arib; Bates, Matt; Park, Jongyeob; Shukla, Devansh; Mishra,
Pankaj; Dubey, Sanjeev; Taylor, Garrison; Dacie, Sally; Jacob; Goel,
Dhruv; Sharma, Deepankar; Inchaurrandieta, Mateo; Cetusic, Goran;
Reiter, Guntbert; Zahniy, Serge; Sidhu, Sudeep; Bray, Erik M.;
Meszaros, Tomas; Eigenbrot, Arthur; Surve, Rutuja; Parkhi, Utkarsh;
Robitaille, Thomas; Pandey, Abhishek; Price-Whelan, Adrian; J, Amogh;
Chicrala, André; Ankit; Guennou, Chloé; D'Avella, Daniel; Williams,
Daniel; Verma, Dipanshu; Ballew, Jordan; Murphy, Nick; Lodha, Priyank;
Bose, Abhigyan; Augspurger, Tom; Krishan, Yash; Honey; Neerajkulk;
Altunian, Noah; Ranjan, Kritika; Bhope, Adwait; Molina, Carlos;
Gomillion, Reid; Kothari, Yash; Streicher, Ole; Wiedemann, Bernhard
M.; Mampaey, Benjamin; Nomiya, Yukie; Mridulpandey; Habib, Ishtyaq;
Letts, Joseph; Agarwal, Samriddhi; Singh Gaba, Amarjit; Hill, Andrew;
Keşkek, Duygu; Kumar, Gulshan; Verstringe, Freek; Mackenzie Dover,
Fionnlagh; Tollerud, Erik; Arias, Emmanuel; Srikanth, Shashank; Jain,
Shubham; Stone, Brandon; Kustov, Arseniy; Smith, Arfon; Sinha, Anubhav;
Kannojia, Swapnil; Mehrotra, Ambar; Yadav, Tannmay; Paul, Tathagata;
Wilkinson, Tessa D.; Caswell, Thomas A; Braccia, Thomas; Pereira, Tiago
M. D.; Gates, Tim; Yasintoda; Kien Dang, Trung; Wilson, Alasdair;
Bankar, Varun; Bahuleyan, Abijith; B, Abijith; Platipo; Stevens,
Abigail L.; Gyenge, Norbert G; Schoentgen, Mickaël; Shahdadpuri,
Nakul; Dedhia, Megh; Mendero, Matthew; Cheung, Mark; Agrawal, Yudhik;
Mangaonkar, Manas; Lyes, MOULOUDI Mohamed; Resakra; Ghosh, Koustav;
Hiware, Kaustubh; Chaudhari, Kaustubh; Reddy Mekala, Rajasekhar;
Krishna, Kalpesh; Buitrago-Casas, Juan Camilo; Das, Ratul; Mishra,
Rishabh; Sharma, Rohan; Wimbish, Jaylen; Calixto, James; Babuschkin,
Igor; Mathur, Harsh; Murray, Sophie A.; Nakul-Shahdadpuri
Bibcode: 2022zndo....591887M
Altcode: 2021zndo....591887M
The community-developed, free and open-source solar data analysis
environment for Python.
Title: The Coronal Veil
Authors: Malanushenko, A.; Cheung, M. C. M.; DeForest, C. E.; Klimchuk,
J. A.; Rempel, M.
Bibcode: 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.
Title: SynthIA: A Synthetic Inversion Approximation for the Stokes
Vector Fusing SDO and Hinode into a Virtual Observatory
Authors: Higgins, Richard E. L.; Fouhey, David F.; Antiochos, Spiro K.;
Barnes, Graham; Cheung, Mark C. M.; Hoeksema, J. Todd; Leka, K. D.;
Liu, Yang; Schuck, Peter W.; Gombosi, Tamas I.
Bibcode: 2022ApJS..259...24H
Altcode: 2021arXiv210812421H
Both NASA's Solar Dynamics Observatory (SDO) and the JAXA/NASA
Hinode mission include spectropolarimetric instruments designed
to measure the photospheric magnetic field. SDO's Helioseismic
and Magnetic Imager (HMI) emphasizes full-disk, high-cadence,
and good-spatial-resolution data acquisition while Hinode's Solar
Optical Telescope Spectro-Polarimeter (SOT-SP) focuses on high
spatial resolution and spectral sampling at the cost of a limited
field of view and slower temporal cadence. This work introduces a
deep-learning system, named the Synthetic Inversion Approximation
(SynthIA), that can enhance both missions by capturing the best of
each instrument's characteristics. We use SynthIA to produce a new
magnetogram data product, the Synthetic Hinode Pipeline (SynodeP),
that mimics magnetograms from the higher-spectral-resolution
Hinode/SOT-SP pipeline, but is derived from full-disk, high-cadence,
and lower-spectral-resolution SDO/HMI Stokes observations. Results
on held-out data show that SynodeP has good agreement with the
Hinode/SOT-SP pipeline inversions, including magnetic fill fraction,
which is not provided by the current SDO/HMI pipeline. SynodeP further
shows a reduction in the magnitude of the 24 hr oscillations present in
the SDO/HMI data. To demonstrate SynthIA's generality, we show the use
of SDO/Atmospheric Imaging Assembly data and subsets of the HMI data as
inputs, which enables trade-offs between fidelity to the Hinode/SOT-SP
inversions, number of observations used, and temporal artifacts. We
discuss possible generalizations of SynthIA and its implications for
space-weather modeling. This work is part of the NASA Heliophysics
DRIVE Science Center at the University of Michigan under grant NASA
80NSSC20K0600E, and will be open-sourced.
Title: The Solar Internetwork. III. Unipolar versus Bipolar Flux
Appearance
Authors: Gošić, M.; Bellot Rubio, L. R.; Cheung, M. C. M.; Orozco
Suárez, D.; Katsukawa, Y.; del Toro Iniesta, J. C.
Bibcode: 2022ApJ...925..188G
Altcode: 2021arXiv211103208G
Small-scale internetwork (IN) magnetic fields are considered to be the
main building blocks of quiet Sun magnetism. For this reason, it is
crucial to understand how they appear on the solar surface. Here,
we employ a high-resolution, high-sensitivity, long-duration
Hinode/NFI magnetogram sequence to analyze the appearance modes and
spatiotemporal evolution of individual IN magnetic elements inside a
supergranular cell at the disk center. From identification of flux
patches and magnetofrictional simulations, we show that there are
two distinct populations of IN flux concentrations: unipolar and
bipolar features. Bipolar features tend to be bigger and stronger
than unipolar features. They also live longer and carry more flux
per feature. Both types of flux concentrations appear uniformly over
the solar surface. However, we argue that bipolar features truly
represent the emergence of new flux on the solar surface, while
unipolar features seem to be formed by the coalescence of background
flux. Magnetic bipoles appear at a faster rate than unipolar features
(68 as opposed to 55 Mx cm-2 day-1), and provide
about 70% of the total instantaneous IN flux detected in the interior
of the supergranule.
Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
Leon; The
Bibcode: 2022ApJ...926...53C
Altcode: 2021arXiv210615591C
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (subarcseconds) and temporal (less than a few tens of
seconds) scales of the coronal dynamics of solar flares and eruptive
phenomena. The highest-resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by the Interface Region Imaging
Spectrograph for the low solar atmosphere, we need high-resolution
spectroscopic measurements with simultaneous imaging to understand the
dominant processes. In this paper: (1) we introduce the Multi-slit Solar
Explorer (MUSE), a spaceborne observatory to fill this observational
gap by providing high-cadence (<20 s), subarcsecond-resolution
spectroscopic rasters over an active region size of the solar transition
region and corona; (2) using advanced numerical models, we demonstrate
the unique diagnostic capabilities of MUSE for exploring solar coronal
dynamics and for constraining and discriminating models of solar flares
and eruptions; (3) we discuss the key contributions MUSE would make
in addressing the science objectives of the Next Generation Solar
Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
(and other ground-based observatories) can operate as a distributed
implementation of the NGSPM. This is a companion paper to De Pontieu
et al., which focuses on investigating coronal heating with MUSE.
Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). I. Coronal Heating
Authors: De Pontieu, Bart; Testa, Paola; Martínez-Sykora, Juan;
Antolin, Patrick; Karampelas, Konstantinos; Hansteen, Viggo; Rempel,
Matthias; Cheung, Mark C. M.; Reale, Fabio; Danilovic, Sanja; Pagano,
Paolo; Polito, Vanessa; De Moortel, Ineke; Nóbrega-Siverio, Daniel;
Van Doorsselaere, Tom; Petralia, Antonino; Asgari-Targhi, Mahboubeh;
Boerner, Paul; Carlsson, Mats; Chintzoglou, Georgios; Daw, Adrian;
DeLuca, Edward; Golub, Leon; Matsumoto, Takuma; Ugarte-Urra, Ignacio;
McIntosh, Scott W.; the MUSE Team
Bibcode: 2022ApJ...926...52D
Altcode: 2021arXiv210615584D
The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of
a multislit extreme ultraviolet (EUV) spectrograph (in three spectral
bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in
two passbands around 195 Å and 304 Å). MUSE will provide unprecedented
spectral and imaging diagnostics of the solar corona at high spatial
(≤0.″5) and temporal resolution (down to ~0.5 s for sit-and-stare
observations), thanks to its innovative multislit design. By obtaining
spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX-Fe
XXI 108 Å) covering a wide range of transition regions and coronal
temperatures along 37 slits simultaneously, MUSE will, for the first
time, "freeze" (at a cadence as short as 10 s) with a spectroscopic
raster the evolution of the dynamic coronal plasma over a wide range of
scales: from the spatial scales on which energy is released (≤0.″5)
to the large-scale (~170″ × 170″) atmospheric response. We use
numerical modeling to showcase how MUSE will constrain the properties of
the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and
the large field of view on which state-of-the-art models of the physical
processes that drive coronal heating, flares, and coronal mass ejections
(CMEs) make distinguishing and testable predictions. We describe the
synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
spectrograph, and ground-based observatories (DKIST and others), and
the critical role MUSE plays because of the multiscale nature of the
physical processes involved. In this first paper, we focus on coronal
heating mechanisms. An accompanying paper focuses on flares and CMEs.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Stansby, David; Shih, Albert Y.; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet;
Panda, Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar,
Ankit; Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael
S; Konge, Sudarshan; Mueller, Michael; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Maloney, Shane;
Charlton, Michael; Mishra, Sashank; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Modi, Sanskar; Mason, James Paul; Sharma, Yash; Naman9639;
Zivadinovic, Lazar; Campos Rozo, Jose Ivan; Bobra, Monica G.; Manley,
Larry; Paul, Jeffrey Aaron; Ivashkiv, Kateryna; Chatterjee, Agneet;
Akira Stern, Kris; Von Forstner, Johan Freiherr; Bazán, Juanjo; Jain,
Sarthak; Evans, John; Ghosh, Sourav; Malocha, Michael; Stańczak,
Dominik; SophieLemos; Verma, Shresth; De Visscher, Ruben; Ranjan Singh,
Rajiv; Airmansmith97; Buddhika, Dumindu; Pathak, Himanshu; Alam, Arib;
Agrawal, Ankit; Sharma, Swapnil; Rideout, Jai Ram; Bates, Matt; Park,
Jongyeob; Mishra, Pankaj; Goel, Dhruv; Sharma, Deepankar; Taylor,
Garrison; Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta,
Mateo; Dacie, Sally; Dubey, Sanjeev; Parkhi, Utkarsh; Sidhu, Sudeep;
Surve, Rutuja; Eigenbrot, Arthur; Meszaros, Tomas; Bray, Erik M.;
Zahniy, Serge; Guennou, Chloé; Bose, Abhigyan; Ankit; Chicrala,
André; J, Amogh; D'Avella, Daniel; Ballew, Jordan; Price-Whelan,
Adrian; Robitaille, Thomas; Augspurger, Tom; Murphy, Nick; Lodha,
Priyank; Krishan, Yash; Pandey, Abhishek; Honey; Verma, Dipanshu;
Neerajkulk; Williams, Daniel; Wiedemann, Bernhard M.; Kothari, Yash;
Mridulpandey; Habib, Ishtyaq; Molina, Carlos; Mampaey, Benjamin;
Streicher, Ole; Nomiya, Yukie; Gomillion, Reid; Letts, Joseph; Bhope,
Adwait; Hill, Andrew; Keşkek, Duygu; Ranjan, Kritika; Pereira,
Tiago M. D.; Kien Dang, Trung; Bankar, Varun; Bahuleyan, Abijith; B,
Abijith; Stevens, Abigail L.; Agrawal, Yudhik; Nakul-Shahdadpuri;
Ghosh, Koustav; Hiware, Kaustubh; Yasintoda; Krishna, Kalpesh;
Lyes, MOULOUDI Mohamed; Mangaonkar, Manas; Cheung, Mark; Platipo;
Buitrago-Casas, Juan Camilo; Mendero, Matthew; Dedhia, Megh; Wimbish,
Jaylen; Calixto, James; Babuschkin, Igor; Schoentgen, Mickaël; Mathur,
Harsh; Kumar, Gulshan; Verstringe, Freek; Mackenzie Dover, Fionnlagh;
Tollerud, Erik; Gyenge, Norbert G; Arias, Emmanuel; Reddy Mekala,
Rajasekhar; MacBride, Conor; Das, Ratul; Mishra, Rishabh; Stone,
Brandon; Resakra; Agarwal, Samriddhi; Chaudhari, Kaustubh; Kustov,
Arseniy; Smith, Arfon; Srikanth, Shashank; Jain, Shubham; Mehrotra,
Ambar; Singh Gaba, Amarjit; Kannojia, Swapnil; Yadav, Tannmay; Paul,
Tathagata; Wilkinson, Tessa D.; Caswell, Thomas A; Murray, Sophie A.
Bibcode: 2021zndo...5751998M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: Ultraviolet Spectropolarimetry With Polstar: Hot Star
Magnetospheres
Authors: Shultz, M. E.; Casini, R.; Cheung, M. C. M.; David-Uraz, A.;
del Pino Alemán, T.; Erba, C.; Folsom, C. P.; Gayley, K.; Ignace,
R.; Keszthelyi, Z.; Kochukhov, O.; Nazé, Y.; Neiner, C.; Oksala,
M.; Petit, V.; Scowen, P. A.; Sudnik, N.; ud-Doula, A.; Vink, J. S.;
Wade, G. A.
Bibcode: 2021arXiv211106434S
Altcode:
Polstar is a proposed NASA MIDEX space telescope that will provide
high-resolution, simultaneous full-Stokes spectropolarimetry in the far
ultraviolet, together with low-resolution linear polarimetry in the
near ultraviolet. In this white paper, we describe the unprecedented
capabilities this observatory would offer in order to obtain unique
information on the magnetic and plasma properties of the magnetospheres
of hot stars. This would enable a test of the fundamental hypothesis
that magnetospheres should act to rapidly drain angular momentum,
thereby spinning the star down, whilst simultaneously reducing the
net mass-loss rate. Both effects are expected to lead to dramatic
differences in the evolution of magnetic vs. non-magnetic stars.
Title: The Magnetic Origin of Solar Campfires
Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Berghmans, David;
Cheung, Mark C. M.; Müller, Daniel; Auchere, Frederic; Zhukov, Andrei
Bibcode: 2021ApJ...921L..20P
Altcode: 2021arXiv211006846P
Solar campfires are fine-scale heating events, recently observed by
Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Here we use EUI
174 Å images, together with EUV images from Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly (AIA), and line-of-sight magnetograms
from SDO/Helioseismic and Magnetic Imager (HMI) to investigate the
magnetic origin of 52 randomly selected campfires in the quiet solar
corona. We find that (i) the campfires are rooted at the edges of
photospheric magnetic network lanes; (ii) most of the campfires reside
above the neutral line between majority-polarity magnetic flux patch and
a merging minority-polarity flux patch, with a flux cancelation rate of
~1018 Mx hr-1; (iii) some of the campfires occur
repeatedly from the same neutral line; (iv) in the large majority of
instances, campfires are preceded by a cool-plasma structure, analogous
to minifilaments in coronal jets; and (v) although many campfires have
"complex" structure, most campfires resemble small-scale jets, dots,
or loops. Thus, "campfire" is a general term that includes different
types of small-scale solar dynamic features. They contain sufficient
magnetic energy (~1026-1027 erg) to heat the solar
atmosphere locally to 0.5-2.5 MK. Their lifetimes range from about 1
minute to over 1 hr, with most of the campfires having a lifetime of
<10 minutes. The average lengths and widths of the campfires are 5400
± 2500 km and 1600 ± 640 km, respectively. Our observations suggest
that (a) the presence of magnetic flux ropes may be ubiquitous in the
solar atmosphere and not limited to coronal jets and larger-scale
eruptions that make CMEs, and (b) magnetic flux cancelation is the
fundamental process for the formation and triggering of most campfires.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Stansby, David; Shih, Albert Y.; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet;
Panda, Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar,
Ankit; Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael
S; Konge, Sudarshan; Mueller, Michael; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Maloney, Shane;
Charlton, Michael; Mishra, Sashank; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Modi, Sanskar; Mason, James Paul; Sharma, Yash; Naman9639;
Zivadinovic, Lazar; Campos Rozo, Jose Ivan; Bobra, Monica G.; Manley,
Larry; Paul, Jeffrey Aaron; Ivashkiv, Kateryna; Chatterjee, Agneet;
Akira Stern, Kris; Von Forstner, Johan Freiherr; Bazán, Juanjo; Jain,
Sarthak; Evans, John; Ghosh, Sourav; Malocha, Michael; Stańczak,
Dominik; SophieLemos; Verma, Shresth; De Visscher, Ruben; Ranjan Singh,
Rajiv; Airmansmith97; Buddhika, Dumindu; Pathak, Himanshu; Alam, Arib;
Agrawal, Ankit; Sharma, Swapnil; Rideout, Jai Ram; Bates, Matt; Park,
Jongyeob; Mishra, Pankaj; Goel, Dhruv; Sharma, Deepankar; Taylor,
Garrison; Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta,
Mateo; Dacie, Sally; Dubey, Sanjeev; Parkhi, Utkarsh; Sidhu, Sudeep;
Surve, Rutuja; Eigenbrot, Arthur; Meszaros, Tomas; Bray, Erik M.;
Zahniy, Serge; Guennou, Chloé; Bose, Abhigyan; Ankit; Chicrala,
André; J, Amogh; D'Avella, Daniel; Ballew, Jordan; Price-Whelan,
Adrian; Robitaille, Thomas; Augspurger, Tom; Murphy, Nick; Lodha,
Priyank; Krishan, Yash; Pandey, Abhishek; Honey; Verma, Dipanshu;
Neerajkulk; Williams, Daniel; Wiedemann, Bernhard M.; Kothari, Yash;
Mridulpandey; Habib, Ishtyaq; Molina, Carlos; Mampaey, Benjamin;
Streicher, Ole; Nomiya, Yukie; Gomillion, Reid; Letts, Joseph; Bhope,
Adwait; Hill, Andrew; Keşkek, Duygu; Ranjan, Kritika; Pereira,
Tiago M. D.; Kien Dang, Trung; Bankar, Varun; Bahuleyan, Abijith; B,
Abijith; Stevens, Abigail L.; Agrawal, Yudhik; Nakul-Shahdadpuri;
Ghosh, Koustav; Hiware, Kaustubh; Yasintoda; Krishna, Kalpesh;
Lyes, MOULOUDI Mohamed; Mangaonkar, Manas; Cheung, Mark; Platipo;
Buitrago-Casas, Juan Camilo; Mendero, Matthew; Dedhia, Megh; Wimbish,
Jaylen; Calixto, James; Babuschkin, Igor; Schoentgen, Mickaël; Mathur,
Harsh; Kumar, Gulshan; Verstringe, Freek; Mackenzie Dover, Fionnlagh;
Tollerud, Erik; Gyenge, Norbert G; Arias, Emmanuel; Reddy Mekala,
Rajasekhar; MacBride, Conor; Das, Ratul; Mishra, Rishabh; Stone,
Brandon; Resakra; Agarwal, Samriddhi; Chaudhari, Kaustubh; Kustov,
Arseniy; Smith, Arfon; Srikanth, Shashank; Jain, Shubham; Mehrotra,
Ambar; Singh Gaba, Amarjit; Kannojia, Swapnil; Yadav, Tannmay; Paul,
Tathagata; Wilkinson, Tessa D.; Caswell, Thomas A; Murray, Sophie A.
Bibcode: 2021zndo...5068086M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS)
Authors: Caspi, A.; Shih, A. Y.; Panchapakesan, S.; Warren, H. P.;
Woods, T. N.; Cheung, M.; DeForest, C. E.; Klimchuk, J. A.; Laurent,
G. T.; Mason, J. P.; Palo, S. E.; Seaton, D. B.; Steslicki, M.;
Gburek, S.; Sylwester, J.; Mrozek, T.; Kowaliński, M.; Schattenburg,
M.; The CubIXSS Team
Bibcode: 2021AAS...23821609C
Altcode:
The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS) is a 6U
CubeSat proposed to NASA H-FORT. CubIXSS is motivated by a compelling
overarching science question: what are the origins of hot plasma in
solar flares and active regions? Elemental abundances are a unique
diagnostic of how mass and energy flow into and within the corona,
and CubIXSS addresses its science question through sensitive, precise
measurements of abundances of key trace ion species, whose spectral
signatures reveal the chromospheric or coronal origins of heated plasma
across the entire temperature range from ~1 to >30 MK. CubIXSS
measurements of the coronal temperature distribution and elemental
abundances directly address longstanding inconsistencies from prior
studies using instruments with limited, differing temperature and
composition sensitivities. CubIXSS comprises two co-optimized
and cross-calibrated instruments that fill a critical observational
gap: MOXSI, a novel diffractive spectral imager using a pinhole
camera and X-ray transmission diffraction grating for spectroscopy of
flares and active regions from 1 to 55 Å, with spectral and spatial
resolutions of 0.28-0.37 Å and 29-39 arcsec FWHM, respectively;
and SASS, a suite of four spatially-integrated off-the-shelf
spectrometers for high-cadence, high-sensitivity X-ray spectra from
0.5 to 50 keV, with spectral resolution of 0.06-0.5 keV FWHM across
that range. If selected for implementation, CubIXSS will launch
in late 2023 to mid-2024 to observe intense solar flares and active
regions during the rising phase and peak of the solar cycle. Its 1-year
prime mission is well timed with perihelia of Parker Solar Probe and
Solar Orbiter, and with the launches of complementary missions such
as the PUNCH Small Explorer. CubIXSS is a pathfinder for the next
generation of Explorer-class missions with improved capabilities for
SXR imaging spectroscopy. We present the CubIXSS motivating science
background, its suite of instruments and expected performances, and
other highlights from the completed Concept Study Report, including
novel analysis techniques to fully exploit the rich data set of CubIXSS
spectral observations.
Title: Are Potential Field Source Surface models from different
magnetic maps sufficiently robust to track the evolution of the
coronal magnetic topology?
Authors: Barnes, G.; DeRosa, M.; Jones, S.; Cheung, M.; Arge, C.;
Henney, C.
Bibcode: 2021AAS...23821308B
Altcode:
The geometry, connectivity, and topology of the large-scale coronal
magnetic field play a key role in determining whether a solar
reconnection event will result in an eruption, either by influencing
the location where magnetic reconnection releases energy for an event,
or by determining the pathways and access to open field that allow an
eruption to proceed. Knowing how reliably the coronal magnetic field
can be inferred is critical to understanding its role in energetic
events. Potential Field Source Surface (PFSS) models are a commonly
used tool for both modeling the coronal field itself, and as input
to other models. Multiple methods exist for generating the boundary
condition needed for a PFSS model. We present here results of examining
how robust the PFSS model topology is to different boundary maps, as
measured by the presence of coronal magnetic null points and solar wind
predictions from the Wang-Sheely-Arge (WSA) model, and characterize the
evolution of these null points within a given model. This material
is based upon work supported by NASA under award No. 80NSSC19K0087. Any
opinions, findings, and conclusions or recommendations expressed in
this material are those of the authors and do not necessarily reflect
the views of the National Aeronautics and Space Administration.
Title: Non-neutralized Electric Current Of Active Regions Explained
As A Projection Effect
Authors: Sun, X.; Cheung, M.
Bibcode: 2021AAS...23811308S
Altcode:
Active regions (ARs) often possess an observed net electric current in a
single magnetic polarity. We show that such "non-neutralized" currents
can arise from a geometric projection effect when a twisted flux tube
obliquely intersects the photosphere. To this end, we emulate surface
maps of an emerging AR by sampling horizontal slices of a semi-torus
flux tube at various heights. Although the tube has no net toroidal
current, its poloidal current, when projected along the vertical
direction, amounts to a significant non-neutralized component on the
surface. If the tube emerges only partially as in realistic settings,
the non-neutralized current will 1) develop as double ribbons near the
sheared polarity inversion line, 2) positively correlate with the twist,
and 3) reach its maximum before the magnetic flux. The projection
effect may be important to the photospheric current distribution,
in particular during the early stages of flux emergence.
Title: Sun-as-a-star Spectral Irradiance Observations: Milestone
For Characterizing The Stellar Active Regions
Authors: Toriumi, S.; Airapetian, V.; Hudson, H.; Schrijver, C.;
Cheung, M.; DeRosa, M.
Bibcode: 2021AAS...23820503T
Altcode:
For understanding the physical mechanism behind the solar flares, it
is crucial to measure the magnetic fields of active regions (ARs) from
the photosphere to the corona and investigate their scale, complexity,
and evolution. This is true for the stellar flares. However, it is
still difficult to spatially resolve the starspots, and one possible
way to probe their evolution and structure is to monitor the star in
multiple wavelengths. To test this possibility with the solar data,
we perform multi-wavelength irradiance monitoring of transiting solar
ARs by using full-disk observation data from SDO, Hinode, GOES, and
SORCE. As a result, we find, for instance, that the near UV light
curves show strong correlations with photospheric total magnetic flux
and that there are time lags between the coronal and photospheric light
curves when ARs are close to the limb, which together may enable one
to discern how high bright coronal loops extend above stellar ARs. It
is also revealed that the sub-MK (i.e. transition-region temperature)
EUV light curves are sometimes dimmed because the emission measure
is reduced owing to the heating over a wide area around the AR. These
results indicate that, by measuring the stellar light curves in multiple
wavelengths, we may obtain information on the structure and evolution
of stellar ARs.
Title: Homologous Explosive Activity Driven By The Collisional
Shearing Mechanism
Authors: Chintzoglou, G.; Cheung, M. C.
Bibcode: 2021AAS...23812709C
Altcode:
Active Regions (ARs) in their emergence phase are known to be more flare
productive and eruptive than ARs in their decay phase. In this work,
we focus on complex emerging ARs composed of multiple bipoles. Due
to the compact clustering of the different emerging bipoles within
such complex multipolar ARs, collision and shearing between opposite
non-conjugated polarities produce "collisional polarity inversion lines"
(cPILs) and drive rapid photospheric cancellation of magnetic flux. The
strength and the duration of the collision, shearing, and cancellation
are defined by the natural separation of the conjugated polarities
during the emergence phase of each bipole in the AR. This mechanism
is called "collisional shearing". In Chintzoglou et al (2019), it
was demonstrated that collisional shearing occurred in two emerging
flare- and CME-productive ARs (NOAA AR11158 and AR12017) by measuring
significant amounts of magnetic flux canceling at the cPIL. This
finding supported the formation and energization of magnetic flux ropes
before their eruption as CMEs and the associated flare activity. Here,
we provide additional evidence from HINODE observations that confirm
the occurrence of strong magnetic cancellation at the cPIL of these
ARs. In addition, we provide results from data-driven 3D modeling of the
coronal magnetic field, capturing the recurrent formation and eruption
of energized structures during the collisional shearing process. We
discuss our results in relation to flare and eruptive activity.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Stansby, David; Shih, Albert Y.; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet;
Panda, Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar,
Ankit; Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael
S; Konge, Sudarshan; Mueller, Michael; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Maloney, Shane;
Charlton, Michael; Mishra, Sashank; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Modi, Sanskar; Mason, James Paul; Sharma, Yash; Naman9639;
Zivadinovic, Lazar; Campos Rozo, Jose Ivan; Bobra, Monica G.; Manley,
Larry; Paul, Jeffrey Aaron; Ivashkiv, Kateryna; Chatterjee, Agneet;
Akira Stern, Kris; Von Forstner, Johan Freiherr; Bazán, Juanjo; Jain,
Sarthak; Evans, John; Ghosh, Sourav; Malocha, Michael; Stańczak,
Dominik; SophieLemos; Verma, Shresth; De Visscher, Ruben; Ranjan Singh,
Rajiv; Airmansmith97; Buddhika, Dumindu; Pathak, Himanshu; Alam, Arib;
Agrawal, Ankit; Sharma, Swapnil; Rideout, Jai Ram; Bates, Matt; Park,
Jongyeob; Mishra, Pankaj; Goel, Dhruv; Sharma, Deepankar; Taylor,
Garrison; Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta,
Mateo; Dacie, Sally; Dubey, Sanjeev; Parkhi, Utkarsh; Sidhu, Sudeep;
Surve, Rutuja; Eigenbrot, Arthur; Meszaros, Tomas; Bray, Erik M.;
Zahniy, Serge; Guennou, Chloé; Bose, Abhigyan; Ankit; Chicrala,
André; J, Amogh; D'Avella, Daniel; Ballew, Jordan; Price-Whelan,
Adrian; Robitaille, Thomas; Augspurger, Tom; Murphy, Nick; Lodha,
Priyank; Krishan, Yash; Pandey, Abhishek; Honey; Verma, Dipanshu;
Neerajkulk; Williams, Daniel; Wiedemann, Bernhard M.; Kothari, Yash;
Mridulpandey; Habib, Ishtyaq; Molina, Carlos; Mampaey, Benjamin;
Streicher, Ole; Nomiya, Yukie; Gomillion, Reid; Letts, Joseph; Bhope,
Adwait; Hill, Andrew; Keşkek, Duygu; Ranjan, Kritika; Pereira,
Tiago M. D.; Kien Dang, Trung; Bankar, Varun; Bahuleyan, Abijith; B,
Abijith; Stevens, Abigail L.; Agrawal, Yudhik; Nakul-Shahdadpuri;
Ghosh, Koustav; Hiware, Kaustubh; Yasintoda; Krishna, Kalpesh;
Lyes, MOULOUDI Mohamed; Mangaonkar, Manas; Cheung, Mark; Platipo;
Buitrago-Casas, Juan Camilo; Mendero, Matthew; Dedhia, Megh; Wimbish,
Jaylen; Calixto, James; Babuschkin, Igor; Schoentgen, Mickaël; Mathur,
Harsh; Kumar, Gulshan; Verstringe, Freek; Mackenzie Dover, Fionnlagh;
Tollerud, Erik; Gyenge, Norbert G; Arias, Emmanuel; Reddy Mekala,
Rajasekhar; MacBride, Conor; Das, Ratul; Mishra, Rishabh; Stone,
Brandon; Resakra; Agarwal, Samriddhi; Chaudhari, Kaustubh; Kustov,
Arseniy; Smith, Arfon; Srikanth, Shashank; Jain, Shubham; Mehrotra,
Ambar; Singh Gaba, Amarjit; Kannojia, Swapnil; Yadav, Tannmay; Paul,
Tathagata; Wilkinson, Tessa D.; Caswell, Thomas A; Murray, Sophie A.
Bibcode: 2021zndo...4762113M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: Coupling a Global Heliospheric Magnetohydrodynamic Model to
a Magnetofrictional Model of the Low Corona
Authors: Hayashi, Keiji; Abbett, William P.; Cheung, Mark C. M.;
Fisher, George H.
Bibcode: 2021ApJS..254....1H
Altcode:
Recent efforts coupling our Sun-to-Earth magnetohydrodynamics (MHD)
model and lower-corona magnetofrictional (MF) model are described. Our
Global Heliospheric MHD (GHM) model uses time-dependent three-component
magnetic field data from the lower-corona MF model as time-dependent
boundary values. The MF model uses data-assimilation techniques to
introduce the vector magnetic field data from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager, hence as a whole this
simulation coupling structure is driven with actual observations. The
GHM model employs a newly developed interface boundary treatment that
is based on the concept of characteristics, and it properly treats
the interface boundary sphere set at a height of the sub-Alfvénic
lower corona (1.15 R⊙ in this work). The coupled model
framework numerically produces twisted nonpotential magnetic features
and consequent eruption events in the solar corona in response to the
time-dependent boundary values. The combination of our two originally
independently developed models presented here is a model framework
toward achieving further capabilities of modeling the nonlinear
time-dependent nature of magnetic field and plasma, from small-scale
solar active regions to large-scale solar wind structures. This work is
a part of the Coronal Global Evolutionary Model project for enhancing
our understanding of Sun-Earth physics to help improve space weather
capabilities.
Title: Multichannel autocalibration for the Atmospheric Imaging
Assembly using machine learning
Authors: Dos Santos, Luiz F. G.; Bose, Souvik; Salvatelli, Valentina;
Neuberg, Brad; Cheung, Mark C. M.; Janvier, Miho; Jin, Meng; Gal,
Yarin; Boerner, Paul; Baydin, Atılım Güneş
Bibcode: 2021A&A...648A..53D
Altcode: 2020arXiv201214023D
Context. Solar activity plays a quintessential role in affecting the
interplanetary medium and space weather around Earth. Remote-sensing
instruments on board heliophysics space missions provide a pool of
information about solar activity by measuring the solar magnetic
field and the emission of light from the multilayered, multithermal,
and dynamic solar atmosphere. Extreme-UV (EUV) wavelength observations
from space help in understanding the subtleties of the outer layers
of the Sun, that is, the chromosphere and the corona. Unfortunately,
instruments such as the Atmospheric Imaging Assembly (AIA) on board
the NASA Solar Dynamics Observatory (SDO), suffer from time-dependent
degradation that reduces their sensitivity. The current best calibration
techniques rely on flights of sounding rockets to maintain absolute
calibration. These flights are infrequent, complex, and limited to
a single vantage point, however.
Aims: We aim to develop a
novel method based on machine learning (ML) that exploits spatial
patterns on the solar surface across multiwavelength observations to
autocalibrate the instrument degradation.
Methods: We established
two convolutional neural network (CNN) architectures that take either
single-channel or multichannel input and trained the models using the
SDOML dataset. The dataset was further augmented by randomly degrading
images at each epoch, with the training dataset spanning nonoverlapping
months with the test dataset. We also developed a non-ML baseline model
to assess the gain of the CNN models. With the best trained models,
we reconstructed the AIA multichannel degradation curves of 2010-2020
and compared them with the degradation curves based on sounding-rocket
data.
Results: Our results indicate that the CNN-based models
significantly outperform the non-ML baseline model in calibrating
instrument degradation. Moreover, multichannel CNN outperforms
the single-channel CNN, which suggests that cross-channel relations
between different EUV channels are important to recover the degradation
profiles. The CNN-based models reproduce the degradation corrections
derived from the sounding-rocket cross-calibration measurements
within the experimental measurement uncertainty, indicating that
it performs equally well as current techniques.
Conclusions:
Our approach establishes the framework for a novel technique based
on CNNs to calibrate EUV instruments. We envision that this technique
can be adapted to other imaging or spectral instruments operating at
other wavelengths.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Shih, Albert Y.; Stansby, David; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet;
Panda, Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar,
Ankit; Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael
S; Mueller, Michael; Konge, Sudarshan; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Charlton, Michael;
Mishra, Sashank; Maloney, Shane; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Mason, James Paul; Modi, Sanskar; Sharma, Yash; Zivadinovic,
Lazar; Naman9639; Campos Rozo, Jose Ivan; Manley, Larry; Bobra,
Monica G.; Chatterjee, Agneet; Ivashkiv, Kateryna; Von Forstner,
Johan Freiherr; Bazán, Juanjo; Akira Stern, Kris; Evans, John; Jain,
Sarthak; Malocha, Michael; Ghosh, Sourav; Airmansmith97; Stańczak,
Dominik; Ranjan Singh, Rajiv; De Visscher, Ruben; Verma, Shresth;
SophieLemos; Agrawal, Ankit; Alam, Arib; Buddhika, Dumindu; Pathak,
Himanshu; Rideout, Jai Ram; Sharma, Swapnil; Park, Jongyeob; Bates,
Matt; Mishra, Pankaj; Sharma, Deepankar; Goel, Dhruv; Taylor, Garrison;
Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta, Mateo;
Dacie, Sally; Dubey, Sanjeev; Eigenbrot, Arthur; Bray, Erik M.; Paul,
Jeffrey Aaron; Surve, Rutuja; Zahniy, Serge; Sidhu, Sudeep; Meszaros,
Tomas; Parkhi, Utkarsh; Bose, Abhigyan; Pandey, Abhishek; Price-Whelan,
Adrian; J, Amogh; Chicrala, André; Ankit; Guennou, Chloé; D'Avella,
Daniel; Williams, Daniel; Verma, Dipanshu; Ballew, Jordan; Murphy,
Nick; Lodha, Priyank; Robitaille, Thomas; Augspurger, Tom; Krishan,
Yash; Honey; Neerajkulk; Hill, Andrew; Mampaey, Benjamin; Wiedemann,
Bernhard M.; Molina, Carlos; Keşkek, Duygu; Habib, Ishtyaq; Letts,
Joseph; Streicher, Ole; Gomillion, Reid; Kothari, Yash; Mridulpandey;
Stevens, Abigail L.; B, Abijith; Bahuleyan, Abijith; Mehrotra, Ambar;
Smith, Arfon; Kustov, Arseniy; Stone, Brandon; MacBride, Conor; Arias,
Emmanuel; Tollerud, Erik; Mackenzie Dover, Fionnlagh; Verstringe,
Freek; Kumar, Gulshan; Mathur, Harsh; Babuschkin, Igor; Calixto,
James; Wimbish, Jaylen; Buitrago-Casas, Juan Camilo; Krishna, Kalpesh;
Hiware, Kaustubh; Ghosh, Koustav; Ranjan, Kritika; Mangaonkar, Manas;
Cheung, Mark; Mendero, Matthew; Schoentgen, Mickaël; Gyenge, Norbert
G; Reddy Mekala, Rajasekhar; Mishra, Rishabh; Srikanth, Shashank;
Jain, Shubham; Kannojia, Swapnil; Yadav, Tannmay; Paul, Tathagata;
Wilkinson, Tessa D.; Caswell, Thomas A; Pereira, Tiago M. D.; Kien
Dang, Trung; Agrawal, Yudhik; Nakul-Shahdadpuri; Platipo; Resakra;
Yasintoda; Murray, Sophie A.
Bibcode: 2021zndo...4641821M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Shih, Albert Y.; Stansby, David; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David; I.,
Vishnunarayan K; Hayes, Laura; Chakraborty, Pritish; Inglis, Andrew;
Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh; Leonard,
Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet; Panda,
Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar, Ankit;
Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael S;
Mueller, Michael; Konge, Sudarshan; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Charlton, Michael;
Mishra, Sashank; Maloney, Shane; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Mason, James Paul; Modi, Sanskar; Sharma, Yash; Zivadinovic,
Lazar; Naman9639; Campos Rozo, Jose Ivan; Manley, Larry; Bobra,
Monica G.; Chatterjee, Agneet; Ivashkiv, Kateryna; von Forstner,
Johan Freiherr; Bazán, Juanjo; Akira Stern, Kris; Evans, John; Jain,
Sarthak; Malocha, Michael; Ghosh, Sourav; Airmansmith97; Stańczak,
Dominik; Ranjan Singh, Rajiv; De Visscher, Ruben; Verma, Shresth;
SophieLemos; Agrawal, Ankit; Alam, Arib; Buddhika, Dumindu; Pathak,
Himanshu; Rideout, Jai Ram; Sharma, Swapnil; Park, Jongyeob; Bates,
Matt; Mishra, Pankaj; Sharma, Deepankar; Goel, Dhruv; Taylor, Garrison;
Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta, Mateo;
Dacie, Sally; Dubey, Sanjeev; Eigenbrot, Arthur; Bray, Erik M.; Paul,
Jeffrey Aaron; Surve, Rutuja; Zahniy, Serge; Sidhu, Sudeep; Meszaros,
Tomas; Parkhi, Utkarsh; Bose, Abhigyan; Pandey, Abhishek; Price-Whelan,
Adrian; J, Amogh; Chicrala, André; Ankit; Guennou, Chloé; D'Avella,
Daniel; Williams, Daniel; Verma, Dipanshu; Ballew, Jordan; Murphy,
Nick; Lodha, Priyank; Robitaille, Thomas; Augspurger, Tom; Krishan,
Yash; honey; neerajkulk; Hill, Andrew; Mampaey, Benjamin; Wiedemann,
Bernhard M.; Molina, Carlos; Keşkek, Duygu; Habib, Ishtyaq; Letts,
Joseph; Streicher, Ole; Gomillion, Reid; Kothari, Yash; mridulpandey;
Stevens, Abigail L.; B, Abijith; Bahuleyan, Abijith; Mehrotra, Ambar;
Smith, Arfon; Kustov, Arseniy; Stone, Brandon; MacBride, Conor; Arias,
Emmanuel; Tollerud, Erik; Mackenzie Dover, Fionnlagh; Verstringe,
Freek; Kumar, Gulshan; Mathur, Harsh; Babuschkin, Igor; Calixto,
James; Wimbish, Jaylen; Buitrago-Casas, Juan Camilo; Krishna, Kalpesh;
Hiware, Kaustubh; Ghosh, Koustav; Ranjan, Kritika; Mangaonkar, Manas;
Cheung, Mark; Mendero, Matthew; Schoentgen, Mickaël; Gyenge, Norbert
G; Reddy Mekala, Rajasekhar; Mishra, Rishabh; Srikanth, Shashank;
Jain, Shubham; Kannojia, Swapnil; Yadav, Tannmay; Paul, Tathagata;
Wilkinson, Tessa D.; Caswell, Thomas A; Pereira, Tiago M. D.; Kien
Dang, Trung; Agrawal, Yudhik; nakul-shahdadpuri; platipo; resakra;
yasintoda; Murray, Sophie A.
Bibcode: 2021zndo...4580466M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: Sun-as-a-star Multi-wavelength Observations: A Milestone for
Characterization of Stellar Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2021csss.confE..46T
Altcode:
It has been revealed that "superflares" can occur on solar-type
stars. The magnetic energy of the flares is likely to be stored in
active-region atmospheres. Therefore, to explain the energy storage and
occurrence of the flares, it is important to monitor the evolutions of
the active regions, not only in visible light but also in ultraviolet
(UV) and X-rays. To demonstrate this, we perform multi-wavelength
irradiance monitoring of transiting solar active regions by using
full-disk observation data. As a result of this sun-as-a-star spectral
irradiance analysis, we confirm that the visible continuum that
corresponds to the photosphere becomes darkened when the spot is at the
central meridian, whereas most of the UV, EUV and X-rays, which are
sensitive to chromospheric to coronal temperatures, are brightened,
reflecting the bright magnetic features above the starspots. The
time lags between the coronal and photospheric light curves have
the potential to probe the extent of coronal magnetic fields above
the starspots. These results indicate that, by measuring the stellar
light curves in multiple wavelengths, we may obtain information on
the structures and evolution of stellar active regions.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Shih, Albert Y.; Stansby, David; Hughitt,
V. Keith; Ryan, Daniel F.; Liedtke, Simon; Pérez-Suárez, David;
Vishnunarayan K, I.; Hayes, Laura; Chakraborty, Pritish; Inglis,
Andrew; Pattnaik, Punyaslok; Sipőcz, Brigitta; Sharma, Rishabh;
Leonard, Andrew; Hewett, Russell; Hamilton, Alex; Manhas, Abhijeet;
Panda, Asish; Earnshaw, Matt; Barnes, Will; Choudhary, Nitin; Kumar,
Ankit; Singh, Raahul; Chanda, Prateek; Akramul Haque, Md; Kirk, Michael
S; Mueller, Michael; Konge, Sudarshan; Srivastava, Rajul; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Charlton, Michael;
Mishra, Sashank; Maloney, Shane; Chorley, Nicky; Himanshu; Chouhan,
Aryan; Mason, James Paul; Modi, Sanskar; Sharma, Yash; Zivadinovic,
Lazar; Naman9639; Campos Rozo, Jose Ivan; Manley, Larry; Bobra,
Monica G.; Chatterjee, Agneet; Ivashkiv, Kateryna; Von Forstner,
Johan Freiherr; Bazán, Juanjo; Akira Stern, Kris; Evans, John; Jain,
Sarthak; Malocha, Michael; Ghosh, Sourav; Airmansmith97; Stańczak,
Dominik; Ranjan Singh, Rajiv; De Visscher, Ruben; Verma, Shresth;
SophieLemos; Agrawal, Ankit; Alam, Arib; Buddhika, Dumindu; Pathak,
Himanshu; Rideout, Jai Ram; Sharma, Swapnil; Park, Jongyeob; Bates,
Matt; Mishra, Pankaj; Sharma, Deepankar; Goel, Dhruv; Taylor, Garrison;
Cetusic, Goran; Reiter, Guntbert; Jacob; Inchaurrandieta, Mateo;
Dacie, Sally; Dubey, Sanjeev; Eigenbrot, Arthur; Bray, Erik M.; Paul,
Jeffrey Aaron; Surve, Rutuja; Zahniy, Serge; Sidhu, Sudeep; Meszaros,
Tomas; Parkhi, Utkarsh; Bose, Abhigyan; Pandey, Abhishek; Price-Whelan,
Adrian; J, Amogh; Chicrala, André; Ankit; Guennou, Chloé; D'Avella,
Daniel; Williams, Daniel; Verma, Dipanshu; Ballew, Jordan; Murphy,
Nick; Lodha, Priyank; Robitaille, Thomas; Augspurger, Tom; Krishan,
Yash; Honey; Neerajkulk; Hill, Andrew; Mampaey, Benjamin; Wiedemann,
Bernhard M.; Molina, Carlos; Keşkek, Duygu; Habib, Ishtyaq; Letts,
Joseph; Streicher, Ole; Gomillion, Reid; Kothari, Yash; Mridulpandey;
Stevens, Abigail L.; B, Abijith; Bahuleyan, Abijith; Mehrotra, Ambar;
Smith, Arfon; Kustov, Arseniy; Stone, Brandon; MacBride, Conor; Arias,
Emmanuel; Tollerud, Erik; Mackenzie Dover, Fionnlagh; Verstringe,
Freek; Kumar, Gulshan; Mathur, Harsh; Babuschkin, Igor; Calixto,
James; Wimbish, Jaylen; Buitrago-Casas, Juan Camilo; Krishna, Kalpesh;
Hiware, Kaustubh; Ghosh, Koustav; Ranjan, Kritika; Mangaonkar, Manas;
Cheung, Mark; Mendero, Matthew; Schoentgen, Mickaël; Gyenge, Norbert
G; Reddy Mekala, Rajasekhar; Mishra, Rishabh; Srikanth, Shashank;
Jain, Shubham; Kannojia, Swapnil; Yadav, Tannmay; Paul, Tathagata;
Wilkinson, Tessa D.; Caswell, Thomas A; Pereira, Tiago M. D.; Kien
Dang, Trung; Agrawal, Yudhik; Nakul-Shahdadpuri; Platipo; Resakra;
Yasintoda; Murray, Sophie A.
Bibcode: 2021zndo...4555172M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: Global Earth Magnetic Field Modeling and Forecasting with
Spherical Harmonics Decomposition
Authors: Tigas, Panagiotis; Bloch, Téo; Upendran, Vishal; Ferdoushi,
Banafsheh; Cheung, Mark C. M.; Ganju, Siddha; McGranaghan, Ryan M.;
Gal, Yarin; Bhatt, Asti
Bibcode: 2021arXiv210201447T
Altcode:
Modeling and forecasting the solar wind-driven global magnetic
field perturbations is an open challenge. Current approaches
depend on simulations of computationally demanding models like the
Magnetohydrodynamics (MHD) model or sampling spatially and temporally
through sparse ground-based stations (SuperMAG). In this paper, we
develop a Deep Learning model that forecasts in Spherical Harmonics
space 2, replacing reliance on MHD models and providing global coverage
at one minute cadence, improving over the current state-of-the-art
which relies on feature engineering. We evaluate the performance in
SuperMAG dataset (improved by 14.53%) and MHD simulations (improved by
24.35%). Additionally, we evaluate the extrapolation performance of
the spherical harmonics reconstruction based on sparse ground-based
stations (SuperMAG), showing that spherical harmonics can reliably
reconstruct the global magnetic field as evaluated on MHD simulation.
Title: Plasma heating induced by tadpole-like downflows in the
flaring solar corona
Authors: Samanta, T.; Tian, H.; Chen, B.; Reeves, K. K.; Cheung,
M. C. M.; Vourlidas, A.; Banerjee, D.
Bibcode: 2021Innov...200083S
Altcode: 2021arXiv210314257S
As one of the most spectacular energy release events in the solar
system, solar flares are generally powered by magnetic reconnection in
the solar corona. As a result of the re-arrangement of magnetic field
topology after the reconnection process, a series of new loop-like
magnetic structures are often formed and are known as flare loops. A
hot diffuse region, consisting of around 5-10 MK plasma, is also
observed above the loops and is called a supra-arcade fan. Often,
dark, tadpole-like structures are seen to descend through the bright
supra-arcade fans. It remains unclear what role these so-called
supra-arcade downflows (SADs) play in heating the flaring coronal
plasma. Here we show a unique flare observation, where many SADs collide
with the flare loops and strongly heat the loops to a temperature
of 10-20 MK. Several of these interactions generate clear signatures
of quasi-periodic enhancement in the full-Sun-integrated soft X-ray
emission, providing an alternative interpretation for quasi-periodic
pulsations that are commonly observed during solar and stellar flares.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Hughitt, V. Keith; Shih, Albert Y.; Ryan,
Daniel F.; Liedtke, Simon; Stansby, David; Pérez-Suárez, David;
Vishnunarayan K, I.; Chakraborty, Pritish; Inglis, Andrew; Pattnaik,
Punyaslok; Sipőcz, Brigitta; Hayes, Laura; Sharma, Rishabh; Leonard,
Andrew; Hewett, Russell; Hamilton, Alex; Panda, Asish; Earnshaw,
Matt; Choudhary, Nitin; Kumar, Ankit; Singh, Raahul; Barnes, Will;
Chanda, Prateek; Akramul Haque, Md; Kirk, Michael S; Konge, Sudarshan;
Mueller, Michael; Srivastava, Rajul; Manhas, Abhijeet; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Charlton, Michael;
Maloney, Shane; Mishra, Sashank; Chorley, Nicky; Himanshu; Modi,
Sanskar; Mason, James Paul; Sharma, Yash; Naman9639; Bobra, Monica G.;
Campos Rozo, Jose Ivan; Manley, Larry; Chatterjee, Agneet; Bazán,
Juanjo; Jain, Sarthak; Evans, John; Ghosh, Sourav; Malocha, Michael;
De Visscher, Ruben; Ranjan Singh, Rajiv; Stańczak, Dominik; Verma,
Shresth; Airmansmith97; Agrawal, Ankit; Buddhika, Dumindu; Pathak,
Himanshu; Sharma, Swapnil; Alam, Arib; Bates, Matt; Park, Jongyeob;
Mishra, Pankaj; Rideout, Jai Ram; Sharma, Deepankar; Dubey, Sanjeev;
Inchaurrandieta, Mateo; Reiter, Guntbert; Goel, Dhruv; Dacie, Sally;
Jacob; Cetusic, Goran; Taylor, Garrison; Meszaros, Tomas; Bray,
Erik M.; Eigenbrot, Arthur; Zahniy, Serge; Zivadinovic, Lazar;
Parkhi, Utkarsh; Robitaille, Thomas; J, Amogh; Chicrala, André;
Ankit; Guennou, Chloé; D'Avella, Daniel; Williams, Daniel; Ballew,
Jordan; Murphy, Nick; Lodha, Priyank; Surve, Rutuja; Bose, Abhigyan;
Augspurger, Tom; Krishan, Yash; Neerajkulk; Habib, Ishtyaq; Letts,
Joseph; Kothari, Yash; Keşkek, Duygu; Honey; Molina, Carlos;
Streicher, Ole; Gomillion, Reid; Wiedemann, Bernhard M.; Mampaey,
Benjamin; Hill, Andrew; Akira Stern, Kris; Mittal, Gulshan; Verstringe,
Freek; Mackenzie Dover, Fionnlagh; Arias, Emmanuel; Stone, Brandon;
Kannojia, Swapnil; Kustov, Arseniy; Yadav, Tannmay; Wilkinson, Tessa
D.; Pereira, Tiago M. D.; Mridulpandey; Smith, Arfon; Kien Dang, Trung;
Mehrotra, Ambar; Price-Whelan, Adrian; B, Abijith; Yasintoda; Stevens,
Abigail L.; Agrawal, Yudhik; Gyenge, Norbert; Schoentgen, Mickaël;
Abijith-Bahuleyan; Mendero, Matthew; Mangaonkar, Manas; Cheung, Mark;
Reddy Mekala, Rajasekhar; Hiware, Kaustubh; Mishra, Rishabh; Krishna,
Kalpesh; Buitrago-Casas, Juan Camilo; Shashank, S; Wimbish, Jaylen;
Calixto, James; Babuschkin, Igor; Mathur, Harsh; Srikanth, Shashank;
Jamescalixto; Kumar, Gulshan; Gyenge, Norbert G; Murray, Sophie A.
Bibcode: 2021zndo...4421322M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: Coronal observations with the Multi-Slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Lemen, James; Cheung, Mark; Boerner, Paul
Bibcode: 2021cosp...43E1803D
Altcode:
Observations of the corona are key to constrain magnetic field
models of the solar atmosphere. In this abstract we describe novel
observations that will be enabled by the Multi-Slit Solar Explorer
(MUSE), a proposed MIDEX mission for studying the dynamics of the
corona and transition region. MUSE will use both conventional and novel
spectral imaging techniques, coupled to state-of-the-art numerical
modeling. MUSE will obtain EUV spectra and images with the highest
resolution in space (1/3 arcsec) and time (1-4 s) ever achieved for
the transition region and corona, along 37 slits and a large context
FOV simultaneously. The science goals of MUSE are to understand the
physical mechanisms responsible for energy release in the corona
and for driving flares and coronal mass ejections. MUSE contains two
instruments: an EUV spectrograph and an EUV context imager. The MUSE
spectrograph employs a novel multi-slit design that enables a 100x
improvement in spectral scanning rates, which will reveal crucial
information about the dynamics of the physical processes that are not
observable with current instruments. MUSE will provide key constraints
on the morphology and dynamics of the magnetic field. We will discuss
the MUSE design and how it has been optimized to minimize effects
from overlapping spectra dispersed from different slits. We will also
illustrate how MUSE observations will lead to a better understanding
of how the dynamic magnetic field drives flares and eruptions.
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Determine Coronal Magnetic Field
Evolution
Authors: Kazachenko, Maria; Abbett, Bill; Liu, Yang; Fisher, George;
Welsch, Brian; Bercik, Dave; DeRosa, Marc; Cheung, Mark; Sun, Xudong;
Hoeksema, J. Todd; Erkka Lumme, .; Hayashi, Keiji; Lynch, Benjamin
Bibcode: 2021cosp...43E1785K
Altcode:
The Coronal Global Evolutionary Model (CGEM) provides data-driven
simulations of the magnetic field in the solar corona to better
understand the build-up of magnetic energy that leads to eruptive
events. The CGEM project has developed six capabilities. CGEM modules
(1) prepare time series of full-disk vector magnetic field observations
to (2) derive the changing electric field in the solar photosphere over
active-region scales. This local electric field is (3) incorporated
into a surface flux transport model that reconstructs a global
electric field that evolves magnetic flux in a consistent way. These
electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
either at high resolution over a restricted range of solid angles or
at lower resolution over a global domain to determine the magnetic
field and current density in the low corona. An SMF-generated initial
field above an active region and the evolving electric field at the
photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
simulations of active regions in the low corona. SMF or MHD solutions
are then used to compute emissivity proxies that can be compared
with coronal observations. Finally, a lower-resolution SMF magnetic
field is used to initialize (6) a global MHD model that is driven by
an SMF electric field time series to simulate the outer corona and
heliosphere, ultimately connecting Sun to Earth. As a demonstration,
this report features results of CGEM applied to observations of the
evolution of NOAA Active Region 11158 in 2011 February.
Title: Using artificial intelligence to augment science prioritization
Authors: Barbier, Louis; Cheung, Mark; Thronson, Harley; Mason, James;
Green, James; Thomas, Brian; Adrian, Andrew; Memarsadeghi, Nargess;
Varsi, Giulio; Lowndes, Alison; Samadi, Shahin
Bibcode: 2021cosp...43E1526B
Altcode:
The rapidly growing capabilities of Artificial Intelligence (AI)
appear able to improve significantly the current processes for science
prioritization by American government agencies. We report here on
our progress in applying AI to augment in particular the US National
Academies' Decadal Surveys. Science funding agencies in the US (NASA,
Department of Energy, and National Science Foundation), the science
community, and the US taxpayer have all benefited enormously from the
several-decade series of National Academies' Decadal Surveys. These
Surveys are one of the primary means whereby these federal agencies may
align multiyear strategic priorities and funding to guide the scientific
community. They comprise highly regarded Subject Matter Experts (SMEs)
whose goal is to develop a set of science and program priorities
that are recommended for major investments in the subsequent 10+
years. The SMEs do this using both their own professional knowledge
and by synthesizing details from many thousands of existing and
solicited documents. Congress, the relevant government funding
agencies, and the scientific community have placed great respect and
value on these recommendations. Consequently, any significant changes
to the process of determining these recommendations should be done
cautiously and scrutinized carefully. That said, we believe that there
is currently sufficient experience, albeit often preliminary, to justify
a trial application of AI to science and technology prioritization via
augmentation of existing processes. We will present our application of
AI to aid the Decadal Survey panel in prioritizing science objectives
using AI techniques that are being applied elsewhere in long-range
planning and prioritization. At present, our concentration is on using
AI algorithms to assess the very large body of published research,
as well as observational data. We strongly emphasize that while AI can
assist a mass review of papers, the decision-making and interpretation
remains with humans. In our presentation we will summarize the case for
using AI in this manner and report on a workshop held in the US that
brought together AI experts and practicing scientists to discuss this
process and its applications. The workshop focuses on advances of AI
and more specifically Machine Learning for the purpose of predicting
scientific trends from the canvassing of the large opus of published
work and archival data. Further, it explores how recent advances in AI
support these predictions. Finally, the workshop identifies compelling
scientific queries to be proposed as simple "test cases" in order
to properly validate the potential usefulness of such algorithms for
assisting humans' strategic planning.
Title: Monitoring of Solar Soft X-ray Emission with NASA's Solar
Dynamics Observatory
Authors: Shirman, Nina; Cheung, Mark
Bibcode: 2021cosp...43E.918S
Altcode:
Since its launch in 2010, NASA's Solar Dynamics Observatory (SDO)
has been continuously monitoring the Sun for progenitors of space
weather. SDO's Atmospheric Imaging Assembly (AIA) has captured more
than 200 million full disk ultraviolet (UV) and extreme UV (EUV)
images of the Sun. Validated differential emission measure (DEM)
inversion algorithms are now available to estimate the multi-thermal
distribution of coronal plasma up to tens of mega-Kelvins (see Cheung
et al. 2015; Su et al. 2018). In this work, we show how AIA-derived
DEMs can be used to generate proxy measurements of solar soft X-ray
emission, such as from the GOES X-ray sensors (XRS). The relative
good match with ground truth GOES measurements suggests AIA may act
as a proxy X-ray imaging instrument. This would allow unambiguous
association of peaks in GOES-measured X-ray fluxes with their sources
on the Sun. Implications for space climate studies will be discussed.
Title: The Action of the Collisional Shearing Mechanism in Complex
Emerging and Developing Active Regions Revealed by SDO and Hinode
Observations and Data-Driven Modeling
Authors: Chintzoglou, Georgios; Cheung, Mark
Bibcode: 2021cosp...43E.991C
Altcode:
Active Regions (ARs) in their emergence phase are known to be more flare
productive and eruptive than ARs in their decay phase. In this work,
we focus on complex emerging ARs composed of multiple bipoles. Due
to the compact clustering of the different emerging bipoles within
such complex multipolar ARs, collision and shearing between opposite
non-conjugated polarities produces "collisional polarity inversion
lines" (cPILs) and drives rapid photospheric cancellation of magnetic
flux. The strength and the duration of the collision, shearing, and
cancellation is defined by the natural separation of the conjugated
polarities during the emergence phase of each bipole in the AR. This
mechanism is called "collisional shearing". In Chintzoglou et al (2019),
it was demonstrated that collisional shearing occurred in two emerging
flare- and CME-productive ARs (NOAA AR11158 and AR12017) by measuring
significant amounts of magnetic flux cancelling at the cPIL. This
finding supported the formation and energization of magnetic flux ropes
before their eruption as CMEs and the associated flare activity. Here,
we provide additional evidence from HINODE observations that confirm
the occurrence of strong magnetic cancellation at the cPIL of these
ARs. In addition, we provide results from data-driven 3D modeling of
the coronal magnetic field, capturing the formation and evolution of
the energized structures during the collisional shearing process. We
discuss our results in relation to flare and eruptive activity.
Title: Non-Neutralized Electric Current of Active Regions Explained
as a Projection Effect
Authors: Sun, Xudong; Cheung, Mark C. M.
Bibcode: 2021SoPh..296....7S
Altcode: 2020arXiv201111873S
Active regions (ARs) often possess an observed net electric current in a
single magnetic polarity. We show that such "non-neutralized" currents
can arise from a geometric projection effect when a twisted flux tube
obliquely intersects the photosphere. To this end, we emulate surface
maps of an emerging AR by sampling horizontal slices of a semi-torus
flux tube at various heights. Although the tube has no net toroidal
current, its poloidal current, when projected along the vertical
direction, amounts to a significant non-neutralized component on the
surface. If the tube emerges only partially as in realistic settings,
the non-neutralized current will 1) develop as double ribbons near
the sheared polarity inversion line, (2) positively correlate with the
twist, and 3) reach its maximum before the magnetic flux. The projection
effect may be important to the photospheric current distribution,
in particular during the early stages of flux emergence.
Title: Flare simulations with the MURaM radiative MHD code
Authors: Rempel, Matthias; Cheung, Mark; Chintzoglou, Georgios
Bibcode: 2021cosp...43E1772R
Altcode:
Over the past few years the MURaM radiative MHD code was expanded
for its capability to simulate the coupled solar atmosphere from the
upper convection zone into the lower solar corona. The code includes
the essential physics to synthesize thermal emission ranging from
the visible spectrum in the photosphere to EUV and soft X-ray from
transition region and corona. A more sophisticated treatment of the
chromosphere is currently under development. After a brief review of
the code's capabilities and limitations we present a new setup that
allows to create collisional polarity inversion lines (cPILs) and study
the coronal response including flares. In the setup we start with a
bipolar sunspot configuration and set the spots on collision course
by imposing the appropriate velocity field at the footpoints in the
subphotospheric boundary. We vary parameters such as the initial spot
separation, collision speed and collision distance. While all setups
lead to the formation of a sigmoid structure, only the cases with a
close passing of the spots cause flares and mass eruptions. The energy
release is in the $1-2\times 10^{31}$ erg range, putting the simulated
flares into the upper C to lower M-class range. While the case with the
more distant passing of the spots does not lead to a flare, the corona
is nonetheless substantially heated, suggesting non-eruptive energy
release mechanisms. We discuss the applicability/implications of our
setups for investigating the way cPILs form and produce eruptions and
present preliminary results.
Title: aiapy
Authors: Barnes, W. T.; Cheung, M. C. M; Bobra, M. G.; Boerner, P. F.;
Chintzoglou, G.; Leonard, D.; Mumford, S. J.; Padmanabhan, N.; Shih,
A. Y.; Shirman, N.; Stansby, D.; Wright, P. J.
Bibcode: 2020zndo...4315741B
Altcode:
aiapy is a Python package for analyzing data from the Atmospheric
Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory
spacecraft.
Title: aiapy: A Python Package for Analyzing Solar EUV Image Data
from AIA
Authors: Barnes, W. T.; Cheung, M. C. M; Bobra, M. G.; Boerner, P. F.;
Chintzoglou, G.; Leonard, D.; Mumford, S. J.; Padmanabhan, N.; Shih,
A. Y.; Shirman, N.; Stansby, D.; Wright, P. J.
Bibcode: 2020zndo...4274931B
Altcode:
aiapy is a Python package for analyzing data from the Atmospheric
Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory
spacecraft.
Title: aiapy: A Python Package for Analyzing Solar EUV Image Data
from AIA
Authors: Barnes, Will; Cheung, Mark; Bobra, Monica; Boerner, Paul;
Chintzoglou, Georgios; Leonard, Drew; Mumford, Stuart; Padmanabhan,
Nicholas; Shih, Albert; Shirman, Nina; Stansby, David; Wright, Paul
Bibcode: 2020JOSS....5.2801B
Altcode:
No abstract at ADS
Title: Erratum: "A Machine-learning Data Set Prepared from the NASA
Solar Dynamics Observatory Mission" (2019, ApJS, 242, 7)
Authors: Galvez, Richard; Fouhey, David F.; Jin, Meng; Szenicer,
Alexandre; Muñoz-Jaramillo, Andrés; Cheung, Mark C. M.; Wright,
Paul J.; Bobra, Monica G.; Liu, Yang; Mason, James; Thomas, Rajat
Bibcode: 2020ApJS..250...38G
Altcode:
No abstract at ADS
Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2020ApJ...902...36T
Altcode: 2020arXiv200804319T
Major solar flares are prone to occur in active-region (AR) atmospheres
associated with large, complex, dynamically evolving sunspots. This
points to the importance of monitoring the evolution of starspots,
not only in visible but also in ultraviolet (UV) and X-rays, in
understanding the origin and occurrence of stellar flares. To this end,
we perform spectral irradiance analysis on different types of transiting
solar ARs by using a variety of full-disk synoptic observations. The
target events are an isolated sunspot, spotless plage, and emerging flux
in prolonged quiet-Sun conditions selected from the past decade. We find
that the visible continuum and total solar irradiance become darkened
when the spot is at the central meridian, whereas it is bright near
the solar limb; UV bands sensitive to the chromosphere correlate well
with the variation of total unsigned magnetic flux in the photosphere;
amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with
the characteristic temperature, whose light curves are flat-topped
due to their sensitivity to the optically thin corona; the transiting
spotless plage does not show the darkening in the visible irradiance,
while the emerging flux produces an asymmetry in all light curves about
the central meridian. The multiwavelength Sun-as-a-star study described
here indicates that the time lags between the coronal and photospheric
light curves have the potential to probe the extent of coronal magnetic
fields above the starspots. In addition, EUV wavelengths that are
sensitive to temperatures just below 1 MK sometimes show antiphased
variations, which may be used for diagnosing plasmas around starspots.
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Determine Coronal Magnetic Field
Evolution
Authors: Hoeksema, J. Todd; Abbett, William P.; Bercik, David J.;
Cheung, Mark C. M.; DeRosa, Marc L.; Fisher, George H.; Hayashi, Keiji;
Kazachenko, Maria D.; Liu, Yang; Lumme, Erkka; Lynch, Benjamin J.;
Sun, Xudong; Welsch, Brian T.
Bibcode: 2020ApJS..250...28H
Altcode: 2020arXiv200614579H
The Coronal Global Evolutionary Model (CGEM) provides data-driven
simulations of the magnetic field in the solar corona to better
understand the build-up of magnetic energy that leads to eruptive
events. The CGEM project has developed six capabilities. CGEM modules
(1) prepare time series of full-disk vector magnetic field observations
to (2) derive the changing electric field in the solar photosphere over
active-region scales. This local electric field is (3) incorporated
into a surface flux transport model that reconstructs a global
electric field that evolves magnetic flux in a consistent way. These
electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
either at high resolution over a restricted range of solid angles or
at lower resolution over a global domain to determine the magnetic
field and current density in the low corona. An SMF-generated initial
field above an active region and the evolving electric field at the
photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
simulations of active regions in the low corona. SMF or MHD solutions
are then used to compute emissivity proxies that can be compared
with coronal observations. Finally, a lower-resolution SMF magnetic
field is used to initialize (6) a global MHD model that is driven by
an SMF electric field time series to simulate the outer corona and
heliosphere, ultimately connecting Sun to Earth. As a demonstration,
this report features results of CGEM applied to observations of the
evolution of NOAA Active Region 11158 in 2011 February.
Title: Solar Wind Prediction Using Deep Learning
Authors: Upendran, Vishal; Cheung, Mark C. M.; Hanasoge, Shravan;
Krishnamurthi, Ganapathy
Bibcode: 2020SpWea..1802478U
Altcode: 2020arXiv200605825U
Emanating from the base of the Sun's corona, the solar wind fills the
interplanetary medium with a magnetized stream of charged particles
whose interaction with the Earth's magnetosphere has space weather
consequences such as geomagnetic storms. Accurately predicting the
solar wind through measurements of the spatiotemporally evolving
conditions in the solar atmosphere is important but remains an unsolved
problem in heliophysics and space weather research. In this work,
we use deep learning for prediction of solar wind (SW) properties. We
use extreme ultraviolet images of the solar corona from space-based
observations to predict the SW speed from the National Aeronautics and
Space Administration (NASA) OMNIWEB data set, measured at Lagragian
Point 1. We evaluate our model against autoregressive and naive
models and find that our model outperforms the benchmark models,
obtaining a best fit correlation of 0.55 ± 0.03 with the observed
data. Upon visualization and investigation of how the model uses data
to make predictions, we find higher activation at the coronal holes
for fast wind prediction (≈3 to 4 days prior to prediction), and
at the active regions for slow wind prediction. These trends bear an
uncanny similarity to the influence of regions potentially being the
sources of fast and slow wind, as reported in literature. This suggests
that our model was able to learn some of the salient associations
between coronal and solar wind structure without built-in physics
knowledge. Such an approach may help us discover hitherto unknown
relationships in heliophysics data sets.
Title: aiapy
Authors: Barnes, W. T.; Cheung, M. C. M; Padmanabhan, N.; Chintzoglou,
G.; Mumford, S.; Wright, P. J.; Shih, A. Y.; Bobra, M. G.; Shirman,
N.; Kocher, M.
Bibcode: 2020zndo...4016983B
Altcode:
aiapy is a Python package for analyzing data from the Atmospheric
Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory
spacecraft.
Title: SunPy
Authors: Mumford, Stuart J.; Freij, Nabil; Christe, Steven; Ireland,
Jack; Mayer, Florian; Hughitt, V. Keith; Shih, Albert Y.; Ryan,
Daniel F.; Liedtke, Simon; Stansby, David; Pérez-Suárez, David;
Vishnunarayan K, I.; Chakraborty, Pritish; Inglis, Andrew; Pattnaik,
Punyaslok; Sipőcz, Brigitta; Hayes, Laura; Sharma, Rishabh; Leonard,
Andrew; Hewett, Russell; Hamilton, Alex; Panda, Asish; Earnshaw,
Matt; Choudhary, Nitin; Kumar, Ankit; Singh, Raahul; Barnes, Will;
Chanda, Prateek; Akramul Haque, Md; Kirk, Michael S; Konge, Sudarshan;
Mueller, Michael; Srivastava, Rajul; Manhas, Abhijeet; Jain, Yash;
Bennett, Samuel; Baruah, Ankit; Arbolante, Quinn; Charlton, Michael;
Maloney, Shane; Mishra, Sashank; Chorley, Nicky; Himanshu; Modi,
Sanskar; Mason, James Paul; Sharma, Yash; Naman9639; Bobra, Monica G.;
Campos Rozo, Jose Ivan; Manley, Larry; Chatterjee, Agneet; Bazán,
Juanjo; Jain, Sarthak; Evans, John; Ghosh, Sourav; Malocha, Michael;
De Visscher, Ruben; Ranjan Singh, Rajiv; Stańczak, Dominik; Verma,
Shresth; Airmansmith97; Agrawal, Ankit; Buddhika, Dumindu; Pathak,
Himanshu; Sharma, Swapnil; Alam, Arib; Bates, Matt; Park, Jongyeob;
Mishra, Pankaj; Rideout, Jai Ram; Sharma, Deepankar; Dubey, Sanjeev;
Inchaurrandieta, Mateo; Reiter, Guntbert; Goel, Dhruv; Dacie, Sally;
Jacob; Cetusic, Goran; Taylor, Garrison; Meszaros, Tomas; Bray,
Erik M.; Eigenbrot, Arthur; Zahniy, Serge; Zivadinovic, Lazar;
Parkhi, Utkarsh; Robitaille, Thomas; J, Amogh; Chicrala, André;
Ankit; Guennou, Chloé; D'Avella, Daniel; Williams, Daniel; Ballew,
Jordan; Murphy, Nick; Lodha, Priyank; Surve, Rutuja; Bose, Abhigyan;
Augspurger, Tom; Krishan, Yash; Neerajkulk; Habib, Ishtyaq; Letts,
Joseph; Kothari, Yash; Keşkek, Duygu; Honey; Molina, Carlos;
Streicher, Ole; Gomillion, Reid; Wiedemann, Bernhard M.; Mampaey,
Benjamin; Hill, Andrew; Akira Stern, Kris; Mittal, Gulshan; Verstringe,
Freek; Mackenzie Dover, Fionnlagh; Arias, Emmanuel; Stone, Brandon;
Kannojia, Swapnil; Kustov, Arseniy; Yadav, Tannmay; Wilkinson, Tessa
D.; Pereira, Tiago M. D.; Mridulpandey; Smith, Arfon; Kien Dang, Trung;
Mehrotra, Ambar; Price-Whelan, Adrian; B, Abijith; Yasintoda; Stevens,
Abigail L.; Agrawal, Yudhik; Gyenge, Norbert; Schoentgen, Mickaël;
Abijith-Bahuleyan; Mendero, Matthew; Mangaonkar, Manas; Cheung, Mark;
Reddy Mekala, Rajasekhar; Hiware, Kaustubh; Mishra, Rishabh; Krishna,
Kalpesh; Buitrago-Casas, Juan Camilo; Shashank, S; Wimbish, Jaylen;
Calixto, James; Babuschkin, Igor; Mathur, Harsh; Srikanth, Shashank;
Jamescalixto; Kumar, Gulshan; Gyenge, Norbert G; Murray, Sophie A.
Bibcode: 2020zndo...3940415M
Altcode:
The community-developed, free and open-source solar data analysis
environment for Python.
Title: The PDFI_SS Electric Field Inversion Software
Authors: Fisher, George H.; Kazachenko, Maria D.; Welsch, Brian T.;
Sun, Xudong; Lumme, Erkka; Bercik, David J.; DeRosa, Marc L.; Cheung,
Mark C. M.
Bibcode: 2020ApJS..248....2F
Altcode: 2019arXiv191208301F
We describe the PDFI_SS software library, which is designed to
find the electric field at the Sun's photosphere from a sequence of
vector magnetogram and Doppler velocity measurements and estimates of
horizontal velocities obtained from local correlation tracking using the
recently upgraded Fourier Local Correlation Tracking code. The library,
a collection of FORTRAN subroutines, uses the "PDFI" technique described
by Kazachenko et al., but modified for use in spherical, Plate Carrée
geometry on a staggered grid. The domain over which solutions are found
is a subset of the global spherical surface, defined by user-specified
limits of colatitude and longitude. Our staggered grid approach, based
on that of Yee, is more conservative and self-consistent compared to
the centered, Cartesian grid used by Kazachenko et al. The library can
be used to compute an end-to-end solution for electric fields from data
taken by the HMI instrument aboard NASA's SDO mission. This capability
has been incorporated into the HMI pipeline processing system operating
at SDO's Joint Science Operations Center. The library is written in a
general and modular way so that the calculations can be customized to
modify or delete electric field contributions, or used with other data
sets. Other applications include "nudging" numerical models of the solar
atmosphere to facilitate assimilative simulations. The library includes
an ability to compute "global" (whole-Sun) electric field solutions. The
library also includes an ability to compute potential magnetic field
solutions in spherical coordinates. This distribution includes a number
of test programs that allow the user to test the software.
Title: Comparative Study of Data-driven Solar Coronal Field Models
Using a Flux Emergence Simulation as a Ground-truth Data Set
Authors: Toriumi, Shin; Takasao, Shinsuke; Cheung, Mark C. M.; Jiang,
Chaowei; Guo, Yang; Hayashi, Keiji; Inoue, Satoshi
Bibcode: 2020ApJ...890..103T
Altcode: 2020arXiv200103721T
For a better understanding of the magnetic field in the solar corona
and dynamic activities such as flares and coronal mass ejections, it
is crucial to measure the time-evolving coronal field and accurately
estimate the magnetic energy. Recently, a new modeling technique called
the data-driven coronal field model, in which the time evolution of
magnetic field is driven by a sequence of photospheric magnetic and
velocity field maps, has been developed and revealed the dynamics
of flare-productive active regions. Here we report on the first
qualitative and quantitative assessment of different data-driven
models using a magnetic flux emergence simulation as a ground-truth
(GT) data set. We compare the GT field with those reconstructed from
the GT photospheric field by four data-driven algorithms. It is found
that, at minimum, the flux rope structure is reproduced in all coronal
field models. Quantitatively, however, the results show a certain
degree of model dependence. In most cases, the magnetic energies and
relative magnetic helicity are comparable to or at most twice of the GT
values. The reproduced flux ropes have a sigmoidal shape (consistent
with GT) of various sizes, a vertically standing magnetic torus, or
a packed structure. The observed discrepancies can be attributed to
the highly non-force-free input photospheric field, from which the
coronal field is reconstructed, and to the modeling constraints such
as the treatment of background atmosphere, the bottom boundary setting,
and the spatial resolution.
Title: The Multi-slit Approach to Coronal Spectroscopy with the
Multi-slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Martínez-Sykora, Juan; Testa, Paola;
Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo; Cheung, Mark C. M.;
Antolin, Patrick
Bibcode: 2020ApJ...888....3D
Altcode: 2019arXiv190908818D
The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed
at understanding the physical mechanisms driving the heating of the
solar corona and the eruptions that are at the foundation of space
weather. MUSE contains two instruments, a multi-slit extreme ultraviolet
(EUV) spectrograph and a context imager. It will simultaneously
obtain EUV spectra (along 37 slits) and context images with the
highest resolution in space (0.″33-0.″4) and time (1-4 s) ever
achieved for the transition region (TR) and corona. The MUSE science
investigation will exploit major advances in numerical modeling, and
observe at the spatial and temporal scales on which competing models
make testable and distinguishable predictions, thereby leading to a
breakthrough in our understanding of coronal heating and the drivers
of space weather. By obtaining spectra in four bright EUV lines (Fe
IX 171 Å, Fe XV 284 Å, Fe XIX 108Å, Fe XXI 108 Å) covering a wide
range of TR and coronal temperatures along 37 slits simultaneously,
MUSE will be able to “freeze” the evolution of the dynamic
coronal plasma. We describe MUSE’s multi-slit approach and show
that the optimization of the design minimizes the impact of spectral
lines from neighboring slits, generally allowing line parameters to
be accurately determined. We also describe a Spectral Disambiguation
Code to resolve multi-slit ambiguity in locations where secondary lines
are bright. We use simulations of the corona and eruptions to perform
validation tests and show that the multi-slit disambiguation approach
allows accurate determination of MUSE observables in locations where
significant multi-slit contamination occurs.
Title: Coronal dimming as a proxy for stellar coronal mass ejections
Authors: Jin, M.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.;
Schrijver, C. J.; France, K.; Kowalski, A.; Mason, J. P.; Osten, R.
Bibcode: 2020IAUS..354..426J
Altcode: 2020arXiv200206249J
Solar coronal dimmings have been observed extensively in the past
two decades and are believed to have close association with coronal
mass ejections (CMEs). Recent study found that coronal dimming
is the only signature that could differentiate powerful flares
that have CMEs from those that do not. Therefore, dimming might be
one of the best candidates to observe the stellar CMEs on distant
Sun-like stars. In this study, we investigate the possibility of using
coronal dimming as a proxy to diagnose stellar CMEs. By simulating a
realistic solar CME event and corresponding coronal dimming using a
global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model),
we first demonstrate the capability of the model to reproduce solar
observations. We then extend the model for simulating stellar CMEs
by modifying the input magnetic flux density as well as the initial
magnetic energy of the CME flux rope. Our result suggests that with
improved instrument sensitivity, it is possible to detect the coronal
dimming signals induced by the stellar CMEs.
Title: Using U-Nets to Create High-Fidelity Virtual Observations of
the Solar Corona
Authors: Salvatelli, Valentina; Bose, Souvik; Neuberg, Brad; dos
Santos, Luiz F. G.; Cheung, Mark; Janvier, Miho; Gunes Baydin, Atilim;
Gal, Yarin; Jin, Meng
Bibcode: 2019arXiv191104006S
Altcode:
Understanding and monitoring the complex and dynamic processes of
the Sun is important for a number of human activities on Earth and
in space. For this reason, NASA's Solar Dynamics Observatory (SDO)
has been continuously monitoring the multi-layered Sun's atmosphere
in high-resolution since its launch in 2010, generating terabytes of
observational data every day. The synergy between machine learning
and this enormous amount of data has the potential, still largely
unexploited, to advance our understanding of the Sun and extend the
capabilities of heliophysics missions. In the present work, we show that
deep learning applied to SDO data can be successfully used to create a
high-fidelity virtual telescope that generates synthetic observations of
the solar corona by image translation. Towards this end we developed
a deep neural network, structured as an encoder-decoder with skip
connections (U-Net), that reconstructs the Sun's image of one instrument
channel given temporally aligned images in three other channels. The
approach we present has the potential to reduce the telemetry needs
of SDO, enhance the capabilities of missions that have less observing
channels, and transform the concept development of future missions.
Title: Auto-Calibration of Remote Sensing Solar Telescopes with
Deep Learning
Authors: Neuberg, Brad; Bose, Souvik; Salvatelli, Valentina; dos
Santos, Luiz F. G.; Cheung, Mark; Janvier, Miho; Gunes Baydin, Atilim;
Gal, Yarin; Jin, Meng
Bibcode: 2019arXiv191104008N
Altcode:
As a part of NASA's Heliophysics System Observatory (HSO) fleet of
satellites,the Solar Dynamics Observatory (SDO) has continuously
monitored the Sun since2010. Ultraviolet (UV) and Extreme UV (EUV)
instruments in orbit, such asSDO's Atmospheric Imaging Assembly
(AIA) instrument, suffer time-dependent degradation which reduces
instrument sensitivity. Accurate calibration for (E)UV instruments
currently depends on periodic sounding rockets, which are infrequent
and not practical for heliophysics missions in deep space. In the
present work, we develop a Convolutional Neural Network (CNN) that
auto-calibrates SDO/AIA channels and corrects sensitivity degradation
by exploiting spatial patterns in multi-wavelength observations to
arrive at a self-calibration of (E)UV imaging instruments. Our results
remove a major impediment to developing future HSOmissions of the
same scientific caliber as SDO but in deep space, able to observe the
Sun from more vantage points than just SDO's current geosynchronous
orbit.This approach can be adopted to perform autocalibration of other
imaging systems exhibiting similar forms of degradation
Title: Three-dimensional modeling of chromospheric spectral lines
in a simulated active region
Authors: Bjørgen, Johan P.; Leenaarts, Jorrit; Rempel, Matthias;
Cheung, Mark C. M.; Danilovic, Sanja; de la Cruz Rodríguez, Jaime;
Sukhorukov, Andrii V.
Bibcode: 2019A&A...631A..33B
Altcode: 2019arXiv190601098B
Context. Because of the complex physics that governs the formation of
chromospheric lines, interpretation of solar chromospheric observations
is difficult. The origin and characteristics of many chromospheric
features are, because of this, unresolved.
Aims: We focus on
studying two prominent features: long fibrils and flare ribbons. To
model these features, we use a 3D magnetohydrodynamic simulation of
an active region, which self-consistently reproduces both of these
features.
Methods: We modeled the Hα, Mg II k, Ca II K,
and Ca II 8542 Å lines using the 3D non-LTE radiative transfer
code Multi3D. To obtain non-LTE electron densities, we solved the
statistical equilibrium equations for hydrogen simultaneously with the
charge conservation equation. We treated the Ca II K and Mg II k lines
with partially coherent scattering.
Results: This simulation
reproduces long fibrils that span between the opposite-polarity
sunspots and go up to 4 Mm in height. They can be traced in all lines
owing to density corrugation. In contrast to previous studies, Hα,
Mg II h&k, and Ca II H&K are formed at similar height in this
model. Although some of the high fibrils are also visible in the Ca II
8542 Å line, this line tends to sample loops and shocks lower in the
chromosphere. Magnetic field lines are aligned with the Hα fibrils,
but the latter holds to a lesser extent for the Ca II 8542 Å line. The
simulation shows structures in the Hα line core that look like flare
ribbons. The emission in the ribbons is caused by a dense chromosphere
and a transition region at high column mass. The ribbons are visible in
all chromospheric lines, but least prominent in Ca II 8542 Å line. In
some pixels, broad asymmetric profiles with a single emission peak
are produced similar to the profiles observed in flare ribbons. They
are caused by a deep onset of the chromospheric temperature rise
and large velocity gradients.
Conclusions: The simulation
produces long fibrils similar to what is seen in observations. It
also produces structures similar to flare ribbons despite the lack
of nonthermal electrons in the simulation. The latter suggests that
thermal conduction might be a significant agent in transporting flare
energy to the chromosphere in addition to nonthermal electrons.
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.
Bibcode: 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 systems1,2. On
the Sun, strong flares are usually found in newly emerging sunspot
regions3. 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 corona4
and on how three-dimensional magnetic reconnection allows for rapid
energy release5,6, 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 flares7,
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 plasmas8 up to and beyond 100 million K.
Title: A deep learning virtual instrument for monitoring extreme UV
solar spectral irradiance
Authors: Szenicer, Alexandre; Fouhey, David F.; Munoz-Jaramillo,
Andres; Wright, Paul J.; Thomas, Rajat; Galvez, Richard; Jin, Meng;
Cheung, Mark C. M.
Bibcode: 2019SciA....5.6548S
Altcode:
Measurements of the extreme ultraviolet (EUV) solar spectral irradiance
(SSI) are essential for understanding drivers of space weather effects,
such as radio blackouts, and aerodynamic drag on satellites during
periods of enhanced solar activity. In this paper, we show how to
learn a mapping from EUV narrowband images to spectral irradiance
measurements using data from NASA's Solar Dynamics Observatory obtained
between 2010 to 2014. We describe a protocol and baselines for measuring
the performance of models. Our best performing machine learning (ML)
model based on convolutional neural networks (CNNs) outperforms other
ML models, and a differential emission measure (DEM) based approach,
yielding average relative errors of under 4.6% (maximum error over
emission lines) and more typically 1.6% (median). We also provide
evidence that the proposed method is solving this mapping in a way that
makes physical sense and by paying attention to magnetic structures
known to drive EUV SSI variability.
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark C. M.; De Pontieu, Bart; Martínez-Sykora,
Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo;
Antolin, Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young,
Peter; MUSE Team
Bibcode: 2019ApJ...882...13C
Altcode: 2019arXiv190203890C
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g., temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission), and slot spectrometers (which produce overlappograms).
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.
Bibcode: 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: Multi-instrument Comparative Study of Temperature, Number
Density and Emission Measure during the Precursor Phase of a Solar
Flare
Authors: Liu, Nian; Jing, Ju; Wang, Haimin; Xu, Yan; Cheung, Mark;
Fleishman, G. D.
Bibcode: 2019AAS...23420407L
Altcode:
The precursor brightenings of solar flares hold valuable clues
concerning the flare triggering and energy release mechanisms, but
have not been well studied. This paper presents a multi-instrument
study of the two precursor brightenings prior to the M6.5 flare
(SOL2015-06-22T18:23) in NOAA active region 12371, with a focus on
the temperature (T), number density (n) and emission measure (EM)
of these two precursors. The multi-instrument data used in this study
were obtained from four instruments with variety of wavelengths, i.e.,
the Solar Dynamics Observatory's Atmospheric Imaging Assembly (AIA)
in six EUV passbands, the Expanded Owens Valley Solar Array (EOVSA)
in microwave, RHESSI in hard X-ray and GOES in soft X-ray. We compare
the temporal variation of T, n and EM derived from different data sets
during the precursor period and discuss the differences in terms of
the sensitivity of the instruments.
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark; De Pontieu, Bart; Martinez-Sykora, Juan; Testa,
Paola; Winebarger, Amy R.; Daw, Adrian N.; Hansteen, Viggo; Antolin,
Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young, Peter R.
Bibcode: 2019AAS...23411603C
Altcode:
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g. temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission; MUSE) and slot spectrometers (which produce overlappograms).
Title: Measuring and Characterizing the Importance of Magnetic Flux
Cancellation in Solar Active Regions during their Emergence Phase
Authors: Chintzoglou, Georgios; Cheung, Mark
Bibcode: 2019AAS...23440202C
Altcode:
Active Regions (ARs) in their emergence phase are known to be more flare
productive and eruptive than ARs in their decay phase. For decaying ARs,
the flaring and eruptive activity is thought to be a consequence of
the formation of magnetic flux ropes through photospheric magnetic flux
cancellation, often occurring at the internal polarity inversion line
(PIL) of the AR. Typically, during the AR decay phase, flux cancellation
manifests itself by a clear decay of the total unsigned magnetic flux,
sometimes preceding and even accompanying the flaring and eruptive
activity. In emerging ARs, however, no cancellation can be seen in the
total unsigned magnetic flux owing to sustained flux emergence. In this
work we focus on complex emerging ARs composed of multiple bipoles. Due
to the compact clustering of the different bipoles within such complex
multipolar ARs, collision and shearing between opposite nonconjugated
polarities drives rapid photospheric cancellation. This mechanism
is called collisional shearing. In Chintzoglou et al (2019), it was
demonstrated that collisional shearing occurred in two emerging flare
and CME productive ARs (NOAA AR11158 and AR12017) and a significant
amount of cancelled flux was measured by applying the conjugate
flux deficit method (Chintzoglou et al 2019). Here, we employ a new
methodology based on a novel electric field inversion method and we
calculate the time evolution of magnetic flux through Faraday's law
at the internal PIL of emerging ARs. We compare this methodology with
the conjugate flux deficit method on magnetogram series of synthetic
and observed emerging ARs and discuss our results in relation to flare
and eruptive activity.
Title: Machine learning reveals systematic accumulation of electric
current in lead-up to solar flares
Authors: Dhuri, Dattaraj B.; Hanasoge, Shravan M.; Cheung, Mark C. M.
Bibcode: 2019PNAS..11611141D
Altcode: 2019arXiv190510167D
Solar flares—bursts of high-energy radiation responsible for
severe space weather effects—are a consequence of the occasional
destabilization of magnetic fields rooted in active regions
(ARs). The complexity of AR evolution is a barrier to a comprehensive
understanding of flaring processes and accurate prediction. Although
machine learning (ML) has been used to improve flare predictions, the
potential for revealing precursors and associated physics has been
underexploited. Here, we train ML algorithms to classify between
vector-magnetic-field observations from flaring ARs, producing
at least one M-/X-class flare, and nonflaring ARs. Analysis of
magnetic-field observations accurately classified by the machine
presents statistical evidence for (i) ARs persisting in flare-productive
states—characterized by AR area—for days, before and after M-
and X-class flare events; (ii) systematic preflare buildup of free
energy in the form of electric currents, suggesting that the associated
subsurface magnetic field is twisted; and (iii) intensification of
Maxwell stresses in the corona above newly emerging ARs, days before
first flares. These results provide insights into flare physics and
improving flare forecasting.
Title: COHERENT: Studying the corona as a holistic environment
Authors: Caspi, Amir; Seaton, Daniel B.; Case, Traci; Cheung, Mark;
Cranmer, Steven; DeForest, Craig E.; de Toma, Giuliana; Downs, Cooper;
Elliott, Heather; Gold, Anne U.; Longcope, Dana; Savage, Sabrina L.;
Sullivan, Susan; Viall, Nicholeen; Vourlidas, Angelos; West, Matthew J.
Bibcode: 2019shin.confE.241C
Altcode:
The solar corona and the heliosphere must be part of a single
physical system, but because the dominant physical processes change
dramatically from the magnetically-dominated low corona, through the
sparsely-observed middle corona, and into the plasma flow-dominated
outer corona and heliospheric interface, unified frameworks to study
the corona as a whole are essentially nonexistent. Understanding how
physical processes shape and drive the dynamics of the corona as a
global system, on all spatiotemporal scales, is critical for solving
many fundamental problems in solar and heliospheric physics. However,
the lack of unifying observations and models has led to a fragmentation
of the community into distinct regimes of plasma parameter space,
largely clustering around regions where existing instrumentation has
made observations widely available and where models can be sufficiently
self-contained to be tractable. We describe COHERENT, the 'Corona as a
Holistic Environment' Research Network, a focused effort to facilitate
interdisciplinary collaborative research to develop frameworks for
unifying existing and upcoming observations, theory, models, and
analytical tools to study the corona as a holistic system.
Title: A Machine-learning Data Set Prepared from the NASA Solar
Dynamics Observatory Mission
Authors: Galvez, Richard; Fouhey, David F.; Jin, Meng; Szenicer,
Alexandre; Muñoz-Jaramillo, Andrés; Cheung, Mark C. M.; Wright,
Paul J.; Bobra, Monica G.; Liu, Yang; Mason, James; Thomas, Rajat
Bibcode: 2019ApJS..242....7G
Altcode: 2019arXiv190304538G
In this paper, we present a curated data set from the NASA
Solar Dynamics Observatory (SDO) mission in a format suitable for
machine-learning research. Beginning from level 1 scientific products
we have processed various instrumental corrections, down-sampled
to manageable spatial and temporal resolutions, and synchronized
observations spatially and temporally. We illustrate the use of this
data set with two example applications: forecasting future extreme
ultraviolet (EUV) Variability Experiment (EVE) irradiance from present
EVE irradiance and translating Helioseismic and Magnetic Imager
observations into Atmospheric Imaging Assembly observations. For
each application, we provide metrics and baselines for future model
comparison. We anticipate this curated data set will facilitate
machine-learning research in heliophysics and the physical sciences
generally, increasing the scientific return of the SDO mission. This
work is a direct result of the 2018 NASA Frontier Development Laboratory
Program. Please see the Appendix for access to the data set, totaling
6.5TBs.
Title: Detection of Strong Photospheric Downflows Accompanying
Magnetic Cancellation in Collisional Polarity Inversion Lines of
Flare- and CME-Productive Active Regions
Authors: Chintzoglou, Georgios; Cheung, Mark C. M.
Bibcode: 2019shin.confE..38C
Altcode:
Individual events of cancellation of small magnetic features in
the quiet Sun seen in photospheric magnetogram observations can be
attributed to either the submergence of Omega-loops or the emergence
of U-loop structures through the solar photosphere. As the opposite
polarities of these small features converge and cancel, they form
very compact polarity inversion lines (PILs). In Active Regions (ARs)
cancellation of such small opposite polarity features is typically
seen to occur during the decay phase of ARs. However, compact PILs can
form earlier in an AR’s lifetime, e.g. in complex and developing
multipolar ARs, as a result of the collision between at least two
emerging flux tubes nested within the same AR. This process is called
collisional shearing, as to emphasize that the shearing and flux
cancellation develop owing to the collision. High spatial and temporal
resolution observations from the Solar Dynamics Observatory for two
emerging ARs, AR 11158 and AR 12017, show the continuous cancellation
at the collisional PIL for as long as the collision persists. The flux
cancellation is accompanied by a succession of solar flares and CMEs,
products of magnetic reconnection along the collisional PIL. Here,
we use high spatial resolution magneto grams and Doppler observations
from HINODE/SP to confirm that the cancellation is consistent with
the submergence of Omega-loops, resulting to a twisted magnetic flux
rope in the corona. Such confirmation with HINODE/SP is important
to elucidate the role of the collisional shearing process on the
formation of magnetic flux ropes. This finding has implications in
our understanding of extreme solar activity.
Title: DeepEM: Demonstrating a Deep Learning Approach to DEM Inversion
Authors: Wright, Paul J.; Cheung, Mark C. M.; Thomas, Rajat; Galvez,
Richard; Szenicer, Alexandre; Jin, Meng; Muñoz-Jaramillo, Andrés;
Fouhey, David
Bibcode: 2019zndo...2587015W
Altcode:
DeepEM is a (supervised) deep learning approach to differential
emission measure (DEM) inversion that is currently under
development on GitHub. This first release coincides with the
version of DeepEM demonstrated in Chapter 4 of the Machine Learning,
Statistics, and Data Mining for Heliophysics e-book (Bobra & Mason
2018). Within the chapter (and the code provided here, DeepEM.ipynb)
we demonstrate how a simple implementation of supervised learning
can be used to reconstruct DEM maps from SDO/AIA data. Caveats
of this simple implementation and future work are also discussed.
The Machine Learning, Statistics, and Data Mining for Heliophysics
e-book can be accessed at https://helioml.github.io/HelioML/,
and the interactive DeepEM notebook (Chapter 4) is located at
https://helioml.github.io/HelioML/04/1/notebook.
Title: The Origin of Major Solar Activity: Collisional Shearing
between Nonconjugated Polarities of Multiple Bipoles Emerging within
Active Regions
Authors: Chintzoglou, Georgios; Zhang, Jie; Cheung, Mark C. M.;
Kazachenko, Maria
Bibcode: 2019ApJ...871...67C
Altcode: 2018arXiv181102186C
Active regions (ARs) that exhibit compact polarity inversion
lines (PILs) are known to be very flare productive. However, the
physical mechanisms behind this statistical inference have not been
demonstrated conclusively. We show that such PILs can occur owing to
the collision between two emerging flux tubes nested within the same
AR. In such multipolar ARs, the flux tubes may emerge simultaneously
or sequentially, each initially producing a bipolar magnetic region
(BMR) at the surface. During each flux tube’s emergence phase, the
magnetic polarities can migrate such that opposite polarities belonging
to different BMRs collide, resulting in shearing and cancellation of
magnetic flux. We name this process “collisional shearing” to
emphasize that the shearing and flux cancellation develop owing to
the collision. Collisional shearing is a process different from the
known concept of flux cancellation occurring between polarities of a
single bipole, a process that has been commonly used in many numerical
models. High spatial and temporal resolution observations from the Solar
Dynamics Observatory for two emerging ARs, AR 11158 and AR 12017, show
the continuous cancellation of up to 40% of the unsigned magnetic flux
of the smallest BMR, which occurs at the collisional PIL for as long
as the collision persists. The flux cancellation is accompanied by a
succession of solar flares and CMEs, products of magnetic reconnection
along the collisional PIL. Our results suggest that the quantification
of magnetic cancellation driven by collisional shearing needs to be
taken into consideration in order to improve the prediction of solar
energetic events and space weather.
Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
Bibcode: 2018SSRv..214..120Y
Altcode: 2018arXiv180505850Y
The term "ultraviolet (UV) burst" is introduced to describe small,
intense, transient brightenings in ultraviolet images of solar active
regions. We inventorize their properties and provide a definition
based on image sequences in transition-region lines. Coronal signatures
are rare, and most bursts are associated with small-scale, canceling
opposite-polarity fields in the photosphere that occur in emerging flux
regions, moving magnetic features in sunspot moats, and sunspot light
bridges. We also compare UV bursts with similar transition-region
phenomena found previously in solar ultraviolet spectrometry and
with similar phenomena at optical wavelengths, in particular Ellerman
bombs. Akin to the latter, UV bursts are probably small-scale magnetic
reconnection events occurring in the low atmosphere, at photospheric
and/or chromospheric heights. Their intense emission in lines with
optically thin formation gives unique diagnostic opportunities
for studying the physics of magnetic reconnection in the low solar
atmosphere. This paper is a review report from an International Space
Science Institute team that met in 2016-2017.
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester,
Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola
Bibcode: 2018csc..confE..66J
Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed > 3000 km/s, which is one of the fastest
CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10 event
using a global MHD model (AWSoM: Alfven Wave Solar Model) within the
Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux
rope. We conduct detailed comparisons of the synthesized EUV images with
SDO/AIA observations of global EUV waves. We find that the simulated
EUV wave morphology and kinematics are sensitive to the orientation
of the initial flux rope introduced to the source active region. An
orientation with the flux-rope axis in the north-south direction
produces the best match to the observations, which suggests that EUV
waves may potentially be used to constrain the flux-rope geometry for
such limb or behind-the-limb eruptions that lack good magnetic field
observations. We also compare observed and simulated EUV intensities
in multiple AIA channels to perform thermal seismology of the global
corona. Furthermore, we track the 3D CME-driven shock surface in the
simulation and derive the time-varying shock parameters together with
the dynamic magnetic connectivity between the shock and the surface
of the Sun, with which we discuss the role of CME-driven shocks in
the long-duration Gamma-ray events.
Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10
X8.2+ Solar Flare-Coronal Mass Ejection
Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung,
Mark C. M.; Nitta, Nariaki V.
Bibcode: 2018csc..confE..40L
Altcode:
We report SDO/AIA observations of an extraordinary global extreme
ultraviolet (EUV) wave triggered by the X8.2+ flare-CME eruption on 2017
September 10. This was one of the best EUV waves ever observed with
modern instruments, yet it was likely the last one of such magnitudes
of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable
characteristics include the following. (1) The wave was observed,
for the first time, to traverse the full-Sun corona over the entire
visible solar disk and off-limb circumference, manifesting a truly
global nature, owing to its exceptionally large amplitude, e.g., with
EUV enhancements by up to 300% at 1.1 Rsun from the eruption. (2)
This leads to strong transmissions (in addition to commonly observed
reflections) in and out of both polar coronal holes, which are usually
devoid of EUV waves. It has elevated wave speeds >2000 km/s within
them, consistent with the expected higher fast-mode magnetosonic wave
speeds. The coronal holes essentially serve as new "radiation centers"
for the waves being refracted out of them, which then travel toward the
equator and collide head-on, causing additional EUV enhancements. (3)
The wave produces significant compressional heating to local plasma
upon its impact, indicated by long-lasting EUV intensity changes and
differential emission measure increases at higher temperatures (e.g.,
log T=6.2) accompanied by decreases at lower temperatures (e.g.,
log T=6.0). These characteristics signify the potential of such EUV
waves for novel magnetic and thermal diagnostics of the solar corona
on global scales.
Title: HMI Data Corrected for Scattered Light Compared to Hinode
SOT-SP Data
Authors: Norton, A. A.; Duvall, T. L., Jr.; Schou, J.; Cheung,
M. C. M.; Scherrer, P. H.; Chu, K. C.; Sommers, J.
Bibcode: 2018csc..confE.101N
Altcode:
In March 2018, the Helioseismic Magnetic Imager (HMI) team began
providing full-disk data to the public on a daily basis that were
corrected for scattered light. In addition to the intensity and
magnetogram data, the improved vector magnetic field maps are also
provided. The process uses a Richardson-Lucy algorithm and a known
PSF. The deconvolution results in a few percent decrease in umbral
intensity corresponding to a 200 K decrease in temperature, a doubling
of the intensity contrast of granulation from 3.6 to 7.2%, an increase
in total field strength values (not only line-of-sight B) in plage by
1.4, faculae brightening and network darkening, and a partial correction
for the convective blue-shift. The new data series can be found in
JSOC with names similar to the original but with the qualifying term
'_dcon' or '_dconS' appended (denoting whether the deconvolution
was applied to the filtergrams or Stokes images). Comparisons to
near-simultaneous Hinode SOT-SP data demonstrate that the correction
brings the two instruments into much better agreement, including the
inverted magnetic field parameters. We compare our results to similar
efforts in the literature such as work by Diaz Baso and Asensio Ramos
(2018) in which HMI intensity and magnetogram data was enhanced using
neural networks and super-resolution.
Title: An Observationally Constrained Model of a Flux Rope that
Formed in the Solar Corona
Authors: James, Alexander W.; Valori, Gherardo; Green, Lucie M.; Liu,
Yang; Cheung, Mark C. M.; Guo, Yang; van Driel-Gesztelyi, Lidia
Bibcode: 2018csc..confE...9J
Altcode:
Coronal mass ejections (CMEs) are large-scale eruptions of plasma
from the coronae of stars, and it is important to study the plasma
processes involved in their initiation. This first requires us to
understand the pre-eruptive configuration of CMEs. To this end, we used
extreme-ultraviolet (EUV) observations from SDO/AIA to conclude that a
magnetic flux rope formed high-up in the solar corona above NOAA Active
Region 11504 before it erupted on 2012 June 14. Then, we used data from
SDO/HMI and our knowledge of the EUV observations to model the coronal
magnetic field of the active region one hour prior to eruption using a
nonlinear force-free field extrapolation. The extrapolation revealed
a flux rope that matches the EUV observations remarkably well, with
its axis 120 Mm above the photosphere. The erupting structure was not
observed to kink, but the decay index near the apex of the axis of
the extrapolated flux rope is comparable to typical critical values
required for the onset of the torus instability. Therefore, we suggest
that the torus instability drove the eruption of the flux rope.
Title: Solar EUV Spectral Irradiance by Deep Learning
Authors: Wright, Paul; Galvez, Richard; Szenicer, Alexandre; Thomas,
Rajat; Jin, Meng; Fouhey, David; Cheung, Mark; Munoz-Jaramillo,
Andres; Mackintosh, Graham
Bibcode: 2018csc..confE..90W
Altcode:
Extreme UV (EUV) radiation from the Sun's transition region and
corona is an important driver for the energy balance of the Earth's
thermosphere and ionosphere. To characterise and monitor solar forcing
on this system and associated space weather impacts, the EUV Variability
Experiment (EVE) instrument onboard NASA's Solar Dynamics Observatory
(SDO) was designed to measure solar spectral irradiance (SSI) in the
0.1 to 105 nm wavelength range. As the result of an electrical short,
the MEGS-A component of EVE stopped delivering SSI data in the 5 - 35
nm wavelength range in May 2014. We demonstrate how a Residual Neural
Network (ResNet) augmented with a Multi-Layer Perceptron (MLP) can
fill this gap using narrowband UV and EUV images from the Atmospheric
Imaging Assembly (AIA) on SDO. As a performance benchmark, we also show
how our deep learning approach outperforms a physics model based on
differential emission measure inversions. This work was performed at
NASA's Frontier Development Lab, a public-private initiative to apply
AI techniques to accelerate space science discovery and exploration.
Title: The Origin of Major Solar Activity - Collisional Shearing
Between Nonconjugated Polarities of Different Bipoles Nested Within
Active Regions
Authors: Chintzoglou, Georgios; Zhang, Jie; Cheung, Mark C. M.;
Kazachenko, Maria
Bibcode: 2018csc..confE..18C
Altcode:
Active Regions (ARs) that exhibit compact Polarity Inversion
Lines (PILs) are known to be very flare-productive. However, the
physical mechanisms behind this statistical inference have not been
demonstrated conclusively. We show that such PILs can occur due to
the collision between two emerging flux tubes nested within the same
AR. In such multipolar ARs, the flux tubes may emerge simultaneously
or sequentially, each initially producing a bipolar magnetic region
(BMR) at the surface. During each flux tube's emergence phase, the
magnetic polarities can migrate such that opposite polarities belonging
to different BMRs collide, resulting in shearing and cancellation
of magnetic flux. We name this process "collisional shearing" to
emphasize that the shearing and flux cancellation develops due to
the collision. Collisional shearing is a process different from the
known concept of flux cancellation occurring between polarities of a
single bipole, a process that has been commonly used in many numerical
models. High spatial and temporal resolution observations from the
Solar Dynamics Observatory for two emerging ARs, AR11158 and AR12017,
show the continuous cancellation of up to 25% of the unsigned magnetic
flux of the smallest BMR, which occurs at the collisional PIL for as
long as the collision persists. The flux cancellation is accompanied by
a succession of solar flares and CMEs, products of magnetic reconnection
along the collisional PIL. Our results suggest that the quantification
of magnetic cancellation driven by collisional shearing needs to be
taken into consideration in order to improve the prediction of solar
energetic events and space weather.
Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10
X8.2+ Solar Flare-Coronal Mass Ejection
Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung,
Mark C. M.; Nitta, Nariaki V.
Bibcode: 2018ApJ...864L..24L
Altcode: 2018arXiv180709847L
We report Solar Dynamics Observatory/Atmospheric Imaging Assembly
(SDO/AIA) observations of an extraordinary global extreme ultraviolet
(EUV) wave triggered by the X8.2+ flare-CME eruption on 2017 September
10. This was one of the best EUV waves ever observed with modern
instruments, yet it was likely the last one of such magnitudes of
Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable
characteristics include the following. (1) The wave was observed,
for the first time, to traverse the full-Sun corona over the entire
visible solar disk and off-limb circumference, manifesting a truly
global nature, owing to its exceptionally large amplitude, e.g.,
with EUV enhancements by up to 300% at 1.1 {R}⊙ from
the eruption. (2) This leads to strong transmissions (in addition to
commonly observed reflections) in and out of both polar coronal holes
(CHs), which are usually devoid of EUV waves. It has elevated wave
speeds >2000 {km} {{{s}}}-1 within the CHs, consistent
with the expected higher fast-mode magnetosonic wave speeds. The CHs
essentially serve as new “radiation centers” for the waves being
refracted out of them, which then travel toward the equator and collide
head-on, causing additional EUV enhancements. (3) The wave produces
significant compressional heating to local plasma upon its impact,
indicated by long-lasting EUV intensity changes and differential
emission measure increases at higher temperatures (e.g., {log}T=6.2)
accompanied by decreases at lower temperatures (e.g., {log}T=6.0). These
characteristics signify the potential of such EUV waves for novel
magnetic and thermal diagnostics of the solar corona on global scales.
Title: Extended Kilogauss Bald Patches in the Super-Flaring Active
Region 12673
Authors: Sun, Xudong; Titov, Viacheslav; Cheung, Mark; Kazachenko,
Maria
Bibcode: 2018shin.confE.209S
Altcode:
Magnetic field in the active region core holds the key to its eruptive
potential. An interesting topological feature is the 'bald patch'
(BP) - a segment of the polarity inversion line (PIL) at which
the photospheric magnetic field is directed from the negative to
positive side, implying the presence of U-shaped magnetic loops in
the immediate low corona. When accompanied by strong shear, coherent
BPs can provide evidence for pre-eruption flux ropes (FRs). Here we
report on an archetypical BP structure observed in the super-flaring
active region 12673, which extended over tens of Mm with a typical
field of 2-3 kG. The structure formed gradually over several hours
prior to an X9-class flare, featuring smooth azimuth rotation, field
strength reduction, and vertical field gradient enhancement. Fast,
persistent photospheric downflow developed along the PIL one day prior,
which weakened as the BP formed. The coronal magnetic field inferred
from a nonlinear force-free field model reveals textbook morphology
of a low-lying, twisted FR wrapped inside intersecting BP separatrix
surfaces. We discuss the formation mechanism of such extended BPs and
its role in initiating major eruptions.
Title: The Origin of Major Solar Activity - Magnetic Flux Cancellation
due to Collisional Shearing Between Polarities of Different Bipoles
Nested Within Active Regions
Authors: Chintzoglou, Georgios; Zhang, Jie; Cheung, Mark C. M.;
Kazachenko, Maria
Bibcode: 2018shin.confE.146C
Altcode:
Active Regions (ARs) that exhibit compact Polarity Inversion Lines
(PILs) are known to be very flare-productive. However, the basis for
this statistical inference has not been demonstrated conclusively. We
show that such PILs can occur due to the collision between two emerging
flux tubes nested within the same AR. In such multipolar ARs, the
flux tubes may emerge simultaneously or sequentially, each initially
producing a bipolar magnetic region (BMR) at the surface. During each
flux tube's emergence phase, the magnetic polarities can migrate in
such ways that opposite polarities belonging to different BMRs collide,
resulting in shearing and cancellation of magnetic flux. We name this
process 'collisional shearing' to emphasize that the shearing and flux
cancellation develops due to the collision. Collisional shearing is a
process different from the known concept of flux cancellation occurring
between conjugated polarities of a single bipole, a process that has
been commonly used in many numerical models. High spatial and temporal
resolution observations from the Solar Dynamics Observatory for two
emerging ARs, AR11158 and AR12017, show the continuous cancellation of
up to 25% of the unsigned magnetic flux, which occurs at the collisional
PIL for as long as the collision persists. The flux cancellation is
accompanied by a succession of solar flares and CMEs, products of
magnetic reconnection along the collisional PIL. Our results suggest
that the quantification of magnetic cancellation driven by collisional
shearing needs to be taken into consideration for the improvement of
predicting solar energetic events and space weather.
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester,
Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola
Bibcode: 2018shin.confE.207J
Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed > 3000 km/s, which is one of the fastest
CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10 event
using a global MHD model (AWSoM: Alfven Wave Solar Model) within the
Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux
rope. We conduct detailed comparisons of the synthesized EUV images with
SDO/AIA observations of global EUV waves. We find that the simulated
EUV wave morphology and kinematics are sensitive to the orientation
of the initial flux rope introduced to the source active region. An
orientation with the flux-rope axis in the north-south direction
produces the best match to the observations, which suggests that EUV
waves may potentially be used to constrain the flux-rope geometry for
such limb or behind-the-limb eruptions that lack good magnetic field
observations. We also compare observed and simulated EUV intensities
in multiple AIA channels to perform thermal seismology of the global
corona. Furthermore, we track the 3D CME-driven shock surface in the
simulation and derive the time-varying shock parameters together with
the dynamic magnetic connectivity between the shock and the surface
of the Sun, with which we discuss the role of CME-driven shocks in
the long-duration Gamma-ray events.
Title: Extended Kilogauss Bald Patches in the Super-Flaring Active
Region 12673
Authors: Sun, Xudong; Kazachenko, Maria; Titov, Viacheslav; Cheung,
Mark
Bibcode: 2018cosp...42E3296S
Altcode:
Magnetic field in the active region core holds the key to its eruptive
potential. An interesting topological feature is the "bald patch"
(BP) - a segment of the polarity inversion line (PIL) at which
the photospheric magnetic field is directed from the negative to
positive side, implying the presence of U-shaped magnetic loops in the
immediate low corona. When accompanied by strong shear, coherent BPs
can provide evidence for pre-eruption flux ropes (FRs). Here we report
on an archetypical BP structure observed in the super-flaring active
region 12673, which extends over 30 Mm with a typical field of 2-3
kG. The structure formed gradually over one day prior to an X9-class
flare. Co-spatial photospheric downflow developed and sustained
near the PIL. The coronal magnetic field inferred from a nonlinear
force-free field model reveals textbook morphology of a low-lying,
twisted FR. We discuss the formation mechanism of such extended BPs
and its role in initiating major eruptions.
Title: The Best and Last of Solar Cycle 24 - The Global EUV Wave from
the X8 Flare-CME Eruption on 2017-Sept-10: SDO/AIA Observations and
Data-constrained Simulations
Authors: Liu, Wei; Ofman, Leon; Nitta, Nariaki; Cheung, Mark; Downs,
Cooper; Jin, Meng
Bibcode: 2018cosp...42E2051L
Altcode:
Global extreme ultraviolet (EUV) waves are commonly associated with
coronal mass ejections (CMEs) and flares. One particular EUV wave
that was triggered by the X8 flare-CME eruption on 2017 September
10 was extraordinary - one of the best EUV waves ever observed with
modern instruments (e.g., SDO/AIA and GOES/SUVI), yet likely the last
one of such magnitudes in Cycle 24 as the Sun heads toward the solar
minimum. We present here detailed analysis of SDO/AIA observations
of this event and comparison with high-fidelity, data-constrained MHD
simulations using the University of Michigan Alfven Wave Solar Model
(AWSoM). Observational highlights include: (1) The EUV wave traverses
almost the entire visible solar disk and circumference, manifesting its
truly global nature. This vast range is mainly due to the exceptionally
large wave amplitude, with EUV intensity changes by up to a factor of
3 (as opposed to, e.g., 30% for moderate events). (2) The large wave
amplitude also leads to the novel detection of strong transmission
components (in addition to commonly observed reflections) into and
through both polar coronal holes, at elevated apparent wave speeds up
to 2600 km/s. (3) The wave also produces significant heating, indicated
by long-lasting EUV intensity changes. As such, this EUV wave offers
unique magnetic and thermal diagnostics of the global, CME-spawning
corona. Our MHD simulations have largely reproduced the observed
features. We find that the simulated EUV wave morphology and kinematics
are sensitive to the orientation of the initial flux rope introduced to
the host active region. An orientation with the flux-rope axis in the
north-south direction produces the best match to the observations. This
suggests that EUV waves may potentially be used to constrain the
flux-rope geometry for such limb or behind-the-limb eruptions, whose
source-region magnetic fields cannot be directly observed, and thus
offer useful implications for space-weather predictions.
Title: Data-inspired, Data-Constrained and Data-Driven Modeling of
Solar Active Regions
Authors: Cheung, Mark
Bibcode: 2018cosp...42E.627C
Altcode:
Recent advances in numerical modeling have provided important
lessons on the physics that cause solar active regions to erupt and
flare. While the majority of past work has been data-inspired (and
based on somewhat idealized scenarios), improvements in observational
coverage is beginning to facilitate data-constrained and data-driven
modeling. Data-constrained models are those that use observational
constraints in one instance in time, while data-driven models are
evolved in response to changing boundary conditions (e.g. at the solar
photosphere) consistent with observations. In this talk, we review some
recent results from these three classes of models. The implications
of the models for desired future instrumentation will also be discussed.
Title: An Observationally Constrained Model of a Flux Rope that
Formed in the Solar Corona
Authors: James, Alexander W.; Valori, Gherardo; Green, Lucie M.; Liu,
Yang; Cheung, Mark C. M.; Guo, Yang; van Driel-Gesztelyi, Lidia
Bibcode: 2018ApJ...855L..16J
Altcode: 2018arXiv180207965J
Coronal mass ejections (CMEs) are large-scale eruptions of plasma
from the coronae of stars. Understanding the plasma processes involved
in CME initiation has applications for space weather forecasting and
laboratory plasma experiments. James et al. used extreme-ultraviolet
(EUV) observations to conclude that a magnetic flux rope formed in
the solar corona above NOAA Active Region 11504 before it erupted on
2012 June 14 (SOL2012-06-14). In this work, we use data from the Solar
Dynamics Observatory (SDO) to model the coronal magnetic field of the
active region one hour prior to eruption using a nonlinear force-free
field extrapolation, and find a flux rope reaching a maximum height
of 150 Mm above the photosphere. Estimations of the average twist of
the strongly asymmetric extrapolated flux rope are between 1.35 and
1.88 turns, depending on the choice of axis, although the erupting
structure was not observed to kink. The decay index near the apex
of the axis of the extrapolated flux rope is comparable to typical
critical values required for the onset of the torus instability,
so we suggest that the torus instability drove the eruption.
Title: Determination of Differential Emission Measure from Solar
Extreme Ultraviolet Images
Authors: Su, Yang; Veronig, Astrid M.; Hannah, Iain G.; Cheung, Mark
C. M.; Dennis, Brian R.; Holman, Gordon D.; Gan, Weiqun; Li, Youping
Bibcode: 2018ApJ...856L..17S
Altcode:
The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
Observatory (SDO) has been providing high-cadence, high-resolution,
full-disk UV-visible/extreme ultraviolet (EUV) images since 2010, with
the best time coverage among all the solar missions. A number of codes
have been developed to extract plasma differential emission measures
(DEMs) from AIA images. Although widely used, they cannot effectively
constrain the DEM at flaring temperatures with AIA data alone. This
often results in much higher X-ray fluxes than observed. One way
to solve the problem is by adding more constraint from other data
sets (such as soft X-ray images and fluxes). However, the spatial
information of plasma DEMs are lost in many cases. In this Letter,
we present a different approach to constrain the DEMs. We tested the
sparse inversion code and show that the default settings reproduce
X-ray fluxes that could be too high. Based on the tests with both
simulated and observed AIA data, we provided recommended settings of
basis functions and tolerances. The new DEM solutions derived from AIA
images alone are much more consistent with (thermal) X-ray observations,
and provide valuable information by mapping the thermal plasma from
∼0.3 to ∼30 MK. Such improvement is a key step in understanding
the nature of individual X-ray sources, and particularly important
for studies of flare initiation.
Title: Order out of Randomness: Self-Organization Processes in
Astrophysics
Authors: Aschwanden, Markus J.; Scholkmann, Felix; Béthune, William;
Schmutz, Werner; Abramenko, Valentina; Cheung, Mark C. M.; Müller,
Daniel; Benz, Arnold; Chernov, Guennadi; Kritsuk, Alexei G.; Scargle,
Jeffrey D.; Melatos, Andrew; Wagoner, Robert V.; Trimble, Virginia;
Green, William H.
Bibcode: 2018SSRv..214...55A
Altcode: 2017arXiv170803394A
Self-organization is a property of dissipative nonlinear processes
that are governed by a global driving force and a local positive
feedback mechanism, which creates regular geometric and/or
temporal patterns, and decreases the entropy locally, in contrast
to random processes. Here we investigate for the first time a
comprehensive number of (17) self-organization processes that
operate in planetary physics, solar physics, stellar physics,
galactic physics, and cosmology. Self-organizing systems create
spontaneous " order out of randomness", during the evolution from an
initially disordered system to an ordered quasi-stationary system,
mostly by quasi-periodic limit-cycle dynamics, but also by harmonic
(mechanical or gyromagnetic) resonances. The global driving force
can be due to gravity, electromagnetic forces, mechanical forces
(e.g., rotation or differential rotation), thermal pressure, or
acceleration of nonthermal particles, while the positive feedback
mechanism is often an instability, such as the magneto-rotational
(Balbus-Hawley) instability, the convective (Rayleigh-Bénard)
instability, turbulence, vortex attraction, magnetic reconnection,
plasma condensation, or a loss-cone instability. Physical models
of astrophysical self-organization processes require hydrodynamic,
magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical
formulations of self-organizing systems generally involve coupled
differential equations with limit-cycle solutions of the Lotka-Volterra
or Hopf-bifurcation type.
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
Bibcode: 2018smf..book..317C
Altcode:
No abstract at ADS
Title: Field distribution of magnetograms from simulations of active
region formation
Authors: Dacie, S.; van Driel-Gesztelyi, L.; Démoulin, P.; Linton,
M. G.; Leake, J. E.; MacTaggart, D.; Cheung, M. C. M.
Bibcode: 2017A&A...606A..34D
Altcode:
Context. The evolution of the photospheric magnetic field distributions
(probability densities) has previously been derived for a set of active
regions. Photospheric field distributions are a consequence of physical
processes that are difficult to determine from observations alone.
Aims: We analyse simulated magnetograms from numerical simulations,
which model the emergence and decay of active regions. These simulations
have different experimental set-ups and include different physical
processes, allowing us to investigate the relative importance of
convection, magnetic buoyancy, magnetic twist, and braiding for flux
emergence.
Methods: We specifically studied the photospheric
field distributions (probability densities found with a kernel density
estimation analysis) and compared the results with those found from
observations.
Results: Simulations including convection most
accurately reproduce the observed evolution of the photospheric field
distributions during active region evolution.
Conclusions: This
indicates that convection may play an important role during the decay
phase and also during the formation of active regions, particularly
for low flux density values.
Title: The Life Cycle of Active Region Magnetic Fields
Authors: Cheung, M. C. M.; van Driel-Gesztelyi, L.; Martínez Pillet,
V.; Thompson, M. J.
Bibcode: 2017SSRv..210..317C
Altcode: 2016SSRv..tmp...46C
We present a contemporary view of how solar active region
magnetic fields are understood to be generated, transported and
dispersed. Empirical trends of active region properties that guide model
development are discussed. Physical principles considered important
for active region evolution are introduced and advances in modeling
are reviewed.
Title: From Emergence to Eruption: The Physics and Diagnostics of
Solar Active Regions
Authors: Cheung, Mark
Bibcode: 2017SPD....4830201C
Altcode:
The solar photosphere is continuously seeded by the emergence of
magnetic fields from the solar interior. In turn, photospheric evolution
shapes the magnetic terrain in the overlying corona. Magnetic fields
in the corona store the energy needed to power coronal mass ejections
(CMEs) and solar flares. In this talk, we recount a physics-based
narrative of solar eruptive events from cradle to grave, from
emergence to eruption, from evaporation to condensation. We review the
physical processes which are understood to transport magnetic flux
from the interior to the surface, inject free energy and twist into
the corona, disentangle the coronal field to permit explosive energy
release, and subsequently convert the released energy into observable
signatures. Along the way, we review observational diagnostics used to
constrain theories of active region evolution and eruption. Finally, we
discuss the opportunities and challenges enabled by the large existing
repository of solar observations. We argue that the synthesis of physics
and diagnostics embodied in (1) data-driven modeling and (2) machine
learning efforts will be an accelerating agent for scientific discovery.
Title: Witnessing a Large-scale Slipping Magnetic Reconnection along
a Dimming Channel during a Solar Flare
Authors: Jing, Ju; Liu, Rui; Cheung, Mark; Lee, Jeongwoo; Xu, Yan;
Liu, Chang; Zhu, Chunming; Wang, Haimin
Bibcode: 2017SPD....4840601J
Altcode:
We report the intriguing large-scale dynamic phenomena associated
with the M6.5 flare~(SOL2015-06-22T18:23) in NOAA active region
12371, observed by RHESSI, Fermi, and the Atmospheric Image Assembly
(AIA) and Magnetic Imager (HMI) on the Solar Dynamic Observatory
(SDO). The most interesting feature of this event is a third ribbon
(R3) arising in the decay phase, propagating along a dimming channel
(seen in EUV passbands) towards a neighboring sunspot. The propagation
of R3 occurs in the presence of hard X-ray footpoint emission, and
is broadly visible at temperatures from 0.6 MK to over 10 MK through
the Differential Emission Measure (DEM) analysis. The coronal loops
then undergo an apparent slipping motion following the same path of
R3, after a ~80 min delay. To understand the underlying physics, we
investigate the magnetic configuration and the thermal structure of the
flaring region. Our results are in favor of a slipping-type reconnection
followed by the thermodynamic evolution of coronal loops. In comparison
with those previously reported slipping reconnection events, this
one proceeds across a particularly long distance (~60 Mm) over a long
period of time ~50 min), and shows two clearly distinguished phases:
the propagation of the footpoint brightening driven by nonthermal
particle injection and the apparent slippage of loops governed by
plasma heating and subsequent cooling.
Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
Bibcode: 2017SPD....4840001R
Altcode:
We present a recently developed version of the MURaM radiative
MHD code that includes coronal physics in terms of optically thin
radiative loss and field aligned heat conduction. The code employs
the "Boris correction" (semi-relativistic MHD with a reduced speed
of light) and a hyperbolic treatment of heat conduction, which allow
for efficient simulations of the photosphere/corona system by avoiding
the severe time-step constraints arising from Alfven wave propagation
and heat conduction. We demonstrate that this approach can be used
even in dynamic phases such as a flare. We consider a setup in which
a flare is triggered by flux emergence into a pre-existing bipolar
active region. After the coronal energy release, efficient transport
of energy along field lines leads to the formation of flare ribbons
within seconds. In the flare ribbons we find downflows for temperatures
lower than ~5 MK and upflows at higher temperatures. The resulting
soft X-ray emission shows a fast rise and slow decay, reaching a peak
corresponding to a mid C-class flare. The post reconnection energy
release in the corona leads to average particle energies reaching 50
keV (500 MK under the assumption of a thermal plasma). We show that
hard X-ray emission from the corona computed under the assumption of
thermal bremsstrahlung can produce a power-law spectrum due to the
multi-thermal nature of the plasma. The electron energy flux into the
flare ribbons (classic heat conduction with free streaming limit) is
highly inhomogeneous and reaches peak values of about 3x1011
erg/cm2/s in a small fraction of the ribbons, indicating
regions that could potentially produce hard X-ray footpoint sources. We
demonstrate that these findings are robust by comparing simulations
computed with different values of the saturation heat flux as well as
the "reduced speed of light".
Title: 3D Collision of Active Region-Sized Emerging Flux Tubes in
the Solar Convection Zone and its Manifestation in the Photospheric
Surface
Authors: Chintzoglou, Georgios; Cheung, Mark; Rempel, Matthias D.
Bibcode: 2017SPD....4830004C
Altcode:
We present observations obtained with the Solar Dynamics Observatory’s
Helioseismic Magnetic Imager (SDO/HMI) of target NOAA Active Regions
(AR) 12017 and 12644, which initially were comprised of a simple bipole
and later on became quadrupolar via parasitic bipole emergence right
next to their leading polarities. Once these ARs became quadrupolar,
they spewed multiple Coronal Mass Ejections (CMEs) and a multitude
of highly energetic flares (a large number of M class flares). The
proximity of the parasitic bipole to one of the two pre-existing
sunspots forms a compact polarity inversion line (PIL). This type of
quadrupolar ARs are known to be very flare- and CME-productive due
to the continuous interaction of newly emerging non-potential flux
with pre-existing flux in the photosphere. We show that well before
the emergence of the parasitic bipole, the pre-existing polarity
(typically a well-developed sunspot) undergoes interesting precursor
dynamic evolution, namely (a) displacement of pre-existing sunspot’s
position, (b) progressive and significant oblateness of its initially
nearly-circular shape, and (c) opposite polarity enhancement in the
divergent moat flow around the sunspot. We employ high-resolution
radiative-convective 3D MHD simulations of an emerging parasitic bipole
to show that all these activity aspects seen in the photosphere are
associated with the collision of a parasitic bipole with the nearby
pre-existing polarity below the photospheric surface. Given the rich
flare and CME productivity of this class of ARs and the precursor-like
dynamic evolution of the pre-existing polarity, this work presents
the potential for predicting inclement space weather.
Title: Stray Light Correction of HMI Data
Authors: Norton, Aimee Ann; Duvall, Thomas; Schou, Jesper; Cheung,
Mark; Scherrer, Philip H.
Bibcode: 2017SPD....4820705N
Altcode:
The point spread function (PSF) for HMI is an Airy function convolved
with a Lorentzian. The parameters are bound by ground-based testing
before launch, then post-launch off-limb light curves, lunar eclipse
and Venus transit data. The PSF correction is programmed in C and runs
within the HMI data processing pipeline environment. A single full-disk
intensity image can be processed in less than one second. Deconvolution
of the PSF on the Stokes profile data (a linear combination of
original filtergrms) is less computationally expensive and is shown
to be equivalent to deconvolution applied at the original filtergram
level. Results include a decrease in umbral darkness of a few percent
(~200 K cooler), a doubling of the granulation contrast in intensity
from 3.6 to 7.2%, an increase in plage field strengths by a factor of
1.5, and a partial correction of the convective blueshift in Doppler
velocities. Requests for data corrected for stray light are welcome
and will be processed by the HMI team.
Title: Global Evolving Models of Photospheric Flux as Driven by
Electric Fields
Authors: DeRosa, Marc L.; Cheung, Mark; Kazachenko, Maria D.; Fisher,
George H.
Bibcode: 2017SPD....4811105D
Altcode:
We present a novel method for modeling the global radial magnetic field
that is based on the incorporation of time series of photospheric
electric fields. The determination of the electric fields is the
result of a recently developed method that uses as input various data
products from SDO/HMI, namely vector magnetic fields and line-of-sight
Doppler images. For locations on the sphere where electric field data
are unavailable, we instead use electric fields that are consistent
with measurements of the mean differential rotation, meridional flow,
and flux dispersal profiles. By combining these electric fields,
a full-Sun model of the photospheric radial magnetic field can be
advanced forward in time via Faraday's Law.
Title: Coronal Mass Ejections and Dimmings: A Comparative Study
using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark; DeRosa, Marc L.; Nitta, Nariaki;
Schrijver, Karel
Bibcode: 2017SPD....4820602J
Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings and determine their relationship
with CMEs. In this study, we investigate coronal dimmings by combining
simulation and observational efforts. By utilizing a data-driven
global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we
simulate coronal dimmings resulting from different CME energetics and
flux rope configurations. We synthesize the emissions of different EUV
spectral bands/lines and compare with SDO/AIA and EVE observations. A
detailed analysis of simulation and observation data suggests that the
“core” dimming is mainly caused by the mass loss from the CME, while
the “remote” dimming could have a different origin (e.g., plasma
heating). Moreover, the interaction between the erupting flux rope with
different orientations and the global solar corona could significantly
influence the coronal dimming patterns. Using metrics such as dimming
depth, dimming slope, and recovery time, we investigate the relationship
between dimmings and CME properties (e.g., CME mass, CME speed) in the
simulation. Our result suggests that coronal dimmings encode important
information about CMEs. We also discuss how our knowledge about solar
coronal dimmings could be extended to the study of stellar CMEs.
Title: Witnessing a Large-scale Slipping Magnetic Reconnection along
a Dimming Channel during a Solar Flare
Authors: Jing, Ju; Liu, Rui; Cheung, Mark C. M.; Lee, Jeongwoo; Xu,
Yan; Liu, Chang; Zhu, Chunming; Wang, Haimin
Bibcode: 2017ApJ...842L..18J
Altcode: 2017arXiv170601355J
We report the intriguing large-scale dynamic phenomena associated with
the M6.5 flare (SOL2015-06-22T18:23) in NOAA active region 12371,
observed by RHESSI, Fermi, and the Atmospheric Image Assembly (AIA)
and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). The
most interesting feature of this event is a third ribbon (R3) arising
in the decay phase, propagating along a dimming channel (seen in EUV
passbands) toward a neighboring sunspot. The propagation of R3 occurs
in the presence of hard X-ray footpoint emission and is broadly visible
at temperatures from 0.6 MK to over 10 MK through the differential
emission measure analysis. The coronal loops then undergo an apparent
slipping motion following the same path of R3, after a ∼80 minute
delay. To understand the underlying physics, we investigate the magnetic
configuration and the thermal structure of the flaring region. Our
results are in favor of a slipping-type reconnection followed by the
thermodynamic evolution of coronal loops. In comparison with those
previously reported slipping reconnection events, this one proceeds
across a particularly long distance (∼60 Mm) over a long period of
time (∼50 minutes) and shows two clearly distinguished phases: the
propagation of the footpoint brightening driven by nonthermal particle
injection and the apparent slippage of loops governed by plasma heating
and subsequent cooling.
Title: Various Local Heating Events in the Earliest Phase of Flux
Emergence
Authors: Toriumi, Shin; Katsukawa, Yukio; Cheung, Mark C. M.
Bibcode: 2017ApJ...836...63T
Altcode: 2017arXiv170101446T
Emerging flux regions (EFRs) are known to exhibit various sporadic
local heating events in the lower atmosphere. To investigate the
characteristics of these events, especially to link the photospheric
magnetic fields and atmospheric dynamics, we analyze Hinode, Interface
Region Imaging Spectrograph (IRIS), and Solar Dynamics Observatory
data of a new EFR in NOAA AR 12401. Out of 151 bright points (BPs)
identified in Hinode/SOT Ca images, 29 are overlapped by an SOT/SP
scan. Seven BPs in the EFR center possess mixed-polarity magnetic
backgrounds in the photosphere. Their IRIS UV spectra (e.g., Si IV
1402.8 Å) are strongly enhanced and red- or blueshifted, with tails
reaching +/- 150 {km} {{{s}}}-1, which is highly suggestive
of bi-directional jets; each brightening lasts for 10-15 minutes,
leaving flare-like light curves. Most of this group show bald patches,
the U-shaped photospheric magnetic loops. Another 10 BPs are found in
unipolar regions at the EFR edges. They are generally weaker in UV
intensities and exhibit systematic redshifts with Doppler speeds up
to 40 {km} {{{s}}}-1, which could exceed the local sound
speed in the transition region. Both types of BPs show signs of strong
temperature increase in the low chromosphere. These observational
results support the physical picture that heating events in the EFR
center are due to magnetic reconnection within cancelling undular
fields like Ellerman bombs, while the peripheral heating events are
due to shocks or strong compressions caused by fast downflows along
the overlying arch filament system.
Title: HMI Data Corrected for Stray Light Now Available
Authors: Norton, A. A.; Duvall, T. L.; Schou, J.; Cheung, M. C. M.;
Scherrer, P. H.
Bibcode: 2016usc..confE..95N
Altcode:
The form of the point spread function (PSF) derived for HMI is an
Airy function convolved with a Lorentzian. The parameters are bound
by observational ground-based testing of the instrument conducted
prior to launch (Wachter et al., 2012), by full-disk data used to
evaluate the off-limb behavior of the scattered light, as well as by
data obtained during the Venus transit. The PSF correction has been
programmed in both C and cuda C and runs within the JSOC environment
using either a CPU or GPU. A single full-disk intensity image can
be deconvolved in less than one second. The PSF is described in more
detail in Couvidat et al. (2016) and has already been used by Hathaway
et al. (2015) to forward-model solar-convection spectra, by Krucker et
al. (2015) to investigate footpoints of off-limb solar flares and by
Whitney, Criscuoli and Norton (2016) to examine the relations between
intensity contrast and magnetic field strengths. In this presentation,
we highlight the changes to umbral darkness, granulation contrast
and plage field strengths that result from stray light correction. A
twenty-four hour period of scattered-light corrected HMI data from
2010.08.03, including the isolated sunspot NOAA 11092, is currently
available for anyone. Requests for additional time periods of interest
are welcome and will be processed by the HMI team.
Title: 3D MHD simulation of a Solar Flare
Authors: Rempel, M.; Cheung, M. C. M.; HGCR Team
Bibcode: 2016usc..confE...4R
Altcode:
We present results from a numerical 3D simulation of a solar flare
triggered by flux emergence into a pre-existing bipolar active
region. The simulation is performed with a recently developed version
of the MURaM radiative MHD code and includes coronal physics in terms of
optically thin radiative loss and field-aligned heat conduction. Severe
time-step constraints arising from Alfven wave propagation and heat
conduction are avoided through the use of the Boris correction and a
hyperbolic treatment of heat conduction. In the simulation we find a
flare releasing about 5x10^30 erg over a time of about 1-2 minutes. The
efficient transport of energy along field lines leads to the formation
of flare ribbons within seconds and at later times to chromospheric
evaporation filling coronal flare loops. Since the efficiency of
energy transport by electrons (classic heat conduction vs. non-thermal
electrons) is one of the main uncertainties, we compare simulations
with different values for the saturation of the heat flux. We present
synthetic observables in the form of UV, EUV and soft and hard Xray
emission.
Title: Flare-associated Fast-mode Coronal Wave Trains Detected by
SDO/AIA: Recent Observational Advances
Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Cheung, Mark; De
Pontieu, Bart
Bibcode: 2016usc..confE.107L
Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are new observational
phenomena discovered by SDO/AIA in extreme ultraviolet (EUV). They
were interpreted as fast-mode magnetosonic waves using MHD modeling,
and also found to be closely related to quasi-periodic pulsations
in solar flare emission ranging from radio to X-ray wavelengths. The
significance of QFPs lies in their diagnostic potential (and possibly
in flare energy transport), because they can provide critical clues to
flare energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing QFPs. In
particular, using differential emission measure (DEM) inversion,
we found clear evidence of heating and cooling cycles that are
consistent with alternating compression and rarefaction expected for
magnetosonic wave pulses. We also found that different local magnetic
and plasma environments can lead to two distinct types of QFPs located
in different spatial domains with respect to their accompanying coronal
mass ejections (CMEs). More interestingly, from a statistical survey of
over 100 QFP events, we found a preferential association with eruptive
flares rather than confined flares. We will discuss the implications
of these results and the potential roles of QFPs in coronal heating,
energy transport, and solar eruptions.
Title: Investigation of the role of magnetic cancellation in
triggering solar eruptions in NOAA AR12017
Authors: Chintzoglou, G.; Cheung, M. C. M.; De Pontieu, B.
Bibcode: 2016usc..confE.121C
Altcode:
During its evolution, NOAA AR12017 was the source of 3 Coronal Mass
Ejections (CMEs) and a multitude of energetic flares. In its early
stages of its evolution it appeared to emerge as a single bipole, which
was followed by the emergence of a smaller (secondary) bipole near
its pre-existing leading polarity, forming a new polarity inversion
line (PIL) between the non-conjugated opposite polarities as well as
an evolving magnetic topology in the solar corona. Using photospheric
magnetic field observations from SDO/HMI, spectra and imaging from IRIS
covering the photosphere and transition region, coronal observations
from SDO/AIA and flare centroids from RHESSI, we investigate the
cause(s) of activity associated with the new PIL. The time range of
the observations spans several hours prior and up to the time of the
X1.0 flare (associated with a CME eruption). Continuous photospheric
cancellation correlates with flaring activity in the X-rays right at
the new PIL, which suggests that cancellation is dominant mechanism
for the activity of this extremely flare-productive AR.
Title: a Numerical Study of Long-Range Magnetic Impacts during
Coronal Mass Ejections
Authors: Jin, Meng; Schrijver, Karel; Cheung, Mark; DeRosa, Marc;
Nitta, Nariaki; Title, Alan
Bibcode: 2016shin.confE..38J
Altcode:
With the global view and high-cadence observations from SDO/AIA and
STEREO, many spatially separated solar eruptive events appear to be
coupled. However, the mechanisms for 'sympathetic' events are still
largely unknown. In this study, we investigate the impact of an erupting
flux rope on surrounding solar structures through large-scale magnetic
coupling. We build a realistic environment of the solar corona on
2011 February 15 using a global magnetohydrodynamics (MHD) model and
initiate coronal mass ejections (CMEs) in active region (AR) 11158
by inserting Gibson-Low analytical flux ropes. We show that a CME's
impact on the surrounding structures depends not only on the magnetic
strength of these structures and their distance to the source region,
but also on the interaction between the CME with the large-scale
magnetic field. Within the CME expansion domain where the flux rope
field directly interacts with the solar structures, expansion-induced
reconnection often modifies the overlying field, thereby increasing
the decay index. This effect may provide a primary coupling mechanism
underlying the sympathetic eruptions. The magnitude of the impact
is found to depend on the orientation of the erupting flux rope,
with the largest impacts occurring when the flux rope is favorably
oriented for reconnecting with the surrounding regions. Outside the
CME expansion domain, the influence of the CME is mainly through field
line compression or post-eruption relaxation. Based on our numerical
experiments, we discuss a way to quantify the eruption impact, which
could be useful for forecasting purposes.
Title: Coronal extension of the MURaM radiative MHD code: From quiet
sun to flare simulations
Authors: Rempel, Matthias D.; Cheung, Mark
Bibcode: 2016SPD....4720803R
Altcode:
We present a new version of the MURaM radiative MHD code, which
includes a treatment of the solar corona in terms of MHD, optically thin
radiative loss and field-aligned heat conduction. In order to relax the
severe time-step constraints imposed by large Alfven velocities and heat
conduction we use a combination of semi-relativistic MHD with reduced
speed of light ("Boris correction") and a hyperbolic formulation of
heat conduction. We apply the numerical setup to 4 different setups
including a mixed polarity quiet sun, an open flux region, an arcade
solution and an active region setup and find all cases an amount of
coronal heating sufficient to maintain a corona with temperatures from
1 MK (quiet sun) to 2 MK (active region, arcade). In all our setups
the Poynting flux is self-consistently created by photospheric and
sub-photospheric magneto-convection in the lower part of our simulation
domain. Varying the maximum allowed Alfven velocity ("reduced speed of
light") leads to only minor changes in the coronal structure as long
as the limited Alfven velocity remains larger than the speed of sound
and about 1.5-3 times larger than the peak advection velocity. We also
found that varying details of the numerical diffusivities that govern
the resistive and viscous energy dissipation do not strongly affect
the overall coronal heating, but the ratio of resistive and viscous
energy dependence is strongly dependent on the effective numerical
magnetic Prandtl number. We use our active region setup in order to
simulate a flare triggered by the emergence of a twisted flux rope
into a pre-existing bipolar active region. Our simulation yields a
series of flares, with the strongest one reaching GOES M1 class. The
simulation reproduces many observed properties of eruptions such as
flare ribbons, post flare loops and a sunquake.
Title: Distortions of Magnetic Flux Tubes in the Presence of Electric
Currents
Authors: Malanushenko, Anna; Rempel, Matthias; Cheung, Mark
Bibcode: 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: Physics & Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
Bibcode: 2016SPD....47.0607C
Altcode:
We provide an update on our NASA Heliophysics Grand Challenges Research
(HGCR) project on the ‘Physics & Diagnostics of the Drivers of
Solar Eruptions’. This presentation will focus on results from a
data-inspired, 3D radiative MHD model of a solar flare. The model
flare results from the interaction of newly emerging flux with a
pre-existing active region. Synthetic observables from the model
reproduce observational features compatible with actual flares. These
include signatures of coronal magnetic reconnection, chromospheric
evaporation, EUV flare arcades, sweeping motion of flare ribbons
and sunquakes.
Title: A Numerical Study of Long-range Magnetic Impacts during
Coronal Mass Ejections
Authors: Jin, M.; Schrijver, C. J.; Cheung, M. C. M.; DeRosa, M. L.;
Nitta, N. V.; Title, A. M.
Bibcode: 2016ApJ...820...16J
Altcode: 2016arXiv160304900J
With the global view and high-cadence observations from Solar Dynamics
Observatory/Atmospheric Imaging Assembly and Solar TErrestrial RElations
Observatory, many spatially separated solar eruptive events appear
to be coupled. However, the mechanisms for “sympathetic” events
are still largely unknown. In this study, we investigate the impact
of an erupting flux rope on surrounding solar structures through
large-scale magnetic coupling. We build a realistic environment of the
solar corona on 2011 February 15 using a global magnetohydrodynamics
model and initiate coronal mass ejections (CMEs) in active region
11158 by inserting Gibson-Low analytical flux ropes. We show that a
CME’s impact on the surrounding structures depends not only on the
magnetic strength of these structures and their distance to the source
region, but also on the interaction between the CME and the large-scale
magnetic field. Within the CME expansion domain where the flux rope
field directly interacts with the solar structures, expansion-induced
reconnection often modifies the overlying field, thereby increasing
the decay index. This effect may provide a primary coupling mechanism
underlying the sympathetic eruptions. The magnitude of the impact
is found to depend on the orientation of the erupting flux rope,
with the largest impacts occurring when the flux rope is favorably
oriented for reconnecting with the surrounding regions. Outside the
CME expansion domain, the influence of the CME is mainly through field
line compression or post-eruption relaxation. Based on our numerical
experiments, we discuss a way to quantify the eruption impact, which
could be useful for forecasting purposes.
Title: Numerical Study on the Emergence of Kinked Flux Tube for
Understanding of Possible Origin of δ-spot Regions
Authors: Takasao, Shinsuke; Fan, Yuhong; Cheung, Mark C. M.; Shibata,
Kazunari
Bibcode: 2015ApJ...813..112T
Altcode: 2015arXiv151102863T
We carried out an magnetohydrodynamic simulation where a subsurface
twisted kink-unstable flux tube emerges from the solar interior to the
corona. Unlike the previous expectations based on the bodily emergence
of a knotted tube, we found that the kinked tube can spontaneously
form a complex quadrupole structure at the photosphere. Due to the
development of the kink instability before the emergence, the magnetic
twist at the kinked apex of the tube is greatly reduced, although the
other parts of the tube are still strongly twisted. This leads to the
formation of a complex quadrupole structure: a pair of the coherent,
strongly twisted spots and a narrow complex bipolar pair between it. The
quadrupole is formed by the submergence of a portion of emerged magnetic
fields. This result is relevant for understanding the origin of the
complex multipolar δ-spot regions that have a strong magnetic shear
and emerge with polarity orientations not following Hale-Nicholson
and Joy Laws.
Title: Multi-parametric Study of Rising 3D Buoyant Flux Tubes in an
Adiabatic Stratification Using AMR
Authors: Martínez-Sykora, Juan; Moreno-Insertis, Fernando; Cheung,
Mark C. M.
Bibcode: 2015ApJ...814....2M
Altcode: 2015arXiv150701506M
We study the buoyant rise of magnetic flux tubes embedded in
an adiabatic stratification using two-and three-dimensional,
magnetohydrodynamic simulations. We analyze the dependence of the tube
evolution on the field line twist and on the curvature of the tube axis
in different diffusion regimes. To be able to achieve a comparatively
high spatial resolution we use the FLASH code, which has a built-in
Adaptive Mesh Refinement (AMR) capability. Our 3D experiments reach
Reynolds numbers that permit a reasonable comparison of the results
with those of previous 2D simulations. When the experiments are run
without AMR, hence with a comparatively large diffusivity, the amount
of longitudinal magnetic flux retained inside the tube increases
with the curvature of the tube axis. However, when a low-diffusion
regime is reached by using the AMR algorithms, the magnetic twist is
able to prevent the splitting of the magnetic loop into vortex tubes
and the loop curvature does not play any significant role. We detect
the generation of vorticity in the main body of the tube of opposite
sign on the opposite sides of the apex. This is a consequence of the
inhomogeneity of the azimuthal component of the field on the flux
surfaces. The lift force associated with this global vorticity makes
the flanks of the tube move away from their initial vertical plane in
an antisymmetric fashion. The trajectories have an oscillatory motion
superimposed, due to the shedding of vortex rolls to the wake, which
creates a Von Karman street.
Title: Light Bridge in a Developing Active Region. II. Numerical
Simulation of Flux Emergence and Light Bridge Formation
Authors: Toriumi, Shin; Cheung, Mark C. M.; Katsukawa, Yukio
Bibcode: 2015ApJ...811..138T
Altcode: 2015arXiv150900205T
Light bridges, the bright structure dividing umbrae in sunspot regions,
show various activity events. In Paper I, we reported on an analysis
of multi-wavelength observations of a light bridge in a developing
active region (AR) and concluded that the activity events are caused
by magnetic reconnection driven by magnetconvective evolution. The
aim of this second paper is to investigate the detailed magnetic and
velocity structures and the formation mechanism of light bridges. For
this purpose, we analyze numerical simulation data from a radiative
magnetohydrodynamics model of an emerging AR. We find that a weakly
magnetized plasma upflow in the near-surface layers of the convection
zone is entrained between the emerging magnetic bundles that appear
as pores at the solar surface. This convective upflow continuously
transports horizontal fields to the surface layer and creates a light
bridge structure. Due to the magnetic shear between the horizontal
fields of the bridge and the vertical fields of the ambient pores,
an elongated cusp-shaped current layer is formed above the bridge,
which may be favorable for magnetic reconnection. The striking
correspondence between the observational results of Paper I and the
numerical results of this paper provides a consistent physical picture
of light bridges. The dynamic activity phenomena occur as a natural
result of the bridge formation and its convective nature, which has
much in common with those of umbral dots and penumbral filaments.
Title: Light Bridge in a Developing Active Region. I. Observation
of Light Bridge and its Dynamic Activity Phenomena
Authors: Toriumi, Shin; Katsukawa, Yukio; Cheung, Mark C. M.
Bibcode: 2015ApJ...811..137T
Altcode: 2015arXiv150900183T
Light bridges, the bright structures that divide the umbra of sunspots
and pores into smaller pieces, are known to produce a wide variety
of activity events in solar active regions (ARs). It is also known
that the light bridges appear in the assembling process of nascent
sunspots. The ultimate goal of this series of papers is to reveal
the nature of light bridges in developing ARs and the occurrence of
activity events associated with the light bridge structures from
both observational and numerical approaches. In this first paper,
exploiting the observational data obtained by Hinode, the Interface
Region Imaging Spectrograph, and the Solar Dynamics Observatory, we
investigate the detailed structure of the light bridge in NOAA AR 11974
and its dynamic activity phenomena. As a result, we find that the light
bridge has a weak, horizontal magnetic field, which is transported from
the interior by a large-scale convective upflow and is surrounded by
strong, vertical fields of adjacent pores. In the chromosphere above the
bridge, a transient brightening occurs repeatedly and intermittently,
followed by a recurrent dark surge ejection into higher altitudes. Our
analysis indicates that the brightening is the plasma heating due
to magnetic reconnection at lower altitudes, while the dark surge is
the cool, dense plasma ejected from the reconnection region. From the
observational results, we conclude that the dynamic activity observed
in a light bridge structure such as chromospheric brightenings and dark
surge ejections are driven by magnetoconvective evolution within the
light bridge and its interaction with the surrounding magnetic fields.
Title: Evolving Models of Surface and Coronal Activity of Sun-Like
Stars
Authors: DeRosa, Marc; Cheung, Mark
Bibcode: 2015IAUGA..2257506D
Altcode:
Surface flux transport models have proven useful for modeling the
evolution of magnetic patterns on the solar photospheric surface on
timescales ranging from as short as a few days to as long as multiple
magnetic cycles. In the work presented here, we use surface flux
transport models to study variations in the magnetic activity of
Sun-like stars, and to explore the dependence of flux evolution on
the properties of flux emergence, large-scale flows, and dispersal
by convective turbulence. These time sequences of surface magnetic
evolution are then used to drive magnetofrictional models of stellar
coronal fields to study how coronal fields evolve. From such models,
we can begin to assess how the evolution of various stellar features,
such as interacting starspot groups, might affect the overlying
stellar coronae.
Title: Magnetic Flux Emergence in the Solar Atmosphere
Authors: Cheung, Mark
Bibcode: 2015IAUGA..2255821C
Altcode:
The emergence of magnetic flux from the solar interior into the
atmosphere drives a diverse range of dynamic phenomena. In this talk, we
review physical concepts important for understanding the flux emergence
process and discuss advances drawn from a synthesis of observations and
magnetohydrodynamics simulations. The development of data-driven models
promises to bring the two approaches ever closer. Recent results and
possibilities for future studies enabled by data-driven models will
be discussed.
Title: Physics and Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark C. M.
Bibcode: 2015shin.confE..43C
Altcode:
Recent advances in numerical modeling of magnetic flux emergence and
solar eruptions have provided important insights about the physical
drivers of these systems. At the same time, advances in capabilities of
both ground-based and space borne observatories offer unprecedented
opportunities to track how active regions on the Sun evolve. As
numerical models become ever more sophisticated (some may say more
`realistic') and as observational data reveal increasing complexity
on the Sun, studies of the physics and diagnostics of eruptive active
regions have become inextricably linked. On the one hand, there is
ample data to test the validity of numerical models. On the other hand,
analysis of observational data increasingly relies upon sophisticated
modeling efforts (e.g. solving physics-based inverse problems).
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.
Bibcode: 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: Magnetic jam in the corona of the Sun
Authors: Chen, F.; Peter, H.; Bingert, S.; Cheung, M. C. M.
Bibcode: 2015NatPh..11..492C
Altcode: 2015arXiv150501174C
The outer solar atmosphere, the corona, contains plasma at temperatures
of more than a million kelvin--more than 100 times hotter than
the solar surface. How this gas is heated is a fundamental question
tightly interwoven with the structure of the magnetic field. Together
this governs the evolution of coronal loops, the basic building block
prominently seen in X-rays and extreme ultraviolet (EUV) images. Here
we present numerical experiments accounting for both the evolving
three-dimensional structure of the magnetic field and its complex
interaction with the plasma. Although the magnetic field continuously
expands as new magnetic flux emerges through the solar surface, plasma
on successive field lines is heated in succession, giving the illusion
that an EUV loop remains roughly at the same place. For each snapshot
the EUV images outline the magnetic field. However, in contrast to
the traditional view, the temporal evolution of the magnetic field
and the EUV loops can be quite different. This indicates that the
thermal and the magnetic evolution in the outer atmosphere of a cool
star should be treated together, and should not be simply separated
as predominantly done so far.
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Model the Buildup of Free Magnetic
Energy in the Solar Corona
Authors: Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko,
M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.;
Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.;
Cheung, M. C. M.
Bibcode: 2015SpWea..13..369F
Altcode: 2015arXiv150506018F
The most violent space weather events (eruptive solar flares and
coronal mass ejections) are driven by the release of free magnetic
energy stored in the solar corona. Energy can build up on timescales
of hours to days, and then may be suddenly released in the form of a
magnetic eruption, which then propagates through interplanetary space,
possibly impacting the Earth's space environment. Can we use the
observed evolution of the magnetic and velocity fields in the solar
photosphere to model the evolution of the overlying solar coronal
field, including the storage and release of magnetic energy in such
eruptions? The objective of CGEM, the Coronal Global Evolutionary Model,
funded by the NASA/NSF Space Weather Modeling program, is to develop
and evaluate such a model for the evolution of the coronal magnetic
field. The evolving coronal magnetic field can then be used as a
starting point for magnetohydrodynamic (MHD) models of the corona,
which can then be used to drive models of heliospheric evolution and
predictions of magnetic field and plasma density conditions at 1AU.
Title: Thermal Diagnostics of Reconnection Outflows with SDO/AIA
Authors: Cheung, Mark CM
Bibcode: 2015TESS....110406C
Altcode:
We present a new method for performing differential emission measure
(DEM) inversions on narrow-band EUV images from the Atmospheric Imaging
Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). 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 (AR) 11158 comprising
quasi-steady loop atmospheres in a non- linear force-free field, and
(3) thermodynamic models from a fully-compressible, 3D MHD simulation
of AR corona formation following magnetic flux emergence. We illustrate
the utility of the method by applying it to an offlimb, eruptive M7.7
flare from NOAA AR 11520. DEM inversions from this method allow us to
study the thermal distribution and evolution of plasma expelled from
the reconnection region and their relation to plasma heated at the
footpoints of flare loops.
Title: The Coronal Global Evolutionary Model (CGEM): Toward Routine,
Time-Dependent, Data-Driven Modeling of the Active Corona
Authors: Welsch, Brian T.; Cheung, Mark CM; Fisher, George H.;
Kazachenko, Maria D.; Sun, Xudong
Bibcode: 2015TESS....131106W
Altcode:
The Coronal Global Evolutionary Model (CGEM) is a model for the
evolution of the magnetic field in the solar corona, driven using
photospheric vector magnetic field and Doppler measurements by the
HMI instrument on NASA's Solar Dynamics Observatory. Over days-long
time scales, the coronal magnetic field configuration is determined
quasi-statically using magnetofrictional relaxation. For a configuration
that becomes unstable and erupts or undergoes rapid evolution, we
can use the magnetofrictional configuration as the initial state for
MHD simulations. The model will be run in both global configurations,
covering the entire Sun, and local configurations, designed to model
the evolution of the corona above active regions. The model uses
spherical coordinates to realistically treat the large-scale coronal
geometry. The CGEM project also includes the dissemination of other
information derivable from HMI magnetogram data, such as (i) vertical
and horizontal Lorentz forces computed over active region domains,
to facilitate easier comparisons of flare/CME behavior and observed
changes of the photospheric magnetic field, and (ii) estimates of the
photospheric electric field and Poynting flux. We describe progress
that we have made in development of both the coronal model and its
input data, and discuss magnetic evolution in (i) the well-studied
NOAA AR 11158 around the time of the 2011 February 15 X2.2 flare, and
(ii) AR 11944 around the time of the 2014 January 7 X1.2 flare.
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
Carlsson, M.; Hansteen, V.
Bibcode: 2015ApJ...801...83C
Altcode: 2015arXiv150101593C
We report on observations of recurrent jets by instruments on board
the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
(SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
recurrent coronal jets were observed to emanate from NOAA Active Region
11793. Far-ultraviolet spectra probing plasma at transition region
temperatures show evidence of oppositely directed flows with components
reaching Doppler velocities of ±100 km s-1. Raster Doppler
maps using a Si iv transition region line show all four jets to have
helical motion of the same sense. Simultaneous observations of the
region by SDO and Hinode show that the jets emanate from a source
region comprising a pore embedded in the interior of a supergranule. The
parasitic pore has opposite polarity flux compared to the surrounding
network field. This leads to a spine-fan magnetic topology in the
coronal field that is amenable to jet formation. Time-dependent
data-driven simulations are used to investigate the underlying drivers
for the jets. These numerical experiments show that the emergence of
current-carrying magnetic field in the vicinity of the pore supplies
the magnetic twist needed for recurrent helical jet formation.
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
Bibcode: 2014SoPh..289.2733D
Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s−1 velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.
Title: Flux Emergence (Theory)
Authors: Cheung, Mark C. M.; Isobe, Hiroaki
Bibcode: 2014LRSP...11....3C
Altcode:
Magnetic flux emergence from the solar convection zone into the
overlying atmosphere is the driver of a diverse range of phenomena
associated with solar activity. In this article, we introduce
theoretical concepts central to the study of flux emergence and
discuss how the inclusion of different physical effects (e.g.,
magnetic buoyancy, magnetoconvection, reconnection, magnetic twist,
interaction with ambient field) in models impact the evolution of the
emerging field and plasma.
Title: From Emergence to Eruption: Challenges and Opportunities in
Data-Driven Modeling of Solar Active Regions
Authors: Cheung, Mark C. M.
Bibcode: 2014shin.confE...5C
Altcode:
Advances in theory and numerical modeling have yielded important
insights regarding the key physical processes responsible for the
evolution of active regions (ARs) and their associated eruptions. While
the majority of this work has been based on idealized scenarios, they
have been helpful in providing qualitative guidance for interpreting
observations. At the same time, our observational capability has been
greatly enhanced by new instruments on space borne and ground-based
telescopes. In particular, high cadence, full-disk observations of the
solar corona and the underlying photosphere by NASA"s Solar Dynamics
Observatory presents us an unprecedented opportunity to bring numerical
models closer to observations. In this talk, we will discuss the
challenges in data-driven and data-constrained modeling of AR evolution
and survey some recent progress in this active field of research.
Title: Thermal Diagnostics with SDO/AIA: A new method and application
to Eruptive Active Regions
Authors: Cheung, Mark; Boerner, Paul; Testa, Paola
Bibcode: 2014AAS...22432322C
Altcode:
We present a new method for the retrieval of the emission measure (EM)
distribution of coronal plasma using SDO/AIA EUV images. Unlike some
existing EM inversion algorithms, this inversion scheme does not make
assumptions about the functional form (e.g. Gaussian, power law etc.) of
the solution. The method returns positive definite solutions and runs
at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We
apply the method to a selection of eruptive active regions (ARs) to
study the thermal evolution of AR loops. In terms of both morphology
and temporal evolution, synthetic Hinode/XRT images calculated from
EM solutions retrieved using only AIA data show good agreement with
actual XRT images.
Title: High-resolution Observations of the Shock Wave Behavior for
Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
Bibcode: 2014ApJ...786..137T
Altcode: 2014arXiv1404.6291T
We present the first results of sunspot oscillations from observations
by the Interface Region Imaging Spectrograph. The strongly nonlinear
oscillation is identified in both the slit-jaw images and the
spectra of several emission lines formed in the transition region and
chromosphere. We first apply a single Gaussian fit to the profiles of
the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
sunspot. The intensity change is ~30%. The Doppler shift oscillation
reveals a sawtooth pattern with an amplitude of ~10 km s-1
in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
~12 s, respectively. The line width suddenly increases as the Doppler
shift changes from redshift to blueshift. However, we demonstrate
that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at
a few selected locations on the slit. The temporal evolution of the
line core is dominated by the following behavior: a rapid excursion
to the blue side, accompanied by an intensity increase, followed by a
linear decrease of the velocity to the red side. The maximum intensity
slightly lags the maximum blueshift in Si IV, whereas the intensity
enhancement slightly precedes the maximum blueshift in Mg II. We find
a positive correlation between the maximum velocity and deceleration,
a result that is consistent with numerical simulations of upward
propagating magnetoacoustic shock waves.
Title: A model for the formation of the active region corona driven
by magnetic flux emergence
Authors: Chen, F.; Peter, H.; Bingert, S.; Cheung, M. C. M.
Bibcode: 2014A&A...564A..12C
Altcode: 2014arXiv1402.5343C
Aims: We present the first model that couples the formation of
the corona of a solar active region to a model of the emergence of
a sunspot pair. This allows us to study when, where, and why active
region loops form, and how they evolve.
Methods: We use a 3D
radiation magnetohydrodynamics (MHD) simulation of the emergence of an
active region through the upper convection zone and the photosphere as
a lower boundary for a 3D MHD coronal model. The coronal model accounts
for the braiding of the magnetic fieldlines, which induces currents in
the corona to heat up the plasma. We synthesize the coronal emission
for a direct comparison to observations. Starting with a basically
field-free atmosphere we follow the filling of the corona with magnetic
field and plasma.
Results: Numerous individually identifiable
hot coronal loops form, and reach temperatures well above 1 MK with
densities comparable to observations. The footpoints of these loops
are found where small patches of magnetic flux concentrations move
into the sunspots. The loop formation is triggered by an increase in
upward-directed Poynting flux at their footpoints in the photosphere. In
the synthesized extreme ultraviolet (EUV) emission these loops develop
within a few minutes. The first EUV loop appears as a thin tube, then
rises and expands significantly in the horizontal direction. Later,
the spatially inhomogeneous heat input leads to a fragmented system
of multiple loops or strands in a growing envelope. Animation
associated with Fig. 2 is available in electronic form at http://www.aanda.org
Title: Numerical Simulations of Active Region Scale Flux Emergence:
From Spot Formation to Decay
Authors: Rempel, M.; Cheung, M. C. M.
Bibcode: 2014ApJ...785...90R
Altcode: 2014arXiv1402.4703R
We present numerical simulations of active region scale flux emergence
covering a time span of up to 6 days. Flux emergence is driven by
a bottom boundary condition that advects a semi-torus of magnetic
field with 1.7 × 1022 Mx flux into the computational
domain. The simulations show that, even in the absence of twist,
the magnetic flux is able the rise through the upper 15.5 Mm of the
convection zone and emerge into the photosphere to form spots. We find
that spot formation is sensitive to the persistence of upflows at the
bottom boundary footpoints, i.e., a continuing upflow would prevent
spot formation. In addition, the presence of a torus-aligned flow
(such flow into the retrograde direction is expected from angular
momentum conservation during the rise of flux ropes through the
convection zone) leads to a significant asymmetry between the pair
of spots, with the spot corresponding to the leading spot on the Sun
being more axisymmetric and coherent, but also forming with a delay
relative to the following spot. The spot formation phase transitions
directly into a decay phase. Subsurface flows fragment the magnetic
field and lead to intrusions of almost field free plasma underneath
the photosphere. When such intrusions reach photospheric layers, the
spot fragments. The timescale for spot decay is comparable to the
longest convective timescales present in the simulation domain. We
find that the dispersal of flux from a simulated spot in the first
two days of the decay phase is consistent with self-similar decay by
turbulent diffusion.
Title: Thermal Diagnostics with SDO/AIA: A new method and application
to Eruptive Active Regions
Authors: Cheung, Mark; Testa, Paola; Boerner, Paul
Bibcode: 2014cosp...40E.535C
Altcode:
We present a new method for the retrieval of the emission measure (EM)
distribution of coronal plasma using SDO/AIA EUV images. Unlike some
existing EM inversion algorithms, this inversion scheme does not make
assumptions about the functional form (e.g. Gaussian, power law etc.) of
the solution. The method returns positive definite solutions and runs
at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We
apply the method to a selection of eruptive active regions (ARs) to
study the thermal evolution of AR loops. In terms of both morphology
and temporal evolution, synthetic Hinode/XRT images calculated from
EM solutions retrieved using only AIA data show good agreement with
actual XRT images.
Title: The Location of Non-thermal Velocity in the Early Phases of
Large Flares—Revealing Pre-eruption Flux Ropes
Authors: Harra, Louise K.; Matthews, Sarah; Culhane, J. L.; Cheung,
Mark C. M.; Kontar, Eduard P.; Hara, Hirohisa
Bibcode: 2013ApJ...774..122H
Altcode:
Non-thermal velocity measurements of the solar atmosphere, particularly
from UV and X-ray emission lines have demonstrated over the decades
that this parameter is important in understanding the triggering of
solar flares. Enhancements have often been observed before intensity
enhancements are seen. However, until the launch of Hinode, it has
been difficult to determine the spatial location of the enhancements to
better understand the source region. The Hinode EUV Imaging Spectrometer
has the spectral and spatial resolution to allow us to probe the early
stages of flares in detail. We analyze four events, all of which
are GOES M- or X-classification flares, and all are located toward
the limb for ease of flare geometry interpretation. Three of the
flares were eruptive and one was confined. In all events, pre-flare
enhancement in non-thermal velocity at the base of the active region
and its surroundings has been found. These enhancements seem to be
consistent with the footpoints of the dimming regions, and hence may
be highlighting the activation of a coronal flux rope for the three
eruptive events. In addition, pre-flare enhancements in non-thermal
velocity were found above the looptops for the three eruptive events.
Title: Illusions in solar photosphere
Authors: Hurlburt, Neal E.; Cheung, M.
Bibcode: 2013SPD....4440306H
Altcode:
An array of methods have been developed over the past few decades aimed
at inferring the surface motion in the solar photosphere. These methods
are generally based on tracking the apparent motion of features seen
in the data which are, for the most part, manifestations of the thermal
or magnetic structuring generated by solar magnetoconvection. Patterns
formed by nonlinear magnetoconvection are known change dramatically
depending on the configuration and strength of the magnetic
field. These changes should be taken into account in assessing the
performance of any flow-tracking method. Here we assess one method
using high-fidelity numerical models of the magnetoconvection in the
presence of a large-scale region of emerging flux. We compare the
flow structure derived from the opflow3d method against the surface
velocities contained within the simulation and investigate systematic
errors introduced by local variations in field strength and inclination.
Title: Stray Light Correction for HMI Data
Authors: Norton, A. A.; Duvall, T.; Schou, J.; Cheung, M.
Bibcode: 2013enss.confE..95N
Altcode:
Our goal is to find a deconvolution routine that can remove scattered
light in sunspot umbrae without introducing extraneous power in high
spatial frequencies in helioseismology analysis of the same data. Using
ground-based calibration data, a third-order polynomial fit was obtained
for the instrumental modulation transfer function (MTF). Images of the
solar limb and the limb and disk of Venus during its transit were used
to model stray light. An Airy function and a Lorentzian are used in
combination to model the instrumental point spread function (PSF) for
HMI which is made to be positive definite everywhere and zero above
the ideal optical Nyquist frequency. Deconvolution was carried out
using a Lucy-Richardson algorithm on a graphics processing unit. The
deconvolved image is then compared to the original to determine the
extent of introduced Gibb's phenomenon (ringing) and how the power
changes as a function of spatial frequency.
Title: Coupled model for the formation of an active region corona
Authors: Chen, Feng; Bingert, Sven; Peter, Hardi; Cameron, Robert;
Schüssler; , Manfred; Cheung, Mark C. M.
Bibcode: 2013enss.confE..21C
Altcode:
We will present the first model that couples the formation of an active
region corona to a model of the emergence. This allows us to study
when, where, and why active region loops form, and how they evolve. For
this we use an existing 3D radiation MHD model of the emergence of an
active region through the upper convection zone and the photosphere
as a lower boundary for a coronal model. Our 3D MHD coronal model
accounts for the braiding of the magnetic field lines that induces
currents in the corona that is getting filled with the emerging magnetic
field. Starting with a basically field-free atmosphere we follow the
flux emergence until numerous individually identifiable hot coronal
loops have been formed. The temperatures in the coronal loops of well
above 1 MK are reached at densities corresponding to actually observed
active region loops. The loops develop over a very short time period
of the order of several minutes through the evaporation of material
from the chromosphere. Because we have full access to the heating
rate as a function of time and space in our computational domain we
can determine the conditions under which these loops form.
Title: The Coronal Mass Source for Post-Eruption Arcade Loops
Authors: Cheung, M. C. M.; Title, A. M.; Boerner, P.
Bibcode: 2013enss.confE.113C
Altcode:
Dark, sunward propagating features above post-eruption arcades have
long been studied using X-ray and EUV data since their first reported
discovery in the Yohkoh era. The data suggests that these so-called
supra-arcade downflows (SADs, sometimes referred to as tadpoles)
may be evacuated field lines retracting from the current sheet
beneath a coronal mass ejection. In this study, we focus on the bright
material in between tadpoles. AIA observations indicate that this high
emission-measure (EM) material is also propagating sunward. From this
empirical detection, we argue that a large fraction of retracting
field lines is loaded with mass. This plasma, which was initially
thrown up into the high coronal during the preceding CME launch, is
trapped in the reconnected magnetic field lines. As these field lines
retract toward a more force-free configuration, they pump the plasma
sunward and compress the plasma to high densities, temperatures (T >
10 MK) and EMs, leading to the fuzzy haze above the post-eruption arcade
loops. The fuzzy haze actually precedes the formation of distinct arcade
loops, which originate starting from the loop tops (which are near the
bottom of the haze) instead of the footpoints. We suggest this occurs
because the bottom of the haze is the region that has experienced
the most compression (due to pile-up up of retracting field lines)
and is thus an ideal location for catastrophic cooling to occur.
Title: Photospheric Drivers of Coronal Evolution
Authors: Welsch, B. T.; Kazachenko, M.; Fisher, G. H.; Cheung,
M. C. M.; DeRosa, M. L.; CGEM Team
Bibcode: 2013enss.confE.108W
Altcode:
Flares and coronal mass ejections (CMEs) are driven by the release
of free magnetic energy stored in the coronal magnetic field. While
this energy is stored in the corona, photospheric driving must play
a central role in its injection, storage, and release, since magnetic
fields present in the corona originated within the solar interior, and
are anchored at the photosphere. Also, the corona's low diffusivity
and high Alfven speed (compared to that at the photosphere) imply
that the large-scale coronal field essentially maintains equilibrium
(outside of episodic flares and CMEs!), and therefore only evolves
due to forcing from photospheric evolution. But fundamental questions
about each stage of this "storage and release" paradigm remain open:
How does free magnetic energy build up in the corona? How is this energy
stored? And what triggers its release? The unprecedented combination of
high cadence, resolution, and duty cycle of the HMI vector magnetograph
enables modeling coronal magnetic evolution in response to photospheric
driving, a powerful approach to addressing these questions. I will
discuss our efforts to use HMI vector magneotgrams of AR 11158 to derive
time-dependent boundary conditions for a data-driven coronal magnetic
field model. These efforts will play a key role in the planned Coronal
Global Evolutionary Model (CGEM), a data-driven, time-dependent model of
the global coronal field. This work is supported by NASA's Living With
a Star program and NSF's Division of Atmospheric and Geospace Sciences.
Title: On the Effects of the SDO Orbital Motion on the HMI Vector
Magnetic Field Measurements
Authors: Fleck, B.; Centeno, R.; Cheung, M.; Couvidat, S.; Hayashi,
K.; Rezaei, R.; Steiner, O.; Straus, T.
Bibcode: 2013enss.confE.145F
Altcode:
In a previous study we have investigated the magnetic field diagnostics
potential of SDO/HMI. We have used the output of high-resolution
3D, time-dependent, radiative magneto-hydrodynamics simulations to
calculate Stokes profiles for the Fe I 6173 Å line. From these we
constructed Stokes filtergrams using a representative set of HMI filter
response functions. The magnetic field vector (x,y) and line-of-sight
Doppler velocities V(x,y) were determined from these filtergrams using
a simplified version of the HMI magnetic field processing pipeline,
and the reconstructed magnetic field (x,y) and line-of-sight velocity
V(x,y) were compared to the actual magnetic field (x,y,z) and vertical
velocity V0(x,y,z) in the simulations. The present investigation expands
this analysis to include the effects of the significant orbital motions
of SDO, which, given the limited wavelength range of the HMI filter
profiles, affects the outer wing measurements and therefore might impact
the magnetic field measurements. We find that the effects of the orbital
movement of SDO are noticeable, in particular for the strongest fields
(B > 3 kG) and the maximum wavelength shift of 5.5 km/s (3.5 km/s
orbital movement + 2 km/s solar rotation). Saturation effects for strong
fields (B > 3 kG) are already visible for wavelength shifts of 3.2
km/s (orbital movement, disk center). The measurements of inclination
and vertical velocity are more robust. Compared to other factors of
uncertainty in the inversion of HMI Stokes measurements the orbital
movement is not a major concern or source of error.
Title: It's not raining frogs. It's raining tadpoles!
Authors: Cheung, M.; Title, A. M.
Bibcode: 2012AGUFMSH51A2195C
Altcode:
Dark, downflowing structures with tadpole-like morphologies were
discovered in TRACE EUV observations of supra-arcades of active region
eruptions. Recent EUV observations of large active region eruptions by
SDO/AIA reveal that broods of coronal condensations in post-eruption
arcades preferentially originate near the tops of arcade loops. The
time lag between the appearance of tadpoles and the appearance of dense
condensations in post-eruption arcade loops suggests a possible casual
relation. We will discuss possible explanations for this tentative
connection. One possible explanation is that tadpoles serve as sources
of mass for coronal condensations.
Title: A Method for Data-driven Simulations of Evolving Solar
Active Regions
Authors: Cheung, Mark C. M.; DeRosa, Marc L.
Bibcode: 2012ApJ...757..147C
Altcode: 2012arXiv1208.2954C
We present a method for performing data-driven simulations of
solar active region formation and evolution. The approach is based
on magnetofriction, which evolves the induction equation assuming
that the plasma velocity is proportional to the Lorentz force. The
simulations of active region (AR) coronal field are driven by temporal
sequences of photospheric magnetograms from the Helioseismic Magnetic
Imager instrument on board the Solar Dynamics Observatory (SDO). Under
certain conditions, the data-driven simulations produce flux ropes that
are ejected from the modeled AR due to loss of equilibrium. Following
the ejection of flux ropes, we find an enhancement of the photospheric
horizontal field near the polarity inversion line. We also present
a method for the synthesis of mock coronal images based on a proxy
emissivity calculated from the current density distribution in the
model. This method yields mock coronal images that are somewhat
reminiscent of images of ARs taken by instruments such as SDO's
Atmospheric Imaging Assembly at extreme ultraviolet wavelengths.
Title: How the inclination of Earth's orbit affects incoming solar
irradiance
Authors: Vieira, L. E. A.; Norton, A.; Dudok de Wit, T.; Kretzschmar,
M.; Schmidt, G. A.; Cheung, M. C. M.
Bibcode: 2012GeoRL..3916104V
Altcode:
The variability in solar irradiance, the main external energy source
of the Earth's system, must be critically studied in order to place
the effects of human-driven climate change into perspective and allow
plausible predictions of the evolution of climate. Accurate measurements
of total solar irradiance (TSI) variability by instruments onboard
space platforms during the last three solar cycles indicate changes of
approximately 0.1% over the sunspot cycle. Physics-based models also
suggest variations of the same magnitude on centennial to millennia
time-scales. Additionally, long-term changes in Earth's orbit modulate
the solar irradiance reaching the top of the atmosphere. Variations of
orbital inclination in relation to the Sun's equator could potentially
impact incoming solar irradiance as a result of the anisotropy of
the distribution of active regions. Due to a lack of quantitative
estimates, this effect has never been assessed. Here, we show that
although observers with different orbital inclinations experience
various levels of irradiance, modulations in TSI are not sufficient
to drive observed 100 kyr climate variations. Based on our model we
find that, due to orbital inclination alone, the maximum change in
the average TSI over timescales of kyrs is ∼0.003 Wm-2,
much smaller than the ∼1.5 Wm-2 annually integrated change
related to orbital eccentricity variations, or the 1-8 Wm-2
variability due to solar magnetic activity. Here, we stress that
out-of-ecliptic measurements are needed in order to constrain models
for the long-term evolution of TSI and its impact on climate.
Title: Using Electric Fields to drive simulations of the solar
coronal magnetic field
Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko,
Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong
Bibcode: 2012shin.confE..47F
Altcode:
The availability of high-cadence vector magnetograms and Doppler flow
information measured from the HMI instrument on SDO make it possible to
determine the electric field at the solar photosphere. This electric
field, in turn, can be used to drive time-dependent simulations of
the magnetic field in the solar corona, employing the MHD equations,
or simpler time-dependent models such as the magneto-frictional (MF)
model. Here, we demonstrate these concepts by using electric fields
determined from HMI data to drive a time-dependent MF model of the
solar corona in the volume overlying the photosphere near NOAA AR 11158.
Title: Topology of Coronal Fields from Evolving Magnetofrictional
Models
Authors: DeRosa, Marc L.; Cheung, M.
Bibcode: 2012AAS...22041104D
Altcode:
The evolving magnetofrictional (MF) scheme enables the construction
of time-dependent models of the active region coronal magnetic field
in response to photospheric driving. When advancing such models, only
the magnetic induction is solved, during which the velocity at each
point is assumed to be oriented parallel to the Lorentz force. This
leads to the field to evolve toward a force-free state. We present
results from an evolving MF model of NOAA AR11158 using driving
from time sequences of SDO/HMI data. Utilizing this simulation, we
investigate changes in magnetic configurations and topology,
including the number of null points, evolution of quasi-separatrix
layers, and the time-history of total and free magnetic energies as
well as relative helicity. This work seeks to elucidate the relation(s)
between topological and energetic properties of the AR.
Title: On The Magnetic-Field Diagnostics Potential of SDO/HMI
Authors: Fleck, Bernard; Hayashi, K.; Rezaei, R.; Vitas, N.; Centeno,
R.; Cheung, M.; Couvidat, S.; Fischer, C.; Steiner, O.; Straus, T.;
Viticchie, B.
Bibcode: 2012AAS...22020701F
Altcode:
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) is designed to study oscillations and the magnetic
field in the solar photosphere. It observes the full solar disk
in the Fe I absorption line at 6173 Å. We use the output of three
high-resolution 3D, time-dependent, radiative magneto-hydrodynamics
simulations (two based on the MURaM code, one on the CO5BOLD
code) to calculate Stokes profiles for the Fe I 6173 Å line
for snapshots of a sunspot, a plage area and an enhanced network
region. Stokes filtergrams are constructed for the 6 nominal HMI
wavelengths by multiplying the Stokes profiles with a representative
set of HMI filter response functions. The magnetic field vector B(x,y)
and line-of-sight Doppler velocities V(x,y) are determined from these
filtergrams using a simplified version of the HMI magnetic field
processing pipeline. Finally, the reconstructed magnetic field B(x,y)
and line-of-sight velocity V(x,y) are compared to the actual magnetic
field B0(x,y,z) and vertical velocity V0(x,y,z)
in the simulations.
Title: Magnetohydrodynamics of the Weakly Ionized Solar Photosphere
Authors: Cheung, Mark C. M.; Cameron, Robert H.
Bibcode: 2012ApJ...750....6C
Altcode: 2012arXiv1202.1937C
We investigate the importance of ambipolar diffusion and Hall
currents for high-resolution comprehensive ("realistic") photospheric
simulations. To do so, we extended the radiative magnetohydrodynamics
code MURaM to use the generalized Ohm's law under the assumption
of local thermodynamic equilibrium. We present test cases comparing
analytical solutions with numerical simulations for validation of the
code. Furthermore, we carried out a number of numerical experiments
to investigate the impact of these neutral-ion effects in the
photosphere. We find that, at the spatial resolutions currently used
(5-20 km per grid point), the Hall currents and ambipolar diffusion
begin to become significant—with flows of 100 m s-1 in
sunspot light bridges, and changes of a few percent in the thermodynamic
structure of quiet-Sun magnetic features. The magnitude of the effects
is expected to increase rapidly as smaller-scale variations are resolved
by the simulations.
Title: Data-Driven Modeling of the Evolution of Active Regions and
Coronal Holes
Authors: Cheung, M. C. M.; DeRosa, M. L.
Bibcode: 2012decs.confE..83C
Altcode:
We present results from numerical simulations of the evolution of
solar Active Regions (ARs) and Coronal Holes (CHs). The simulations
use the magnetofrictional method, which solves the induction equation
to drive magnetic configurations toward force-free states in response
to photospheric changes. The method is applied to modeling energy
build-up in ARs and morphological changes in CHs. Comparisons with
AIA data will be presented.
Title: On the Magnetic-Field Diagnostics Potential of SDO/HMI
Authors: Fleck, B.; Hayashi, K.; Rezaei, R.; Vitas, N.; Centeno,
R.; Cheung, M.; Couvidat, S.; Fischer, C.; Steiner, O.; Straus, T.;
Viticchie, B.
Bibcode: 2012decs.confE.104F
Altcode:
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) is designed to study oscillations and the magnetic
field in the solar photosphere. It observes the full solar disk
in the Fe I absorption line at 6173 Å. We use the output of three
high-resolution 3D, time-dependent, radiative magneto-hydrodynamics
simulations (two based on the MURaM code, one on the CO5BOLD code)
to calculate Stokes profiles Fi(λ,x,y; i=I, V, Q, U) for the Fe I
6173 Å line for snapshots of a sunspot, a plage area and an enhanced
network region. Stokes filtergrams are constructed for the 6 nominal
HMI wavelengths by multiplying the Stokes profiles with a representative
set of HMI filter response functions. The magnetic field vector B(x,y)
and line-of-sight Doppler velocities V(x,y) are determined from these
filtergrams using a simplified version of the HMI magnetic field
processing pipeline. Finally, the reconstructed magnetic field B(x,y)
and line-of-sight velocity V(x,y) are compared to the actual magnetic
field B0(x,y,z) and vertical velocity V0(x,y,z) in the simulations.
Title: Heliophysics Event Knowledgebase for the Solar Dynamics
Observatory (SDO) and Beyond
Authors: Hurlburt, N.; Cheung, M.; Schrijver, C.; Chang, L.; Freeland,
S.; Green, S.; Heck, C.; Jaffey, A.; Kobashi, A.; Schiff, D.; Serafin,
J.; Seguin, R.; Slater, G.; Somani, A.; Timmons, R.
Bibcode: 2012SoPh..275...67H
Altcode: 2010arXiv1008.1291H
The immense volume of data generated by the suite of instruments
on the Solar Dynamics Observatory (SDO) requires new tools for
efficient identifying and accessing data that is most relevant for
research. We have developed the Heliophysics Events Knowledgebase
(HEK) to fill this need. The HEK system combines automated data mining
using feature-detection methods and high-performance visualization
systems for data markup. In addition, web services and clients are
provided for searching the resulting metadata, reviewing results,
and efficiently accessing the data. We review these components and
present examples of their use with SDO data.
Title: Data Discovery and Access via the Heliophysics Events
Knowledgebase (HEK)
Authors: Somani, A.; Hurlburt, N. E.; Schrijver, C. J.; Cheung, M.;
Freeland, S.; Slater, G. L.; Seguin, R.; Timmons, R.; Green, S.;
Chang, L.; Kobashi, A.; Jaffey, A.
Bibcode: 2011AGUFMSM21A1989S
Altcode:
The HEK is a integrated system which helps direct scientists to solar
events and data from a variety of providers. The system is fully
operational and adoption of HEK has been growing since the launch of
NASA's SDO mission. In this presentation we describe the different
components that comprise HEK. The Heliophysics Events Registry (HER)
and Heliophysics Coverage Registry (HCR) form the two major databases
behind the system. The HCR allows the user to search on coverage event
metadata for a variety of instruments. The HER allows the user to
search on annotated event metadata for a variety of instruments. Both
the HCR and HER are accessible via a web API which can return search
results in machine readable formats (e.g. XML and JSON). A variety
of SolarSoft services are also provided to allow users to search the
HEK as well as obtain and manipulate data. Other components include
- the Event Detection System (EDS) continually runs feature finding
algorithms on SDO data to populate the HER with relevant events, -
A web form for users to request SDO data cutouts for multiple AIA
channels as well as HMI line-of-sight magnetograms, - iSolSearch,
which allows a user to browse events in the HER and search for specific
events over a specific time interval, all within a graphical web page,
- Panorama, which is the software tool used for rapid visualization of
large volumes of solar image data in multiple channels/wavelengths. The
user can also easily create WYSIWYG movies and launch the Annotator
tool to describe events and features. - EVACS, which provides a JOGL
powered client for the HER and HCR. EVACS displays the searched for
events on a full disk magnetogram of the sun while displaying more
detailed information for events.
Title: Data-driven Simulations of Evolving Active Regions
Authors: Cheung, M.; DeRosa, M. L.
Bibcode: 2011AGUFMSH33C..04C
Altcode:
We present results from numerical simulations of coronal field evolution
in response to photospheric driving. In the simulations, the coronal
field evolves according to magnetofriction, which ensures that the
model field evolves toward a non-linear force-free state. Unlike
static field extrapolation methods, this approach takes into account
the history of the photospheric field evolution. This allows for the
formation of flux ropes as well as current sheets between magnetic
domains of connectivity. Using time sequences of HMI magnetograms
as the bottom boundary condition, we apply this method to model the
emergence and evolution of various active regions. Comparisons of the
models with AIA observations and with HMI vector magnetogram inversions
will be discussed.
Title: Numerical simulations of the subsurface structure of sunspots
Authors: Rempel, M.; Cheung, M.; Birch, A. C.; Braun, D. C.
Bibcode: 2011AGUFMSH52B..02R
Altcode:
Knowledge of the subsurface magnetic field and flow structure of
sunspots is essential for understanding the processes involved in their
formation, dynamic evolution and decay. Information on the subsurface
structure can be obtained by either direct numerical modeling or
helioseismic inversions. Numerical simulations have reached only
in recent years the point at which entire sunspots or even active
regions can be modeled including all relevant physical processes
such as 3D radiative transfer and a realistic equation of state. We
present in this talk results from a series of different models: from
simulations of individual sunspots (with and without penumbrae) in
differently sized computational domains to simulations of the active
region formation process (flux emergence). It is found in all models
that the subsurface magnetic field fragments on an intermediate scale
(larger than the scale of sunspot fine structure such as umbral dots);
most of these fragmentations become visible as light bridges or flux
separation events in the photosphere. The subsurface field strength is
found to be in the 5-10 kG range. The simulated sunspots are surrounded
by large scale flows, the most dominant and robust flow component is
a deep reaching outflow with an amplitude reaching about 50% of the
convective RMS velocity at the respective depth. The simulated sunspots
show helioseismic signatures (frequency dependent travel time shifts)
similar to those in observed sunspots. On the other hand it is clear
from the simulations that these signatures originate in the upper
most 2-3 Mm of the convection zone, since only there substantial
perturbations of the wave speed are present. The contributions from
deeper layers are insignificant, in particular a direct comparison
between an 8 Mm and 16 Mm deep simulation leads to indiscernible
helioseismic differences. The National Center for Atmospheric Research
is sponsored by the National Science Foundation. This work is in part
supported through the NASA SDO Science Center.
Title: Mechanisms of sunspot formation
Authors: Cheung, M. C. M.; Rempel, M.
Bibcode: 2011sdmi.confE..34C
Altcode:
We present numerical MHD simulations that model the rise of magnetic
flux tubes through the upper 16 Mm of the solar convection zone and
into the photosphere. Due to the strong stratification (a density
contrast of 10^4), the emerging field is initially dispersed over
a wide area. Nevertheless, the dispersed flux is eventually able to
reorganize into coherent spots with photospheric field strengths of 3
kG. In the models, sunspot formation is weakly sensitive to the initial
subsurface field strength and to the presence of magnetic twist. As a
consequence sunspots can form from untwisted flux tubes with as little
as 5 kG average field strength at 16 Mm depth. The physical mechanisms
which enables this robust formation process to occur will be discussed.
Title: Waves and oscillations in the solar atmosphere
Authors: Ballou, Christopher; Cheung, Mark; Zita, E. J.; Smith,
Christina
Bibcode: 2010APS..NWS.D1006B
Altcode:
The high temperature plasma of the solar corona and chromosphere is
permeated by magnetic fields. The field lines are traced by superheated
plasma which allows for observations with diverse wavelengths of
light. We can observe and analyze waves and oscillations excited in
the solar atmosphere, to gain insight into structures and dynamics
of solar active regions. Using images from the Atmospheric Imaging
Assembly onboard NASA's Solar Dynamics Observatory, we analyze select
oscillations in the solar corona and chromosphere. We use computational
and analytical techniques to calculate wave properties and to develop
deeper understanding of compelling observations.
Title: Simulation of the Formation of a Solar Active Region
Authors: Cheung, M. C. M.; Rempel, M.; Title, A. M.; Schüssler, M.
Bibcode: 2010ApJ...720..233C
Altcode: 2010arXiv1006.4117C
We present a radiative magnetohydrodynamics simulation of the formation
of an active region (AR) on the solar surface. The simulation models
the rise of a buoyant magnetic flux bundle from a depth of 7.5 Mm in
the convection zone up into the solar photosphere. The rise of the
magnetic plasma in the convection zone is accompanied by predominantly
horizontal expansion. Such an expansion leads to a scaling relation
between the plasma density and the magnetic field strength such that
B vprop rhov1/2. The emergence of magnetic flux into the
photosphere appears as a complex magnetic pattern, which results
from the interaction of the rising magnetic field with the turbulent
convective flows. Small-scale magnetic elements at the surface
first appear, followed by their gradual coalescence into larger
magnetic concentrations, which eventually results in the formation
of a pair of opposite polarity spots. Although the mean flow pattern
in the vicinity of the developing spots is directed radially outward,
correlations between the magnetic field and velocity field fluctuations
allow the spots to accumulate flux. Such correlations result from
the Lorentz-force-driven, counterstreaming motion of opposite polarity
fragments. The formation of the simulated AR is accompanied by transient
light bridges between umbrae and umbral dots. Together with recent
sunspot modeling, this work highlights the common magnetoconvective
origin of umbral dots, light bridges, and penumbral filaments.
Title: An Introduction to the Heliophysics Event Knowledgebase
Authors: Hurlburt, Neal E.; Cheung, M.; Schrijver, C.; Chang, L.;
Freeland, S.; Green, S.; Heck, C.; Jaffey, A.; Kobashi, A.; Schiff,
D.; Serafin, J.; Seguin, R.; Slater, G.; Somani, A.; Timmons, R.
Bibcode: 2010AAS...21640222H
Altcode: 2010BAAS...41T.876H
The immense volume of data generated by the suite of instruments on
SDO requires new tools for efficiently identifying and accessing data
that are most relevant to research investigations. We have developed
the Heliophysics Events Knowledgebase (HEK) to fill this need. The
system developed to support the HEK combines automated datamining using
feature detection methods; high-performance visualization systems for
data markup; and web-services and clients for searching the resulting
metadata, reviewing results and efficient access to the data. We will
review these components and present examples of their use with SDO data.
Title: The Heliophysics Event Knowledgebase for the Solar Dynamics
Observatory - A User's Perspective
Authors: Slater, Gregory L.; Cheung, M.; Hurlburt, N.; Schrijver,
C.; Somani, A.; Freeland, S. L.; Timmons, R.; Kobashi, A.; Serafin,
J.; Schiff, D.; Seguin, R.
Bibcode: 2010AAS...21641505S
Altcode: 2010BAAS...41S.825S
The recently launched Solar Dynamics Observatory (SDO) will
generated over 2 petabytes of imagery in its 5 year mission. The
Heliophysics Events Knowledgebase (HEK) system has been developed to
continuously build a database of solar features and events contributed
by a combination of machine recognition algorithms run on every single
image, and human interactive data exploration. Access to this growing
database is provided through a set of currently existing tools as well
as an open source API. We present an overview of the user interface
tools including illustrative examples of their use.
Title: An Introduction to the Heliophysics Event Knowledgebase for SDO
Authors: Hurlburt, Neal; Schrijver, Carolus; Cheung, Mark
Bibcode: 2010cosp...38.2879H
Altcode: 2010cosp.meet.2879H
The immense volume of data generated by the suite of instruments on
SDO requires new tools for efficient identifying and accessing data
that is most relevant to research investigations. We have developed the
Heliophysics Events Knowledgebase (HEK) to fill this need. The system
developed in support of the HEK combines automated datamining using
feature detection methods; high-performance visualization systems for
data markup; and web-services and clients for searching the resulting
metadata, reviewing results and efficient access to the data. We will
review these components and present examples of their use with SDO data.
Title: Simulation of a flux emergence event and comparison with
observations by Hinode
Authors: Yelles Chaouche, L.; Cheung, M. C. M.; Solanki, S. K.;
Schüssler, M.; Lagg, A.
Bibcode: 2009A&A...507L..53Y
Altcode: 2009arXiv0910.5737Y
Aims: We study the observational signature of flux emergence in
the photosphere using synthetic data from a 3D MHD simulation of the
emergence of a twisted flux tube.
Methods: Several stages in the
emergence process are considered. At every stage we compute synthetic
Stokes spectra of the two iron lines Fe I 6301.5 Å and Fe I 6302.5
Å and degrade the data to the spatial and spectral resolution of
Hinode's SOT/SP. Then, following observational practice, we apply
Milne-Eddington-type inversions to the synthetic spectra in order
to retrieve various atmospheric parameters and compare the results
with recent Hinode observations.
Results: During the emergence
sequence, the spectral lines sample different parts of the rising
flux tube, revealing its twisted structure. The horizontal component
of the magnetic field retrieved from the simulations is close to the
observed values. The flattening of the flux tube in the photosphere is
caused by radiative cooling, which slows down the ascent of the tube
to the upper solar atmosphere. Consistent with the observations, the
rising magnetized plasma produces a blue shift of the spectral lines
during a large part of the emergence sequence. Figure 3 is only
available in electronic form at http://www.aanda.org
Title: Magnetic Flux Emergence on Different Scales
Authors: Hagenaar, M.; Cheung, M.
Bibcode: 2009ASPC..415..167H
Altcode:
Magnetic flux emerges on the Sun on many different scales, from
weak intranetwork to network concentrations and (ephemeral) active
regions. Methods previously developed to recognize regions of magnetic
emergence on MDI Full Disk magnetograms fail when applied to Hinode/SOT
Stokes maps: the resolution is so much higher that simple bipoles on
MDI are observed as collections of fragments. We present a new method
for the automatic detection and characterization of flux emergence on
a range of scales.
Title: The Second Hinode Science Meeting: Beyond Discovery-Toward
Understanding
Authors: Lites, B.; Cheung, M.; Magara, T.; Mariska, J.; Reeves, K.
Bibcode: 2009ASPC..415.....L
Altcode:
No abstract at ADS
Title: Solar Surface Emerging Flux Regions: A Comparative Study of
Radiative MHD Modeling and Hinode SOT Observations
Authors: Cheung, M.; Schüssler, M.; Tarbell, T. D.; Title, A. M.
Bibcode: 2009ASPC..415...79C
Altcode:
We present results from three-dimensional radiative MHD simulations
of the rise of buoyant magnetic flux tubes through the convection
zone and into the photosphere. Due to the strong stratification
of the convection zone, the rise results in a lateral expansion
of the tube into a magnetic sheet, which acts as a reservoir for
small-scale flux emergence events at the scale of granulation. The
interaction of the convective downflows and the rising magnetic flux
tube undulates it to form serpentine field lines that emerge into the
photosphere. Observational characteristics of the simulated emerging
flux regions are discussed in the context of new observations from
Hinode SOT.
Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953:
A Critical Assessment
Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan,
J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.;
Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.;
Inhester, B.; Tadesse, T.
Bibcode: 2009SPD....40.3102D
Altcode:
Nonlinear force-free field (NLFFF) modeling seeks to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have failed to arrive at consistent solutions when
applied to (thus far, two) cases using the highest-available-resolution
vector magnetogram data from Hinode/SOT-SP (in the region of the
modeling area of interest) and line-of-sight magnetograms from
SOHO/MDI (where vector data were not available). One issue is that
NLFFF models require consistent, force-free vector magnetic boundary
data, and vector magnetogram data sampling the photosphere do not
satisfy this requirement. Consequently, several problems have arisen
that are believed to affect such modeling efforts. We use AR 10953
to illustrate these problems, namely: (1) some of the far-reaching,
current-carrying connections are exterior to the observational field
of view, (2) the solution algorithms do not (yet) incorporate the
measurement uncertainties in the vector magnetogram data, and/or (3)
a better way is needed to account for the Lorentz forces within the
layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
Title: A Critical Assessment of Nonlinear Force-Free Field Modeling
of the Solar Corona for Active Region 10953
Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham;
Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar;
Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann,
Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas;
Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester,
Bernd; Tadesse, Tilaye
Bibcode: 2009ApJ...696.1780D
Altcode: 2009arXiv0902.1007D
Nonlinear force-free field (NLFFF) models are thought to be viable
tools for investigating the structure, dynamics, and evolution of
the coronae of solar active regions. In a series of NLFFF modeling
studies, we have found that NLFFF models are successful in application
to analytic test cases, and relatively successful when applied
to numerically constructed Sun-like test cases, but they are less
successful in application to real solar data. Different NLFFF models
have been found to have markedly different field line configurations
and to provide widely varying estimates of the magnetic free energy in
the coronal volume, when applied to solar data. NLFFF models require
consistent, force-free vector magnetic boundary data. However,
vector magnetogram observations sampling the photosphere, which is
dynamic and contains significant Lorentz and buoyancy forces, do not
satisfy this requirement, thus creating several major problems for
force-free coronal modeling efforts. In this paper, we discuss NLFFF
modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT,
STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process
illustrate three such issues we judge to be critical to the success of
NLFFF modeling: (1) vector magnetic field data covering larger areas
are needed so that more electric currents associated with the full
active regions of interest are measured, (2) the modeling algorithms
need a way to accommodate the various uncertainties in the boundary
data, and (3) a more realistic physical model is needed to approximate
the photosphere-to-corona interface in order to better transform the
forced photospheric magnetograms into adequate approximations of nearly
force-free fields at the base of the corona. We make recommendations
for future modeling efforts to overcome these as yet unsolved problems.
Title: The Heliophysics Event Knowledgebase for the Solar Dynamics
Observatory
Authors: Hurlburt, Neal E.; Cheung, M.; Schrijver, K.; HEK development
Team
Bibcode: 2009SPD....40.1511H
Altcode:
The Solar Dynamics Observatory will generated over 2 petabytes
of imagery in its 5 year mission. In order to improve scientific
productivity and to reduce system requirements , we have developed
a system for data markup to identify "interesting” datasets and
direct scientists to them through an event-based querying system. The
SDO Heliophysics Event Knowledgebase (HEK) will enable caching of
commonly accessed datasets within the Joint Science Operations Center
(JSOC) and reduces the (human) time spent searching for and downloading
relevant data. We present an overview of our HEK including the ingestion
of images, automated and manual tools for identifying and annotation
features within the images, and interfaces and web tools for querying
and accessing events and their associated data.
Title: Interaction Between Emerging Magnetic Flux And The Ambient
Solar Coronal Field
Authors: Cheung, Mark; De Rosa, M.
Bibcode: 2009SPD....40.3103C
Altcode:
We study the interaction between emerging magnetic flux and
pre-existing coronal field by means of numerical simulations using
the magneto-frictional method. By advancing the induction equation,
the magneto-frictional method models the coronal magnetic field as a
quasi-static sequence of non-linear force-free field configurations
evolving in response to photospheric driving. A general feature of the
simulations is the spontaneous formation of current sheets. At these
interfaces, the field line torsional coefficient changes abruptly
across separate domains of connectivity. Since the code evolves the
vector potential, it allows us to calculate how much relative magnetic
helicity and free energy is stored in the system. By using temporal
sequences of observed vector magnetograms as the boundary condition,
this model is potentially suitable for modeling the evolution of solar
coronal fields.
Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar
Corona: A Critical Assessment
Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.;
Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung,
M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.
Bibcode: 2008AGUFMSH41A1604D
Altcode:
Nonlinear force-free field (NLFFF) modeling promises to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have so far failed to arrive at consistent solutions
when applied to cases using the highest-available-resolution vector
magnetogram data from Hinode/SOT-SP (in the region of the modeling
area of interest) and line-of-sight magnetograms from SOHO/MDI (where
vector data were not been available). It is our view that the lack of
robust results indicates an endemic problem with the NLFFF modeling
process, and that this process will likely continue to fail until (1)
more of the far-reaching, current-carrying connections are within the
observational field of view, (2) the solution algorithms incorporate
the measurement uncertainties in the vector magnetogram data, and/or
(3) a better way is found to account for the Lorentz forces within
the layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
Title: A Distributed Processing and Analysis System for Heliophysic
Events
Authors: Hurlburt, N.; Cheung, M.; Bose, P.
Bibcode: 2008AGUFMSA53A1580H
Altcode:
With several Virtual Observatories now under active development, the
time is ripe to consider how they will interact to enable integrated
studies that span the full range of Heliophysics. We present a solution
that builds upon components of the Heliophysics Event Knowledgebase
(HEK) being developed for the Solar Dynamics Observatory and the
Heliophysics Event List Manager (HELMS), recently selected as
part of the NASA VxO program. A Heliophysics Event Analysis and
Processing System (HEAPS) could increase the scientific productivity
of Heliophysics data by increasing the visibility of relevant events
contained within them while decreasing the incremental costs of
incorporating more events in research studies. Here we present the
relevant precursors to such a system and show how it could operate
within the Heliophysics Data Environment.
Title: Solar Surface Emerging Flux Regions: A Comparative Study of
Radiative MHD Modeling and Hinode SOT Observations
Authors: Cheung, M. C. M.; Schüssler, M.; Tarbell, T. D.; Title, A. M.
Bibcode: 2008ApJ...687.1373C
Altcode: 2008arXiv0810.5723C
We present results from numerical modeling of emerging flux regions
on the solar surface. The modeling was carried out by means of
three-dimensional (3D) radiative MHD simulations of the rise of
buoyant magnetic flux tubes through the convection zone and into the
photosphere. Due to the strong stratification of the convection zone,
the rise results in a lateral expansion of the tube into a magnetic
sheet, which acts as a reservoir for small-scale flux emergence
events at the scale of granulation. The interaction of the convective
downflows and the rising magnetic flux tube undulates it to form
serpentine field lines that emerge into the photosphere. Observational
characteristics, including the pattern of the emerging flux regions,
the cancellation of surface flux and associated high-speed downflows,
the convective collapse of photospheric flux tubes, the appearance
of anomalous darkenings, the formation of bright points, and the
possible existence of transient kilogauss horizontal fields are
discussed in the context of new observations from the Hinode Solar
Optical Telescope. Implications for the local helioseismology of
emerging flux regions are also discussed.
Title: Magnetic Flux Emergence on Different Scales
Authors: Hagenaar, H.; Cheung, M.
Bibcode: 2008ESPM...12.2.53H
Altcode:
Magnetic flux emerges on the Sun on many different scales, from
weak intranetwork to network concentrations and (ephemeral) active
regions. Methods previously developed to recognize regions of
magnetic emergence on MDI Full Disk magnetograms fail when applied to
Hinode/SOT Stokes maps: the resolution is so much higher that simple
bipoles on MDI are observed as collections of fragments. We present
a new method for the automatic detection and characterization of
flux emergence on a range of scales. Our findings are compared with
simulations and discuss the implications for our understanding of
emerging flux ropes.
Title: Patterns of Flux Emergence
Authors: Title, A.; Cheung, M.
Bibcode: 2008AGUSMSH54A..01T
Altcode:
The high spatial resolution and high cadence of the Solar Optical
Telescope on the JAXA Hinode spacecraft have allowed capturing many
examples of magnetic flux emergence from the scale of granulation
to active regions. The observed patterns of emergence are quite
similar. Flux emerges as a array of small bipoles on scales from
1 to 5 arc seconds throughout the region that the flux eventually
condenses. Because the fields emerging from the underlying flux rope
my appear many in small segments and the total flux (absolute sum) is
not a conserved quantity the amount of total flux on the surface may
vary significantly during the emergence process. Numerical simulations
of flux emergence exhibit patterns similar to observations. Movies of
both observations and numerical simulations will be presented.
Title: The Atmospheric Imaging Array Feature and Event System (AFES)
for SDO
Authors: Hurlburt, N.; Freeland, S.; Cheung, M.; Schrijver, C.
Bibcode: 2008AGUSMSM21A..07H
Altcode:
The great data volumes involved in Solar Dynamics Observatory impose
the need to have efficient means to access, process and transport
data products that goes beyond basic data discovery. In order to
reduce system requirements and to improve scientific productivity,
we pre-package Ðinterestingî datasets and direct scientists to them
through an event-based querying system. This will enable caching of
commonly accessed datasets within the Joint Science Operations Center
(JSOC) and reduces the (human) time spent searching for and downloading
relevant data. This system leverages the infrastructure developed
for the Hinode Observation System (http://sot.lmsal.com/sot-data)
and incorporates elements of the evolving heliophysics knowledgebase
(http://www.lmsal.com/helio-informatics/hpkb). We present the details
of the AFES including the ingestion of images, automated and manual
tools for identifying and annotation features within the images, and
interfaces and webtools for querying and accessing events and their
associated data. This work has been supported by NASA through contract
NNG04AE00C and Lockheed Martin Research Funds.
Title: On resolving the 180 deg ambiguity for a temporal sequence
of vector magnetograms
Authors: Cheung, M. C.
Bibcode: 2008AGUSMSP51D..04C
Altcode:
The solar coronal magnetic field evolves in response to the underlying
photospheric driving. To study this connection by means of data-driven
modeling, an accurate knowledge of the evolution of the photospheric
vector field is essential. While there is a large body of work on
attempts to resolve the 180 deg ambiguity in the component of the
magnetic field transverse to the line of sight, most of these methods
are applicable only to individual frames. With the imminent launch
of the Solar Dynamics Observatory, it is especially timely for us
to develop possible automated methods to resolve the ambiguity for
temporal sequences of magnetograms. We present here the temporal acute
angle method, which makes use of preceding disambiguated magnetograms as
reference solutions for resolving the ambiguity in subsequent frames. To
find the strengths and weaknesses of this method, we have carried out
tests (1) on idealized magnetogram sequences involving simple rotating,
shearing and straining flows and (2) on a synthetic magnetogram sequence
from a 3D radiative MHD simulation of an buoyant magnetic flux tube
emerging through granular convection. A metric for automatically picking
out regions where the method is likely to fail is also presented.
Title: Magnetic Flux Emergence in the Solar Photosphere
Authors: Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.
Bibcode: 2008ASPC..384..181C
Altcode: 2008csss...14..181C
The most prominent magnetic structures on the surface of the Sun are
bipolar active regions. These magnetic complexes are comprised of
a hierarchy of magnetic structures of different sizes, the largest
of which are sunspots. Observations indicate that the appearance
of active regions on the solar surface result from the emergence of
bundles of magnetic flux from the underlying convection zone. We study
the emergence process by means of 3D radiation MHD simulations. In the
simulations, an initially buoyant magnetic flux tube is introduced into
the near-surface layers of the convection zone. Subject to the buoyancy
force, the flux tube rises towards the photosphere. Our simulations
highlight the importance of magneto-convection on the evolution of
the magnetic flux tube. The external convective flow field has an
important influence on the emergence morphology of the emerging magnetic
field. Depending on the initial properties of the magnetic flux tube
(e.g. field strength, twist, entropy etc.), flux emergence may lead
to a disturbance of the local granulation pattern. The observational
signatures associated with emerging magnetic flux in our simulations
are in qualitative and quantitative agreement with observational
studies of emerging flux regions on the Sun.
Title: The Collaborative Heliophysics Observatory
Authors: Hurlburt, N.; Freeland, S.; Cheung, M.; Bose, P.
Bibcode: 2007AGUFMSH51A0256H
Altcode:
The Collaborative Heliophysics Observatory (CHO) would provide a robust
framework and enabling tools to fully utilize the VOs for scientific
discovery and collaboration. Scientists across the realm of heliophysics
would be able to create, use and share applications -- either as
services using familiar tools or through intuitive workflows -- that
orchestrate access to data across all virtual observatories. These
applications can be shared freely knowing that proper recognition of
data and processing components are acknowledged; that erroneous use
of data is flagged; and that results from the analysis runs will in
themselves be shared Ð all in a transparent and automatic fashion. In
addition, the CHO would incorporate cross-VO models and tools to weave
the various virtual observatories into a unified system. These provide
starting points for interactions across the solar/heliospheric and
heliospheric/magnetospheric boundaries.
Title: Photospheric Magnetic Flux Emergence: A comparative study
between Hinode/SOT Observations and MHD simulations
Authors: Cheung, M. C.; Schüssler, M.; Moreno-Insertis, F.; Tarbell,
T. D.
Bibcode: 2007AGUFMSH53A1073C
Altcode:
With high angular resolution, high temporal cadence and a stable
point spread function, the Solar Optical Telescope (SOT) onboard the
Hinode satellite is the ideal instrument for the study of magnetic
flux emergence and its manifestations on the solar surface. In this
presentation, we focus on the development of ephemeral regions and
small active regions. In many instances, SOT has been able to capture
the entire emergence process from beginning to end: i.e. from the
initial stages of flux appearance in granule interiors, through the
intermediate stages of G-band bright point formation, and finally
to the coalescence of small vertical flux elements to form pores. To
investigate the physics of the flux emergence process, we performed
3D numerical MHD simulations with the MURaM code. The models are able
to reproduce, and help us explain, various observational signatures
of magnetic flux emergence.
Title: Magnetic Flux Emergence In Granular Convection: Radiative
MHD Simulations And Hinode SOT Observations
Authors: Cheung, Mark; Schüssler, M.; Moreno-Insertis, F.; Tarbell,
T.; SOT Team
Bibcode: 2007AAS...210.9425C
Altcode: 2007BAAS...39..221C
We model the emergence of buoyant magnetic flux from the convection
zone into the photosphere by means of 3D radiative MHD simulations
using the MURaM code. In a series of simulations, we study how
an initially buoyant magnetic flux tube rises in the presence of
granular convection. The simulations take into account the effects of
radiative energy exchange, ionization effects in the equation of state
and compressibility. An emphasis of this talk is the comparison of
observational diagnostics from the simulations with recent observations
from Hinode SOT.
Title: Helio-informatics: Preparing For The Future Of Heliophysics
Research.
Authors: Schrijver, Carolus J.; Hurlburt, N. E.; Cheung, M. C.; Title,
A. M.; Delouille, V.; Hochedez, J.; Berghmans, D.
Bibcode: 2007AAS...210.2514S
Altcode: 2007BAAS...39..133S
The rapidly growing data volumes for space- and ground-based
observatories for Sun and heliosphere will soon make it impractical,
costly, and perhaps effectively impossible for researchers to download
and locally inspect substantial portions of the data archives. By
the end of 2008, for example, the Solar Dynamics Observatory will
downlink over 2TB/day of compressed data; such a large volume would
readily saturate internet connections to the archive site if it were
exported to a handful of researchers around the world. We envision a
revolution in research methodology towards a mode in which researchers
run autonomous event-finding algorithms at a primary data archive in
order to pre-select relatively small subsets of the data that can
subsequently be inspected and analyzed in detail at a researcher's
home institution. Teams from the SDO, Hinode, STEREO, and TRACE
missions are developing the infrastructure that is needed to make this
into a useful research tool: we are (1) defining standardized event
attributes compatible with the Virtual Observatory and EGSO concepts,
(2) developing a knowledge base supported by a web-based tool for
compound queries based on the contents of solar and heliospheric
observations, and (3) assembling a group of researchers who are
interested in helping us develop a prototype system while beta-testing
it in real scientific studies. We invite you to contact us (a) if you
have feature-finding algorithms that you would like to see applied to
existing data archives, (b) if you would like to contribute expertise
in developing the knowledge-base system, or (c) if you would like
to participate in the testing of the system for scientific use. More
information on our plans, target dates, and contact information can
be found at http://www.lmsal.com/helio-informatics/hpkb/. The
helio-informatics project is being developed with support from
the HINODE/SOT (NNM07AA01C), SDO/AIA (NNG04EA00C), STEREO/SECCHI
(N00173-02-C-2035), and TRACE (NAS5-38099) science investigations.
Title: Magnetic flux emergence in granular convection: radiative
MHD simulations and observational signatures
Authors: Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.
Bibcode: 2007A&A...467..703C
Altcode: 2007astro.ph..2666C
Aims:We study the emergence of magnetic flux from the near-surface
layers of the solar convection zone into the photosphere.
Methods:
To model magnetic flux emergence, we carried out a set of numerical
radiative magnetohydrodynamics simulations. Our simulations take into
account the effects of compressibility, energy exchange via radiative
transfer, and partial ionization in the equation of state. All these
physical ingredients are essential for a proper treatment of the
problem. Furthermore, the inclusion of radiative transfer allows us
to directly compare the simulation results with actual observations
of emerging flux.
Results: We find that the interaction between
the magnetic flux tube and the external flow field has an important
influence on the emergent morphology of the magnetic field. Depending
on the initial properties of the flux tube (e.g. field strength,
twist, entropy etc.), the emergence process can also modify the local
granulation pattern. The emergence of magnetic flux tubes with a
flux of 1019 Mx disturbs the granulation and leads to the
transient appearance of a dark lane, which is coincident with upflowing
material. These results are consistent with observed properties of
emerging magnetic flux. Movies are only available in electronic
form at http://www.aanda.org
Title: The origin of the reversed granulation in the solar photosphere
Authors: Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.
Bibcode: 2007A&A...461.1163C
Altcode: 2006astro.ph.12464C
Aims:We study the structure and reveal the physical nature of the
reversed granulation pattern in the solar photosphere by means of
3-dimensional radiative hydrodynamics simulations.
Methods: We
used the MURaM code to obtain a realistic model of the near-surface
layers of the convection zone and the photosphere.
Results:
The pattern of horizontal temperature fluctuations at the base of
the photosphere consists of relatively hot granular cells bounded by
the cooler intergranular downflow network. With increasing height
in the photosphere, the amplitude of the temperature fluctuations
diminishes. At a height of z=130-140 km in the photosphere, the pattern
of horizontal temperature fluctuations reverses so that granular regions
become relatively cool compared to the intergranular network. Detailed
analysis of the trajectories of fluid elements through the photosphere
reveal that the motion of the fluid is non-adiabatic, owing to strong
radiative cooling when approaching the surface of optical depth
unity followed by reheating by the radiation field from below. The
temperature structure of the photosphere results from the competition
between expansion of rising fluid elements and radiative heating. The
former acts to lower the temperature of the fluid whereas the latter
acts to increase it towards the radiative equilibrium temperature with
a net entropy gain. After the fluid overturns and descends towards the
convection zone, radiative energy loss again decreases the entropy
of the fluid. Radiative heating and cooling of fluid elements that
penetrate into the photosphere and overturn do not occur in equal
amounts. The imbalance in the cumulative heating and cooling of
these fluid elements is responsible for the reversal of temperature
fluctuations with respect to height in the photosphere.
Title: Flux Emergence at the Photosphere
Authors: Cheung, M. C. M.; Schüssler, M.; Moreno-Insertis, F.
Bibcode: 2006ASPC..354...97C
Altcode:
To model the emergence of magnetic fields at the photosphere, we
carried out 3D magneto-hydrodynamics (MHD) simulations using the MURaM
code. Our simulations take into account the effects of compressibility,
energy exchange via radiative transfer and partial ionization in the
equation of state. All these physical ingredients are essential for
a proper treatment of the problem. In the simulations, an initially
buoyant magnetic flux tube is embedded in the upper layers of the
convection zone. We find that the interaction between the flux tube
and the external flow field has an important influence on the emergent
morphology of the magnetic field. Depending on the initial properties of
the flux tube (e.g. field strength, twist, entropy etc.), the emergence
process can also modify the local granulation pattern. The inclusion
of radiative transfer allows us to directly compare the simulation
results with real observations of emerging flux.
Title: Flux Emergence In The Solar Photosphere - Diagnostics Based
On 3-D Rradiation-MHD Simulations
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
Bibcode: 2006IAUJD...3E..75Y
Altcode:
We investigate flux tube emergence in the solar photosphere using a
diagnostic procedure based on analyzing Stokes signals from different
spectral lines calculated in 3-D radiation-MHD simulations. The
simulations include the effects of radiative transport and partial
ionization and cover layers both above and below the solar surface. The
simulations consider the emergence of a twisted magnetic flux tube
through the solar surface. We consider different stages in the emergence
process, starting from the early appearance of the flux tube at the
solar surface, and following the emergence process until the emerged
flux looks similar to a normal bipolar region. At every stage we compute
line profiles by numerically solving the Unno-Rachkovsky equations at
every horizontal grid point. Then, following observational practice,
we apply Milne-Eddington-type inversions to the synthetic spectra in
order to retrieve different atmospheric parameters. We include the
influence of spatial smearing on the deduced atmospheric parameters
to identify signatures of different stages of flux emergence in the
solar photosphere.
Title: Moving magnetic tubes: fragmentation, vortex streets and the
limit of the approximation of thin flux tubes
Authors: Cheung, M. C. M.; Moreno-Insertis, F.; Schüssler, M.
Bibcode: 2006A&A...451..303C
Altcode:
Aims.We study the buoyant rise of magnetic flux tubes in a stratified
layer over a range of Reynolds numbers (25 ⪉ Re ⪉ 2600) by means
of numerical simulations. Special emphasis is placed on studying the
fragmentation of the rising tube, its trailing wake and the formation
of a vortex street in the high-Reynolds number regime. Furthermore,
we evaluate the relevance of the thin flux tube approximation
with regard to describing the evolution of magnetic flux tubes
in the simulations.
Methods: .We used the FLASH code, which
has an adaptive mesh refinement (AMR) algorithm, thus allowing the
simulations to be carried out at high Reynolds numbers.
Results:
.The evolution of the magnetic flux tube and its wake depends on the
Reynolds number. At Re up to a few hundred, the wake consists of two
counter-rotating vortex rolls. At higher Re, the vortex rolls break up
and the shedding of flux into the wake occurs in a more intermittent
fashion. The amount of flux retained by the central portion of the
tube increases with the field line twist (in agreement with previous
literature) and with Re. The time evolution of the twist is compatible
with a homologous expansion of the tube. The motion of the central
portion of the tube in the simulations is very well described by the
thin flux tube model whenever the effects of flux loss or vortex forces
can be neglected. If the flux tube has an initial net vorticity, it
undergoes asymmetric vortex shedding. In this case, the lift force
accelerates the tube in such a way that an oscillatory horizontal
motion is super-imposed on the vertical rise of the tube, which leaves
behind a vortex street. This last result is in accordance with previous
simulations reported in the literature, which were carried out at
lower Reynolds number.
Title: Diagnostics of a Simulated Flux Tube Emergence
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
Bibcode: 2005ESASP.600E..74Y
Altcode: 2005ESASP.600E..74C; 2005ESPM...11...74C; 2005dysu.confE..74C
No abstract at ADS
Title: D Magneto-Convection and Flux Emergence in the Photosphere
Authors: Cheung, M.; Schüssler, M.; Moreno-Insertis, F.
Bibcode: 2005ESASP.596E..54C
Altcode: 2005ccmf.confE..54C
No abstract at ADS
Title: Supernova remnant G292.2-0.5, its pulsar, and the Galactic
magnetic field
Authors: Caswell, J. L.; McClure-Griffiths, N. M.; Cheung, M. C. M.
Bibcode: 2004MNRAS.352.1405C
Altcode: 2004MNRAS.tmp..180C
The extended low-brightness Galactic radio source G292.2-0.5 is one of
the few supernova remnants (SNRs) showing a likely association with
a young pulsar. New observations of the remnant with the Australia
Telescope Compact Array yield a distance of 8.4 kpc determined
from HI absorption measurements, and the first detection of linear
polarization. The polarization was studied at two frequencies near
5 GHz, revealing a high mean rotation measure, approximately +800
rad m-2, strikingly similar to that of the pulsar. This
similarity, and the compatibility of the pulsar distance estimate with
the new SNR distance, now provides overwhelming evidence that the pulsar
is indeed embedded within the SNR, and that both were presumably born in
the same supernova event. The ratio of rotation measure to pulsar
dispersion measure yields a value of -1.4 μG (towards us) for the
(density-weighted) average line-of-sight component of magnetic field
for the 8.4-kpc path-length to the SNR and pulsar. The unusually high
rotation measure, together with the large distance over which it has
accumulated, argues that this field is a persistent feature on a large
scale that outweighs smaller-scale fluctuations and reversals. The
8.4-kpc path-length lies almost wholly within the Carina spiral arm
of our Galaxy and thus this portion of the arm possesses an average
clockwise field of 1.4 μG. We interpret other evidence to suggest
that the clockwise field extends for at least a further 8.5 kpc along
the same arm, in the region where it is usually referred to as the
Sagittarius arm. Observations such as these provide a powerful tool
for exploring the large-scale structure of the Galactic magnetic field
in relation to the spiral-arm structure.