explanation      blue bibcodes open ADS page with paths to full text
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
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
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
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
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
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
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
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
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
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.
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.
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
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
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.
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
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.
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.
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.
2022ApJ...925..188G    Altcode: 2021arXiv211103208G
  Small-scale internetwork (IN) magnetic fields are considered to be the
  main building blocks of quiet Sun magnetism. For this reason, it is
  crucial to understand how they appear on the solar surface. Here,
  we employ a high-resolution, high-sensitivity, long-duration
  Hinode/NFI magnetogram sequence to analyze the appearance modes and
  spatiotemporal evolution of individual IN magnetic elements inside a
  supergranular cell at the disk center. From identification of flux
  patches and magnetofrictional simulations, we show that there are
  two distinct populations of IN flux concentrations: unipolar and
  bipolar features. Bipolar features tend to be bigger and stronger
  than unipolar features. They also live longer and carry more flux
  per feature. Both types of flux concentrations appear uniformly over
  the solar surface. However, we argue that bipolar features truly
  represent the emergence of new flux on the solar surface, while
  unipolar features seem to be formed by the coalescence of background
  flux. Magnetic bipoles appear at a faster rate than unipolar features
  (68 as opposed to 55 Mx cm<SUP>-2</SUP> day<SUP>-1</SUP>), and provide
  about 70% of the total instantaneous IN flux detected in the interior
  of the supergranule.

---------------------------------------------------------
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
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 (&lt;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
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.
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.
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
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
  ~10<SUP>18</SUP> Mx hr<SUP>-1</SUP>; (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 (~10<SUP>26</SUP>-10<SUP>27</SUP> 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
  &lt;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.
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
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 &gt;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. <P />CubIXSS comprises two co-optimized
  and cross-calibrated instruments that fill a critical observational
  gap: <P />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 <P />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. <P />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.
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. <P />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.
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.
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.
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.
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.
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<SUB>⊙</SUB> 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
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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.
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.
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.
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.
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
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.
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.
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
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
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
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
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
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.
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
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.
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.
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
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
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.
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.
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
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.
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.
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.
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
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
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.
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
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
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.
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. <BR /> 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. <BR /> 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. <BR /> 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&amp;k, and Ca II H&amp;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. <BR /> 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.
2019NatAs...3..160C    Altcode: 2018NatAs...3..160C
  Solar and stellar flares are the most intense emitters of X-rays and
  extreme ultraviolet radiation in planetary systems<SUP>1,2</SUP>. On
  the Sun, strong flares are usually found in newly emerging sunspot
  regions<SUP>3</SUP>. The emergence of these magnetic sunspot groups
  leads to the accumulation of magnetic energy in the corona. When
  the magnetic field undergoes abrupt relaxation, the energy released
  powers coronal mass ejections as well as heating plasma to temperatures
  beyond tens of millions of kelvins. While recent work has shed light
  on how magnetic energy and twist accumulate in the corona<SUP>4</SUP>
  and on how three-dimensional magnetic reconnection allows for rapid
  energy release<SUP>5,6</SUP>, a self-consistent model capturing how
  such magnetic changes translate into observable diagnostics has remained
  elusive. Here, we present a comprehensive radiative magnetohydrodynamics
  simulation of a solar flare capturing the process from emergence to
  eruption. The simulation has sufficient realism for the synthesis of
  remote sensing measurements to compare with observations at visible,
  ultraviolet and X-ray wavelengths. This unifying model allows us to
  explain a number of well-known features of solar flares<SUP>7</SUP>,
  including the time profile of the X-ray flux during flares, origin
  and temporal evolution of chromospheric evaporation and condensation,
  and sweeping of flare ribbons in the lower atmosphere. Furthermore,
  the model reproduces the apparent non-thermal shape of coronal X-ray
  spectra, which is the result of the superposition of multi-component
  super-hot plasmas<SUP>8</SUP> up to and beyond 100 million K.

---------------------------------------------------------
Title: 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.
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
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.
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.
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.
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
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.
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.
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
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.
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
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
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
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
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 &gt; 3000 km/s, which is one of the fastest
  CMEs ever recorded, and &gt;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.
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 &gt;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.
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
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
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
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.
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}<SUB>⊙ </SUB> 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 &gt;2000 {km} {{{s}}}<SUP>-1</SUP> 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
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
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
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 &gt; 3000 km/s, which is one of the fastest
  CMEs ever recorded, and &gt;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
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
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
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
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
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.
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.
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.
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. <BR
  /> 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. <BR /> 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. <BR /> Results: Simulations including convection most
  accurately reproduce the observed evolution of the photospheric field
  distributions during active region evolution. <BR /> 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.
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
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
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.
2017SPD....4840001R    Altcode:
  We present a recently developed version of the MURaM radiative
  MHD code that includes coronal physics in terms of optically thin
  radiative loss and field aligned heat conduction. The code employs
  the "Boris correction" (semi-relativistic MHD with a reduced speed
  of light) and a hyperbolic treatment of heat conduction, which allow
  for efficient simulations of the photosphere/corona system by avoiding
  the severe time-step constraints arising from Alfven wave propagation
  and heat conduction. We demonstrate that this approach can be used
  even in dynamic phases such as a flare. We consider a setup in which
  a flare is triggered by flux emergence into a pre-existing bipolar
  active region. After the coronal energy release, efficient transport
  of energy along field lines leads to the formation of flare ribbons
  within seconds. In the flare ribbons we find downflows for temperatures
  lower than ~5 MK and upflows at higher temperatures. The resulting
  soft X-ray emission shows a fast rise and slow decay, reaching a peak
  corresponding to a mid C-class flare. The post reconnection energy
  release in the corona leads to average particle energies reaching 50
  keV (500 MK under the assumption of a thermal plasma). We show that
  hard X-ray emission from the corona computed under the assumption of
  thermal bremsstrahlung can produce a power-law spectrum due to the
  multi-thermal nature of the plasma. The electron energy flux into the
  flare ribbons (classic heat conduction with free streaming limit) is
  highly inhomogeneous and reaches peak values of about 3x10<SUP>11</SUP>
  erg/cm<SUP>2</SUP>/s in a small fraction of the ribbons, indicating
  regions that could potentially produce hard X-ray footpoint sources. We
  demonstrate that these findings are robust by comparing simulations
  computed with different values of the saturation heat flux as well as
  the "reduced speed of light".

---------------------------------------------------------
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.
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.
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.
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
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
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.
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}}}<SUP>-1</SUP>, 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}}}<SUP>-1</SUP>, 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.
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
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
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.
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
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
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
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 &amp; 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 &amp;
  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 &amp; Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
   Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
   Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
   Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
2016SPD....47.0607C    Altcode:
  We provide an update on our NASA Heliophysics Grand Challenges Research
  (HGCR) project on the ‘Physics &amp; 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.
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
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.
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
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.
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
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
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.
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.
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.
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.
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
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
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.
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<SUP>-1</SUP>. 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.
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<SUP>−1</SUP> 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
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.
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
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.
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<SUP>-1</SUP>
  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.
2014A&A...564A..12C    Altcode: 2014arXiv1402.5343C
  <BR /> 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. <BR /> 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. <BR /> 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. <P />Animation
  associated with Fig. 2 is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322859/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Numerical Simulations of Active Region Scale Flux Emergence:
    From Spot Formation to Decay
Authors: Rempel, M.; Cheung, M. C. M.
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 × 10<SUP>22</SUP> 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
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
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.
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.
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.
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.
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 &gt;
  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
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.
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 &gt; 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 &gt; 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.
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.
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.
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<SUP>-2</SUP>,
  much smaller than the ∼1.5 Wm<SUP>-2</SUP> annually integrated change
  related to orbital eccentricity variations, or the 1-8 Wm<SUP>-2</SUP>
  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
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.
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
  <P />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.
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 CO<SUP>5</SUP>BOLD
  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 B<SUB>0</SUB>(x,y,z) and vertical velocity V<SUB>0</SUB>(x,y,z)
  in the simulations.

---------------------------------------------------------
Title: Magnetohydrodynamics of the Weakly Ionized Solar Photosphere
Authors: Cheung, Mark C. M.; Cameron, Robert H.
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<SUP>-1</SUP> 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.
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.
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.
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.
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.
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.
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.
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
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.
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 rhov<SUP>1/2</SUP>. 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.
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.
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
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.
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. <BR />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. <BR />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. <P />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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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. <P />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.
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.
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.
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.
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.
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.
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
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.
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/. <P />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.
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. <BR />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. <BR />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 10<SUP>19</SUP> 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. <P />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.
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. <BR />Methods: We
  used the MURaM code to obtain a realistic model of the near-surface
  layers of the convection zone and the photosphere. <BR />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.
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.
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.
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.<BR /> 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.<BR /> 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.<BR />

---------------------------------------------------------
Title: Diagnostics of a Simulated Flux Tube Emergence
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
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.
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.
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<SUP>-2</SUP>, 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. <P />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.