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The "middle corona," defined by West et al. (2022) as the region between ~1.5-6 solar radii, is a critical transition region that connects the highly structured lower corona to the outer corona where the magnetic field becomes predominantly radial. At radio wavelengths, remote-sensing of the middle corona falls in the meter-decameter wavelength range where a critical transition of radio emission mechanisms occurs. In addition, plasma properties of the middle corona can be probed by trans-coronal radio propagation methods including radio scintillation and Faraday rotation techniques. Together they offer a wealth of diagnostic tools for the middle corona, complementing current and planned missions at other wavelengths. These diagnostics include unique means for detecting and measuring the magnetic field and energetic electrons associated with coronal mass ejections, mapping coronal shocks and electron beam trajectories, as well as constraining the plasma density, magnetic field, and turbulence of the "young" solar wind. Following a brief overview of pertinent radio diagnostic methods, this white paper will discuss the current state of radio studies on the middle corona, challenges to obtaining a more comprehensive picture, and recommend an outlook in the next decade. Our specific recommendations for advancing the middle coronal sciences from the radio perspective are: (1) Prioritizing solar-dedicated radio facilities in the ~0.1-1 GHz range with broadband, high-dynamic-range imaging spectropolarimetry capabilities. (2) Developing facilities and techniques to perform multi-perspective, multiple lines-of-sight trans-coronal radio Faraday Rotation measurements., Science white paper submitted to the 2024 Solar and Space Physics Decadal Survey. All submitted white papers (including this one) are available at https://www.nationalacademies.org/our-work/decadal-survey-for-solar-and-space-physics-heliophysics-2024-2033. arXiv admin note: text overlap with arXiv:2208.04485

To facilitate the study of solar active regions and flaring loops, we have created a modeling framework, the freely distributed GX Simulator IDL package, that combines 3D magnetic and plasma structures with thermal and non-thermal models of the chromosphere, transition region, and corona. The package has integrated tools to visualize the model data cubes, compute multi-wavelength emission maps from them, and quantitatively compare the resulting maps with observations. Its object-based modular architecture, which runs on Windows, Mac, and Unix/Linux platforms, offers capabilities that include the ability to either import 3D density and temperature distribution models, or to assign numerically defined coronal or chromospheric temperatures and densities, or their distributions to each individual voxel. The application integrates FORTRAN and C++ libraries for fast calculation of radio emission (free-free, gyroresonance, and gyrosynchrotron emission) along with soft and hard X-ray and EUV codes developed in IDL. To facilitate the creation of models, we have developed a fully automatic model production pipeline that downloads the required SDO/HMI vector magnetic field data and (optionally) the contextual SDO/AIA images, performs potential or nonlinear force free field extrapolations, populates the magnetic field skeleton with parameterized heated plasma coronal models that assume either steady-state or impulsive plasma heating, and generates non-LTE density and temperature distribution models of the chromosphere that are constrained by photospheric measurements. The standardized models produced by this pipeline may be further customized through a set of interactive tools provided by the graphical user interface. Here we describe the GX Simulator framework and its applications.

Coronal mass ejections (CMEs) are the most important drivers of space weather. Central to most CMEs is thought to be the eruption of a bundle of highly twisted magnetic field lines known as magnetic flux ropes. A comprehensive understanding of CMEs and their impacts hence requires detailed observations of physical parameters that lead to the formation, destabilization, and eventual eruption of the magnetic flux ropes. Recent advances in remote-sensing observations of coronal cavities, filament channels, sigmoids, EUV "hot channels," white light CMEs, and in situ observations of magnetic clouds points to the possibility of significant progress in understanding CMEs. In this white paper, we provide a brief overview of the potential of radio diagnostics for CMEs and CME progenitors, with a particular focus on the unique means for constraining their magnetic field and energetic electron population. Using synthetic observations based on realistic 3D MHD models, we also demonstrate the transformative potential of advancing such diagnostics by using broadband radio imaging spectropolarimetry with a high image dynamic range and high image fidelity. To achieve this goal, a solar-dedicated radio facility with such capabilities is recommended for implementation in the coming decade., Comment: Science white paper submitted to the 2024 Solar and Space Physics Decadal Survey. All submitted white papers (including this one) are available at https://www.nationalacademies.org/our-work/decadal-survey-for-solar-and-space-physics-heliophysics-2024-2033

Solar type III radio bursts are generated by beams of energetic electrons that travel along open magnetic field lines through the corona and into interplanetary space. However, understanding the source of these electrons and how they escape into interplanetary space remains an outstanding topic. Here we report multi-instrument, multi-perspective observations of an interplanetary type III radio burst event shortly after the second perihelion of the Parker Solar Probe (PSP). This event was associated with a solar jet that produced an impulsive microwave burst event recorded by the Expanded Owens Valley Solar Array (EOVSA). The type III burst event also coincided with the detection of enhanced in situ energetic electrons recorded by both PSP at 0.37 AU and WIND at 1 AU, which were located very closely on the Parker spiral longitudinally. The close timing association and magnetic connectivity suggest that the in situ energetic electrons originated from the jet's magnetic reconnection region. Intriguingly, microwave imaging spectroscopy results suggest that the escaping energetic electrons were injected into a large opening angle of about 90 degrees, which is at least nine times broader than the apparent width of the jet spire. Our findings provide an interpretation for the previously reported, longitudinally broad spatial distribution of flare locations associated with prompt energetic electron events and have important implications for understanding the origin and distribution of energetic electrons in the interplanetary space., Comment: 20 pages, 12 figures, Accepted for publication in The Astrophysical Journal

Particles are accelerated to very high, non-thermal energies during explosive energy-release phenomena in space, solar, and astrophysical plasma environments. In the case of solar flares, it has been established that magnetic reconnection plays an important role for releasing the magnetic energy, but it remains unclear if or how magnetic reconnection can further explain particle acceleration during flares. Here we argue that the key issue is the lack of understanding of the precise context of particle acceleration but it can be overcome, in the near future, by performing imaging-spectroscopy in soft X-rays (SXRs). Such observations should be complemented by observations in other wavelengths such as extreme-ultraviolets (EUVs), microwaves, hard X-rays (HXRs), and gamma-rays. Also, numerical simulations will be crucial for further narrowing down the particle acceleration mechanism in the context revealed by the observations. Of all these efforts, imaging-spectroscopy in SXRs, if successfully applied to large limb flares, will be a milestone in our challenge of understanding electron acceleration in solar flares and beyond, i.e. the Plasma Universe., Comment: White paper submitted to the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033; 10 pages, 2 figures

Solar flares and the often associated solar eruptive events serve as an outstanding laboratory to study the magnetic reconnection and the associated energy release and conversion processes under plasma conditions difficult to reproduce in the laboratory, and with considerable spatiotemporal details not possible elsewhere in the universe. In the past decade, thanks to advances in multi-wavelength imaging spectroscopy, as well as developments in theories and numerical modeling, significant progress has been made in improving our understanding of solar flare/eruption energy release. In particular, broadband imaging spectroscopy at microwave wavelengths offered by the Expanded Owens Valley Solar Array (EOVSA) has enabled the revolutionary capability of measuring the time-evolving coronal magnetic fields at or near the flare reconnection region. However, owing to EOVSA's limited dynamic range, imaging fidelity, and angular resolution, such measurements can only be done in a region around the brightest source(s) where the signal-to-noise is sufficiently large. In this white paper, after a brief introduction to the outstanding questions and challenges pertinent to magnetic energy release in solar flares and eruptions, we will demonstrate how a next-generation radio facility with many (~100-200) antenna elements can bring the next revolution by enabling high dynamic range, high fidelity broadband imaging spectropolarimetry along with a sub-second time resolution and arcsecond-level angular resolution. We recommend to prioritize the implementation of such a ground-based instrument within this decade. We also call for facilitating multi-wavelength, multi-messenger observations and advanced numerical modeling in order to achieve a comprehensive understanding of the "system science" of solar flares and eruptions., Comment: Science white paper submitted to the 2024 Solar and Space Physics Decadal Survey. All submitted white papers (including this one) are available at https://www.nationalacademies.org/our-work/decadal-survey-for-solar-and-space-physics-heliophysics-2024-2033

Context. The energy release in eruptive flares and the kinematics of the associated coronal mass ejections (CMEs) are interlinked and require favorable observing positions as both on-disk and off-limb signatures are necessary to characterize these events. Aims. We combine observations from different vantage points to perform a detailed study of a long duration eruptive C7 class flare that occurred on 17 April 2021 and was partially occulted from Earth view. The dynamics and thermal properties of the flare-related plasma flows, the flaring arcade, and the energy releases and particle acceleration are studied together with the kinematic evolution of the associated CME in order to place this long duration event in context of previous eruptive flare studies. Methods. We use data from the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter to analyze the spectral characteristics, timing, and spatial distribution of the flare X-ray emission. Data from the Extreme Ultraviolet Imager (EUVI) onboard the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft are used for context images as well as to track the ejected plasma close to the Sun. With Atmospheric Imaging Assembly extreme ultraviolet (EUV) images from the Solar Dynamics Observatory, the flare is observed off-limb and differential emission measure maps are reconstructed. The coronagraphs onboard STEREO-A are used to track the CME out to around 8 R·. Results. The flare showed hard X-ray (HXR) bursts over the duration of an hour in two phases lasting from 16:04 UT to 17:05 UT. During the first phase, a strong increase in emission from hot plasma and impulsive acceleration of the CME was observed. The CME acceleration profile shows a three-part evolution of slow rise, acceleration, and propagation in line with the first STIX HXR burst phase, which is triggered by a rising hot (14 MK) plasmoid. During the CME acceleration phase, we find signatures of ongoing magnetic reconnection behind the erupting structure, in agreement with the standard eruptive flare scenario. The subsequent HXR bursts that occur about 30 min after the primary CME acceleration show a spectral hardening (from δ 7 to δ 4) but do not correspond to further CME acceleration and chromospheric evaporation. Therefore, the CME-flare feedback relationship may only be of significance within the first 25 min. of the event under study, as thereafter the flare and the CME eruption evolve independently of each other., Astronomy & Astrophysics, 672, ISSN:0004-6361, ISSN:1432-0746

Solar and Heliosphere physics are areas of remarkable data-driven discoveries. Recent advances in high-cadence, high-resolution multiwavelength observations, growing amounts of data from realistic modeling, and operational needs for uninterrupted science-quality data coverage generate the demand for a solar metadata standardization and overall healthy data infrastructure. This white paper is prepared as an effort of the working group "Uniform Semantics and Syntax of Solar Observations and Events" created within the "Towards Integration of Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research Coordination Network (@HDMIEC RCN), with primary objectives to discuss current advances and identify future needs for the solar research cyberinfrastructure. The white paper summarizes presentations and discussions held during the special working group session at the EarthCube Annual Meeting on June 19th, 2020, as well as community contribution gathered during a series of preceding workshops and subsequent RCN working group sessions. The authors provide examples of the current standing of the solar research cyberinfrastructure, and describe the problems related to current data handling approaches. The list of the top-level recommendations agreed by the authors of the current white paper is presented at the beginning of the paper., Comment: White Paper

The Frequency Agile Solar Radiotelescope (FASR) has been strongly endorsed as a top community priority by both Astronomy & Astrophysics Decadal Surveys and Solar & Space Physics Decadal Surveys in the past two decades. Although it was developed to a high state of readiness in previous years (it went through a CATE analysis and was declared ``doable now"), the NSF has not had the funding mechanisms in place to fund this mid-scale program. Now it does, and the community must seize this opportunity to modernize the FASR design and build the instrument in this decade. The concept and its science potential have been abundantly proven by the pathfinding Expanded Owens Valley Solar Array (EOVSA), which has demonstrated a small subset of FASR's key capabilities such as dynamically measuring the evolving magnetic field in eruptive flares, the temporal and spatial evolution of the electron energy distribution in flares, and the extensive coupling among dynamic components (flare, flux rope, current sheet). The FASR concept, which is orders of magnitude more powerful than EOVSA, is low-risk and extremely high reward, exploiting a fundamentally new research domain in solar and space weather physics. Utilizing dynamic broadband imaging spectropolarimetry at radio wavelengths, with its unique sensitivity to coronal magnetic fields and to both thermal plasma and nonthermal electrons from large flares to extremely weak transients, the ground-based FASR will make synoptic measurements of the coronal magnetic field and map emissions from the chromosphere to the middle corona in 3D. With its high spatial, spectral, and temporal resolution, as well as its superior imaging fidelity and dynamic range, FASR will be a highly complementary and synergistic component of solar and heliospheric capabilities needed for the next generation of solar science., White Paper submitted to the Solar and Space Physics 2024 Decadal Survey

The authors of this white paper met on 16-17 January 2020 at the New Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that brought together a group of heliophysicists, data providers, expert modelers, and computer/data scientists. Their objective was to discuss critical developments and prospects of the application of machine and/or deep learning techniques for data analysis, modeling and forecasting in Heliophysics, and to shape a strategy for further developments in the field. The workshop combined a set of plenary sessions featuring invited introductory talks interleaved with a set of open discussion sessions. The outcome of the discussion is encapsulated in this white paper that also features a top-level list of recommendations agreed by participants., Workshop Report

We present first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9--s cadence are used to analyze the event over a 120-minute period, and solar emission is observed out to a distance of $\approx3.5\,R_\odot$, with an instantaneous bandwidth covering 22~MHz within the frequency range of 40--70~MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the LASCO(C2) coronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell (GCS) reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source., Comment: 22 Pages, 10 figures, 1 table

Magnetic reconnection is a fundamental physical process in many laboratory, space, and astrophysical plasma contexts. Solar flares serve as an outstanding laboratory to study the magnetic reconnection and the associated energy release and conversion processes under plasma conditions difficult to reproduce in the laboratory, and with considerable spatiotemporal details not possible elsewhere in astrophysics. Here we emphasize the unique power of remote-sensing observations of solar flares at radio wavelengths. In particular, we discuss the transformative technique of broadband radio dynamic imaging spectroscopy in making significant contributions to addressing several outstanding challenges in magnetic reconnection, including the capability of pinpointing magnetic reconnection sites, measuring the time-evolving reconnecting magnetic fields, and deriving the spatially and temporally resolved distribution function of flare-accelerated electrons., Submitted to the Astro2020 Decadal Survey call for science white papers (5 pages + references, 2 figures)

The solar burst of 2006 December 06 reached a radio flux density of more than 1 million solar flux units (1 sfu = $10^{-22}$ W/m$^2$/Hz), as much as 10 times the previous record, and caused widespread loss of satellite tracking by GPS receivers. The event was well observed by NJITs Owens Valley Solar Array (OVSA). This work concentrates on an accurate determination of the flux density (made difficult due to the receiver systems being driving into non-linearity), and discuss the physical conditions on the Sun that gave rise to this unusual event. At least two other radio outbursts occurred in the same region (on 2006 December 13 and 14) that had significant, but smaller effects on GPS. We discuss the differences among these three events, and consider the implications of these events for the upcoming solar cycle., Comment: 8 pages, 8 figures, presented at the 2008 Ionospheric Effects Symposium, Alexandria VA

We present the first high-resolution, simultaneous observations of the solar chromosphere in the optical and millimeter wavelength ranges, obtained with ALMA and the IBIS instrument at the Dunn Solar Telescope. In this paper we concentrate on the comparison between the brightness temperature observed in ALMA Band 3 (3 mm; 100 GHz) and the core width of the H$��$ 656.3 nm line, previously identified as a possible diagnostic of the chromospheric temperature. We find that in the area of plage, network and fibrils covered by our FOV the two diagnostics are well correlated, with similar spatial structures observed in both. The strength of the correlation is remarkable, given that the source function of the mm-radiation obeys local thermodynamic equilibrium, while the H$��$ line has a source function that deviates significantly from the local Planck function. The observed range of ALMA brightness temperatures is sensibly smaller than the temperature range that was previously invoked to explain the observed width variations in H$��$. We employ analysis from forward modeling with the RH code to argue that the strong correlation between H$��$ width and ALMA brightness temperature is caused by their shared dependence on the population number $n_2$ of the first excited level of hydrogen. This population number drives millimeter opacity through hydrogen ionization via the Balmer continuum, and H$��$ width through a curve-of-growth-like opacity effect. Ultimately, the $n_2$ population is regulated by the enhancement or lack of downward Ly$��$ flux, which coherently shifts the formation height of both diagnostics to regions with different temperature, respectively., Accepted for publication in ApJ

The Sun is an active star that can have a direct impact on the Earth, its magnetosphere, and the technological infrastructure on which modern society depends. Among the phenomena that drive "space weather" are fast solar wind streams and co-rotating interaction regions, solar flares, coronal mass ejections, the shocks they produce, and the energetic particles they accelerate. Radio emission from these and associated phenomena offer unique diagnostic possibilities that complement those available at other wavelengths. Here, the relevant space weather drivers are briefly described, the potential role of radio observations is outlined, and the requirements of an instrument to provide them are provided: specifically, ultrabroadband imaging spectropolarimetry. The insights provided by radio observations of space weather drivers will not only inform the science of space weather, they will pave the way for new tools for forecasting and "nowcasting" space weather. They will also serve as an important touchstone against which local environment of exoplanets and the impact of "exo-space weather" can be evaluated., Comment: White paper submitted to the Astronomy and Astrophysics decadal survey

Identification of the mechanisms responsible for heating the solar chromosphere and corona remains an outstanding problem, one of great relevance to late-type stars as well. There has been tremendous progress in the past decade, largely driven by new instruments, new observations, and sophisticated modeling efforts. Despite this progress, gaps remain. We briefly discuss the need for radio coverage of the 3D solar atmosphere and discuss the requirements., Comment: White paper submitted to the Astronomy and Astrophysics decadal survey

Solar flares are due to the catastrophic release of magnetic energy in the Sun's corona, resulting in plasma heating, mass motions, particle acceleration, and radiation emitted from radio to $\gamma$-ray wavelengths. They are associated with global coronal eruptions of plasma into the interplanetary medium---coronal mass ejections---that can result in a variety of "space weather" phenomena. Flares release energy over a vast range of energies, from $\sim\!10^{23}$ ergs (nanoflares) to more than $10^{32}$ ergs. Solar flares are a phenomenon of general astrophysical interest, allowing detailed study of magnetic energy release, eruptive processes, shock formation and propagation, particle acceleration and transport, and radiative processes. Observations at radio wavelengths offer unique diagnostics of the physics of flares. To fully exploit these diagnostics requires the means of performing time-resolved imaging spectropolarimetry. Recent observations with the Jansky Very Large Array (JVLA) and the Expanded Owens Valley Solar Array (EOVSA), supported by extensive development in forward modeling, have demonstrated the power of the approach. The ngVLA has the potential to bring our understanding of flare processes to a new level through its combination of high spatial resolution, broad frequency range, and imaging dynamic range---especially when used in concert with multi-wavelength observations and data at hard X-ray energies., Comment: To be published in the ASP Monograph Series, "Science with a Next-Generation VLA," ed. E. J. Murphy (ASP, San Francisco, CA)

Energy stored in the magnetic field in the solar atmosphere above active regions is a key driver of all solar activity (e.g., solar flares and coronal mass ejections), some of which can affect life on Earth. Radio observations provide a unique diagnostic of the coronal magnetic fields that make them a critical tool for the study of these phenomena, using the technique of broadband radio imaging spectropolarimetry. Observations with the ngVLA will provide unique observations of coronal magnetic fields and their evolution, key inputs and constraints for MHD numerical models of the solar atmosphere and eruptive processes, and a key link between lower layers of the solar atmosphere and the heliosphere. In doing so they will also provide practical "research to operations" guidance for space weather forecasting., 9 pages, 2 figures. To be published in the ASP Monograph Series, "Science with a Next-Generation VLA," ed. E. J. Murphy (ASP, San Francisco, CA)

How impulsive magnetic energy release leads to solar eruptions and how those eruptions are energized and evolve are vital unsolved problems in Heliophysics. The standard model for solar eruptions summarizes our current understanding of these events. Magnetic energy in the corona is released through drastic restructuring of the magnetic field via reconnection. Electrons and ions are then accelerated by poorly understood processes. Theories include contracting loops, merging magnetic islands, stochastic acceleration, and turbulence at shocks, among others. Although this basic model is well established, the fundamental physics is poorly understood. HXR observations using grazing-incidence focusing optics can now probe all of the key regions of the standard model. These include two above-the-looptop (ALT) sources which bookend the reconnection region and are likely the sites of particle acceleration and direct heating. The science achievable by a direct HXR imaging instrument can be summarized by the following science questions and objectives which are some of the most outstanding issues in solar physics (1) How are particles accelerated at the Sun? (1a) Where are electrons accelerated and on what time scales? (1b) What fraction of electrons is accelerated out of the ambient medium? (2) How does magnetic energy release on the Sun lead to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI) instrument, which can be built now using proven technology and at modest cost, would enable revolutionary advancements in our understanding of impulsive magnetic energy release and particle acceleration, a process which is known to occur at the Sun but also throughout the Universe., Next Generation Solar Physics Mission white paper, 2 figures

Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of the dense photosphere involving bulk motion. Here we report the sudden flare-induced rotation of a sunspot using the unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, supplemented by magnetic data from the Solar Dynamics Observatory. It is clearly observed that the rotation is non-uniform over the sunspot: as the flare ribbon sweeps across, its different portions accelerate (up to 50 deg per hr) at different times corresponding to peaks of flare hard X-ray emission. The rotation may be driven by the surface Lorentz-force change due to the back reaction of coronal magnetic restructuring and is accompanied by a downward Poynting flux. These results have direct consequences for our understanding of energy and momentum transportation in the flare-related phenomena., 9 pages, 8 figures, published in Nature Communications under a Creative Commons license; typos corrected

Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles which have adverse effects in the near Earth environment. By definition, flares are usually referred to bright features resulting from excess emission. Using the newly commissioned 1.6~m New Solar Telescope at Big Bear Solar Observatory, here we show a striking "negative" flare with a narrow, but unambiguous "dark" moving front observed in He I 10830 ��, which is as narrow as 340 km and is associated with distinct spectral characteristics in H-alpha and Mg II lines. Theoretically, such negative contrast in He I 10830 �� can be produced under special circumstances, by nonthermal-electron collisions, or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects.

Previous studies have shown that the energy release mechanism of some solar flares follow the Standard magnetic-reconnection model, but the detailed properties of high-energy electrons produced in the flare are still not well understood. We conducted a unique, multi-wavelength study that discloses the spatial, temporal and energy distributions of the accelerated electrons in the X2.2 solar flare on 2011, Feb. 15. We studied the source locations of seven distinct temporal peaks observed in hard X-ray (HXR) and microwave (MW) lightcurves using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in 50 to 75 keV channels and Nobeyama Radioheliograph (NoRH) in 34 GHz, respectively. We found that the seven emission peaks did not come from seven spatially distinct sites in HXR and MW, but rather in HXR we observed a sudden change in location only between the second and the third peak, with the same pattern occurring, but evolving more slowly in MW. Comparison between the HXR lightcurve and the temporal variations in intensity in the two MW source kernels also confirmed that the seven peaks came predominantly from two sources, each with multiple temporal peaks. In addition, we studied the polarization properties of MW sources, and time delay between HXR and MW. We discuss our results in the context of the tether-cutting model.

We have undertaken a major enhancement of our IDL-based simulation tools developed earlier for modeling microwave and X-ray emission. The object-based architecture provides an interactive graphical user interface that allows the user to import photospheric magnetic field maps and perform magnetic field extrapolations to almost instantly generate 3D magnetic field models, to investigate the magnetic topology of these models by interactively creating magnetic field lines and associated magnetic flux tubes, to populate the flux tubes with user-defined nonuniform thermal plasma and anisotropic, nonuniform, nonthermal electron distributions; to investigate the spatial and spectral properties of radio and X-ray emission calculated from the model, and to compare the model-derived images and spectra with observational data. The application integrates shared-object libraries containing fast gyrosynchrotron emission codes developed in FORTRAN and C++, soft and hard X-ray codes developed in IDL, a FORTRAN-based potential-field extrapolation routine and an IDL-based linear force free field extrapolation routine. The interactive interface allows users to add any user-defined radiation code that adheres to our interface standards, as well as user-defined magnetic field extrapolation routines. Here we use this tool to analyze a simple single-loop flare and use the model to constrain the 3D structure of the magnetic flaring loop and 3D spatial distribution of the fast electrons inside this loop. We iteratively compute multi-frequency microwave and multi-energy X-ray images from realistic magnetic fluxtubes obtained from an extrapolation of a magnetogram taken prior to the flare, and compare them with imaging data obtained by SDO, NoRH, and RHESSI instruments. We use this event to illustrate use of the tool for general interpretation of solar flares to address disparate problems in solar physics., Comment: 12 pages, 11 figures, ApJ accepted

We use rotation stereoscopy to estimate the height of a steady-state solar feature relative to the photosphere, based on its apparent motion in the image plane recorded over several days of observation. The stereoscopy algorithm is adapted to work with either one- or two-dimensional data (i.e. from images or from observations that record the projected position of the source along an arbitrary axis). The accuracy of the algorithm is tested on simulated data, and then the algorithm is used to estimate the coronal radio source heights associated with the active region NOAA 10956, based on multifrequency imaging data over 7 days from the Siberian Solar Radio Telescope near 5.7 GHz, the Nobeyama Radio Heliograph at 17 GHz, as well as one-dimensional scans at multiple frequencies spanning the 5.98--15.95 GHz frequency range from the RATAN-600 instrument. The gyroresonance emission mechanism, which is sensitive to the coronal magnetic field strength, is applied to convert the estimated radio source heights at various frequencies, h(f), to information about magnetic field vs. height B(h), and the results are compared to a magnetic field extrapolation derived from photospheric magnetic field observations obtained by Hinode and MDI. We found that the gyroresonant emission comes from the heights exceeding location of the third gyrolayer irrespectively on the magnetic extrapolation method; implications of this finding for the coronal magnetography and coronal plasma physics are discussed., 26 pages, 13 figures, ApJ accepted

The coming decade will see the routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness. To capitalize on the new (or soon to be available) facilities such as SDO, ATST and FASR, and the challenges they present in the visualization and synthesis of multi-wavelength datasets, we propose that realistic, sophisticated, 3D active region and flare modeling is timely and critical, and will be a forefront of coronal studies over the coming decade. To make such modeling a reality, a broad, concerted effort is needed to capture the wealth of information resulting from the data, develop a synergistic modeling effort, and generate the necessary visualization, interpretation and model-data comparison tools to accurately extract the key physics., Comment: 3D Theory and Modeling Concept Paper submitted to 'A Decadal Strategy for Solar and Space Physics (Heliophysics)' Survey. 8 pages