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Abstract The solar corona is much hotter than the photosphere and chromosphere, but the physical mechanism responsible for heating the coronal plasma remains unidentified. The thermal microwave emission, which is produced in a strong magnetic field above sunspots, is a promising but barely exploited tool for studying the coronal magnetic field and plasma. We analyzed the microwave observations of eight solar active regions obtained with the Siberian Radioheliograph in the years 2022–2024 in the frequency range of 6–12 GHz. We produced synthetic microwave images based on various coronal heating models, and determined the model parameters that provided the best agreement with the observations. The observations and simulations strongly favor either a steady-state (continuous) plasma heating process or high-frequency heating by small energy release events with a short cadence. The average magnetic field strength in a coronal loop was found to decrease with the loop length, following a scaling law with the most probable index of about −0.55. In the majority of cases, the estimated volumetric heating rate was weakly dependent on the magnetic field strength and decreased with the coronal loop length following a scaling law with an index of about −2.5. Among the known theoretical heating mechanisms, the model based on wave transmission or reflection in coronal loops acting as resonance cavities was found to provide the best agreement with the observations. The obtained results did not demonstrate a significant dependence on the emission frequency in the considered range. 

Abstract The solar corona is much hotter than lower layers of the solar atmosphere—the photosphere and chromosphere. The coronal temperature is up to 1 MK in quiet Sun areas, while up to several megakelvins in active regions, which implies a key role of the magnetic field in coronal heating. This means that understanding coronal heating requires reliable modeling of the underlying 3D magnetic structure of an active region validated by observations. Here, we employ synergy between 3D modeling, optically thick gyroresonant microwave emission, and optically thin EUV emission to (i) obtain and validate the best magnetothermal model of the active region and (ii) disentangle various components of the EUV emission known as diffuse component, bright loops, open-field regions, and “moss” component produced at the transition region. Surprisingly, the best thermal model corresponds to high-frequency energy release episodes, similar to a steady-state heating. Our analysis did not reveal significant deviations of the elemental abundances from the standard coronal values. 

Abstract A subclass of early impulsive solar flares, cold flares, was proposed to represent a clean case, where the release of the free magnetic energy (almost) entirely goes to the acceleration of the nonthermal electrons, while the observed thermal response is entirely driven by the nonthermal energy deposition to the ambient plasma. This paper studies one more example of a cold flare, which was observed by a unique combination of instruments. In particular, this is the first cold flare observed with the Expanded Owens Valley Solar Array and, thus, for which the dynamical measurement of the coronal magnetic field and other parameters at the flare site is possible. With these new data, we quantified the coronal magnetic field at the flare site but did not find statistically significant variations of the magnetic field within the measurement uncertainties. We estimated that the uncertainty in the corresponding magnetic energy exceeds the thermal and nonthermal energies by an order of magnitude; thus, there should be sufficient free energy to drive the flare. We discovered a very prominent soft-hard-soft spectral evolution of the microwave-producing nonthermal electrons. We computed energy partitions and concluded that the nonthermal energy deposition is likely sufficient to drive the flare thermal response similarly to other cold flares. 

pyAMPP Premature Release This is an early preview of pyAMPP – the Python Automatic Model Production Pipeline for solar coronal modeling. Expect things to change quickly as we continue development! What's included: Core functionality for generating 3D solar atmosphere models Tools to download HMI and (optionally) AIA data Magnetic field extrapolations (Potential/NLFFF) Synthetic plasma and chromospheric model generation Interactive GUIs: gxampp (time/coord selector) and gxbox (modeling & visualization) Documentation: pyampp.readthedocs.io Getting Started pip install -U pyampp After installing, launch the GUIs with: gxampp # Time & location selector gxbox ... # Run the modeling viewer with your options Heads up: • This is a very early release—features may be missing or change without warning. • Please report bugs or suggestions via issues. Copyright (c) 2024, SUNCAST team. Released under the 3-clause BSD license.