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Solar flares are powered by a rapid release of energy in the solar corona, thought to be produced by the decay of the coronal magnetic field strength. Direct quantitative measurements of the evolving magnetic field strength are required to test this. We report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field. The field decays at a rate of~5 Gauss per second for 2 minutes, as measured within a flare subvolume of ~1028cubic centimeters. This fast rate of decay implies a sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. The decrease in stored magnetic energy is enough to power the solar flare, including the associated eruption, particle acceleration, and plasma heating.
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This content will become publicly available on September 26, 2026
Magneto-thermal Coupling and Coronal Heating in Solar Active Regions Inferred from Microwave Observations
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.
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- Award ID(s):
- 2324724
- PAR ID:
- 10638360
- Publisher / Repository:
- American Astronomical Society
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 991
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 186
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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