Speaker
Description
Within previous studies, the relationship of microwave signatures in solar flares and in-situ Solar Energetic Particle (SEP) fluxes and spectra has been investigated. This study continues and expands earlier efforts, considering both electron and proton signatures in relation to solar microwave emission in the 8-17 GHz range.
The primary aim of the study was to confirm previous results, using new and corrected data products, and to find new empirical relationships between microwave radiation in solar flares and SEP events, for potential operational use in forecasting.
We found 38 events between the years 2000 and 2024 that were suitable for analysis. The data quality for all events was critically assessed and corrected when necessary. Fluences of the microwave bursts and peak fluxes of the particle events were calculated, considering both electrons and protons across a wide energy range. The resulting data set was then subjected to statistical analysis. We also introduced renewed restraints on confinement in the corona and the magnetic connection of the spacecraft to the flare site, using WIND/WAVES measurements of type III bursts as evidence of escaping electrons.
We confirmed positive correlations between microwave fluences and proton peak fluxes in the tens of MeV range, as well as electron peak fluxes from a few keV up to approximately 1.1 MeV. In contrast, protons in the 250–800 MeV range show no clear association with microwave emission, with several events exhibiting strong microwave bursts but lacking high-energy proton enhancements. No significant correlations were found of the spectral hardness of the SEPs and flare characteristics in the 8-17 GHz range, for either protons or electrons within the studied energy ranges. However, the electron-to-proton peak flux ratio appears to be related to the ratio of microwave fluences at 8–9 GHz to those at 15–17 GHz. In most cases, the limitations regarding magnetic connection and confinement resulted in an increase in correlation quality.
While some findings from previous studies were confirmed, others — despite apparent visual correlations — lack statistical significance. Larger, comparative studies, which extend both to further wavelengths in the GHz/MHz range and to other particle energies, are necessary in order to make statements about the underlying acceleration and transport processes.
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