Diagnostic Analysis of the Solar Proton Flares of September 2017 by Their Radio Bursts

TL;DR

This study analyzes solar proton flares from September 2017 using radio burst data, demonstrating a strong correlation between radio spectra and proton fluxes, and validating microwave radio bursts as diagnostic tools for proton flare characterization.

Contribution

It provides a quantitative diagnostic method linking microwave radio burst spectra to proton fluxes and energy spectra in solar flares, confirming the effectiveness of radio data for flare analysis.

Findings

Radio burst spectra correlate with proton flux intensity and energy spectrum.

Powerful flares show distinct radio and proton flux characteristics.

Radio data can diagnose proton flares regardless of particle acceleration source.

Abstract

The powerful flares that occurred in the Sun on September 4-10, 2017 are analyzed on the basis of the technique for the quantitative diagnostics of proton flares developed in IZMIRAN in 1970-1980s. It is shown that the fluxes and energy spectra of protons with energy of tens of MeV coming to Earth qualitatively and quantitatively correspond to the intensity and frequency spectra of microwave radio bursts in the range 2.7-15.4 GHz. In particular, the flare of 4 Sept. with a peak radio flux S ~ 2000 sfu at the frequency f ~ 3 GHz (i.e., with a soft radio spectrum) was accompanied by a significant proton flux J (> 10 MeV) ~ 100 pfu and soft energy spectrum with the exponent gamma ~ 3.0, and the powerful flare of 10 Sept. with S ~ 21000 sfu at f ~ 15 GHz (i.e., with a hard radio spectrum) led to a very intense proton event with J (> 10 MeV) ~ 1000 pfu with a hard energy spectrum (gamma ~ 1.4), including a ground level enhancement (GLE72). This is further evidence that data on microwave radio bursts can be successfully used to diagnose proton flares, regardless of the particular source of acceleration of particles on the Sun.