Relations between strong high-frequency microwave bursts and proton events

TL;DR

This study investigates the relationship between high-frequency microwave bursts at 35 GHz and solar energetic proton events, highlighting their potential for space weather prediction and understanding flare-CME energy release mechanisms.

Contribution

It establishes a correlation between 35 GHz microwave bursts and proton enhancements, emphasizing the diagnostic potential of high-frequency radio observations for space weather forecasting.

Findings

Strong 35 GHz bursts often precede proton events with >100 MeV.

High microwave flux correlates with intense, hard proton spectra.

Sunspot-associated flares are typical of these energetic events.

Abstract

Proceeding from close association between solar eruptions, flares, shock waves, and CMEs, we analyze relations between bursts at 35 GHz recorded with the Nobeyama Radio Polarimeters during 1990-2012, on the one hand, and solar energetic particle (SEP) events, on the other hand. Most west to moderately east solar events with strong bursts at 35 GHz produced near-Earth proton enhancements of J(E > 100 MeV) > 1 pfu. The strongest and hardest those caused ground level enhancements. There is a general, although scattered, correspondence between proton enhancements and peak fluxes at 35 GHz, especially pronounced if the 35 GHz flux exceeds 10^4 sfu and the microwave peak frequency is high. These properties indicate emission from numerous high-energy electrons in very strong magnetic fields suggesting a high rate of energy release in the flare-CME formation process. Flaring above the sunspot umbrae appears to be typical of such events. Irrespective of the origin of SEPs, these circumstances demonstrate significant diagnostic potential of high-frequency microwave bursts and sunspot-associated flares for space weather forecasting. Strong prolonged bursts at 35 GHz promptly alert to hazardous SEP events with hard spectra. A few exceptional events with moderate bursts at 35 GHz and strong proton fluxes look challenging and should be investigated.