Correlation between active regions' spectra at high radio frequencies and solar flare occurrences

TL;DR

This study analyzes high-frequency radio observations of solar active regions to identify spectral features that correlate with the likelihood of strong solar flares within 30 hours.

Contribution

It introduces a new method for flare prediction based on spectral flattening in high radio frequency observations of active regions.

Findings

Spectral flattening in active regions correlates with an 89% probability of strong flare occurrence within 30 hours.

The method detects ~12% of strong flares that would otherwise be missed.

Radio observations at 18-26 GHz can effectively probe magnetic fields associated with flare activity.

Abstract

High radio frequencies observations with the Italian network of large single-dish radio telescopes resulted in ~450 solar images between 2018 and 2023 in K-band frequency range (18-26 GHz). Solar radio mapping at these frequencies allows the probing of the Active Regions (ARs) chromospheric magnetic field close to the Transition Region, where strong flares and coronal mass ejection events occur. Enhanced magnetic fields up to 1500-2000 G determine anomalous spectra in the ARs brightness compared to pure free-free emission, due to the addition of a steeper gyro-resonance component also associated with circular polarisation up to ~40%. When a significant AR spectral flattening is detected, the probability of a strong flare occurrence within ~30 hours is high (~89% in terms of statistical precision). Despite an approximate weekly cadence of our observations, only ~12% of strong flares are missed/unpredicted within this time interval. Through a correlation analysis, we assess the trade-off on the sensitivity and the robustness of this physics-based flare forecast method.