Quasi periodic oscillations of solar active regions in connection with their flare activity - NoRH observations

TL;DR

This study uses NoRH observations at 17 GHz to analyze short-period oscillations in sunspots, revealing their connection to flare activity and identifying specific oscillation patterns that precede flares.

Contribution

It demonstrates a clear link between MHD wave oscillations in sunspots and solar flare activity, including pre-flare oscillation signatures.

Findings

Pre-flare three-minute oscillations observed before bursts.

Eight-minute oscillations identified in microwave emission.

Differences in oscillation patterns between pre- and post-flare phases.

Abstract

The sunspot-associated sources at the frequency of 17 GHz give information on plasma parameters in the regions of magnetic field about B=2000 G at the level of the chromosphere-corona transition region. The observations of short period (from 1 to 10 minutes) oscillations in sunspots reflect propagation of magnetohydrodynamic (MHD) waves in the magnetic flux tubes of the sunspots. We investigate the oscillation parameters in active regions in connection with their flare activity. We confirm the existence of a link between the oscillation spectrum and flare activity. We find differences in the oscillations between pre-flare and post-flare phases. In particular, we demonstrate a case of powerful three-minute oscillations that start just before the burst. This event is similar to the cases of the precursors investigated by Sych, R. et al. (Astron. Astrophys., vol.505, p.791, 2009). We also found well-defined eight-minute oscillations of microwave emission from sunspot. We interpret our observations in terms of a relationship between MHD waves propagating from sunspot and flare processes.