Discovery of correlated evolution in solar noise storm source parameters: Insights on magnetic field dynamics during a microflare

Abstract

A solar type-I noise storm is produced by accelerated particle beams generated at active regions undergoing magnetic field restructuring. Their intensity varies by orders of magnitude within sub-second and sub-MHz scales. But, the morphological evolution of these sources are not studied at these scales, due to the lack of required imaging cadence and fidelity in metrewave bands. Using data from the Murchison Widefield Array (MWA), this work explores the co-evolution of size, sky-orientation and intensity of a noise storm source associated with a weak microflare. The work presents the discovery of two correlated modes of evolution in the source parameters: a sausage like \s\ mode where the source intensity and size shows an anti-correlated evolution; and a torsional like \T\ mode where the source size and sky-orientation shows a correlated evolution. A flare mediated mode conversion is observed from \T\ to \s\ for the first time in these sources. These results support the idea of build up of magnetic stress energy in braided active region loops, which later go unstable causing flares and particle acceleration until they relax to a minimally braided state. The discovered mode conversion can be a future diagnostic to such active region phenomena.