Insights from snapshot spectroscopic radio observations of a weak Type I noise storm

TL;DR

This study uses high-resolution radio imaging to analyze a weak solar noise storm, revealing anti-correlated flux and area variations that suggest MHD sausage wave modes and small-scale magnetic reconnections.

Contribution

It provides new observational evidence linking flux-area anti-correlation to MHD sausage modes and small-scale reconnection sites in solar magnetic loops.

Findings

Anti-correlation between flux density and area observed.

Evidence for MHD sausage wave modes in magnetic loops.

Reconnection sites are distributed along flux tubes.

Abstract

We present a high fidelity snapshot spectroscopic radio imaging study of a weak type I solar noise storm which took place during an otherwise exceptionally quiet time. Using high fidelity images from the Murchison Widefield Array, we track the observed morphology of the burst source for 70 minutes and identify multiple instances where its integrated flux density and area are strongly anti-correlated with each other. The type I radio emission is believed to arise due to electron beams energized during magnetic reconnection activity. The observed anti-correlation is interpreted as evidence for presence of MHD sausage wave modes in the magnetic loops and strands along which these electron beams are propagating. Our observations suggest that the sites of these small scale reconnections are distributed along the magnetic flux tube. We hypothesise that small scale reconnections produces electron beams which quickly get collisionally damped. Hence, the plasma emission produced by them span only a narrow bandwidth and the features seen even a few MHz apart must arise from independent electron beams.