Relaxation of magnetic field relative to plasma density revealed from microwave zebra patterns associated with solar flares

TL;DR

This study analyzes microwave zebra patterns in solar flares to reveal that magnetic field relaxation relative to plasma density occurs during flares, providing insights into magnetic topology changes and flare energy release.

Contribution

It demonstrates that the ratio of plasma density scale height to magnetic field scale height decreases during flares, indicating magnetic field relaxation relative to plasma density.

Findings

LN/LB ratio decreases from 3-5 to about 2 during flares

Variation of LN/LB linked to magnetic field topological changes

Results constrain solar flare modeling and magnetic field behavior

Abstract

It is generally considered that the emission of microwave zebra pattern (ZP) structures requires high density and high temperatures, which is similar to the situation of the flaring region where primary energy releases. Therefore, the parameters analysis of ZPs may reveal the physical conditions of the flaring source region. This work investigates the variations of 74 microwave ZP structures observed by Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at 2.6-3.8 GHz in 9 solar flares, and found that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission source displays a tendency of decrease during the flaring processes. The ratio LN/LB is about 3-5 before the maximum of flares. It decreases to about 2 after the maximum. The detailed analysis of three typical X-class flares implied that the variation of LN/LB during the flaring process is most likely due to the topological changes of the magnetic field in the flaring source region, and the step-wise decrease of LN/LB possibly reflects the magnetic field relaxation relative to the plasma density when the flaring energy released. This result may also constrain the solar flare modeling to some extent.