Simultaneous Eruption and Shrinkage of Pre-existing Flare Loops during a Subsequent Solar Eruption

TL;DR

This study examines the complex dynamics of flare loops during two consecutive solar eruptions, revealing simultaneous eruption and contraction of different loop segments and proposing an adiabatic heating mechanism.

Contribution

It provides new insights into the behavior of pre-existing flare loops during successive eruptions, highlighting the contraction and heating processes involved.

Findings

E-loops erupted outward during the second flare's initial stage.

I-loops contracted and their plasma was heated to ~6 MK.

Magnetic energy of 10^29-10^30 erg was converted into thermal energy.

Abstract

We investigated two consecutive solar eruption events in the solar active region (AR) 12994 at the solar eastern limb on 2022 April 15. We found that the flare loops formed by the first eruption were involved in the second eruption. During the initial stage of the second flare, the middle part of these flare loops (E-loops) erupted outward along with the flux ropes below, while the parts of the flare loops (I-loops1 and I-loops2) on either side of the E-loops first rose and then contracted. Approximately 1 hour after the eruption, the heights of I-loops1 and I-loops2 decreased by 9 Mm and 45 Mm, respectively, compared to before the eruption. Their maximum descent velocities were 30 km/s and 130 km/s, respectively. The differential emission measure (DEM) results indicate that the plasma above I-loops1 and I-loops2 began to be heated about 23 minutes and 44 minutes after the start of the second flare, respectively. Within 20 minutes, the plasma temperature in these regions increased from ~3 MK to 6 MK. We proposed an adiabatic heating mechanism that magnetic energy would be converted into thermal and kinetic energy when the pre-stretched loops contract. Our calculations show that the magnetic energy required to heat the two high-temperature regions are 10^29-10^30 erg, which correspond to a loss of field strength of 2-3 G.