Diagnostic of Homologous Solar Surge Plasma as observed by IRIS and SDO

TL;DR

This study analyzes the evolution, kinematics, and thermal properties of homologous solar surges using IRIS and SDO data, revealing their heating, rotational motion, and magnetic reconnection triggers, with novel observations in interface-region lines.

Contribution

First detailed analysis of surge response in multiple interface-region lines, linking heating, rotation, and magnetic reconnection as surge triggers.

Findings

Surges show co-existing cool and hot plasma components at their bases.

First-time observation of two peaks in surge emission lines indicating rotation.

Surge properties correlate with magnetic reconnection activity.

Abstract

Surges have regularly been observed mostly in H$_{\alpha}$ 6563~{\AA} and Ca~{\sc ii} 8542~{\AA}. However, surge$'$s response to other prominent lines of the interface-region (Mg~{\sc ii} k 2796.35~{\AA} $\&$ h 2803.52~{\AA}, O~{\sc iv} 1401.15~{\AA}, Si~{\sc iv} 1402.77~{\AA}) is not well studied. Here, the evolution and kinematics of six homologous surges are analysed using IRIS and AIA observations. These surges were observed on 7$^{th}$ July 2014, located very close to the limb. DEM analysis is performed on these surges where the co-existence of cool (log T/K = 6.35) and relatively hot (log T/K = 6.95) components have been found at the base. This demonstrates that the bases of surges undergo substantial heating. During the emission of these surges in the above mentioned interface-region lines, being reported here for the first time, two peaks have been observed in the initial phase of emission, where one peak is found to be constant while other one as varying, i.e., non-constant (observed red to blueshifts across the surge evolution) in nature. This suggests the rotational motion of surge plasma. The heated base and rotating plasma suggests the occurrence of magnetic reconnection, most likely, as the trigger for homologous surges. During the emission of these surges, it is found that despite being optically thick (i.e., R$_{kh}$ < 2.0), central reversal was not observed for Mg~{\sc ii} k $\&$ h lines. Further, R$_{kh}$ increases with surge emission in time and it is found to have positive correlation with Doppler Velocity while negative with Gaussian width.