Empirical atmosphere model in a mini flare during magnetic reconnection

TL;DR

This study uses IRIS spectral data to analyze the dynamics and stratification of a mini flare atmosphere during magnetic reconnection, revealing complex chromospheric cloud structures and energy transfer mechanisms.

Contribution

It provides a detailed empirical analysis of a mini flare's atmospheric dynamics and energy processes using multi-wavelength observations and spectral line profiles.

Findings

Identification of two chromospheric clouds with different Doppler shifts.

Confirmation that non-thermal electrons above 20 keV can produce observed Balmer continuum excess.

Observation of multi-temperature emissions and absorption features during the mini flare.

Abstract

A spatio-temporal analysis of IRIS spectra of MgII, CII, and SiIV ions allows us to study the dynamics and the stratification of the flare atmosphere along the line of sight during the magnetic reconnection phase at the jet base. Strong asymmetric MgII and CII line profiles with extended blue wings observed at the reconnection site are interpreted by the presence of two chromospheric temperature clouds: one explosive cloud with blueshifts at 290 km/s and one cloud with smaller Doppler shift (around 36 km/s). Simultaneously at the same location a mini flare was observed with strong emission in multi temperatures (AIA), in several spectral IRIS lines (e.g. Oiv and Siiv, Mgii), absorption of identified chromospheric lines in Siiv line profile, enhancement of the Balmer continuum and X-ray emission by FERMI/GBM. With the standard thick-target flare model we calculate the energy of non thermal electrons observed by FERMI and compare it to the energy radiated by the Balmer continuum emission. We show that the low energy input by non thermal electrons above 20 keV was still sufficient to produce the excess of Balmer continuum.