Chromospheric UV bursts and turbulent driven magnetic reconnection

TL;DR

This study uses IRIS data to analyze chromospheric UV bursts, revealing magnetic reconnection signatures and turbulence-driven processes through spectral line profiles and flow measurements.

Contribution

It provides the first observational evidence of oppositely directed flows in UV bursts, indicating magnetic reconnection at small scales driven by turbulence.

Findings

Detection of two oppositely directed heated flows in UVBs

Excessive line broadening suggests turbulence-driven reconnection

Classification of UVBs into small and large types based on measurement methods

Abstract

We use Interface Region Imaging Spectrograph (IRIS) spacecraft data to study a group of Chromospheric ultraviolet bursts (UVBs) associated with an active region. We classify the UVBs into two types: smaller ones that can only be measured once by the scanning slit, and larger UVBs that are measured twice by the slit. The UVBs' optically thin Si IV 1402.77 \r{A} line profiles are studied intensively. By fitting the smaller UVBs' lines with 1-2 Gaussians, we obtain a variety of line-of-sight flow measurements that hint various 3-D orientations of small scale magnetic reconnections, each associated with a UVB. The larger UVBs are, however, unique in a way that they each have two sets of measurements at two slit locations. This makes it possible to unambiguously detect two oppositely directed heated flows jetting out of a single UVB, a signature of magnetic reconnection operating at the heart of the UVB. Here we report on the first of such an observation. Additionally, all the optically thin Si IV 1402.77 \r{A} line profiles from those UVBs consistently demonstrate excessive broadening, an order of magnitude larger than would be expected from thermal broadening, suggesting that those small scale reconnections could be driven by large scale (macro-scale) turbulence in the active region.