Chromospheric UV Bursts and Turbulent-driven Magnetic Reconnection

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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 Å 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 3D 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 Å 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 (macroscale) turbulence in the active region.

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