Ellerman bombs and UV bursts: reconnection at different atmospheric layers

Abstract

The emergence of magnetic flux through the photosphere and into the outer solar atmosphere produces, amongst other dynamical phenomena, Ellerman bombs (EBs), which are observed in the wings of Hα and are due to magnetic reconnection in the photosphere below the chromospheric canopy. Signs of magnetic reconnection are also observed in other spectral lines, typical of the chromosphere or the transition region. An example are the UV bursts observed in the transition region lines of Si iv and the upper chromospheric lines of Mg ii. In this work we analyze high cadence, high resolution coordinated observations between the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft. Hα images from the SST provide us with the positions, timings and trajectories of EBs in an emerging flux region. Simultaneous, co-aligned IRIS slit-jaw images at 133 (C ii, transition region), 140 (Si iv, transition region) and 279.6 (Mg ii k, core, upper chromosphere) nm, as well as spectroscopy in the far and near ultraviolet from the fast spectrograph raster, allow us to study the possible chromospheric/transition region counterparts of those EBs. Our main goal is to study the possible temporal and spatial relationship between several reconnection events at different layers in the atmosphere (namely EBs and UV bursts), the timing history between them, and the connection of these dynamical phenomena to the ejection of surges in the chromosphere. We also investigate the properties of an extended UV burst and their variations across the burst domain. Our results suggest a scenario where simultaneous and co-spatial EBs and UV bursts are part of the same reconnection system occurring sequentially along a vertical or nearly vertical current sheet. Heating and bidirectional jets trace the location where reconnection takes place. These results support and expand those obtained from recent numerical simulations of magnetic flux emergence.

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. III. 3D Simulations and Atmospheric Response

“…So, our results demonstrate that, in cancelling regions, a wide spectrum of ejections can be produced, with a wide range of different temperatures and sizes associated with Ellerman bombs, UV bursts and IRIS bombs and other hot and cool ejections (Yang et al 2013;Vissers et al 2015;Reid et al 2016;Rutten 2016;Nelson et al 2017;Rouppe van der Voort et al 2017;Young et al 2018;Tian et al 2018;Chen et al 2019;Guglielmino et al 2019;Ortiz et al 2020;Tiwari et al 2019;Huang et al 2019;Madjarska 2019). The predicted spatial offsets and time delays for hot and cool ejections are in accordance with observational findings.…”

Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)

“…Bright flame-like emission in the wings of Hα, similar to that observed for Ellerman bombs, suggests a common reconnection origin, but the heating profile and the characteristics of the magnetic-field evolution may imply a somewhat different reconnection scenario (Rouppe van der Voort, Rutten, and Vissers, 2016). Similarly, UV bursts appear to be reconnection events that differ from both Ellerman bombs and quiet-Sun Ellerman-like brightenings in their magnetic topology, atmospheric penetration height, and energy, with the plasma in these events heated to transition-region temperatures (Nelson et al, 2017a;Young et al, 2018;Ortiz et al, 2020).…”

ALMA observations of transient heating in a solar active region

“…Numerical simulations have shown that the magnetic topology that determines the height of reconnection along with the line of sight to the reconnection site play a role in the visibility of these small-scale heating events across the wavelength spectrum (Hansteen et al 2019;Peter et al 2019;Ortiz et al Movie associated to Fig. 5 is available at https:// www.aanda.org 2020; Syntelis & Priest 2020).…”