Coronal Condensation as the Source of Transition Region Supersonic Downflows above a Sunspot

Abstract

Plasma loops or plumes rooted in sunspot umbrae often harbor downflows with speeds of 100 km/s. These downflows are supersonic at transition region temperatures of 0.1 MK. The source of these flows is not well understood. We aim to investigate the source of sunspot supersonic downflows (SSDs) in AR 12740 using simultaneous spectroscopic and imaging observations. We identified SSD events from multiple raster scans of a sunspot by the Interface Region Imaging Spectrograph, and calculated the electron densities, mass fluxes and velocities of these SSDs. The EUV images provided by the AIA onboard the SDO and the EUVI onboard the STEREO were employed to investigate the origin of these SSDs and their associated coronal rain. Almost all the identified SSDs appear at the footpoints of sunspot plumes and are temporally associated with appearance of chromospheric bright dots inside the sunspot umbra. Dual-perspective EUV imaging observations reveal a large-scale closed magnetic loop system spanning the sunspot region and a remote region. We observed that the SSDs are caused by repeated coronal rain that forms and flows along these closed magnetic loops toward the sunspot. One episode of coronal rain clearly indicates that reconnection near a coronal X-shaped structure first leads to the formation of a magnetic dip. Subsequently, hot coronal plasma catastrophically cools from 2 MK in the dip region via thermal instability. This results in the formation of a transient prominence in the dip, from which the cool gas mostly slides into the sunspot along inclined magnetic fields under the gravity. This drainage process manifests as a continuous rain flow, which lasts for around 2 hrs and concurrently results in a nearly steady SSD event. Our results demonstrate that coronal condensation in magnetic dips can result in the quasi-steady sunspot supersonic downflows.

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Cited by in corpus (10)

• The Solar Upper Transition Region Imager (SUTRI) onboard the SATech-01 satellite
• Detection of Flare-induced Plasma Flows in the Corona of EV Lac with X-ray Spectroscopy
• Possible detection of coronal mass ejections on late-type main-sequence stars in LAMOST medium-resolution spectra
• Spatial and Temporal Analysis of Quiescent Coronal Rain over an Active Region
• Prevalence of Thermal Non-Equilibrium over an Active Region
• EUV fine structure and variability associated with coronal rain revealed by Solar Orbiter/EUI HRIEUV and SPICE
• From Chromospheric Evaporation to Coronal Rain: An Investigation of the Mass and Energy Cycle of a Flare
• Diffuse solar coronal features and their spicular footpoints
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• Thermal Non-equilibrium Cycles in a Non-eruptive Pseudo-Streamer