Intensity and velocity oscillations in a flaring active region

Millar, D. C.L., Fletcher, L. and Joshi, J. (2024) Intensity and velocity oscillations in a flaring active region. Monthly Notices of the Royal Astronomical Society, 527(3), pp. 5916-5928. (doi: 10.1093/mnras/stad3386)

Abstract

Chromospheric oscillations can give us insight into the physical environment in the solar atmosphere, both in quiet Sun and flaring conditions. Many authors have reported increases in the prevalence of 3-minute oscillations which are thought to be excited by events which impact the chromosphere such as flares. In this study, we utilized the Ca II 8542 Å line to study the oscillatory behaviour of the chromosphere in an active region which underwent two B-class flares. We analysed oscillations in both intensity and velocity, and found different behaviours in both. Intensity oscillations were most prevalent over the umbrae of sunspots and magnetic pores in the active region, and the extent of the area which contained significant oscillations was found to decrease when comparing times after the flares to before. By measuring the evolution of the magnetic field, we found that this could be because the areas surrounding the umbrae were becoming more ‘penumbral’ with an increase to the magnetic field inclination. Velocity oscillations were found across the active region both before and after the flares but were observed clearly in areas which were brightened by the second flare. By comparing to EUV imaging, it was seen that strong chromospheric velocity oscillations with 3–4-minute periods occurred at the same time and location as a flare loop cooling 30 min after the second flare peak. This could be evidence of disturbances in the loop exciting a response from the chromosphere at its acoustic cut-off frequency.

• Item Type: Articles
• Additional Information: This work was supported by The Carnegie Trust for the Universities of Scotland through PhD studentship PHD007733 (DCLM), Glasgow University College of Science and Engineering (DCLM) and the UK’s Science and Technology Facilities Council (LF) [grant numbers ST/T000422/1 and ST/X000990/1].
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Fletcher, Professor Lyndsay and Millar, Mr David
• Authors: Millar, D. C.L., Fletcher, L., and Joshi, J.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Monthly Notices of the Royal Astronomical Society
• Publisher: Oxford University Press
• ISSN: 0035-8711
• ISSN (Online): 1365-2966
• Published Online: 03 November 2023
• Copyright Holders: Copyright © The Author(s) 2023.
• First Published: First published in Monthly Notices of the Royal Astronomical Society 527(3):5916-5928
• Publisher Policy: Reproduced under a Creative Commons license

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
306515		PHAS A&A Group STFC Consolidated	Lyndsay Fletcher	Science and Technology Facilities Council (STFC)	ST/T000422/1	P&S - Physics & Astronomy
317627		Solar Physics at the University of Glasgow	Lyndsay Fletcher	Science and Technology Facilities Council (STFC)	ST/X000990/1	P&S - Physics & Astronomy