Estimate of Plasma Temperatures Across a CME-Driven Shock from a Comparison Between EUV and Radio Data
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Estimate of Plasma Temperatures Across a CME-Driven Shock from a Comparison Between EUV and Radio Data Federica Frassati1 · Salvatore Mancuso1 Alessandro Bemporad1
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Received: 9 March 2020 / Accepted: 6 August 2020 © The Author(s) 2020
Abstract In this work, we analyze the evolution of an EUV wave front associated with a solar eruption that occurred on 30 October 2014, with the aim of investigating, through differential emission measure (DEM) analysis, the physical properties of the plasma compressed and heated by the accompanying shock wave. The EUV wave was observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and was accompanied by the detection of a metric Type II burst observed by ground-based radio spectrographs. The EUV signature of the shock wave was also detected in two of the AIA channels centered at 193 Å and 211 Å as an EUV intensity enhancement propagating ahead of the associated CME. The density compression ratio X of the shock as inferred from the analysis of the EUV data is X ≈ 1.23, in agreement with independent estimates obtained from the analysis of the Type II band-splitting of the radio data and inferred by adopting the upstream–downstream interpretation. By applying the Rankine–Hugoniot jump conditions under the hypothesis of a perpendicular shock, we also estimate the temperature ratio as TD /TU ≈ 1.55 and the post-shock temperature as TD ≈ 2.75 MK. The modest compression ratio and temperature jump derived from the EUV analysis at the shock passage are typical of weak coronal shocks. Keywords shock waves · Sun: activity · Sun: corona · Sun: coronal mass ejections (CMEs) · Sun: radio radiation · Sun: EUV radiation
1. Introduction In the past decades, Type II radio bursts have been recognized as unambiguous diagnostic probes to identify the propagation of shock waves in the corona and infer their speeds (e.g. Thompson, Kennewell, and Prestage, 1996, and references therein). Both UV spectra (Raymond et al., 2000; Mancuso et al., 2002) and white-light coronagraphic observations
B F. Frassati
[email protected]
1
Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
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(Ontiveros and Vourlidas, 2009) have been later used to yield further insight on the evolution and physical properties of coronal shock waves. More recently, EUV waves have been routinely observed as diffuse and irregular arcs of increasing coronal emission in images obtained with the EUV Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO: Domingo, Fleck, and Poland, 1995) and with the Atmospheric Imaging Assembly (AIA: Lemen et al., 2012) onboard the Solar Dynamics Observatory (SDO: Pesnell, Thompson, and Chamberlin, 2012). However, both the physical nature of these coronal waves and their driving mechanism are not yet clear and are still under debate (e.g. Gallagher and Long, 2011; Patsourakos and Vourlidas, 2012; Warmuth, 2015). Notwithstanding th
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