Three-dimensional reconstruction of CME-driven shock–streamer interaction from radio and EUV observations: a different take on the diagnostics of coronal magnetic fields

Abstract

On 2014 October 30, a band-splitted type ii radio burst associated with a coronal mass ejection (CME) observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) occurred over the southeast limb of the Sun. The fast expansion in all directions of the plasma front acted as a piston and drove a spherical fast shock ahead of it, whose outward progression was traced by simultaneous images obtained with the Nançay Radioheliograph (NRH). The geometry of the CME/shock event was recovered through 3D modeling, given the absence of concomitant stereoscopic observations, and assuming that the band-splitted type ii burst was emitted at the intersection of the shock surface with two adjacent low-Alfvén speed coronal streamers. From the derived spatiotemporal evolution of the standoff distance between shock and CME leading edge, we were finally able to infer the magnetic field strength B in the inner corona. A simple radial profile of the form B(r) = (12.6 ± 2.5)r −4 nicely fits our results, together with previous estimates, in the range r = 1.1 − 2.0 R .

Estimate of Plasma Temperatures Across a CME-Driven Shock from a Comparison Between EUV and Radio Data

“…The dynamic spectrum ( Figure 2) of this event shows a complex Type II radio burst, mostly observed as harmonic emission, starting at about 13:08 UT and splitting into several subbands. The primary-band splitting has features suggesting shock/streamer interactions (see Mancuso et al, 2019). The further splitting of the upper-harmonic band (visible in the time interval between 13:08.5 UT and 13:08.7 UT) is most probably originating from simultaneous radio emission occurring in the upstream (ahead) and downstream (behind) region of the shock front (e.g.…”

“…The Type II radio sources were also imaged by the Nançay radioheliograph (NRH: Kerdraon and Delouis, 1997). The CME-driven shock was modeled by Mancuso et al (2019) as a spherical expanding/translating surface assuming that the primary band-splitted Type II radio burst was emitted at the intersection of the shock surface with adjacent low-Alfvén-speed coronal streamers as in the scenario proposed by Mancuso and Raymond (2004). For further details on the instruments and the analysis of the radio data related to this event, please refer to Mancuso et al (2019).…”

“…In this article, we report the EUV analysis of an intriguing CME/shock event, occurred on 30 October 2014, with the aim to shed more light on the above questions. This event was recently analyzed in the metric radio domain by Mancuso et al (2019) through radiospectrograph and radio-heliograph observations. The authors found that the CME-driven shock was located ahead of an expanding bubble-like EUV structure, with metric Type II radio burst emission most probably excited at the locations where the shock surface intersected the overlying streamer's axes as in the scenario proposed by Mancuso and Raymond (2004).…”

“…Through 3D modeling, this analysis allowed the estimate of the density and magnetic-field strength profiles in the inner corona. In this article, taking advantage of the results obtained in Mancuso et al (2019), we focus our attention on the detailed analysis of the EUV data retrieved by SDO/AIA to gather complementary information on the associated density compression ratio and temperature jump, thus providing a comprehensive view of this CME/shock event. The article is organized as follows: Section 2 is devoted to the description of the instruments and observations.…”

Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R⊙: Faraday Rotation and Frequency Shift Analysis

“…Techniques to analyze solar eruptions in the proximity of active regions have been developed to obtain magnetic field strength in the low to middle corona (Gopalswamy et al, 2012;Mancuso & Garzelli, 2013a;Mancuso et al, 2003Mancuso et al, , 2019. Solar outburst radio analysis was derived from a method developed for analysis of the bow shock of the terrestrial magnetosphere, applied in a novel manner to the case of a CME emerging into a background coronal field (Mancuso et al, 2019). The technique provided important information in the heliocentric radial distance range 1.2-1.5 R ⊙ (Gopalswamy et al, 2012) using SDO imaging of CME ejections and the associated Type II radio bursts.…”