Radio Signatures of Coronal-Mass-Ejection-Streamer Interaction and Source Diagnostics of Type Ii Radio Burst

Abstract

It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g. spectral bumps) of the dynamic spectra of type II radio bursts, to imaging features (e.g. CME going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME-streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated electron acceleration by CME-driven shock.

A review of recent studies on coronal dynamics: Streamers, coronal mass ejections, and their interactions

“…A typical type II event with a clear spectral bump feature observed on 1 November 2003 was reported by Feng et al [141]. The dynamic spectrum is shown in Figure 15.…”

“…In recent studies, we have discovered several interesting white-light and radio phenomena associated with CMEstreamer interactions, including streamer waves manifested as the wavy motion of a streamer stalk [138][139][140], and spectral bump and break features of type II radio busts caused by the radio source propagating through a streamer from outside [141] and inside of the streamer [142]. These studies will be reviewed as follows.…”

“…Feng et al [141] and Kong et al [142] proposed a promising approach to resolve the above issue by establishing physical connection between the spectral shape from the radio data and specific eruptive process observed with solar imagings. As mentioned, it is generally believed that the type II frequency is mainly determined by the electron density at the shock, the spectral shape is therefore expected to be affected by coronal structures along the shock path.…”

“…Type II spectra with these features have been reported [141,142] and will be reviewed in the following. We also present how these studies contribute to type II source diagnostics.…”

The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures

“…Statistical analyses have indicated that many CMEs originate from the streamer belt (e.g., Howard et al 1985;Hundhausen 1993;Eselevich & Tong 1997;Zhao & Webb 2003). Furthermore, recent works have shown that type II radio bursts, which are good observational manifestations of energetic electrons accelerated at shocks, reflect the interaction between shocks and streamers (e.g., Reiner et al 2003;Mancuso & Raymond 2004;Cho et al 2008;Feng et al 2012Feng et al , 2013Kong et al 2012Kong et al , 2015Chen et al 2014) or the shock passing through high-density coronal loops (e.g., Pohjolainen et al 2008;Cho et al 2013). Using test-particle simulations, Kong et al (2015Kong et al ( , 2016 studied the effect of streamer-like magnetic fields on electron acceleration at coronal shocks and found that the closed field lines can trap a significant amount of electrons close to the shock front and lead to an efficient acceleration.…”