Abstract
Abstract Type II radio bursts are generally observed in association with flare-generated or coronal-mass-ejection-driven shock waves. The exact shock and coronal conditions necessary for the production of type II radio emission are still under debate. Shock waves are important for the acceleration of electrons necessary for the generation of the radio emission. Additionally, the shock geometry and closed field line topology, e.g., quasi-perpendicular shock regions or shocks interacting with streamers, play an important role for the production of the emission. In this study we perform a 3D reconstruction and modeling of a shock wave observed during the 2014 November 5 solar event. We determine the spatial and temporal evolution of the shock properties and examine the conditions responsible for the generation and evolution of type II radio emission. Our results suggest that the formation and evolution of a strong, supercritical, quasi-perpendicular shock wave interacting with a coronal streamer were responsible for producing type II radio emission. We find that the shock wave is subcritical before and supercritical after the start of the type II emission. The shock geometry is mostly quasi-perpendicular throughout the event. Our analysis shows that the radio emission is produced in regions where the supercritical shock develops with an oblique to quasi-perpendicular geometry.
Highlights
The occurrence of type II radio bursts has long been related to the acceleration of energetic electrons at shock waves driven by the fast expansion of solar transients such as coronal mass ejections (CMEs; see, e.g., Claßen & Aurass 2002; Prakash et al 2009; Magdalenić et al 2010; Nindos et al 2011, and references therein)
In this study we modeled a shock wave associated with a solar event and a complex type II radio burst
Our key findings can be summarized as follows: 1. We show that the shock formation precedes the start of the type II radio burst; the shock wave is subcritical and electron acceleration is at that time too weak to produce radio emission
Summary
The occurrence of type II radio bursts has long been related to the acceleration of energetic electrons at shock waves driven by the fast expansion of solar transients such as coronal mass ejections (CMEs; see, e.g., Claßen & Aurass 2002; Prakash et al 2009; Magdalenić et al 2010; Nindos et al 2011, and references therein). Recent studies have shown that type II radio bursts could be produced in regions where the shock waves propagate into or close to streamers (see, e.g., Mancuso & Raymond 2004; Magdalenić et al 2014; Zucca et al 2018; Frassati et al 2019; Jebaraj et al 2020) In this case the quasi-perpendicular shock geometry could be a key parameter for efficient particle acceleration (e.g., Cho et al 2011; Kong et al 2015), especially for electrons. We determine the critical parameters that lead to efficient electron acceleration and the production of type II radio emission (Section 4)
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