Diffuse Interplanetary Radio Emission: Shock Emission or a Type III storm?

TL;DR

This paper analyzes a specific diffuse interplanetary radio emission event linked to a CME, clarifying its origin from shock flanks and distinguishing it from type III storms, with implications for understanding solar radio phenomena.

Contribution

It provides a clear case study linking DIRE to CME shock flanks and explains why shock nose emissions are not observed, clarifying the nature of DIRE.

Findings

DIRE originates from CME shock flanks.

Radio emission from shock nose is not observed.

DIRE is distinct from type III storms.

Abstract

We present a clear case of a Diffuse Interplanetary Radio Emission (DIRE) event observed during 2002 March 11-12 in association with a fast coronal mass ejection (CME). In the previous event reported [1], there were two CMEs, and a detailed analysis was required to pin down the underlying CME. In the event presented here, the CME association is unambiguous, and the DIRE is found to originate from the flanks of the CME-driven shock. We also provide quantitative explanation for not observing radio emission from the shock nose. We also clarify that DIRE is not a type III storm because the latter occurs outside of solar eruptions.