Evolution of Coronal and Interplanetary Shock Waves Inferred from a Radio Burst

Studying the evolution of the source of a radio burst, which is recognized as a shock wave, is important for understanding its generation mechanism and predicting its hazards. Estimating the kinematics of radio-burst sources using electron-density models is not easy. In this article, the kinematics of the Type-II radio-burst source is estimated without using electron-density models by studying the density variation along the leading surface of the coronal mass ejections (CMEs) (hereafter ejecta) during Type-II radio-burst emission. This technique is valid for analyzing the Type-II radio-burst spectrum in metric and DH ranges, from which we can infer ejecta propagation from the corona into interplanetary space. It is found that the Type-II radio burst can be described by the Sedov-Taylor blastwave equation by matching the calculated theoretical frequencies with that observed by the RAD1 and RAD2 receivers. The theoretical model showed a good fit with the observed spectra of Type-II radio bursts of different Type-II events. The analysis was consistent with the previous work regarding the conditions of the Sedov-Taylor equation and statistical studies of the density variation on the surface area of an interplanetary CME. The kinematics of a Type-II radio-burst source and the temporal variation of its energy are estimated during the Type-II radio-burst emission. The results of the two cases studied show that the energy of ejecta degraded by similar to 14% of its initial energy at the beginning of metric Type-II radio emission on 16 March 2016, while the energy of ejecta degraded by similar to 86% and similar to 20% for DH Type-II radio burst as recorded by RAD1 and RAD2 on 7 November 2004, respectively. The analysis shows that the radial speed of the blast wave is lower than its transversal speed along the surface of ejecta and extends to a small fraction of R similar to from its source point on the ejecta. The magnetic-field strength of the ejecta and the ambient medium are estimated during the Type-II radio-burst emission. This study emphasizes that the emission of a blast wave from the reconnection sites within the ejecta is one of the processes that degrades the energy of ejecta during their propagation.