On the association between type II radio bursts and CMEs

Abstract

Ground-based observations of metric (coronal) type II radio bursts are compared with observations of coronal mass ejections (CMEs) obtained by the LASCO coronagraph aboard SOHO and with decametric (interplanetary) type II bursts recorded by the WAVES instrument aboard Wind. The basic data sample comprises 63 metric type II radio bursts observed during different phases of the solar cycle, i.e., 20 events in 1997 and 43 events in 1999/2000. Our analysis is based on temporal coincidence and velocity data derived from height-time plots of CMEs and frequency drift rates of type II radio bursts, respectively. The results suggest that there are three scenarios leading to metric type II burst excitation: The radio emission is generated either at flare-related blast wave shocks (class 1), at shocks driven by the leading edge of the CME (class 2), or at shocks driven by internal parts or the flanks of the CME (class 3). This classification is supported by an analysis of the association with Hα flare sites. The first class of events comprises 19 events (30%), the second 19 events (30%), and the third 18 events (29%). 7 events (11%) were not classified. Furthermore, we notice a possible solar cycle dependence of the relative occurrence of the different scenarios.