Analysis of Type II radio burst relationship with CME driven shocks

Abstract

Type II radio bursts are known to be the signatures of coronal shocks. In this paper we examine the relationship between 129 type II bursts in the frequency range 35 – 450 MHz observed at Culgooora observatory during May 2002 – October 2015 and the associated CMEs. We apply Newkirk (1961) density model to determine the formation height of type IIs. We find that in 109/129 cases, type II bursts were preceded/ succeeded by CMEs. The CME associated type II events in which the CME height is above the type II burst source are categorized as group I events (91/129 cases). 91% of the bursts in this group are also associated with flares and 58% of these bursts originate during decaying phase of the flare. The correlation between CME speed and type II shock speed for limb events in this group is 0.33.The CME associated type IIs in which the CME height is below the type II source are categorized as group II (18/129 cases). CME driven shock could have been the exciter of these type II bursts.88% of this group events are associated with flares and 62% of these bursts originate during the rising phase of the flare. The correlation between CME speed and type II shock speed for limb events in this group is 0.96. In 20/129 cases of our data set, type II bursts are not associated with CME and are categorized as group III. 90% of the bursts in this group are associated with flares. 77% of the bursts in the group are originating in the decaying phase of flares. Poor temporal association (9/69 cases) between type IIs and flares of X class during this period. Our results suggest that inspite of temporal association with metric type II bursts, majority of the CME driven shocks (84%) are not successful in exciting type II bursts in 35-450 MHz domain. The type II bursts temporally correlated with CMEs and likely to have been excited by CMEs (type II height > CME height) are originating during the rising phase of the flares in majority of the events. In case of type II bursts temporally correlated with CMEs supposedly not excited by the CMEs (type II height < CME height) ,majority of them are originating in the decaying phase of flares.