Coronal transients and metric type II radio bursts

I. Effects of geometry

¹ Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Strada Osservatorio 20, Pino Torinese 10025, Italy
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 50, Cambridge, MA 02138, USA

Corresponding author: S. Mancuso, mancuso@to.astro.it

Received: 16 June 2003
Accepted: 22 September 2003

Abstract

In this paper we investigate the relationship between type ii and coronal transient activity in terms of emission originating from the top or the flanks of a bow/piston shock surface, extending just above the coronal mass ejection (CME) leading edge surface. For this purpose, we used ground-based metric type ii radio burst observations of twenty-nine events in conjunction with Large Angle and Spectrometric Coronagraph (LASCO/SOHO) and UltraViolet Coronagraph Spectrometer (UVCS/SOHO) observations. With the refined density diagnostic offered by the UVCS instrument, we analyzed the type ii dynamics in conjunction with the associated CME dynamics. Although we found some correlation, in all but a few cases the coronal transients appeared to lead the type ii emission locations by several minutes, in apparent disagreement with a CME-driven origin interpretation. By applying a simple model, we found however that a piston-driven origin is certainly viable for all the events under study on the hypothesis that the radio emission originates in discrete locations above the top or the flanks of bow/piston shock surfaces extending just above the transient leading edges.