Letter to the Editor

Bifurcation of the metric type II radio emission associated with the giant solar flare of April 2 2001

Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, Strada Osservatorio 20, Pino Torinese 10025, Italy

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

Received: 3 December 2003
Accepted: 5 January 2004

Abstract

On April 2 2001, following one of the largest flares of the present solar cycle, intense and complex metric type ii radio bursts were recorded by the Hiraiso Radio Spectrograph. Metric type ii emission is a typical signature of the propagation of a coronal shock. The dynamic spectra of this event present a clear bifurcation of the radio emission lanes, which is very rare in the metric domain and requires a proper interpretation. We model this bifurcation as the result of the interaction of a piston-driven spherical shock with a vertical current sheet located above the active region where the X20 flare occurred. The geometry of the expanding transient and the coronal electron density, necessary to derive the type ii dynamics, are constrained through analysis of data obtained from the Solar and Heliospheric Observatory (SOHO) instruments. The model replicates successfully the observed bifurcation, supporting our interpretation. Furthermore, we propose that magnetic reconnection was triggered in the current sheet by the shock passage.