Simulated enhancement of solar type II radio bursts during the collision of two shocks associated with coronal mass ejections

¹ Laboratory for Plasma Astrophysics, Faculty of Engineering, University of Toyama, 3190, Gofuku, Toyama 930-8555, Japan e-mail: sakaijun@eng.u-toyama.ac.jp
² Astrophysical Institute Potsdam, An der Sternwarte 16a, 14482 Potsdam, Germany

Received: 2 March 2006
Accepted: 3 April 2006

Abstract

Aims.We investigate how solar type II radio bursts can be enhanced when two fast magnetosonic shocks associated with coronal mass ejections (CMEs) collide. This work was motivated by recent observations showing that the radio signature is in the form of intense continuum-like radio emission following an interplanetary type II burst, when a fast CME overtakes a slow CME.

Methods. We used a 2D3V fully relativistic, electromagnetic particle-in-cell (PIC) simulation.

Results. We found that during the collision between a fast shock with Alfvén Mach and a slow wave with Alfvén Mach , the radio emission with a broad band can be enhanced with an amplitude about ten times larger than for the undisturbed type II burst. We also found that when a fast shock with Alfvén Mach overtakes a slow shock with Alfvén Mach , the enhancement of the radio emission is about five times greater than the undisturbed type II burst.