A broken solar type II radio burst induced by a coronal shock propagating across the streamer boundary

Abstract

We discuss an intriguing typeII radio burst that occurred on 2011 March 27. The dynamic spectrum was featured by a sudden break at about 43MHz on the well-observed harmonic branch. Before the break, the spectrum drifted gradually with a mean rate of about -0.05MHzs-1. Following the break, the spectrum jumped to lower frequencies. The post-break emission lasted for about 3 minutes. It consisted of an overall slow drift which appeared to have a few fast-drift sub-bands. Simultaneous observations from the Solar TErrestrial RElations Observatory and the Solar Dynamics Observatory were also available and are examined for this event. We suggest that the slow-drift period before the break was generated inside a streamer by a coronal eruption driven shock, and the spectral break as well as the relatively wide spectrum after the break is a consequence of the shock crossing the streamer boundary where density drops abruptly. It is suggested that this type of radio bursts can be taken as a unique diagnostic tool for inferring the coronal density structure, as well as the radio-emitting source region. © © 2012. The American Astronomical Society. All rights reserved..