A statistical study of the characteristics of type II doublet radio bursts

Indian Institute of Astrophysics, Bangalore 560 034, India e-mail: subra@iiap.res.in

Received: 16 September 2005
Accepted: 16 December 2005

Abstract

Aims.We study the characteristics of doublet type II radio bursts in which two type II bursts occur in sequence and investigate their drivers.

Methods.37 type II bursts reported by the Culgoora radio observatory in the Solar Geophysical data for the period September 1994–July 2004 were used to determine their time and frequency characteristics. In order to investigate their association with flares and Coronal Mass Ejections, flare data from NOAA and Coronal Mass Ejection data from Center for Solar Physics and Space weather, Catholic University of America were used.

Results.The second type II burst starts at a lower frequency than to the first one. The normalized drift rate of the the first II burst is found to be nearly twice that of the second type II burst. For both the first and second type II bursts, their start frequencies and the drift rates are found to be correlated. The mean time difference between the start of the first and second type II burst is 8.1 min. There were no reports of two flares or CMEs except one case each. The first and second type II bursts start 5 and 15 min after the start of the GOES X-ray flares. The time difference between the CME onset and start of the first and second type II burst is close to the above values. The type II doublet bursts have the following association with flares: B class ; C class ; M class and X class . The Coronal Mass Ejections associated with type II doublet bursts have an acceleration of -10 m/s² and angular width of more than 270 degrees.