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
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.
© ESO, 2006