Multiple Type II Solar Radio Bursts |
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| Authors: | A Shanmugaraju Y-J Moon K-S Cho Y-H Kim M Dryer S Umapathy |
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| Institution: | (1) Department of Physics, Arul Anandar College, Karumathur, 625514 Madurai, India;(2) Korea Astronomy and Space Science Institute (KASI), Whaamdong, Yuseong-gu, Daejeon, 305-348, Korea;(3) NOAA Space Environment Center, Boulder, Colorado, 80305, U.S.A.;(4) School of Physics, Madurai Kamaraj University, Madurai, India |
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| Abstract: | We report on the detailed analysis of a set of 38 multiple type II radio bursts observed by Culgoora radio spectrograph from
January 1997 to July 2003. These events were selected on the basis of the following criteria: (i) more than one type II were
reported within 30 min interval, (ii) both fundamental and harmonic were identified for each of them. The X-ray flares and
CMEs associated with these events are identified using GOES, Yohkoh SXT, SOHO/EIT, and SOHO/LASCO data. From the analysis
of these events, the following physical characteristics are obtained: (i) In many cases, two type IIs with fundamental and
harmonic were reported, and the time interval between the two type IIs is within 15 min; (ii) The mean values of starting
frequency, drift rate, and shock speed of the first type II are significantly higher than those of the second type II; (iii)
More than 90% of the events are associated with both X-ray flares and CMEs; (iv) Nearly 75% of the flares are stronger than
M1 X-ray class and 50% of CMEs have their widths larger than 200^∘ or they are halo CMEs; (v) While most of the first type
IIs started within the flare impulsive phase, 22 out of 38 second type IIs started after the flare impulsive phase. Weak correlations
are found between the starting and ending frequencies of these type II events. On the other hand, there was no correlation
between two shock speeds between the first and the second type II. Since most of the events are associated with both the flares
and CMEs, and there are no events which are only associated with multiple impulsive flares or multiple mass ejections, we
suggest that the flares and CMEs (front or flank) both be sources of multiple type IIs. Other possibilities on the origin
of multiple type IIs are also discussed. |
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