Abstracts submitted by NATCHIMUTHUK GOPALSWAMY

Coronal Mass Ejections with and without type II radio bursts

N. Gopalswamy & M. L. Kaiser [1]; H. Xie, S. Yashiro, S. Akiyama , & P.Makela [2]; R. A. Howard [3]; J.-L. Bougeret [4]

[1] NASA Goddard Space Flight Center; [2] The Catholic University of America; [3] Naval Research Laboratory; [4] Observatoire de Paris, Meudon

Fast (>900 km/s) and wide (>60 deg) coronal mass ejections drive shocks that accelerate electrons and protons. Therefore, CMEs producing type II bursts (radio-loud CMEs) are considered good indicators of solar energetic particle (SEP) events. However, about a third of the fast and wide CMEs observed by SOHO/LASCO are not associated with type II bursts (radio quiet) when searched in the dynamic spectra obtained by Wind/WAVES experiment. For the present study we consider all the fast and wide CMEs observed by SOHO from 1996 to 2005 and separate them into radio-quiet and Radio-loud ones. We examine the kinematics and source locations of the radio quiet CMEs and compare them with those of radio loud CMEs. The investigation has led us to the following conclusions: (i) Radio-quiet CMEs are slower the average. (ii) The fraction of full halos is much smaller for the radio-quiet CMEs indicating that they are narrower on the average. Since narrower CMEs are less massive, the radio-quiet CMEs seem to be inherently less energetic. (iii) In addition to being weak, the radio-quiet CMEs may be propagating through an ambient medium that has a higher Alfven speed. (iv) The radio-quiet CMEs are launched at large angles to the Sun-Observer line (mostly back-sided or limb events). (v) The source locations of radio-loud CMEs are in the active region belt, while those of radio-quiet CMEs are mostly outside. (vi) The soft X-ray flare size is slightly smaller for the radio-quiet CMEs consistent with the fact that most of them originate away from the active region belt. (vii) None of the radio-quiet CMEs was associated with large SEP events. (viii) Some (a few percent) radio-quiet CMEs were associated with minor SEP enhancements, suggesting that weak shocks may be present in these cases. This also indicates there may be subtle difference in the requirement for electron and ion acceleration by the shock.