HR: 14:40h
AN: SH23A-05    [Abstracts]
TI: Radio-quiet Fast Coronal Mass Ejections
AU: * Gopalswamy, N
EM: gopals@fugee.gsfc.nasa.gov
AF: NASA/GSFC, Code 695, Greenbelt, MD 20771 United States
AU: Aguilar-Rodriguez, E
EM: ernesto@lepvax.gsfc.nasa.gov
AF: The Catholic University of America, Department of Physics 200 Hannan Hall, Washington, DC 20064 United States
AU: Kaiser, M L
AF: NASA/GSFC, Code 695, Greenbelt, MD 20771 United States
AU: Howard, R A
AF: Naval Research Laboratory, Solar Physics Branch Space Science Division 4555 Overlook Ave SW, Washington, DC 20375 United States
AB: Coronal mass ejections (CMEs) drive shocks in the interplanetary medium that produce type II radio emission. These CMEs are faster and wider on the average, than the general population of CMEs. However, when we start from fast (speed $>$ 900 km/s) and wide (angular width $>$ 60 degrees), more than half of them are not associated with radio bursts. In order to understand why these CMEs are radio quiet, we collected all the fast and wide (FW) CMEs detected by the Solar and Heliospheric Observatory (SOHO) mission's Large Angle and Spectrometric Coronagraph (LASCO) and isolated those without associated type II radio bursts. The radio bursts were identified in the dynamic spectra of the Radio and Plasma Wave (WAVES) Experiment on board the Wind spacecraft. We also checked the list against metric type II radio bursts reported in Solar Geophysical Data and isolated those without any radio emission. This exercise resulted in about 140 radio-quiet FW CMEs. We identified the source regions of these CMEs using the Solar Geophysical Data listings, cross-checked against the eruption regions in the SOHO/EIT movies. We explored a number of possibilities for the radio-quietness: (i) Source region being too far behind the limb, (ii) flare size, (iii) brightness of the CME, and (iv) the density of the ambient medium. We suggest that a combination of CME energy and the Alfven speed profile of the ambient medium is primarily responsible for the radio-quietness of these FW CMEs.
UR: http://cdaw.gsfc.nasa.gov
DE: 7509 Corona
DE: 7513 Coronal mass ejections
DE: 7534 Radio emissions
DE: 7851 Shock waves
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting