Characteristics of flares producing metric type II bursts and coronal mass ejections |
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| Authors: | S Kahler N R Sheeley Jr R A Howard M J Koomen D J Michels |
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| Institution: | (1) American Science and Engineering, 02139 Cambridge, MA, U.S.A.;(2) Emmanuel College, 02115 Boston, MA, U.S.A.;(3) E. O. Hulburt Center for Space Research, Naval Research Laboratory, 20375 Washington, DC, U.S.A. |
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| Abstract: | We attempt to study the origin of coronal shocks by comparing several flare characteristics for two groups of flares: those with associated metric type II bursts and coronal mass ejections (CMEs) and those with associated metric type II bursts but no CMEs. CMEs accompany about 60% of all flares with type II bursts for solar longitudes greater than 30°, where CMEs are well observed with the NRL Solwind coronagraph. H flare areas, 1–8 Å X-ray fluxes, and impulsive 3 cm fluxes are all statistically smaller for events with no CMEs than for events with CMEs. It appears that both compact and large mass ejection flares are associated with type II bursts. The events with no CMEs imply that at least many type II shocks are not piston-driven, but the large number of events of both groups with small 3 cm bursts does not support the usual assumption that type II shocks are produced by large energy releases in flare impulsive phases. The poor correlation between 3 cm burst fluxes and the occurrence of type II bursts may be due to large variations in the coronal Alfvén velocity.Sachs/Freeman Associates, Inc., Bowie, MD 20715, U.S.A. |
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