ESA SP 592, 767, 2005
Solar Wind Eleven / SOHO 16 "Connecting Sun and Heliosphere", B. Fleck, T.H. Zurbuchen, H. Lacoste (eds.)
© ESA Publication Division 2005

CMEs Observed By SMEI Which Are Not Seen By LASCO

G.M. Simnett
School of Physics and Astronomy, Univ. of Birmingham, UK


The Solar Mass Ejection Imager (SMEI) has been observing CMEs in the interplanetary medium since its launch on the Coriolis spacecraft on 6 January 2003. Approximately 1/8th of the events which are readily detected in the all-sky images produced once/orbit (102 minutes) are not accompanied by an event visible in LASCO running difference images within 12 hours of the nominal time the event left the Sun. The latter is based on a back-extrapolation of the elongation-time plot of the SMEI event. A further constraint is that the search of the LASCO data was restricted to a position angle within +/- 60 degrees of the position angle of the SMEI event. A further 1/8th of the SMEI events were accompanied by extremely faint LASCO events, which would not have been detected by a casual observer, but which otherwise matched well with the SMEI elongation-time plot at the same position angle. The conclusion form this work is that erupting magnetic structures from the Sun must frequently accumulate mass as they travel through the interplanetary medium.