SMEI observations in the STEREO era

Abstract

White-light Thomson scattering observations from the Solar Mass Ejection Imager (SMEI) have recorded the inner heliospheric response to many CMEs. Some of these are also observed from the LASCO instrumentation and, most recently, the STEREO spacecraft. Here, we detail several CME events in SMEI observations that have also been observed by the LASCO instrumentation and STEREO spacecrafts. We show how SMEI is able to measure CME events from their first observations as close as 20° from the solar disk until they fade away in the SMEI 180° field of view. We employ a 3D reconstruction technique that provides perspective views as observed from Earth, from outward-flowing solar wind. This is accomplished by iteratively fitting the parameters of a kinematic solar wind density model to the SMEI white-light observations and, where possible, including interplanetary scintillation (IPS) velocity data. This 3D modeling technique enables separating the true heliospheric response in SMEI from background noise, and reconstructing the 3D heliospheric structure as a function of time. These reconstructions allow both separation of CME structure from other nearby heliospheric features and a determination of CME mass. Comparisons with LASCO and STEREO images for individual CMEs or portions of them allow a detailed view of changes to the CME shape and mass as they propagate outward.