Constraints on Coronal Mass Ejection Dynamics from Simultaneous Radio and White‐Light Observations

Abstract

Simultaneous radio and white-light observations are used to deduce information on the dynamics of two coronal mass ejection (CME) events that occurred about 2 hr apart on 2001 January 20 and that were associated with eruptions from the same active region on the Sun. The analysis combines both space-based and ground-based data. The radio data were obtained from the WAVES experiment on the Wind spacecraft and from the Culgoora radiospectrograph in Australia. The white-light data were from the LASCO experiment on SOHO and from the Mk4 coronameter at the Mauna Loa Solar Observatory. For these CME events we demonstrate that the frequency drift rate of the type II radio emissions, generated by the shocks driven by the white-light CMEs, are consistent with the plane-of-sky height-time measurements, provided that the propagation direction of the CMEs and their associated radio sources was along a radial line from the Sun at a solar longitude of ~E50°. These results imply that the true CME speeds were estimated to be ~1.4 times higher than the measured plane-of-sky speeds and that the CMEs originated from solar eruptions centered near E50°. This CME origin is consistent with the known active region and flare site associated with these two CME events. Furthermore, we argue that the type II radio emissions generated by these CMEs must have originated in enhanced density regions of the corona. We investigate whether the type II radiation could have originated in one or more dense coronal streamers, whose densities were estimated from the polarization brightness measurements made by LASCO at that time. Finally, we use these radio and white-light observations to speculate about the dynamics and scales involved in the interaction between these two CMEs.