On the Evolution of Coronal Mass Ejections in the Interplanetary Medium

The Astrophysical Journal 667, 610−625, 2007

On the Evolution of Coronal Mass Ejections in the Interplanetary Medium

T.A. Howard
Department of Physics, Montana State University, Bozeman, MT

C.D. Fry
Exploration Physics International, Inc., Huntsville, AL

J.C. Johnston
Space Weather Center of Excellence, Space Vehicles Directorate, Air Force Research Lab., Hanscom Air Force Base, MA

D.F. Webb
Institute for Scientific Research, Boston College, Chestnut Hill, MA

Abstract

Two coronal mass ejections (CMEs) are presented which were tracked through the LASCO field of view (FOV) within 30 Rsun and later as interplanetary CMEs (ICMEs) through the SMEI FOV from 80 to 150 Rsun. They were also associated with erupting filaments observed by EIT, providing information on trajectory of propagation. This allowed three-dimensional reconstructions of CME/ICME geometry, along with corrected (not sky plane projected) measurements of distance-time (DT) plots for each event to ~0.5 AU. An investigation of morphology was conducted. The results suggest that fine structures of the CMEs are eroded by the solar wind, and curvature becomes more sharply convex outward, suggesting that ICME footpoints remain fixed to the Sun even at 0.5 AU. We also present two models describing the evolution of CMEs/ICMEs at large distances from the Sun (far from the launch mechanism and effects of gravity and solar pressure) and consider two drag models: aerodynamic drag and snowplow. There was little difference between these, and their DT profiles matched well with the SMEI data for event 1. Event 2 showed a net acceleration between the LASCO and SMEI FOVs and we could match the data for this event well by introducing a driving Lorentz force. ICME mass almost doubled as a result of swept-up solar wind material from the snowplow model. Finally, we compared the geometry and kinematics of the ICME with that produced by the HAFv2 model and found that the model reasonably matched the geometry, but overestimated the ICME speed.