Heliophysics Science Division
James Chen - Abstract

A New Theory of CME - Magnetic Cloud Dynamics:
Comparison with LASCO and EIT Data

James Chen
Naval Research Laboratory, Washington, DC

A quantitative theory of coronal mass ejections (CMEs) has been developed within the framework of ideal MHD. The theory assumes that the magnetic geometry underlying a CME is a 3-D magnetic flux rope. As a starting point, the flux rope is assumed to be initially in equilibrium in the corona. The theory computes the forces acting on the 3-D flux rope and the motion of the flux rope in response to increased poloidal flux. The theoretical results are compared with observed CMEs, using data from the LASCO/SOHO instrument, EIT, and HAO's MK3. The results have been compared in detail with several observed CMEs. It is shown that the theoretical solutions can accurately describe the dynamical behavior of a class of observed CMEs. Furthermore, the initial-value solutions that fit CMEs near the Sun evolve into flux ropes closely resembling observed interplanetary magnetic clouds (MCs). Thus, the model provides, for the first time, a unified and quantitative description of CMEs and MCs. The physical forces responsible for the initial acceleration and subsequent evolution in the interplanetary medium are discussed. The forces are purely 3-D with no 2-D counterparts. The apparent good agreement with both observed CMEs and MCs is significant because a viable model of CMEs (or any solar eruptions) must correctly produce, as a consequence, solar wind structures known to be associated with the respective eruptions. Potentially observable signatures in the photosphere and in the low corona resulting from the increasing poloidal flux are calculated. It is shown that the plasma motion occurs at the local Alfvenic speed or slower in the photosphere and is not easily distinguishable from the typical motion, but that the tangential magnetic component in the photosphere may exhibit certain subtle but changes detectable by high-resolution and high-time cadence vector magnetographs. Changes in the tangential magnetic field have been reported in a few observations of flares, but confirmation must await more systematic future observations. Physical differences between the present theory and the prevailing storage-release paradigm are discussed. It is argued that the new approach, which views the magnetic energy input into the corona as part of a dynamic process, is physically more realistic.