Driving Force of CMEs: Acceleration and Propagation

James Chen

Plasma Physics Division
Naval Research Laboratory
Washington, DC 20375

An identifiable class of geoeffective structures associated with CMEs and eruptive prominences (EPs) is the class of solar wind structures referred to as magnetic clouds (MCs). I will discuss theoretical and observational evidence that CME-MC connection can be consistently described as the eruption and subsequent expansion of an initial magnetic flux rope (MFR). The erupting flux rope (EFR) model of CMEs and MCs (Chen and Garren, GRL, 20, 2319, 1993; Chen, JGR, 101, 27499, 1996) is used to understand the magnetic topology and physical forces involved in the eruption and propagation. In this model, the underlying magnetic structure of a CME is assumed to be an MFR, initially in equilibrium with the Lorentz force (including that due to the overlying field), pressure force, and gravity balanced. The flux rope expands through a model corona and solar wind under the action of Lorentz force, interacting with the ambient medium via drag. Quantitative theoretical predictions are compared with LASCO, radio, and ACE data, showing excellent agreement. As an example, the halo CME of 28 Oct 2003 is modeled, with the calculations and the synthetic coronagraph images tested against both LASCO and ACE data. The CME-MC phenomenon can be consistently and in a unified way understood as the evolution of magnetic flux ropes. The emphasis of the talk will be on how the contributions to the net force acting on a CME flux rope continually change as the structure erupts, accelerates through the corona, and propagates through the interplanetary medium.

Work supported by ONR and NASA