Effects of reconnection on the coronal mass ejection process

This work investigates how magnetic reconnection affects the acceleration o f coronal mass ejections (CMEs) and how the acceleration in turn affects th e reconnection pro-cess. To model the CME process, we use a two-dimensional flux rope model, which drives the ejection by means of a catastrophic loss of mechanical equilibrium. Our model provides a method for relating the mo tion of the ejected material to the reconnection rate in the current sheet created by the erupting field. In the complete absence of reconnection the tension force associated with the current sheet is always strong enough to prevent the flux rope from escaping from the Sun. However, our results impl y that even a fairly small reconnection rate is sufficient to allow the flu x rope to escape. Specifically, for a coronal density model that decreases exponentially with height we find that average Alfven Mach number M-A for t he inflow into the reconnection site can be as small as M-A = 0.005 and sti ll be fast enough to give a plausible eruption. The best fit to observation s is obtained by assuming an inflow rate on the order of M-A approximate to 0.1. With this value the energy output matches the temporal behavior infer red for the long duration events often associated with CMEs. The model also suggests an explanation for the peculiar motion of giant X-ray arches repo rted by Svestka et al. [1995, 1997]. X-ray arches are the large loops assoc iated with CMEs which are similar in form to "post"-flare loops, but they h ave an upward motion that is often different. Instead of continually slowin g with time, the arches move upward at a rate that remains nearly constant or may even increase with time. Here we show how the difference can be expl ained by reversal of the gradient of the coronal Alfven speed with height.