The role of flux tube entropy on transport of plasma into the inner magnetosphere (Invited)

It is now almost conventional wisdom that low entropy flux tubes formed in the mid tail are important to the transport of plasma from the magneotail into the ring current. These low entropy flux tubes have been observed as bursty bulk flows (BBF's) or dipolarization fronts. These ``bubbles'' arise spontaneously in some global simulations, and the general characteristics of the resulting flows agree reasonably well with observations. The bubbles arising in the Lyon-Fedder-Mobarry (LFM) simulations tend to be very high velocity and have no trouble penetrating to geosynchronous orbit. This behavior is unusual in the observations; most dipolarization fronts apparently are stopped by 8-10 R_E. In this paper we investigate the effects of changing the flux tube entropy in LFM simulations. The flux tube content of lobe field reconnecting in the tail is problematic since it is difficult to measure the density in lobes. Thus, it makes sense to experiment with floors on the density and pressure. We modify the flux tube entropy within the LFM by tracking a spontaneously forming bubble back to a point near its origin. The density and pressure on the flux tube are then adjusted and the resulting evolution of the bubble tracked. We discuss the relationship between entropy and the actual plasma transport into the ring current using the coupled LFM-RCM model, as well as entropy's effects on the general convection. We will also discuss the effect of oxygen outflow on bubble formation and evolution.