Stability Properties of High-Beta Geotail Flux Tubes

Kinetic theory is used to investigate the stability of ballooning-interchange modes in the high pressure geotail plasma. A variational form of the stability problem is used to compare new kinetic stability results with MHD, FastMHD, and Kruskal-Oberman stability results. Two types of drift modes are analyzed. A kinetic ion pressure gradient drift wave with a frequency given by the ion diamagnetic drift frequency ω∗pi, and a very low-frequency mode |ω| ω∗pi, ωDi that is often called a convective cell or the trapped particle mode. In the high-pressure geotail plasma a general procedure for solving the stability problem in a 1/β expansion for the minimizing δB‖ is carried out to derive an integral-differential equation for the kinetically valid displacement field ξψ for a flux tube. The plasma energy released by these modes is estimated in the nonlinear state. The role of these instabilities in substorm dynamics is assessed in the substorm scenarios described in Maynard et al. (1996).