Magnetic Reconnection in a Non-Maxwellian Neutral Sheet.

Abstract : The collisionless tearing-mode instability is believed to play an important role in magnetospheric reconnection processes. It has been found that the linear growth rate for a non-Maxwellian neutral sheet can be enhanced by a few orders of magnitude in comparison with the conventional isotropic case and that the short wavelength perturbations (k delta is greater than 1) are strongly favored, where delta is the characteristic half-width of the neutral sheet. For typical magnetotail parameters, it is found that the linear e-folding time can be reduced to a small function of a minute. The resulting small scale islands are expected to coalesce rapidly. The additional free-energy is the particle energy is the form of non-Maxwellian distribution. Differential equation analysis and full integro-differential analysis using exact unperturbed orbits are discussed. Physically, if non-Maxwellian features are generated in the plasma distribution by changes in external conditions such as the solar wind conditions, then the magnetotail may become strongly unstable, resulting in rapid development of small scale islands, coalescence and reconnection. This process may manifest itself as triggering of substorms following such changes. (Author)