Asymmetric coupled interchange-ballooning and EMHD magnetic reconnection in the geomagnetic tail

Abstract:

Fast reconnection in the geomagnetic tail involves small scale electron dynamics that includes the electron inertial length and the ion gyroradius. We use the new forms of the FLR-interchange dynamics coupled with EMHD to model geotail reconnection of Nakamura etal CLUSTER data. The asymmetric currents closing in the northern and southern magnetopause, we derive a new onset conditions for the ballooning-interchange and magnetic reconnections modes. While these two eigenmodes have opposite symmetries in the classic symmetric geotail geometry [Prichett-Coroniti-Pellat (1997)], the symmetry is broken for solar winds on to a tilted Earth magnetic dipole. We develop a model that includes distinct north I_N(t) and south I_S(t) magnetopause closing currents with corresponding distinct N-S magnetopause boundary conditions. These conditions drive asymmetric eigenmodes within the geotail. The wave functions in the high-magnetopause give new onset conditions for substorms. The nonlinear growth rates are obtained nonlinear FLR-fluid two component fluid simulations. FLR fluid models and are compared qualitatively with the PIC simulations of Prichett-Coroniti. While the Prichtett-Coroniti simulations capture some features of the THEMIS data and we look for the corresponding features in the FLR-fluid simulations. The reconnection parameter delta ^’ [I_N,I_S] has a complex generalization for the asymmetric magnetotail and magnetopause . When the mid-tail B_z (x,z,t) structure is such as to give the fast ballooning-interchange instability we show that in the nonlinear stage the dynamics changes the structure producing magnetic islands of the scale observed in the CLUSTER substorm data [ Nakamura et al. 2006]. We conclude that asymmetric models are needed to give reliable forecasting of the onset of subtorms and storms.