TURBULENCE AND TRANSPORT IN THE MAGNETOPAUSE CURRENT LAYER

The current convective instability is identified as the dominant mechanism for producing turbulence and transport in the magnetopause current layer. A linear stability analysis demonstrates that the instablility should be robustly unstable for the parameters of the magnetopause current layer. Three-dimensional nonlinear simulations indicate that the current layer evolves to a strongly turbulent, state. The current convective instability is driven unstable by the cross-field gradient of the parallel current in collisionless plasma. A simple physical picture of the instability is presented. For narrow current layers with scale length L less than an ion Larmor radius rho(i), the growth rates exceed the ion gyrofrequency even when T(i) much greater than T(e). A set of nonlinear fluid equations are derived in the unmagnetized ion limit rho(i) > L. In three-dimensional simulations based on these equations the current layer evolves to a turbulent state with layers of extended but irregular clifflike structures with transverse scale length of the order of rho(es), the electron Larmor radius based on T(i). The anomalous cross-field transport rate D(perpendicular-to) of current resulting froin this instability is given by D(perpendicular-to) approximately rho(es) upsilon(y) with upsilon(y) the electron parallel streaming velocity. The present linear theory and simulations are limited to electrostatic disturbances. rhe implications of these results for understanding the structure of the magnetopause current layer are discussed.