Generation of kinetic Alfven waves in the high-latitude near-Earth magnetotail: A global hybrid simulation

Abstract

In this paper, effects of a fast flow in the tail plasma sheet on the generation of kinetic Alfven waves (KAWs) in the high-latitude of the near-Earth magnetotail are investigated by performing a two-dimensional (2-D) global-scale hybrid simulation, where the plasma flow is initialized by the E×B drift near the equatorial plane due to the existence of the dawn-dusk convection electric field. It is found that firstly, the plasma sheet becomes thinned and the dipolarization of magnetic field appears around (x,z)=(−10.5RE,0.3RE), where RE is the radius of the Earth. Then, shear Alfven waves are excited in the plasma sheet, and the strong earthward flow is braked by the dipole-like magnetic field. These waves propagate along the magnetic field lines toward the polar regions later. Subsequently, KAWs with k⊥≫k∥ are generated in the high-latitude magnetotail due to the existence of the non-uniformity of the magnetic field and density in the polar regions. The ratio of the electric field to the magnetic field in these waves is found to obey the relation (δEz)/(δBy )∼ω/k∥ of KAWs. Our simulation provides a mechanism for the generation of the observed low-frequency shear Alfven waves in the plasma sheet and kinetic Alfven waves in the high-latitude near-Earth magnetotail, whose source is suggested to be the flow braking in the low-latitude plasma sheet.