Kinetic Alfvén Waves and Plasma Transport at the Magnetopause
Authors: Jay R. Johnson and C.Z. Cheng
Large amplitude compressional type waves, with frequencies ranging from 10-500 mHz, are nearly always found in the magnetosheath near the magnetopause where there are large gradients in density, pressure and magnetic field. As compressional waves propagate to the magnetopause, these gradients efficiently couple them with shear/kinetic Alfvén waves (KAW) near the Alfvén field-line resonance location ( omega = k|| nuA ). We present a solution of the kinetic-MHD wave equations for this process using a realistic equilibrium profile including full ion Larmor radius effects and wave-particle resonance interactions for electrons and ions to model the dissipation. For northward IMF a KAW propagates backward to the magnetosheath. For southward IMF the wave remains in the magnetopause but can propagate through the k|| = 0 location. The quasi-linear theory predicts that KAWs produce plasma transport with a diffusion coefficient Dperpendicular ~109 m2 /sec and plasma convection on the order of 1 km/sec. However, for southward IMF additional transport can occur because magnetic islands form at the k|| = 0 location. Due to the broadband nature of the observed waves these islands can overlap leading to stochastic transport which is much larger than that due to quasilinear effects.