Generation of kinetic Alfven waves by velocity shear instability on auroral field lines

Ion beams observed in the plasma sheet boundary layer (PSBL), cusp, and on the auroral zone field lines are expected to have spatial gradients in their drift velocity. Generation of kinetic Alfven waves by velocity shear of the ion beams is discussed. It is shown that a hot ion beam can excite both a resonant kinetic Alfven wave instability and a non-resonant coupled Alfven-ion acoustic instability. For typical parameters, observed on the auroral field lines in the altitude range of 5-7 R-E (where R-E is the Earth's radius), the frequency of the velocity shear modes, in the satellite frame of reference, lie in the ultra-low frequency (ULF) range. The noise due to velocity shear driven Alfven modes is electromagnetic in nature, and has a finite parallel electric field component. (C) 2008 COSPAR. Published by Elsevier Ltd. All rights reserved.