ULTRALOW-FREQUENCY FLUCTUATIONS AT THE MAGNETOPAUSE

A high-beta model for the generation of ultralow-frequency (ULF) fluct uations at the magnetopause is presented. The ULF waves are excited by the density gradients in the magnetopause boundary layer. For beta va rying between 0.1 and 1.0, and for realistic values of the density gra dients, the frequency range of the excited modes, their transverse wav elengths and their phase velocities parallel and perpendicular to the geomagnetic field lines seem to be in agreement with recent observatio ns of Alfvenic structures at the magnetopause.