ULF PULSATIONS DRIVEN BY MAGNETOPAUSE MOTIONS - AZIMUTHAL PHASE CHARACTERISTICS

We present numerical simulations of wave coupling: in a cold, ideal, i nhomogeneous plasma waveguide which approximates the flanks of the mag netosphere. Two types of driving conditions are investigated. The firs t corresponds to a displacement of the magnetopause over a fixed azimu thal range. The pulsations driven by this boundary condition have an a zimuthal wavenumber and phase speed determined by the equilibrium stru cture of the magnetosphere. The second condition corresponds to a disp lacement pulse which runs antisunward along the magnetopause and produ ces pulsations with a phase velocity strictly equal to that of the bou ndary pulse. Our results are compared briefly with data and suggest th at on some occasions the magnetosphere is driven in a fashion that is well approximated by a. ''running'' pulse or wave on the magnetopause.