Global simulation of magnetosonic wave instability in the storm time magnetosphere

Coupling between the Rice Convection Model and Ring Current-Atmospheric Interactions Model codes is used to simulate the dynamical evolution of ring current ion phase space density and the thermal electron density distribution for the 22 April 2001 storm. The simulation demonstrates that proton ring distributions (df(perpendicular to)/dv(perpendicular to) > 0) develop over a broad spatial region during the storm main phase, leading to the instability of equatorial magnetosonic waves. Calculations of the convective growth rate of magnetosonic waves for multiples of the proton gyrofrequency from 2 to 42 are performed globally. We find that the ratio between the perpendicular ring velocity and the equatorial Alfven speed determines the frequency range of unstable magnetosonic waves. Low harmonic waves (omega < 10 Omega(H+)) tend to be excited in the high-density nightside plasmasphere and within the duskside plume, whereas higher-frequency waves (omega > 20 Omega(H+)) are excited over a broad spatial region of low density outside the morningside plasmasphere