Magnetospheric Cavity Resonance Oscillations with Energy Flow across the Magnetopause.

We discuss the condition for the presence of a magnetospheric global oscillation having the properties of a cavity resonance oscillation by using a numerical method and assuming that the magnetopause is not a perfect reflector. The cavity resonance oscillation occurs when there is a plasmaspheric trough of the Alfvén speed. The plasmaspheric cavity resonance oscillation is evanescent in the outer magnetosphere, where the Alfvén speed is larger than in the plasmasphere. The plasmaspheric mode is not completely confined within the plasmasphere, but can tunnel into the outer magnetosphere and have finite amplitude at the magnetopause. The nonzero electromagnetic field perturbation at the magnetopause leads to leakage of the Poynting flux across the magnetopause, and the plasmaspheric cavity resonance oscillation is damped by the escaping flux. The perturbations of the damped cavity resonance oscillation exhibit phase shift toward the magnetopause, which does not imply propagation of the wave.