Possible evidence of damped cavity mode oscillations stimulated by the January, 1997 magnetic cloud event

A sudden drastic change in the solar wind dynamic pressure is one proposed mechanism for the excitation of cavity mode resonances in the plasmasphere. To study the possibility of cavity mode occurrence following a 180 cm(-3) solar wind density pulse on January 11, 1992, a numerical MHD simulation wa s run on a dipole grid. The simulated spectra recorded by a virtual satelli te are compared with those produced from the Polar magnetic time signals du ring the interval 0228 - 0304 UT. In both sets of spectra, power is concent rated between 2 and 5 mHz; observed FLR-like spectral peaks in the range 6 - 20 mHz are in rough agreement with simulated plasmaspheric FLRs between 7 -21 mHz. In the simulation, the fundamental plasmaspheric cavity mode is at 3.5 mHz; phase analysis of observed 3.5 mHz electric and magnetic field si gnals from the interval 0230 - 0237 UT supports the possibility of a heavil y damped standing wave at this frequency.