The Field of Shock-Generated Alfven Oscillations Near the Plasmapause

A theoretical interpretation is given for magnetohydrodynamic (MHD) oscillations observed by the GOES and Cluster satellites on November 7, 2004 near the plasmapause (Zong et al., 2009, 2012, , ), before and after an interplanetary shock passes through the magnetosphere (about 18:27 UT). It is shown that, after the shock front passage, the MHD oscillation spectra recorded by Cluster (C1) and GOES 12, located respectively inside and outside the plasmasphere, differ significantly. According to our interpretation, these differences are due to the shock wavefront affecting the plasmapause and exciting broadband resonant Alfven waves, thus significantly changing the MHD oscillation spectrum. A model in the form of a plasma cylinder was developed in order to study MHD oscillations in the dayside magnetosphere numerically. An analytical model is proposed for the source of resonant Alfven waves that has the form of two fast magnetosonic wave packets propagating along the plasmapause, resulting from the shock wave/plasmapause interaction. Numerically calculated parameters of Alfven waves excited by a source based on this model show a good agreement with the oscillation parameters observed by satellites.