Dayside long‐period magnetospheric pulsations: Solar wind dependence

Abstract

The spectral power and occurrence rate of long‐period magnetospheric pulsations (predominantly fundamental mode toroidal Pc 5) observed by the electron beam experiment on board GEOS 2 are compared with IMF and solar wind parameters. No clear influences of IMF orientation and magnitude on pulsation amplitudes and occurrence rate are found. Significant correlations, however, do exist between the spectral power of pulsations and the solar wind bulk velocity, and between the spectral power and the solar wind kinetic energy flux. The sign of the latter correlation depends on the Kp index. For Kp = 0 the pulsation power decreases with increasing solar wind kinetic energy flux, whereas it increases for Kp ≥ 1. Our results are consistent with the Kelvin‐Helmholtz instability at the inner side of the low‐latitude boundary layer being the dominant mechanism for the generation of fundamental mode toroidal Pc 5 magnetospheric pulsations. Flux transfer events play only an inferior role as energy sources for these pulsations. The coupling efficiency of surface waves at the boundary layer to shear Alfvén waves near geostationary orbit seems to change significantly if the geostationary orbit is inside the plasmasphere.