Relationship between the Pi2 pulsations and the localized impulsive current associated with the current disruption in the magnetosphere

Abstract

Behavior of fast-magnetosonic-mode MHD signals in the inner magnetosphere that are driven by the impulsive eastward current is investigated as a model of the Pi2 signal at midnight. The magnetosphere is treated as an axisymmetric cold MHD regime with dipole magnetic fields and has the plasmaspheric structure of the Alfvén speed distribution. MHD perturbation is assumed to be axisymmetric. Numerical calculation revealed the following: 1) The impulsive current induces the plasmasphere virtual resonance oscillation; 2) The compressional magnetic field perturbation is confined near the equator; 3) The waveform of the compressional magnetic perturbation in the plasmasphere depends on the spatial extent of the source current, its temporal variation, as well as its location; 4) The typical Pi2 waveform in the plasmasphere is obtained when the source current is located near the plasmapause (L ≤ 10); 5) When the source current is not located on the equator, the compressional component and the poloidal component have different waveforms.