Relationship between pulsed earthward high-speed flows and Pi2 pulsations

A mechanism proposed for Pi2 pulsations observed at mid/low latitudes is fast-mode waves trapped in the plasmasphere. The trapped waves are associated with an externally applied compressional impulse. Recently earthward high-speed flow burst has been considered as a possible impulsive source. In this case flow burst acts as a broadband energy source. Although several case studies of the relationship between high-speed flow bursts and Pi2 pulsations have been reported, there is no statistical analysis for Pi2-flow relation. In this study we focus on pulsed earthward high-speed (300-1300 km/s) flows to examine whether flow burst can be an impulsive source of Pi2 pulsation on the ground. We examined the nightside plasma and magnetic field data from the Geotail satellite for three years (1996-1998) and selected 64 events of well-defined pulsed earthward high-speed flows perpendicular to the ambient field. We find that only 4 % of the pulsed flows has a causal relationship with Pi2 pulsations at mid/low latitudes. Thus, we suggest that pulsed flow bursts do not play a dominant role in exciting Pi2 pulsations.