Statistical Properties of Long-Period Plasmapause Surface Waves From Van Allen Probes Observations

摘要

Recent work revealed the existence of plasmapause surface waves (PSWs) with Van Allen Probes observations, which are characterized by the periodic modulations of both magnetic/electric fields and plasma densities, and suggested to be the driver of giant undulations (GUs). In this study, six years data from Van Allen Probes were used to investigate the spatial distributions and occurrence conditions of PSWs in the period of 5-30 min. PSWs are found to be mainly distributed at L = 3.5-7 and their occurrence rate is increasing with larger L shells. In the azimuth direction, the spatial distribution of PSWs exhibits an obvious dawn-dusk asymmetry with highest occurrence rates at MLT = 15-21, which is consistent with the spatial distribution of GUs revealed in the previous study. This further demonstrates that PSWs and GUs are connected, and indicates that PSWs differ from Ps6 waves which have a similar wave period and irregular waveform but mainly concentrate in the dawnside and connect with ? bands. PSWs preferentially occur under the condition of high solar wind velocities (V-SW > 500 km/s) and high dynamic pressures (P-dyn > 5 nPa), and their occurrence rate has a negative correlation with IMF B-z, SYMH and AL. Statistical results also reveal that PSWs preferentially occur around the peak of both magnetic storms and substorms. These findings may shed new lights on the further understanding of PSWs' generation and propagation.