Dynamical Variation of Plasmasphere Revealed by PWS Data onboard the Akebono(EXOS-D)Satellite (Recent Results of Studies on Solar Terrestrial Physics Part 4)

Abstract

From the upper hybrid frequency data observed by PWS onboard the Akebono satellite, the entire plasma density profile along the satellite paths have been obtained being based on the plasma neutrality condition. The analyses of the plasma density deduced from the upper hybrid frequency reveal the dynamical variation of the plasmaspheric plasma density profile (PPDP). The PPDP variation is especially characterized by the intimate correspondence to the time variation of Dst that indicates the time derivative-coefficient larger than 5 nT/hour. Variation phenomena of PPDP are divided into two categories depending on the phases of Dst variations; these are the phenomena which occur in the phase of the positive time derivative-coefficient (PDC) of Dst; and the phenomena which occur in the phase of the negative time derivative-coefficient (NDC) of Dst. Both in PDC, and NDC phases, the plasmapause structures show the sharpening of their cliff feature of the plasma density distribution, but a few hours later, all these traditionally convinced enhancement effects of the plasma convection in the neighboring plasma sheet regions are taken. over by the effects of plasmapause disruption without depending on the local time of the consideration. These plasmapause disruptions are caused by the exodus of the plasmaspheric plasma in the NDC phase while the hot plasma sheet plasma immigrates into the plasmasphere in the phase of PDC. Because of extreme inhomogeneity of the plasma temperature between the original plasmaspheric warm plasma and hot plasma from the plasma sheet region, there exist sharp discontinuous boundaries across the magnetic field lines in the plasmasphere. The evidence has been detected as the “donkey ears” phenomena by the observation of PWS onboard the Akebono satellite. It is disclosed that the exodus of plasma from the plasmasphere in NDC phase of Dst, and the immigration of plasma into the plasmasphere in PDC phase are caused by E × B drift due to the induction electric field that is strictly related to ∂B/∂t. The arrival of the front of the injected hot plasma delays with times ranging from 15 h to 2.5 h corresponding to the time derivative-coefficient of Dst, respectively from 5 nT/hour to 30 nT/hour. As higher the time derivative-coefficient becomes, the faster the drift velocity is increased; i.e., the delay time of arrival of the hot plasma front from the original plasmapause position to the satellite level becomes short for the fast E × B drift.