Pitch-Angle Distribution for Electrons at Dipolarization Sites: Radial Dependence

[[abstract]]The observed dipolarization effects on pitch-angle distributions (PAD) of electrons at the tailside in the inner plasmasheet during geomagnetic activity have been studied via analyzing data from THEMIS mission1. We have shown that cigar distributions below about 1keV tend to become isotropized at the fronts whereas isotropic distributions above 1keV tend to become more cigar-shaped and the ineffectiveness of Fermi acceleration at lower energies could be the factor causing this difference. In this study, through investigating the evolution of pitch-angle distributions of multi-events during dipolarization, the dependence of this effect on radial distance from Earth taking place at or near dipolarization sites during times of geomagnetic activity is examined. Because both the field line length and the properties of dipolarizations vary with radial distance, so we anticipate significant dependence of this effect on radial distance. The preliminary results show that the observed radial dependence of evolutions on electrons pitch-angles is consistent with the effectiveness/ineffectiveness of Fermi acceleration.[[notice]]補正完