Dipolarization fronts and associated auroral activities: 2. Acceleration of ions and their subsequent behavior

摘要

[1]We present case studies of THEMIS multipoint observations of ion distributions in the magnetotail plasma sheet at various locations upstream of earthward-propagating dipolarization fronts. Observations made near the neutral sheet show a characteristic signature, enhancements of earthward-moving ion fluxes about 30 s before dipolarization front arrival. In previous studies, this signature has been well explained as front-reflected ions confined to a region characterized by their gyroradii over the background B _z field that coexist with the ambient population. However, at higher latitudes near the plasma sheet boundary layer, observations suggest that earthward-moving ions appear a few minutes earlier than at the central plasma sheet, indicating that the ions reflected at the same dipolarization front could access farther toward the Earth at higher latitudes. These observed phenomena, as also stated in our companion paper, are associated with transient intensifications of proton auroral brightness, which suggests a direct connection between magnetospheric and ionospheric signatures during geomagnetic disturbed conditions. We carry out numerical simulations and theoretical analysis of ion dynamics to interpret and reproduce these observations, to improve our understanding of interactions between earthward-propagating fronts and the ambient plasma in the near-Earth magnetotail, and to establish the proton auroral effects of dipolarization fronts.