Electrostatic potential drop across the ionospheric signature of the low-latitude boundary layer

摘要

A study of the behavior of the ionospheric signature of the low-latitude boundary layer is conducted from signatures of the precipitating electrons and the ionospheric convection velocity. Observations are made under southward interplanetary magnetic field (IMF) conditions in a highly dynamic environment where temporal changes produce large excursions in the location of both the convection reversal boundary and the poleward edge of the particle precipitation associated with the outer edge of the low-latitude boundary layer. We describe the latitudinal width of the boundary layer as the displacement between these boundaries and the bulk plasma flow as the potential difference across the region. On either side of local noon the boundary layer has a latitudinal width of about one degree, widening to about two degrees near dawn and dusk. The potential drop across the boundary layer increases toward local noon and accounts for no more than 30% of the total potential across the polar cap. While the boundary layer is physically wider on the duskside than on the dawnside, the average potential across the dawnside boundary layer is larger than that across the duskside layer. The resulting electric field across the dawnside layer is approximately twice that found in the duskside layer. We also find a higher level of variability in the boundary layer width and potential on the dawnside than on the duskside that may be related to higher levels of turbulence and wave activity associated with the orientation of the IMF with respect to the bow shock.