Correlated observations of the boundary between polar cap and nightside auroral zone by HF radars and the DMSP satellite

Overview & Synopsis

Simultaneous observations from HF radars and the DMSP satellite have been used to relate the ionospheric convection pattern and the nighBide precipitation at the polar cap-auroral zone boundary. The convection is eastward in the poleward part of the radars field of view and predominantly westward at lower latitudes. The DMSP-F9 particle spectrograms exhibit energetic precipitating protons at the poleward edge of an "inverted V". The downward H + flow displays spatial filtering effects with a clear energy-latitude dispersion. Single-particle trajectory simulations in appropriate field models demonstrate that these ions were ejected from the neutral sheet near 120 R E geocentric distance. Most notably, the simulations reveal significant azimuthal dispersion during transport, and the source region in the magnetotail is found to extend over several Earth radii in the dawn-dusk direction, less energetic particles originating duskward of the high-energy ones. The longitudinal spread of the tail source suggests particle precipitation in the ionosphere over at least one hour magnetic local time. Also, as the downflowing protons travel near the lobeward edge of the plasma sheet, the observations suggest that the convection reversal lies inside the boundary layer plasma sheet (PSBL).