Clilverd, Mark and Cobbett, Neil and Roger, Craig and Brundell, James and Denton, Michael and Hartley, Dave and Rodriguez, Juan and Ranskin, Donald and Raita, Tero and Spanswick, Emma (2013) Energetic electron precipitation characteristics observed from Antarctica during a flux dropout event. Journal of Geophysical Research: Space Physics, 118 (11). pp. 6921-6935. ISSN 2169-9402
Abstract
Data from two autonomous VLF radio receiver systems installed in a remote region of the Antarctic in 2012 is used to take advantage of the juxtaposition of the L=4.6 contour, and the Hawaii-Halley, Antarctica, great circle path as it passes over thick Antarctic ice shelf. The ice sheet conductivity leads to high sensitivity to changing D-region conditions, and the quasi-constant L-shell highlights outer radiation belt processes. The ground-based instruments observed several energetic electron precipitation events over a moderately active 24-hour period, during which the outer radiation belt electron flux declined at most energies and subsequently recovered. Combining the ground-based data with low- and geosynchronous-orbiting satellite observations on 27 February 2012, different driving mechanisms were observed for three precipitation events with clear signatures in phase space density and electron anisotropy. Comparison between flux measurements made by Polar-orbiting Operational Environmental Satellites (POES) in low Earth orbit and by the Antarctic instrumentation provides evidence of different cases of weak and strong diffusion into the bounce-loss-cone, helping to understand the physical mechanisms controlling the precipitation of energetic electrons into the atmosphere. Strong diffusion events occurred as the <600 keV fluxes began to recover as a result of adiabatic transport of electrons. One event appeared to have a factor of about 10 to 100 times more flux than was reported by POES, consistent with weak diffusion into the bounce-loss-cone. Two events had a factor of about 3 to 10 times more >30 keV flux than was reported by POES, more consistent with strong diffusion conditions.