Propagating Dipolarization Fronts Earthward of 6 Earth Radii

David Malaspina1, Laila Andersson2, Robert Ergun3, John R Wygant4, John W Bonnell5, Craig Kletzing6, Geoffrey D Reeves7, Ruth M Skoug8 and Brian Larsen8, (1)Univ Colorado, Boulder, CO, United States, (2)Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, United States, (3)University of Colorado Boulder, Laboratory for Atmsopheric and Space Physics, Boulder, United States, (4)University of Minnesota Twin Cities, Minneapolis, MN, United States, (5)University of California Berkeley, Berkeley, CA, United States, (6)University of Iowa, Physics and Astronomy, Iowa City, United States, (7)Los Alamos National Laboratory, Los Alamos, United States, (8)Los Alamos National Laboratory, Los Alamos, NM, United States
Abstract:
During geomagnetically active conditions, the Van Allen Probes observe magnetic dipolarizations associated with enhancements in > 1 keV electron energy flux and the presence of nonlinear electric field structures (e.g. double layers and phase space holes) in the inner magnetosphere (4-6 Re). These dipolarization events are observed most frequently between dusk and midnight, though some appear between midnight and dawn. In some cases, nonlinear electric field power shows abrupt onset that is nearly simultaneous with electron energy flux enhancements across a range of energies. By comparing magnetic field, electric field, and particle data from both spacecraft, recorded when the twin Van Allen Probes are in close proximity, it is found that some of these abrupt onset features can be identified as earthward-propagating fonts with speeds on the order of 30 km/s. The presence of coherent propagating dipolarization fronts well inside the nominal flow breaking region (9 - 12 Re) suggests that earthward plasma flows may influence the magnetospheric plasma environment at the radial distances associated with the ring current and radiation belts. Possible mechanisms for this influence include the localized injection of particles adiabatically energized by their earthward transport, and wave-particle interactions related to the high amplitude parallel electric fields associated with the nonlinear electric field structures observed near these propagating fronts.
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