Shock-Induced Prompt Relativistic Electron Acceleration in the Inner Magnetosphere

Tuesday, 16 December 2014: 11:05 AM
John C Foster1, John R Wygant2, Daniel N. Baker3, Alexander J Boyd4, Philip John Erickson1, Mary K Hudson5 and Harlan E. Spence6, (1)MIT Haystack Observatory, Westford, MA, United States, (2)University of Minnesota Twin Cities, Minneapolis, MN, United States, (3)University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (4)University of New Hampshire Main Campus, Durham, NH, United States, (5)Dartmouth College, Hanover, NH, United States, (6)University of New Hampshire, Durham, NH, United States
The energization of radiation belt particles to relativistic energies is a prime objective of NASA’s Van Allen Probes mission. To date, that mission has been successful in addressing this goal, elucidating the effects of both slow inward diffusion, storm-time local acceleration, and substorm effects. Here we describe the effects of an impulsive solar wind shock on the prompt acceleration of electrons to highly relativistic energies in the inner magnetosphere. On October 8, 2013 the twin Van Allen Probes spacecraft observed both the accelerating shock impulse electric fields and the response of the electron populations across a broad range of energies. The spacecraft were on the dayside where the abrupt shock-induced acceleration to relativistic energies occurs. Simultaneous measurements from spacecraft in the upstream interplanetary medium determined the shock characteristics. Both Probes A and B observe the initial shock at while B is at L~5 and A is further inward near L~3.5. These measurements provide evidence the dayside equatorial magnetosphere experienced a strong dusk-dawn/azimuthal component of the electric field for a period of 1-2 minutes. Both A and B observe order of magnitude “quasi-periodic pulse-like” enhancements in the relativistic (2 – 6 MeV) electron flux. This is a consequence of an extremely rapid energization of electrons due to the shock induced fields on a time scale which is a fraction of their orbital drift period around the Earth, followed by their energy-dependent drift-echo reappearance. With A following B along the same orbit, B observed the pre-shock background for electron flux and phase space density out to Lstar ~ 5 about 1 hr before A observed the post-shock effects across that range of L. While at higher L outer zone electrons were rapidly depleted due to loss to the contracted magnetopause, inside L~4 a new population of highly relativistic electrons was formed and persisted through the recovery of the event.