Competing source and loss mechanisms due to wave-particle interactions in Earth's outer radiation belt during the 30 September to 3 October 2012 geomagnetic storm

Abstract

Drastic variations of Earth's outer radiation belt electrons ultimately result from various competing source, loss, and transport processes, to which wave-particle interactions are critically important. Using 15 spacecraft including NASA's Van Allen Probes, THEMIS, and SAMPEX missions and NOAA's GOES and POES constellations, we investigated the evolution of the outer belt during the strong geomagnetic storm of 30 September to 3 October 2012. This storm's main phase dropout exhibited enhanced losses to the atmosphere at L<4, where the phase space density (PSD) of multi-MeV electrons dropped by over an order of magnitude in <4h. Based on POES observations of precipitating >1MeV electrons and energetic protons, SAMPEX >1MeV electrons, and ground observations of band-limited Pc1-2 wave activity, we show that this sudden loss was consistent with pitch angle scattering by electromagnetic ion cyclotron waves in the dusk magnetic local time sector at 3 300nT, and energetic electron injections and whistler-mode chorus waves were observed throughout the inner magnetosphere for >12h. After this period, Bz turned northward, and injections, chorus activity, and enhancements in PSD ceased. Overall, the outer belt was depleted by this storm. From the unprecedented level of observations available, we show direct evidence of the competitive nature of different wave-particle interactions controlling relativistic electron fluxes in the outer radiation belt. Key Points WPIs compete as source and loss of relativistic outer belt electrons EMIC waves can cause PA- and energy-dependent loss at low L* during storms Chorus waves can cause local acceleration of relativistic electrons ©2014. American Geophysical Union. All Rights Reserved.