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Simulated Trapping of Solar Energetic Protons for the 8-10 March 2012 Geomagnetic Storm: Impact on Inner Zone Protons as Measured by Van Allen Probes
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  • Mary K. Hudson,
  • Miles Ansley Engel,
  • Brian T. Kress,
  • Zhao Li,
  • Maulik Patel,
  • Richard S. Selesnick
Mary K. Hudson
Dartmouth College

Corresponding Author:[email protected]

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Miles Ansley Engel
Los Alamos National Laboratory
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Brian T. Kress
NOAA - National Centers for Environmental Information (NCEI)
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Zhao Li
Dartmouth College
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Maulik Patel
High Altitude Observatory
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Richard S. Selesnick
Air Force Research Laboratory
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Abstract

Solar Energetic Protons (SEPs) have been shown to contribute significantly to the inner zone trapped proton population for energies < 100 MeV and L > 1.3 (Selesnick et al., 2007). The Relativistic Electron Proton Telescope (REPT) on the Van Allen Probes launched 30 August 2012 observed a double-peaked (in L) inner zone population throughout the 7-year lifetime of the mission. It has been proposed that a strong SEP event accompanied by a CME-shock in early March 2012 provided the SEP source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at L ~ 2. Here, we follow trajectories of SEP protons launched isotropically from a sphere at 7 Re in 15s cadence fields from an LFM-RCM global MHD simulation driven by measured upstream solar wind parameters. The timescale of the interplanetary shock arrival is captured, launching a magnetosonic impulse propagating azimuthally along the dawn and dusk flanks inside the magnetosphere, shown previously to produce SEP trapping. The MHD-test particle simulation uses GOES proton energy spectra to weight the initial radial profile required for the radial diffusion calculation over the following two years. GOES proton measurements also provide a dynamic outer boundary condition for radial diffusion. A direct comparison with REPT measurements 20 months following the trapping event in March 2012 provides good agreement with this novel combination of short-term and long-term evolution of the newly trapped protons.