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Rapid Outer Radiation Belt Flux Dropouts and Fast Acceleration during the March 2015 and 2013 Storms: Role of ULF Wave Transport from a Dynamic Outer Boundary
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  • Louis Ozeke,
  • Ian Mann,
  • Sydney Dufresne,
  • Leon Olifer,
  • Steven Morley,
  • Seth Claudepierre,
  • Kyle Murphy,
  • Harlan Spence,
  • Daniel Baker,
  • Alex Degeling
Louis Ozeke
University of Alberta

Corresponding Author:[email protected]

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Ian Mann
University of Alberta
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Sydney Dufresne
University of Alberta
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Leon Olifer
University of Alberta
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Steven Morley
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
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Seth Claudepierre
Space Sciences Department, The Aerospace Corporation, Los Angeles, California, USA
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Kyle Murphy
NASA Goddard Spaceflight Center, Code 674, Greenbelt, Maryland, MD 20771, USA
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Harlan Spence
Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
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Daniel Baker
Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
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Alex Degeling
Institute of Space Science, Shandong University, Weihai, China
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Abstract

We present simulations of the outer radiation belt electron flux during the March 2015 and March 2013 storms using a radial diffusion model. Despite differences in Dst intensity between the two storms the response of the ultra-relativistic electrons in the outer radiation belt was remarkably similar, both showing a sudden drop in the electron flux followed by a rapid enhancement in the outer belt flux to levels over an order of magnitude higher than those observed during the pre-storm interval. Simulations of the ultra-relativistic electron flux during the March 2015 storm show that outward radial diffusion can explain the flux dropout down to L*=4. However, in order to reproduce the observed flux dropout at L*<4 requires the addition of a loss process characterised by an electron lifetime of around one hour operating below L*~3.5 during the flux dropout interval. Nonetheless, during the pre-storm and recovery phase of both storms the radial diffusion simulation reproduces the observed flux dynamics. For the March 2013 storm the flux dropout across all L-shells is reproduced by outward radial diffusion activity alone. However, during the flux enhancement interval at relativistic energies there is evidence of a growing local peak in the electron phase space density at L*~3.8, consistent with local acceleration such as by VLF chorus waves. Overall the simulation results for both storms can accurately reproduce the observed electron flux only when event specific radial diffusion coefficients are used, instead of the empirical diffusion coefficients derived from ULF wave statistics.