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Outer Radiation Belt Flux and Phase Space Density Response to Sheath Regions: Van Allen Probes and GPS Observations
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  • Milla M. H. Kalliokoski,
  • Michael G. Henderson,
  • Steven K. Morley,
  • Emilia Kilpua,
  • Adnane Osmane,
  • Leonid Olifer,
  • Drew L. Turner,
  • Allison N Jaynes,
  • Harriet George,
  • Sanni Hoilijoki,
  • Lucile Turc,
  • Minna Palmroth
Milla M. H. Kalliokoski
University of Helsinki

Corresponding Author:[email protected]

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Michael G. Henderson
Los Alamos National Laboratory
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Steven K. Morley
Los Alamos National Laboratory (DOE)
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Emilia Kilpua
University of Helsinki
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Adnane Osmane
University of Helsinki
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Leonid Olifer
University of Alberta
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Drew L. Turner
The Johns Hopkins University Applied Physics Laboratory
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Allison N Jaynes
University of Iowa
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Harriet George
University of Helsinki
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Sanni Hoilijoki
University of Helsinki
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Lucile Turc
University of Helsinki
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Minna Palmroth
University of Helsinki
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Abstract

Turbulent and compressed sheath regions preceding interplanetary coronal mass ejections (ICMEs) strongly impact electron dynamics in the outer radiation belt. Changes in electron flux can occur on timescales of tens of minutes, which is difficult to capture by a two-satellite mission such as the Van Allen Probes (RBSP). The recently released Global Positioning System (GPS) data set has higher data density owing to the large number of satellites in the constellation equipped with energetic particle detectors. Investigating electron fluxes in a wide range of energies and sheaths observed from 2012 to 2018, we show that the flux response to sheaths on a timescale of 6 hours, previously reported from RBSP data, is reproduced by GPS measurements. Furthermore, GPS data enables derivation of the response on a shorter timescale of 30 minutes, which further confirms that the energy and L-shell dependent changes in electron flux are due to the impact of the sheath. Sheath-driven loss is underestimated over longer timescales as the electrons recover during the ejecta. We additionally show the response of electron phase space density (PSD), which is a key quantity in identifying true loss from the system and electron energization through wave-particle interactions. The PSD response is calculated from both RBSP and GPS data for the 6-hour timescale, as well as from GPS data for the 30-minute timescale. The response is divided based on the geoeffectiveness of the sheaths revealing that electrons are effectively accelerated only during geoeffective sheaths, while loss is commonly caused by all sheaths.