Observations and Simulations of Dropout Events and Flux Decays in October 2013: Comparing MEO Equatorial With LEO Polar Orbit

Journal Article · Wed May 26 00:00:00 EDT 2021 · Journal of Geophysical Research. Space Physics

DOI:https://doi.org/10.1029/2020ja028850· OSTI ID:1874910

Pierrard, Viviane  ^[1]; Ripoll, Jean‐Francois  ^[2]; Cunningham, Gregory  ^[3]; Botek, Edith  ^[4]; Santolik, Ondrej  ^[5]; Thaller, Scott  ^[6]; Kurth, William S.  ^[7]; Cosmides, Mélanie  ^[8]

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1. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels (Belgium); Universite Catholique de Louvain, Louvain-la-Neuve (Belgium)
2. Atomique Energie Commission C.E.A., Arpajon (France); Atomique Energie Commission C.E.A., Bruyeres-Ie-Chayel (France)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels (Belgium)
5. Czech Academy of Sciences, Prague (Czechia);; Charles University, Prague (Czech Republic)
6. University of Colorado, Boulder, CO (United States)
7. University of Iowa, Iowa City, IA (United States)
8. Atomique Energie Commission C.E.A., Arpajon (France)

We compare ESA PROBA-V observations of electron flux at LEO with those from the NASA Van Allen Probes mostly at MEO for October 2013. Dropouts are visible at all energy during four storms from both satellites. Equatorially trapped electron fluxes are higher than at LEO by 10² (<1 MeV) to 10⁵ (>2.5 MeV). We observe a quite isotropic structure of the outer belt during quiet times, contrary to the inner belt, and pitch angle dependence of high energy injection. We find a very good overlap of the outer belt at MEO and LEO at ~0.5 MeV. We use test-particle simulations of the energetic electrons trapped in the terrestrial magnetic field to study the outer radiation belt electron flux changes during geomagnetic storms. We show that the Dst (Disturbance storm time) effect during the main phase of a geomagnetic storm results in a betatron mechanism causing outward radial drift and a deceleration of the electrons. This outward drift motion is energy independent, pitch angle-dependent, and represents a significant distance (~1 L-shell at L = 5 for moderate storms). At fixed L-shell, this causes a decay of the LEO precipitating flux (adiabatic outward motion), followed by a return to the normal state (adiabatic inward motion) during main and recovery phases. Dst effect, associated with magnetopause shadowing and radial diffusion can explain the main characteristics of outer radiation belt electron dropouts in October 2013. We also use Fokker-Planck simulations with event-driven diffusion coefficients at high temporal resolution, to distinguish instantaneous loss from the gradual scattering that depopulates the slot region and the outer belt after storms. Simulations reproduce the slot formation and the gradual loss in the outer belt. The typical energy dependence of these losses leads to the absence of scattering for relativistic and ultra-relativistic electrons in the outer belt, oppositely to dropouts.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program; European Union’s Horizon 2020; JHU/APL; National Aeronautics and Space Administration (NASA)
• Grant/Contract Number: 89233218CNA000001; 921647; NAS5-01072; LTAUSA17070
• OSTI ID: 1874910
• Report Number(s): LA-UR-20-27453; TRN: US2307147
• Journal Information: Journal of Geophysical Research. Space Physics, Vol. 126, Issue 6; ISSN 2169-9380
• Publisher: American Geophysical Union
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Heliospheric and Magnetospheric Physics
radiation belts
relativistic electrons
geomagnetic storms
energetic particles