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Untangling the solar wind and magnetospheric drivers of the radiation belt electrons
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  • Simon Wing,
  • Jay Robert Johnson,
  • Drew L. Turner,
  • Aleksandr Ukhorskiy,
  • Alexander J. Boyd
Simon Wing
Johns Hopkins University

Corresponding Author:simon.wing@jhuapl.edu

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Jay Robert Johnson
Andrews University
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Drew L. Turner
The Johns Hopkins University Applied Physics Laboratory
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Aleksandr Ukhorskiy
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Alexander J. Boyd
The Aerospace Corporation
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Many solar wind parameters correlate with one another, which complicates the causal-effect studies of solar wind driving of the magnetosphere. Conditional mutual information (CMI) is used to untangle and isolate the effect of individual solar wind and magnetospheric drivers of the radiation belt electrons. The solar wind density (nsw) negatively correlates with electron phase space density (PSD) (average energy ~ 1.6 MeV) with time lag (t) = 15 hr. This effect of nsw on PSD has been attributed to magnetopause shadowing losses, but when the effect of solar wind velocity (Vsw) is removed, t shifts to 7–11 hr, which is a more accurate time scale for this process. The peak correlation between Vsw and PSD shifts from t = 38 to 46 hr, when the effect of nsw is removed. This suggests that the time scale for electron acceleration to 1–2 MeV is about 46 hr following Vsw enhancements. The effect of nsw is significant only at L* = 4.5–6 (L* > 6 is highly variable) whereas the effect of Vsw is significant only at L* = 3.5–6.5. The peak response of PSD to Vsw is the shortest and most significant at L* = 4.5–5.5. As time progresses, the peak response broadens and shifts to higher t at higher and lower L*, consistent with local acceleration at L* = 4.5–5.5 followed by outward and inward diffusion. The outward radial diffusion time scale at L* = 5–6 is ~40 hr per RE.
Apr 2022Published in Journal of Geophysical Research: Space Physics volume 127 issue 4. 10.1029/2021JA030246