The Response of Electron Pitch Angle Distributions to the Upper Limit on Stably Trapped Particles

Samuel D. Walton*, I. R. Mann, L. Olifer, L. G. Ozeke, C. Forsyth, I. J. Rae, M.‐T. Walach, K. R. Murphy, S. G. Claudepierre, H. E. Spence, D. N. Baker

*Corresponding author for this work

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Abstract

We use Van Allen Probes electron data during 70 geomagnetic storms to examine the response of equatorial pitch angle distributions (PADs) at L* = 4.0–4.5 to a theoretical upper limit on stably trapped particle fluxes. Of the energies examined, 54 and 108 keV electron PADs isotropize to a previously assumed level within 6 hr of reaching the limit, near‐identically across all 70 storms, consistent with rapid pitch angle scattering due to chorus wave interactions. In around 30% of events, 54 keV electrons completely exceed the KP limit, before being quickly subdued. 470 and 749 keV PADs show clear indications of an upper limit, though less aligned with the calculated limit used here. The consistency of an absolute upper limit shown across all events demonstrates the importance of this phenomena in both the limiting effect on electron flux and consistently influencing electron PAD evolution during geomagnetic storms. These results also highlight the need for further investigation, particularly related to the limiting of higher energy electrons.
Original languageEnglish
Article numbere2023JA031988
Number of pages10
JournalJournal of Geophysical Research: Space Physics
Volume128
Issue number11
DOIs
Publication statusPublished - 1 Nov 2023

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