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Case studies of the impact of high-speed solar-wind streams on the electron radiation belt at geosynchronous orbit: flux, magnetic field and phase space density

Research output: Contribution to journalJournal article

Published

Journal publication date11/2013
JournalJournal of Geophysical Research: Space Physics
Journal number11
Volume118
Number of pages16
Pages6964-6979
Early online date8/11/13
Original languageEnglish

Abstract

Investigation of electron radiation belt dropouts has revealed the importance of a number of loss processes, yet there remains a lack of quantitative detail as to how these processes wax and wane between events. The overarching aim of this study is to address the issue of electron radiation belt dropouts. This is achieved using in situ observations at geostationary orbit from GOES-13 (pitch-angle-resolved electron data and magnetic field measurements) to examine the outer electron radiation belt during three high-speed stream-driven storms. Analysis and interpretation are aided by calculation of the phase space density (PSD) as a function of the three adiabatic invariants. Our results confirm the importance of outwards adiabatic transport as a mechanism for causing electron dropouts at GEO, however study of the pitch-angle distributions indicates that other loss mechanisms are also likely to be occurring during these HSS-driven storms. Two of the studied events exhibit similar evolutionary structure in their pitch-angle distributions, (i) highly peaked distributions immediately prior to the dropout (ii) sharp transitions between peaked and isotropic and then subsequent butterfly distributions, and (iii) isotropic distributions at minimum flux shortly afterwards (dusk). We also address the difficulty in interpreting PSD calculations by comparing the T96 model magnetic field with that measured by GOES-13. Our results are intended as a first step in quantifying the timeline of events that occur in the radiation belts following the arrival of a HSS - particularly timely given the increase in HSS-occurrence expected in the declining phase of the current solar cycle.

Bibliographic note

© 2013 The Authors. Journal of Geophysical Research: Space Physics published by Wiley on behalf of American Geophysical Union. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.