Occurrence Characteristics of Outer Zone Relativistic Electron Butterfly Distribution: A Survey of Van Allen Probes REPT Measurements

TitleOccurrence Characteristics of Outer Zone Relativistic Electron Butterfly Distribution: A Survey of Van Allen Probes REPT Measurements
Publication TypeJournal Article
Year of Publication2016
AuthorsNi, B, Zou, Z, Li, X, Bortnik, J, Xie, L, Gu, X
JournalGeophysical Research Letters
Date Published05/2016
Keywordsbutterfly pitch angle distributions; global occurrence pattern; outer radiation belt; relativistic electrons; Van Allen Probes
AbstractUsing Van Allen Probes REPT pitch angle resolved electron flux data from September 2012 to March 2015, we investigate in detail the global occurrence pattern of equatorial (|λ| ≤ 3°) butterfly distribution of outer zone relativistic electrons and its potential correlation with the solar wind dynamic pressure. The statistical results demonstrate that these butterfly distributions occur with the highest occurrence rate ~ 80% at ~ 20 – 04 MLT and L > ~ 5.5 and with the second peak (> ~ 50 %) at ~ 11 – 15 MLT of lower L-shells ~ 4.0. They can also extend to L = 3.5 and to other MLT intervals but with the occurrence rates predominantly < ~25%. It is further shown that outer zone relativistic electron butterfly distributions are likely to peak between 58° - 79° for L = 4.0 and 5.0 and between 37° - 58° for L = 6.0, regardless of the level of solar wind dynamic pressure. Relativistic electron butterfly distributions at L = 4.0 also exhibit a pronounced day-night asymmetry in response to the Pdynvariations. Compared to the significant L-shell and MLT dependence of the global occurrence pattern, outer zone relativistic electron butterfly distributions show much less but still discernable sensitivity to Pdyn, geomagnetic activity level, and electron energy, the full understanding of which requires future attempts of detailed simulations that combine and differentiate underlying physical mechanisms of the geomagnetic field asymmetry and scattering by various magnetospheric waves.
URLhttp://doi.wiley.com/10.1002/2016GL069350
DOI10.1002/2016GL069350
Short TitleGeophys. Res. Lett.


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