A statistical study of proton pitch angle distributions measured by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE)

TitleA statistical study of proton pitch angle distributions measured by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE)
Publication TypeJournal Article
Year of Publication2016
AuthorsShi, R, Summers, D, Ni, B, Manweiler, JW, Mitchell, DG, Lanzerotti, LJ
JournalJournal of Geophysical Research: Space Physics
Date Published05/2016
Keywordsproton pitch angle distributions; Van Allen Probes
AbstractA statistical study of ring current-energy proton pitch angle distributions (PADs) in Earth's inner magnetosphere is reported here. The data are from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on board the Van Allen Probe B spacecraft from January 1, 2013 to April 15, 2015. By fitting the data to the functional form sinnα, where α is the proton pitch angle, we examine proton PADs at the energies 50, 100, 180, 328 and 488 keV in the L-shell range from L = 2.5 to L = 6. Three PAD types are classified: trapped (90° peaked), butterfly and isotropic. The proton PAD dependence on the particle energy, MLT, L-shell, and geomagnetic activity are analyzed in detail. The results show a strong dependence of the proton PADs on MLT. On the nightside, the n values outside the plasmapause are clearly lower than those inside the plasmapause. At higher energies and during intense magnetic activity, nightside butterfly PADs can be observed at L-shells down to the vicinity of the plasmapause. The averaged n values on the dayside are larger than on the nightside. A maximum of the averagedn values occurs around L = 4.5 in the postnoon sector (12 - 16MLT). The averaged n values show a dawn-dusk asymmetry with lower values on the dawnside at high L-shells, which is consistent with previous studies of butterfly PADs. The MLT dependence of the proton PADs becomes more distinct with increasing particle energy. These features suggest that drift-shell splitting coupled with a radial flux gradient play an important role in the formation of PADs, particularly at L > ~ 4.5
URLhttp://doi.wiley.com/10.1002/2015JA022140
DOI10.1002/2015JA022140
Short TitleJ. Geophys. Res. Space Physics


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