Premium
Butterfly pitch angle distribution of relativistic electrons in the outer radiation belt: Evidence of nonadiabatic scattering
Author(s) -
Artemyev A. V.,
Agapitov O. V.,
Mozer F. S.,
Spence H.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja020865
Subject(s) - van allen radiation belt , pitch angle , physics , magnetosphere , electron , scattering , computational physics , earth's magnetic field , magnetopause , whistler , plasmasphere , van allen probes , magnetic field , atomic physics , geophysics , optics , nuclear physics , quantum mechanics
In this paper we investigate the scattering of relativistic electrons in the nightside outer radiation belt (around the geostationary orbit). We consider the particular case of low geomagnetic activity (| D st |<20 nT), quiet conditions in the solar wind, and absence of whistler wave emissions. For such conditions we find several events of Van Allen probe observations of butterfly pitch angle distributions of relativistic electrons (energies about 1–3 MeV). Many previous publications have described such pitch angle distributions over a wide energy range as due to the combined effect of outward radial diffusion and magnetopause shadowing. In this paper we discuss another mechanism that produces butterfly distributions over a limited range of electron energies. We suggest that such distributions can be shaped due to relativistic electron scattering in the equatorial plane of magnetic field lines that are locally deformed by currents of hot ions injected into the inner magnetosphere. Analytical estimates, test particle simulations, and observations of the A E index support this scenario. We conclude that even in the rather quiet magnetosphere, small scale (magnetic local time (MLT)‐localized) injection of hot ions from the magnetotail can likely influence the relativistic electron scattering. Thus, observations of butterfly pitch angle distributions can serve as an indicator of magnetic field deformations in the nightside inner magnetosphere. We briefly discuss possible theoretical approaches and problems for modeling such nonadiabatic electron scattering.