Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit

Authors

T. Motoba, Johns Hopkins University Applied Physics Laboratory
S. Ohtani, Johns Hopkins University Applied Physics Laboratory
M. Gkioulidou, Johns Hopkins University Applied Physics Laboratory
D. G. Mitchell, Johns Hopkins University Applied Physics Laboratory
A. Y. Ukhorskiy, Johns Hopkins University Applied Physics Laboratory
K. Takahashi, Johns Hopkins University Applied Physics Laboratory
L. J. Lanzerotti, New Jersey Institute of Technology
S. G. Claudepierre, Aerospace Corporation, USA
H. E. Spence, University of New Hampshire Durham
G. D. Reeves, Los Alamos National Laboratory

Document Type

Article

Publication Date

2-1-2020

Abstract

In this study we have statistically examined flux changes of 1–1,000-keV electrons, and hydrogen, helium, and oxygen ions during local magnetic dipolarization inside geosynchronous orbit, with a focus on their pitch angle dependence. Using 144 dipolarization events that were selected in a previous study with Van Allen Probes observations in 2012–2016, we have performed a superposed epoch analysis of differential flux changes after the dipolarization onset for each species. On average the electron flux increases primarily around pitch angle (α) = 90° at >80 keV and almost isotropically at 10–50 keV. The electron flux at <5 keV increases at α = 0° and 180° but slightly decreases (or remains unchanged) at α = 90°. On the other hand, the ion flux at >80 keV increases around α = 90°, while at <30 keV it decreases nearly independent of pitch angle. Only the low-energy (<5 keV) helium and oxygen ion flux changes indicate a strong field-aligned enhancement, which could be attributed to their outflows from the topside ionosphere. After the dipolarization onset, >5-keV electron and >30-keV ion fluxes exhibit a perpendicular anisotropy, which is most pronounced for 50–200-keV electrons. Both distributions become more isotropic with decreasing energy. A noticeable field-aligned anisotropy is seen for <5-keV ion fluxes. These statistical pitch angle-dependent electron and ion properties during dipolarizations may be explained by combining various processes, including adiabatic acceleration and/or transport, wave-particle interactions, and ion outflow.

Identifier

85092585531 (Scopus)

Publication Title

Journal of Geophysical Research Space Physics

External Full Text Location

https://doi.org/10.1029/2019JA027543

e-ISSN

21699402

ISSN

21699380

Issue

2

Volume

125

Grant

967399

Fund Ref

National Aeronautics and Space Administration

Recommended Citation

Motoba, T.; Ohtani, S.; Gkioulidou, M.; Mitchell, D. G.; Ukhorskiy, A. Y.; Takahashi, K.; Lanzerotti, L. J.; Claudepierre, S. G.; Spence, H. E.; and Reeves, G. D., "Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit" (2020). Faculty Publications. 5511.
https://digitalcommons.njit.edu/fac_pubs/5511