AbstractIn 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.
