Relativistic Electron Flux Oscillations in the Earth's Outer Radiation Belt: A Statistical Study

Abstract Using the data from the Van Allen Probes, we statistically studied 2.1 MeV electron flux oscillation events in the Earth's outer radiation belt during non‐storm activities. Based on the different magnetic local times (MLT), the oscillation events are divided into “dayside events” (DE, 6 ≤ MLT ≤ 18) and “nightside events” (NE, 18 < MLT < 6). These NEs are divided into “weak substorm events” (WSE, AE < 200 nT) and “strong substorm events” (SSE, AE > 200 nT). The SSE is further divided into “strong substorm with low solar wind dynamic pressure change (Δ P sw ) events” (SSLP, AE > 200 nT, Δ P sw < 5 nPa) and “strong substorm with high Δ P sw events” (SSHP, AE > 200 nT, Δ P sw > 5 nPa). Our statistical results show that: (a) For DE, WSE, and SSHP, Δ P sw and solar wind speed ( V sw ) are the main factors affecting the oscillation location, while Δ P sw is the dominant factor affecting the oscillation amplitude. The interplanetary magnetic field B z component has no significant effects on the oscillations of DE. These results support the idea that these oscillations are mainly caused by ultralow frequency (ULF) waves excited by Δ P sw ; (b) For SSLP, substorm activity and V sw do not affect the oscillation location. However, the intense substorm activity and Δ P sw can cause a large oscillation amplitude. This shows the idea that these oscillations are mainly caused by a combination of ULF waves excited by Δ P sw and substorm activity. These can help us further understand the ULF waves and relativistic electron dynamics of the Earth's outer radiation belt.