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 (ΔP_sw) events” (SSLP, AE > 200 nT, ΔP_sw < 5 nPa) and “strong substorm with high ΔP_sw events” (SSHP, AE > 200 nT, ΔP_sw > 5 nPa). Our statistical results show that: (a) For DE, WSE, and SSHP, ΔP_sw and solar wind speed (V_sw) are the main factors affecting the oscillation location, while ΔP_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 ΔP_sw; (b) For SSLP, substorm activity and V_sw do not affect the oscillation location. However, the intense substorm activity and ΔP_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 ΔP_sw and substorm activity. These can help us further understand the ULF waves and relativistic electron dynamics of the Earth's outer radiation belt.