Dynamic Responses of Radiation Belt Electron Fluxes to Magnetic Storms and their Correlations with Magnetospheric Plasma Wave Activities

To investigate the responses of Earth's radiation belt electrons during magnetic storms and their correlations with magnetospheric chorus and plasmaspheric hiss waves, a statistical analysis is conducted using high-quality Van Allen Probes measurements during 68 isolated geomagnetic storms from 2012 September to 2017 December. The variations of radiation belt electron fluxes exhibit high dependence on electron kinetic energy, L-shell, and geomagnetic storm magnitude. It is found that the Increase-type events increase considerably with L-shell at L similar to 3.0-5.0, the Decrease-type events tend to occur more frequently at L = 3.7-4.7 for L = 3.5-6 for >1 MeV electrons during moderate storms, and the No-change-type storm events are relatively dominant for extremely high-energy (>5.2 MeV) electrons. Superposed epoch analyses for the three types of storm events indicate that compared to relativistic (604 keV) electrons, ultrarelativistic (3.4 MeV) electron flux enhancements are more likely in association with elevated solar wind pressure during the storm initial phase, enhanced southward initial mass function Bz during the storm main phase, and prolonged high solar wind speed during the storm recovery phase. It is also shown that the dynamic variations of relativistic (604 keV) electron fluxes are closely connected to the activity level of chorus waves, but the three variation categories of ultrarelativistic (3.4 MeV) electrons have basically comparable intensities of chorus waves possibly due to the loss mechanisms becoming more dominate for their No-change-type or Decrease-type events. From a statistically observational perspective, chorus waves act as a critical candidate for relativistic electron acceleration and plasmaspheric hiss as a viable cause for relativistic electron loss.