To better understand rapid enhancements of the seed populations (hundreds of keV electrons) in the heart of the Earth's outer radiation belt (L* ~ 3.5–5.0) during different geomagnetic activities, we investigate three enhancement events measured by Van Allen Probes in detail. Observations of the fluxes and the pitch angle distributions of energetic electrons are analyzed to determine rapid enhancements of the seed populations. Our study shows that three specified processes associated with substorm electron injections can lead to rapid enhancements of the seed populations, and the electron energy increases up to 342 keV. In the first process, substorm electron injections accompanied by the transient and intense substorm electric fields can directly lead to rapid enhancements of the seed populations in the heart of the outer radiation belt. In the second process, the substorm injected electrons are first trapped in the outer radiation belt and subsequently transported into L* < 4.5 by the convection electric field. In the third process, the lower energy electrons are first injected at L* ~ 5.3 and then undergo drift resonance with ultralow-frequency waves. These accelerated electrons by ultralow-frequency waves are further transported into L* < 4.5 due to the convection electric field. This process is consistent with the radial diffusion. Our results suggest that these specified processes are important for understanding the dynamics of the seed populations in the heart of the outer radiation belt.
Bibliographical noteFunding Information:
This work was supported by the National Natural Science Foundation of China grants 41004075, 41331068, 41204120, 41474141, and 41674163, the Shandong Province Natural Science Foundation of grant ZR2014DM003, the Hubei Province Natural Science Excellent Youth Foundation (2016CFA044), and the project sup ported by the Specialized Research Fund for State Key Laboratories. We acknowledge CDAWeb (http://cdaweb. gsfc.nasa.gov/) for the use of solar wind parameters and geomagnetic indices data. Van Allen Probes MagEIS data used in this paper are available from the ECT Science Operations and Data Center, through http://www.rbspect. lanl.gov/data_pub/. EFW electric field and density are located at http://www. space.umn.edu/missions/rbspef-whome-university-of-minnesota/. Electric and magnetic field data from the Van Allen Probes are publicly available at https://emfisis.physics.uiowa. edu/data/index by the EMFISIS suite.
- ULF waves
- enhanced convection
- substorm injections
- the outer radiation belt
- the seed population