Multi-Point Observations of Quasiperiodic Emission Intensification and Effects on Energetic Electron Precipitation

Abstract:

The two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 hours. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies did not exactly match the repetition frequency of QP emissions for most of the time, suggesting that those coherent QP emissions probably originated from a common source, which then propagated over a broad area in the magnetosphere. The embryonic QP emissions were amplified by local anisotropic electron distributions, and their amplitudes were modulated by the plasma density in this process. A novel observation of this event is that upper-band chorus waves grow in one-to-one correlation with QP emissions. Those chorus waves intensified when the QP emissions reach their peak frequency. This indicates that embryonic QP emissions may be critical for its own intensification as well as high-frequency chorus waves under certain circumstance. The low-earth-orbit POES satellite observed enhanced energetic electron precipitation in conjugate with the Van Allen Probe, providing a direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results.