The two Van Allen Probes simultaneously recorded a coherently modulated quasiperiodic (QP) emission that persisted for 3 h. The magnetic field pulsation at the locations of the two satellites showed a substantial difference, and their frequencies were close to but 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 QP emissions were amplified by local anisotropic electron distributions, and their large-scale amplitudes were modulated by the plasma density. A novel observation of this event is that chorus waves at frequencies above QP emissions exhibit a strong 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 chorus waves under certain circumstances. A Low-Earth-Orbit POES satellite observed enhanced energetic electron precipitation in conjunction with the Van Allen Probes, providing direct evidence that QP emissions precipitate energetic electrons into the atmosphere. This scenario is quantitatively confirmed by our quasilinear diffusion simulation results.
Bibliographical noteFunding Information:
J. Li, J. Bortnik, and X. An acknowledge the NSF grant AGS-1923126 and NASA grant LWS-80NSSC20K0201. J. Li and J. Bortnik acknowledge the grant DE-SC0010578 and NASA grants 80NSSC18K1227, and NNX14AI18G. Q. Ma would like to acknowledge the NASA grant 80NSSC20K0196 and 80NSSC19K0844. W. Li acknowledges the NASA grants 80NSSC17K0231, 80NSSC19K0845, and 80NSSC20K0698, NSF grants AGS-1723588 and AGS-1847818, as well as the Alfred P. Sloan Research Fellowship FG-2018-10936. This work was supported by the RBSP-ECT and EMFISIS funding provided by JHU/APL contract No. 967399 and 921647 under NASA's prime contract No. NAS5-01072.
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- ULF wave
- Van Allen Probes
- chorus waves
- electron precipitation
- quasiperiodic emissions
- radiation belt