Outer Radiation Belt Electron Lifetime Model Based on Combined Van Allen Probes and Cluster VLF Measurements

摘要

The flux of energetic electrons in the outer radiation belt shows a high variability. The interactions of electrons with very low frequency (VLF) chorus waves play a significant role in controlling the flux variation of these particles. Quantifying the effects of these interactions is crucially important for accurately modeling the global dynamics of the outer radiation belt and to provide a comprehensive description of electron flux variations over a wide energy range (from the source population of 30 keV electrons up to the relativistic core population of the outer radiation belt). Here, we use a synthetic chorus wave model based on a combined database compiled from the Van Allen Probes and Cluster spacecraft VLF measurements to develop a comprehensive parametric model of electron lifetimes as a function of L-shell, electron energy, and geomagnetic activity. The wave model takes into account the wave amplitude dependence on geomagnetic latitude, wave normal angle distribution, and variations of wave frequency with latitude. We provide general analytical formulas to estimate electron lifetimes as a function of L-shell (for L = 3.0 to L = 6.5), electron energy (from 30 keV to 2 MeV), and geomagnetic activity parameterized by the AE index. The present model lifetimes are compared to previous studies and analytical results and also show a good agreement with measured lifetimes of 30 to 300 keV electrons at geosynchronous orbit. Plain Language Summary The space surrounding our planet is full of charged particles trapped in donut-shaped belts called the Van Allen radiation belts that encircle the Earth. These charged particles can cause significant malfunctions and unexpected failures to spacecraft electronics. The intensity of the radiation belts vary as these energetic particles interact with very low frequency (VLF) waves such as chorus waves. Therefore, it is crucially important to accurately quantify the wave-particle interactions for accurately modeling and forecasting the global dynamics of the Van Allen radiation belts. Predicting the magnitude and duration of potentially hazardous conditions could help satellite operators to switch off nonessential satellite electronic systems to reduce malfunctions and unexpected failures only during the most dangerous periods. In this study, we use a chorus wave model based on multi-satellite wave measurements to calculate the lifetimes of these charged particles in the Earth's Van Allen radiation belts. We then compare our results with previous studies, analytical results, and measured data.