On the Wave-Normal Distribution of Lightning-Generated Whistlers and Their Propagation Modes

Observations from Van Allen Probes are analyzed to obtain the statistical wave normal distribution of lightning-generated whistlers (LGWs). An automatic algorithm is developed to identify burst mode waveform data with LGW signals and analyze the wave polarization information for these LGW signals. The spatial distribution of the LGW occurrence and the probabilities of different propagation types demonstrate that most LGWs can be observed in the low L-shell region (L < 3), where the dominant propagation type is oblique outward. Parallel propagation dominates in the high L-shell region, but the LGW occurrence is very small. Additionally, a small group of oblique but inwardly propagating LGWs are observed at low altitudes (<0.2RE). A ray tracing simulation is performed not only to confirm predominant oblique and outward wave vectors in the vast region of the plasmasphere but also to verify the existence of these inward propagating LGW signals at low altitudes near the topside ionosphere.