Prevalence and Propagation of Lightning-Generated Whistlers in Van Allen Probes EFW Burst Data

Abstract

We assess the prevalence of ducted and non-ducted whistler propagation using burst mode data from the Van Allen Probes Electric Field and Waves instrument (EFW). We have identified burst periods containing lightning-generated whistlers (LGWs), resulting in a data set available for future use. The entire burst data set is filtered through an analysis of the search coil magnetometer (SCM) noise, identifying signals in frequency space that exceed an adaptive noise threshold. We implement DBSCAN (Density-Based Spatial Clustering of Applications with Noise) to identify individual whistlers and clusters of whistlers. With magnetic spectral analysis, we calculate the mean wave normal angle (WNA) for each LGW group. We use ray tracing to estimate the expected WNA distributions for non-ducted LGWs to compare to the data and determine methods for identifying potentially ducted LGWs. The ray-tracing results provide a clear threshold in WNA for ducted whistlers. Using this threshold, we estimate that at least $10.1\%$ of LGWs in this data set are ducted. We find that the majority of potentially ducted whistlers are below $L=2$ and nearly half of LGWs below $L=2$ and within 9–18 MLT may be ducted.