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

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% $10.1\%$ of LGWs in this data set are ducted. We find that the majority of potentially ducted whistlers are below L=2 $L=2$ and nearly half of LGWs below L=2 $L=2$ and within 9-18 MLT may be ducted. Lightning-generated whistlers (LGWs) are very-low-frequency waves produced when lightning-generated radio pulses known as sferics excite whistler mode waves through the ionosphere and into the magnetosphere. LGW wave power contributes to pitch angle scattering and precipitation of trapped energetic electrons, affecting atmospheric chemistry and helping maintain the slot region between the radiation belts. Field-aligned plasma density irregularities, or ducts, affect the propagation of LGWs. Ducting can determine where the wave energy travels, how long it persists, and which energetic particle populations are affected. We present distributions of LGW wave properties and explore methods of determining ducting of LGWs. We present a complete Van Allen Probes Electric Field & Waves whistler data set generated through density-based clustering Most whistlers in this data set have high wave normal angles consistent with non-ducted propagation Likely ducted whistlers are mainly below L=2 $L=2$; about half of whistlers between 9 and 18 MLT and below L=2 $L=2$ are likely ducted