Prevalence and distribution of ducted vs. non-ducted whistlers in the magnetosphere

Abstract:

Lightning generated whistlers (LGWs) are very-low-frequency electromagnetic waves emitted from a lightning strike that travel into the magnetosphere, adding energy into the region and interacting with magnetospheric particles. LGWs can induce pitch-angle scattering and precipitation of trapped energetic particles, called lightning-induced electron precipitation (LEP). These VLF waves are also key in maintaining the slot region between the inner and outer radiation belts. As whistlers affect many key areas of the magnetosphere, it is important to understand how they travel through and interact with this environment. Whistlers are particularly influenced by the presence or absence of plasma density ducts, which can determine where a whistler's energy travels, how long it persists in the magnetosphere, and what effect it has on the radiation belt population. This project assesses the prevalence of ducted vs. non-ducted whistlers using data from the Van Allen Probes.

For a set of LGW events, we collect burst data from Van Allen Probes, together with the corresponding background data (radiation belt fluxes, plasma density, magnetic field). We then filter the burst data to isolate the LGWs, following the method of Malaspina et al. [2017] to isolate hiss. Next, we utilize the Santolik et al. [2003] Singular Value Decomposition method to determine wave properties (power, Poynting vector, k-vector, polarization, and ellipticity) for each LGW. The derived wave normal angles, theta and phi, provide the k-vector direction with respect to the spacecraft coordinates; the vector is rotated into magnetic coordinates using the spacecraft attitude information and the local magnetic field direction. The k-vector direction and Van Allen Probes’ measured plasma density are used to label LGW events as either ducted (k-vector nearly parallel to the background magnetic field) or non-ducted (large k-vector angles). From this classification, we assess the prevalence of ducted and non-ducted whistlers, and describe that prevalence in terms of L-shell, MLT, and other geophysical parameters.