An investigation of lightning-generated whistler waves in the inner magnetosphere

Abstract

In this dissertation, we use a new and unique dataset to investigate lightning-generated whistler waves in the Earth’s inner magnetosphere. Global lightning data and high-resolution waveform data in the inner magnetosphere are combined to study lightning-generated whistler waves including source, propagation, and potential scattering effects. Lightning can produce strong broadband radio waves especially in the very low frequency (VLF) band from 300 Hz to 30 kHz. A fraction of wave energy leaks into the ionosphere during reflections in the Earth-ionosphere waveguide and becomes lightning-generated whistler waves. Lightning-generated whistler waves and energetic electrons are important in the inner magnetosphere dynamics. The recent launch of the near-equatorial Van Allen Probes provides a great opportunity to observe and study lightning-generated whistler waves. During the conjunction work between World Wide Lightning Location Network (WWLLN) and Van Allen Probes, we successfully predict the occurrence of lightning-generated whistler waves near the geomagnetic equator at low L-shells (L < 3) with a rate of ~80%. About 22.6% of whistler waves observed by Van Allen Probes correspond to possible source lightning in the WWLLN data, which agrees with the detection efficiency of WWLLN. About 40.1% additional whistler waves observed by Van Allen Probes may be related with WWLLN lightning if the source region is extended from 2000 km to the global area. The far-field radiated energy of lightning may not be the dominant factor for the appearance of lightning-generated whistler waves if it is larger than 100 J. By using the high-resolution waveform data from Van Allen Probes, we can study the possible pitch angle scattering process in both ducted whistler wave and non-ducted whistler wave events. Diffusion coefficients calculated from the high-resolution waveform data show that strong lightning-generated whistler waves may be important for scattering electrons with energies around 100 keV. Ducted whistler waves may be more effective in pitch angle scattering than non-ducted whistler waves due to smaller wave normal angles. The work in this dissertation shows the possibility to simulate the electron precipitation caused by lighting-generated whistler waves in individual cases.