The Origin of HF and VHF Radio Emissions from Lightning

This project aims to understand the production of high frequency (HF) and very high frequency (VHF) radio emissions by various lightning processes. Lightning can produce a very broad spectrum of electromagnetic radiation, which is an integral part of the earth's electromagnetic environment. Theories currently exist to explain the lightning electromagnetic radiation in the low frequency (30-300 kHz) band and below. The characteristics and physical mechanisms of the HF and VHF emissions from lightning, however, are poorly understood. The project's research effort is focused on characterizing the properties of the HF and VHF emissions from lightning as well as investigating the physical mechanisms of their production through electrical breakdown processes in virgin air such as streamers and electron avalanches. To characterize the HF and VHF radiation, we analyze a rich lightning dataset collected in 2016 and 2017 by using a suite of instruments including a broadband radio interferometer. To understand the production mechanisms of HF and VHF radiation, the radio emissions from streamers and electron avalanches are investigated by performing plasma discharge fluid simulations. Built on the knowledge of the radio emissions from individual streamers To help protect your privacy, Microsoft Office prevented automatic download of this picture from the Internet. AFOSR word mark or electron avalanches, we develop a statistical modeling technique to synthesize the radio emission of a large ensemble of streamers or electron avalanches to explain the lightning data. This is the final year of the research project supported by AFOSR Grant FA9550-18-1-0358. We are very pleased to report that this project has been successfully completed.