Wave-vector-resolved Study of Lightning Whistler Propagation and Energetics in the Low-latitude Plasmasphere

University Of Washington, Seattle WA

Investigators

Abstract

Lightning strikes on Earth generate bursts of radio waves called whistlers that can travel upwards into space and scatter high-energy electrons into the atmosphere causing losses from the trapped radiation belts. When these whistlers are generated, they typically become trapped between the conducting surface of the Earth and the lower ionosphere, the Earth-ionosphere wave-guide, and can be observed thousands of kilometers away from the original lightning strikes. If they strike the ionosphere at the correct angle though, whistlers can pass though the Earth-ionosphere wave-guide and move upward. This is believed to occur mostly at high latitudes dropping in significance approaching the low-latitude ionosphere and ceasing near the magnetic equator. Whistlers moving upward from low latitudes will interact with the inner radiation belt, those moving upward at higher latitudes with the outer radiation belt. Recent observations imply that more whistlers actually enter the ionosphere at low latitudes than previously believed but the reasons are not understood. The goal of this proposal is to assess the influence of lightning-generated whistlers on the low-latitude inner radiation belt. It has recently become apparent that understanding this process and others that control radiation belt intensity is important for national security. A high-altitude nuclear explosion is estimated to enhance the radiation belts by a factor of 1,000 to 10,000 destroying satellites in low and medium Earth orbit in a matter of weeks to months and crippling critical societal infrastructures. A detailed knowledge of the radiation belts will enable the design of technologies to potentially mitigate such hostile enhancements. This project enables the training and mentoring of a graduate student at the University of Washington contributing to the creation of the next generation of scientists. The specific technological approach in the proposed work is novel. An extensive database of 3-channel electric field observations taken at +/- 26 degrees latitude by the C/NOFS satellite will be analyzed to extract information on the wave vectors, polarization and Poynting flux of the whistlers. Normally, this would require observations of both the wave electric and magnetic field vectors. However, by making the reasonable assumption of no wave electric field along the direction of the background magnetic field, this information can be extracted from the wave electric field observations alone. Once the wave vector is calculated in this way, it will be used as input to a chain of modeling tools to trace the whistler backwards from the satellite to the source lightning in the lower ionosphere and then compared to observations at that location from a ground-based lightning detection network.