Simulations and Theory of Streamer Discharges in Transient Luminous Events

This project is a theoretical investigation of the fundamental properties of streamer discharges in transient luminous events. Transient luminous events are recently discovered large scale optical phenomena occurring at stratospheric and mesospheric/lower ionospheric altitudes in the Earth's atmosphere, which are directly related to electrical activity in underlying thunderstorms. Although a typical transient luminous event may occupy a large overall volume of the upper atmosphere, high spatial resolution imagery of these events reveals many internal and not yet fully understood small scale features, including bright filamentary channels of ionization, or streamers, with transverse spatial scales ranging from tens to hundreds of meters. These streamers are plasma structures which can initiate spark discharges in relatively small gaps in air which is near ground pressures. Streamers are commonly observed with branching structures, but the experimental and theoretical work on understanding the branching mechanism in both transient luminous events and in high pressure applications is still in the preliminary stage. The exact mechanism of streamer branching will be explored and quantified as part of this project, as well as the microphysics of streamers and transient luminous events and their effects on the Earth's atmosphere. This project undertakes a focused effort, including numerical simulations and modeling, which will attack a limited set of current outstanding questions on the fundamental properties of streamer discharges in transient luminous events. The specific scientific questions to be investigated are: (1) What is the initiation mechanism for streamers in low applied electric fields? (2) What are the minimum fields required for the propagation of streamers in air at different pressures? (3) What is the mechanism or mechanisms involved in streamer branching? Answering these questions will quantify more accurately the total volume of atmosphere affected by transient luminous events and the ability of these events to establish a direct path of electrical contact between the troposphere and the mesosphere/lower ionosphere regions. The broader impacts of the proposed activity include the education and training of a graduate student, the support and further training of a post-doctoral scholar, the involvement of undergraduate REU students in research activities related to this project during summer time periods.