AGS-PRF: High-Speed Spectral Imaging of Sprite Streamer Systems

Sprites are a form of upper atmospheric electricity that occurs above thunderclouds due to the high electric fields produced during a thunderstorm. These large-scale electrical discharges occur very quickly, motivating the use of high-speed imaging to study their production and development. The project will utilize a system of four high-speed cameras, each capable of measuring different wavelengths of light, to study the evolution of these events and quantitatively identify the physical processes involved. As sprites form at the lower boundary of the ionosphere, they serve as a natural laboratory for understanding how the ionosphere responds to sudden, strong forcing. Ionospheric properties are crucial to maintaining effective defense and communications capabilities, making it imperative to study how the properties change during these extreme forcing events. This proposal provides funding for an early career scientist, and hence encourages workforce development in STEM areas. Sprites consist of complex systems of streamers. Four high-speed cameras (over 500,000 frames per second capability) with narrow-band optical filters will be used to observe emissions from the first negative system of singly ionized molecular nitrogen and the second positive system of molecular nitrogen emitted in every part of the sprite streamer heads and channel bodies throughout the event development. From the high-speed spectral information, empirical relationships between the streamer electric field, electron energies, and charge profiles throughout a streamer system will be derived. The ways in which these parameters inform streamer interactions, such as collisions and branching, and sustained features, such as beads and afterglows, will be studied. The work will also quantify the initiation conditions for upward sprite streamers through the measurement of the electric field in the streamer channels and the charge transfer due to the initial positive streamers. The results will test theoretical models of the formation of sprite features, providing observational evidence for the physical principles behind important structures and phenomena such as beads, streamer collisions, upward propagation, and streamer system collective dynamics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.