Collaborative Research: Cloud Top Discharges and their Parent Storms

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Thunderstorms are highly-electrified phenomena where lightning is formed from the separation of electrical charge within the cloud. Not only do thunderstorms produce cloud-to-ground and cloud-to-cloud lightning, but thunderstorms also can produce upward-pointed electrical discharges from the tops of the clouds. These are known as cloud top discharges and have many different names based on their size and appearance, such as sprites, pixies, and jets. While these discharges have been photographed, there are very few scientific research-quality data available for these events, and a variety of questions remain unanswered. This award will involve the development of two new instruments and a multi-year observational effort to provide the most comprehensive data on cloud top discharges available. The relevance of this project to society is that upward electrical discharges are strong producers of NOx which can affect stratospheric ozone chemistry. This award also includes outreach to rural schools in Georgia to provide science education on the topics of electricity and magnetism. The overall objective of this project is to investigate the electrical nature of cloud top discharges (CTDs) such as sprites, gnomes, pixies, starters, jets and gigantic jets and how thunderstorms produce these unique events. Observations of these CTDs are rare due to prior observational constraints. In this project, the research team will develop and deploy a new ground-based spectroscopic imaging system consisting of two blue-sensitive high-speed cameras. The blue aspect is important because CTDs are characterized by their predominantly blue color, but blue and ultraviolet (UV) light is heavily scattered by the lower atmosphere and most prior optical imagers were not sensitive to blue/UV light. The new system will be deployed in Texas and combined with additional observational information from Very Low Frequency (VLF)/Low Frequency (LF) radio receivers, Lightning Mapping Arrays (LMAs), and traditional meteorological data to answer key questions about the electrical and morphological properties of CTDs and the characterization of CTD thunderstorm charge structures. Specific research questions include:• What are the leader and streamer dynamics of CTDs, such as evolution of thermal temperature for leaders and electron energy for streamers?• What are quantitative characteristics of the leader-to-streamer transition region? • How is the very high frequency (VHF) measured by LMAs produced above the cloud? • What parameters dictate the terminal altitude of a CTD?• What are the parent storm charge structures and what meteorological processes form them?• What is the relationship between cloud top mixing and divergence, the thunderstorm charge structure, and event formation?• How does the storm structure vary for different CTDs?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.