Thunderstorms and their accompanying lightning flashes are responsible for a substantial number of casualties and property damage each year in the USA. However, we still do not understand the physical mechanisms that cause the first spark of a lightning flash or that allow the spark to grow into a conducting channel that travels to ground first through the cloud and then through the air. Intracloud flashes, those which move only inside and around a cloud (but not to ground), are a hazard for aircraft and space-bound rockets just after launch. This project aims to gain a better understanding of the important processes in lightning initiation, lightning propagation through cloud and air, and lightning evolution from a small spark to an electrical discharge that is miles long and can strike in multiple locations that are miles apart. The project will use existing data from a unique array of sensors.
Intellectual Merit: This project will utilize data collected in summer 2011 around NASA Kennedy Space Center (KSC) in Florida, under a prior NSF award. The data come from a combination of six sensor sets, each of which reveals different information about a flash. Three systems were operated by KSC and provided data on the lightning paths (composed of short steps), the overall lightning charge, and lightning ground strike points. Two research arrays of electric field change sensors provided data on the location and amount of electric current for different parts of the flash; these currents can travel 50 yards to several miles in one-thousandth of a second or less. The sixth sensor was a high-speed video camera (operating at 50,000 fps) which yields detailed information on any luminous features of the lightning, including flash initiation and positive and negative charge motion. Seven scientific articles have already been published using this dataset and seven more are either under review or being written. However, the available multi-sensor dataset remains very rich and deep. For example, on one day (August 14, 2011) there were 25,500 intracloud and 1,700 cloud-to-ground flashes within 50 miles of KSC, and there are similarly good data on 15 storm days. Thus, there is much as-yet-unstudied data that can be used to learn new details about lightning initiation, propagation, and evolution. The project will be aided by many computer tools developed in a prior NSF award; these tools will enhance the data analysis from day one of this project. This project will also extend the previous dataset by including archived data from the Melbourne National Weather Service radar located near KSC. The additional radar data will allow comparisons of lightning initiation, propagation, and development to the thunderstorm reflectivity parameters (and other radar parameters) used by weather forecasters. Thus, the main intellectual merit of the study is that it will use existing data to advance the understanding of lightning mechanisms and better characterize the evolution of lightning structure throughout the thunderstorm lifecycle.
Broader Impacts: Kennedy Space Center is located in a region with one of the largest numbers of lightning flashes per year; these flashes endanger the workers, space-bound vehicles, and special equipment at KSC. With its mission to safely launch rockets carrying satellites and astronauts, NASA is especially concerned about lightning. To continue reducing the lightning threat for the general public and for NASA, it is essential to better understand how lightning works; this project aims to advance that understanding. The project will be important for the development and training of several new scientists, including one post-doctoral researcher, one research associate, two graduate students, and two undergraduate physics students interested in scientific research. The training involves data analysis techniques that are specific to electromagnetic measurements of lightning as well as techniques that are generally applicable in many situations (including computer programming, computational modeling, and oral and written dissemination of results). Four of the eight anticipated project personnel are women. The results of this project will also be broadly disseminated in the peer-reviewed literature. Thus, the main broader impacts of this project are the potential reduction in lightning threats based on better understanding of lightning and the training of new and diverse scientists and engineers.
