ABSTRACT

Streamers and leaders are the basic building blocks of electrical discharges found both in the laboratory and in nature. A fundamental difference between streamers and leaders are that streamers do not deposit as much energy to the surrounding environment as leaders. This difference is readily observable in the spectra generated from both streamers and leaders. Streamers observed in the middle atmosphere located above positive cloud to ground lightning strikes are referred to as sprites. Sprite streamers initiate between 70 and 80 km and are observed to propagate first downward and then sometimes upward, at speeds up to one-third the speed of light. We report on the use of high speed (up to 100,000 frames per second) imaging to resolve the structure, dynamics, and spectral content of the visible light emitted by sprite streamers. We then compare streamers with leaders observed in natural lightning. Finally we look at the exciting possibility of studying the streamer to leader transition process by observing gigantic jets, which propagate from cloud tops to the ionosphere.

About the Speaker:

Dr. Geoff McHarg is a Professor of Physics in the Department of Physics at the United States Air Force Academy. He received his Bachelor’s degree in physics at Missouri Southern State College, his M.S. in Physics at the Air Force Institute of Technology, and his PhD in Physics at University of Alaska Fairbanks. Dr. McHarg has been in the Department of Physics at the Air Force Academy since 1988, and after retiring from active duty in the Air Force, started the Space Physics and Atmospheric Research Center (SPARC) in 2003. The SPARC exists to give undergraduate cadets experience working on space missions of interest to the Department of Defense. To date the SPARC has designed, built, tested and flown over 20 science payloads on various DoD and NASA spacecraft.