This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The proposal seeks funding to investigate quantitatively the lightning-induced electron precipitation (LEP) using the ELF/VLF (~5 Hz?32 kHz) observations on the Antarctic continent. A coordinated effort will fully characterize individual lightning strokes occurring in the northern hemisphere while simultaneously observing the associated ELF/VLF waveforms in the Antarctic. In addition to advancing knowledge of the ELF/VLF wave studies in general, these observations will be used to differentiate between lightning energy that couples to the ionosphere/magnetosphere and that which couples to the Earth-ionosphere waveguide. Simultaneous observations of LEP will be conducted in the northern and southern hemispheres in order to: (1) quantitatively relate the upward-coupling lightning energy and LEP production, and (2) evaluate the conditions under which LEP occurs in both hemispheres. Rocket-triggered lightning in Florida allow for the direct measurement of lightning currents and will contribute to both the lightning- and LEP-related research efforts. The Antarctic research stations are ideally situated to perform both the long-distance ELF/VLF lightning observations and the VLF scattering observations for LEP detection in the conjugate region, necessary for the success of this program. Continued reliance on graduate and undergraduate students provides a broader impact to this proposed research and firmly grounds this effort in its educational mission.
(from the Van Allen belts) using low-frequency radio measurements, but the driving force behind the research is to obtain a greater understanding of a phenomenon that takes place in plain sight but which is both scientifically mysterious and dangerously energetic: a thunderstorm. We seek answers to what processes go on in and around thunderstorms - the predominant source of lightning - and what role they play in our enviroment. We all know that thunderstorms produce thunder and lightning, but few know that they can also produce gamma rays, which generally involve some of the most energetic processes known to man. We have only incomplete knowledge of the processes taking place in thunderstorms that lead to lightning discharges in general, but how gamma rays are produced stretches our current understanding. In addition to these gamma rays, it is now known that thunderstorms and their associated lightning produce strange electromagnetic phenomena in the region above them; they have evocative names such as "elves" and "sprites" and they also are not well understood. As we have said, thundersrtorms are scientifically mysterious. Our project involved measurements of the low-frequency radio waves (called sferics) produced by lightning occurring over much of the Earth's surface. The measurements were made at a few fixed low-noise sites, including Arrival Heights, Antarctica, and our research showed, first, that we could locate the lightning with reasonable accuracy, and second, given these locations, we could compensate for the propagation changes taking place with distance in the sferics to obtain information about the details of the causative lightning strikes. The hope is that this latter information will help us probe into the processes occurring in thunderstorms around the world and give new information about what is taking place. One other aspect of our NSF-funded research now shows great promise. Measurements made serendipitously under a thunderstorm in California (a rare occurrence) by one of our measurement systems and another operated by a colleague at U.C. Berkeley, confirmed that thunderstorms clearly produce strong ultra-low frequency magnetic field changes in their vicinity - confirming earlier measurements on another thunderstorm by us alone. These comparatively slow magnetic field fluctuations (as compared with the time taken for a lightning flash) provide invaluable new information about the electric currents flowing in thunderstorms; they now need to be incorporated into the present models for the charging processes within thunderstorms. Also, the presence of strong ultra-low frequncy magnetic fields in the region above thunderstorms has not yet been taken into account in the theories under development to account for the existence of the sprites, elves, and other unusual high-altitude phenomena mentioned above.
