October 21, 2009

"X-ray Emissions from Thunderstorms and Lightning"

Professor Joe Dwyer
Florida Institute of Technology


Until very recently, lightning was thought to be an entirely conventional discharge, involving only low-energy (a few eV) electrons. This picture changed completely with the discovery of intense x-ray emission from natural cloud-to-ground lightning, rocket-triggered lightning and thunderstorms. Indeed, the intensity of the x-rays generated by thunderstorms can be so large that bright bursts of these x-rays are observed from space, 600 km above the storms, as Terrestrial Gamma-ray Flashes (TGFs). In addition, it has been found recently that thunderstorms launch beams of electrons, with energies up to 30 MeV, into the inner magnetosphere, where they are observed by spacecraft thousands of kilometers away. This energetic emission cannot be produced by conventional discharges in air, and so the presence of x-rays strongly implies that relativistic runaway electrons, accelerated in air by strong electric fields, play a role in thunderstorm and lightning processes. In this talk, I will give an overview of the x-ray observations of thunderstorms and lightning, along with new results on terrestrial gamma-ray flashes. Finally, the physics of runaway breakdown will be presented, including some very recent theoretical advances.


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