A Particle Astrophysics Observatory and the Origins of Lightning 

Dr. John Belz
Department of Physics and Astronomy
University of Utah

Terrestrial Gamma Flashes (TGFs) have been observed in satellite-borne gamma ray detectors for several decades. They consist of bursts of upwards of 1018 gamma rays, which endure up to a few milliseconds and originate in the Earth's atmosphere. TGFs are now known to be generated in the leader stage of upward intracloud lightning, suggesting that they may have counterparts in downward-directed lightning as well. 

The Telescope Array Surface Detector (TASD) is a 700 square kilometer cosmic ray observatory, an array of 507 3-square meter scintillators on a 1.2 km grid in Utah's West Desert. Following the observation of bursts of anomalous TASD triggers associated with local lightning activity, a suite of lightning detection instruments was installed at the TASD site in order to study the effect. Early data from this new high energy atmospheric physics observatory indicates that we are indeed observing downward TGFs. The air shower reconstruction abilities of the TASD give it unique abilities to test models of TGF formation, and thus shed new light on the incompletely understood lightning initiation mechanism.