Terrestrial gamma flashes at ground level — TETRA-II

An upgraded version of the TGF and Energetic Thunderstorm Rooftop Array (TETRA-II) consists of an array of BGO scintillators to detect bursts of gamma rays from thunderstorms at ground level in four separate locations: the campus of the University of Puerto Rico at Utuado; the campus of Louisiana State University in Baton Rouge, Louisiana; the Severe Weather Institute and Radar & Lightning Laboratories in Huntsville, Alabama; and the Centro Nacional de Metrologia de Panama (CENAMEP) in Panama City, Panama. TETRA-II began operation in May 2016. The original TETRA-I array of NaI scintillators at Louisiana State University detected 37 millisecond-scale bursts of gamma rays at energies 50 keV-2 MeV associated with nearby (<; 8 km) thunderstorms. When TETRA-II is fully operational, it will have approximately an order of magnitude greater sensitivity than TETRA-I. The ability to observe ground-level Terrestrial Gamma Flashes from close to the source allows a unique analysis of the storm cells producing these events. A brief description of the TETRA-I observations, a description of TETRA-II, and preliminary results will be presented.