TETRA-II Observations of Lightning-Associated X-Ray/Gamma Flashes at Ground Level

The TGF and Energetic Thunderstorm Rooftop Array (TETRA-II) consists of an array of BGO and LaBr scintillators to detect bursts of X-rays and gamma rays from thunderstorms. The BGO scintillators have an energy range ~ 200 keV - 10 MeV and are placed in 18 detector boxes, each with 1180 cm³ of BGO, at 3 separate locations: the campus of Louisiana State University in Baton Rouge, Louisiana; the campus of the University of Puerto Rico at Utuado, Puerto Rico; and the Centro Nacional de Metrologiá de Panamá (CENAMEP) in Panama City, Panama. The high resolution LaBr scintillators are located alongside the BGO scintillators at LSU, and allow for the observation of gamma ray lines in the presence of lightning strikes and BGO-detected bursts. Over 25 events of millisecond-scale duration have been observed associated with nearby lightning together with enhancements of up to several hours. Events are compared with weather data, including lightning maps, cell base-reflectivity, and echo top heights, to study the structure of the storm at the time of the bursts. An overview of the bursts observed and their association with lightning and weather data will be presented.