Gamma-ray emissions observed in a thunderstorm anvil

Balloon-borne gamma-ray and electric-field-change instruments were launched into a daytime summer thunderstorm to evaluate a new experimental design t o test hypotheses for the production of transient luminous events (TLE) (eg . sprites, and blue jets) in the mesosphere. While ascending, the instrumen t triggered many times on the signals from the electric-held-change instrum ent, recording the gamma-ray background at those times. A greater than thre e-fold increase in the gamma-ray flux was observed as the balloon descended through a thunderstorm anvil where a strong electric field was suspected t o be present. These observations suggest that gamma-ray production in thund erstorms may not be as uncommon as previously believed.