Thunderstorms as Particle Accelerators: Observations from the Fermi Gamma-ray Burst Monitor

Michael Briggs

University of Alabama at Huntsville

Deputy PI, Fermi Gamma-ray Burst Monitor (GBM)

It has been known at least since Benjamin Franklin’s kite experiment that thunderstorms contain strong electric fields. In recent years we have learned that these electric fields generate a wide range of high-energy phenomena. Terrestrial Gamma-ray Flashes (TGFs) are the most intense of these, easily detectable with instruments in low-Earth orbit. While designed for astrophysics observations, the Fermi Gamma-ray Burst Monitor (GBM) readily detects TGFs, detecting more than 800 per year. Correlations with ground-based radio observations associates TGFs with particular lightning strokes and confirms that TGFs originate inside thunderstorms. TGFs are found to originate from a variety of storm types. In addition to the broad cone of gamma-rays, TGFs also produce a narrower beam of charged particles.   These Terrestrial Electron Beams are detected a few times a year by GBM