Fermi GBM Observations of Terrestrial Gamma Flashes

Terrestrial Gamma-ray Flashes (TGFs) are brief pulses of energetic radiation associated with thunderstorms and lightning. Observations of TGFs by the Fermi Gamma-ray Burst Monitor (GBM) have yielded rich science and new discoveries. Studies of TGF pulse morphologies reveal that they can be either symmetrical or faster in their rise than their decay, and can occur singly or in multiple, sometimes overlapping, pulses. Correlations of GBM-detected TGFs with groundbased radio observations of lightning discharges made by the World Wide Lightning Location Network show that the discharges and the TGFs are simultaneous to 40µs, with the discharge typically occurring within 300 km of the sub-spacecraft point. Rare TGFs are detected via an electron beam produced in a storm near one of the termini of the magnetic field line crossing Fermi. Bright electron TGFs show a prominent 511 keV annihilation line in their energy spectra, showing that this beam contains not only electrons, but also positrons, with a positron fraction between 10 and 20%.