Radio emissions from terrestrial gamma-ray flashes

The theory of radio frequency (RF) emissions by terrestrial gamma-ray flashes (TGFs) is developed. These radio emissions, which are separate from the emission caused by lightning, are produced by the electric currents generated by runaway electrons and resulting low-energy electrons and ions. It is found from theory that the radio frequency pulses produced by TGFs are large enough to measure. Features of these signals depend strongly on certain aspects of the runaway acceleration process and so should provide additional information about the source mechanism(s) of this interesting atmospheric phenomenon. The RF emissions from several TGF models are calculated and compared with measurements of TGF-associated radio pulses, and it is found that the measured energy densities at higher frequencies support a source mechanism that involves a very large (>10(4)) number of distinct seed particle injections. In particular, the results are consistent with the relativistic feedback discharge model of TGFs.