The Relationship Between Tgf Production In Thunderstorms And Lightning Flash Rates And Amplitudes

We provide evidence that Terrestrial Gamma-Ray Flashes (TGFs), in well isolated thunderstorms, tend to occur during periods of low and declining flash rates, and when the flash amplitudes are larger than average. This conclusion comes from examining the results of 371 manually tracked TGF-producing thunderstorms. Fermi-GBM identified TGFs are used for this analysis and lightning data come from both World Wide Lightning Location Network and Earth Networks Total Lightning Network. The data from these storms suggest that TGFs are likely to occur in almost every phase of storms that last longer than an hour, but tend to occur later on in shorter storms. We also note that, in short storms, TGFs are more likely to accompany a flash when the flash rates of the storm are lower than average, and they are less likely per flash during the peak flash rate periods of the storms. We find that the tendency for TGFs to occur while the flash rate is falling and when the amplitudes of flashes (the sum of the absolute values of peak currents of all constituent sferics in the flash) are larger than average, does not depend strongly on the duration of the storms. This implies that not just any lightning flash can or even will produce a TGF, but that the electrical conditions of the storm play a crucial role in TGF production.Plain Language Summary Terrestrial Gamma-Ray Flashes (TGFs), which are very intense bursts of high energy radiation that are produced by some lighting, occur in almost every phase of the thunderstorms that produce them. We find that TGFs are more likely to occur when the lightning flash rate in the storm is lower than average. We also find that lightning flashes near the time of the TGFs are usually among the stronger flashes in the storms.Key PointsTerrestrial Gamma-Ray Flashes (TGFs) tend to occur when the flash rates in thunderstorms are lower and decliningTGFs are produced less efficiently during the peak lightning flash ratesThe flash amplitudes near the TGF tend to be higher than during other times of the same storms