Abstract
We report on three classes of terrestrial gamma-ray flashes (TGFs) from
the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI)
satellite. The first class drives the detectors into paralysis, being
observed usually through a few counts on the rising edge and the later
tail of Comptonized photons. These events – and any bright TGF –
reveal their true luminosity more clearly via their Compton tail than
via the main peak, since the former is unaffected by the unknown beaming
pattern of the unscattered radiation, and Comptonization mostly
isotropizes the flux. This technique could be applied to TGFs from any
mission. The second class is more than usually bright and long in
duration. When the magnetic field at the conjugate point is stronger
than at the nearby footpoint, we find that 4 out of 11 such events show
a significant signal at the time expected for a relativistic electron
beam to make a round trip to the opposite footpoint and back. We
conclude that a large fraction of TGFs lasting more than a few hundred
microseconds may include counts due to the upward-moving secondary
particle beam ejected from the atmosphere. Finally, using a new search
algorithm to find short TGFs in RHESSI, we see that these tend to occur
more often over the oceans than land, relative to longer-duration
events. In the feedback model of TGF production, this suggests a higher
thunderstorm potential, since more feedback per avalanche implies fewer
“generations” of avalanches needed to complete the TGF discharge.