Observation of TGFs at High-Latitude

Terrestrial Gamma-ray Flashes (TGFs) are short burst of gamma radiation originating from thunderclouds; they propagate upwards and are then detected by satellites such as AGILE, Fermi and ASIM. ASIM is the first mission specifically designed for the study of thunderstorm-related phenomena; it is also placed on the ISS and as such can for the first time detect TGF events up to more than 51 degrees in latitude .

Among the previous missions, RHESSI was the one reaching the highest latitude: 38 degrees. We then consider "high-latitude" for ASIM the band between 35 and 51 degrees of latitude. A number of events have already been observed in this band, including one at +50° (near the border of northeast China) and one at -40° (open sea near South Africa). Such events are associated with subpolar thunderstorms, which are different from the ones produced by deep convection at equatorial and tropical latitudes; moreover, TGFs at such latitudes are expected to experience greater absorption in the troposphere, which makes them more difficult to detect.

In this work we then present the first high-latitude TGFs ever observed and their characteristics, including meteorological contest and associated radio observations .