Mountaintop gamma ray observations of three terrestrial gamma-ray flashes at the Säntis Tower, Switzerland with coincident radio waveforms

We report on the mountain top observation of three terrestrial gamma-ray
flashes (TGFs) that occurred during the summer storm season of 2021. To
our knowledge, these are the first TGFs observed in a mountaintop
environment and the first published European TGFs observed from the
ground. A gamma-ray sensitive detector was located at the base of the
Säntis Tower in Switzerland and observed three unique TGF events with
coincident radio sferic data characteristic of TGFs seen from space. We
will show an example of a 'slow pulse' radio signature, an -EIP,
and a double peak TGF associated with an extraordinarily powerful and
complicated positive-polarity sferic, where each TGF peak is possibly
preceded by a short burst of stepped leader emission.