Quantifying High Probability Deployment Sites for Downward Terrestrial Gamma-Ray Flash Observations.

Abstract:

Observing Terrestrial Gamma-ray Flashes (TGFs) from the ground is quite challenging. Downward beamed TGFs seem to be far less common than typical upward TGFs observed from space and the extremely limited field of view of ground instrumentation as compared to satellite observatories makes choice of deployment site crucial to achieving a successful observation. Thus far the western coast of Japan has seen the most success in observing downward TGFs but it is certainly possible that there exist other downward TGF ‘hot spots’ around the globe with similar geographical and meteorological conditions that make the western coast of Japan observationally successful. In preparation for our six new ground based TGF detectors, the Terrestrial High-energy Observation of Radiation (THOR) instruments, we worked to develop a method to quantify potential high probability deployment sites. We used custom mapping software and the analysis of large data sets including lightning frequency, super bolt frequency (Holzworth 2019), tropopause altitudes, atmospheric temperature data, satellite observations of TGFs, and open source geographical data on man made structures such as TV towers, wind turbines etc.. We distilled this data into a single ‘score’ value, using a weighted algorithm, which defined the geographical locations with the highest probability of downward TGF events based off our understanding of the necessary meteorological, experimental, and infrastructure conditions to successfully observe them. We will present this work and how it will inform our deployment site decisions, hopefully leading to an increased number of downward TGF observations.