Systematic Aircraft-Based Measurement of Thunderstorm Related Gamma-Ray and X-Ray Emissions

Abstract:

Terrestrial Gamma-ray Flashes (TGFs), known to originate from thunderstorms, are the highest-energy natural photon fluxes on Earth. While the FAA advises pilots to avoid flying through or close to thunderclouds, each commercial aircraft is struck by lightning (usually during take-off or landing) on average once a year [Fisher et al., 1999]. According to Dwyer et al. [2010], the radiation dose received by passengers and crew in flight, when airborne vehicles are close to a TGF event, could reach a biologically harmful level (0.1 Sv) in less than 1 millisecond. The mechanism of TGFs remains the subject of debate. To shed more light on the nature of TGFs, we have conducted an aircraft-based X-ray and Gamma-ray measurement campaign. Systematic radiation measurements were performed onboard commercial aircraft using a Cesium Iodide scintillator-based Gamma-ray detector. The current data acquisition system uses time bins of 100 µs, and records photons from 300 keV to 10 MeV in five energy bins. Preliminary results based on several months of systematic observation will be presented. We found that in certain energy bins the radiation levels at cruising altitude are 160 higher than the levels measured on the ground with the same instrument, which will be used in developing a search algorithm with a redefined baseline radiation level. Furthermore, it permitted us to search for the presence of gamma-ray glows at various altitudes. Over land we can use radar networks to identify the weather conditions at the time of gamma-ray glows or TGFs, and lightning detection networks can be used to identify individual lightning flashes.