HR: 0800h
AN: AE31A-0045    [Abstracts]
TI: Monte Carlo simulation of the temporal behavior of Terrestrial Gamma ray Flashes
AU: * Gjesteland, T
EM: thomas.gjesteland@ift.uib.no
AF: University of Bergen, Allegaten 55, Bergen, 5007, Norway
AU: Ostgaard, N
EM: nikolai.ostgaard@ift.uib.no
AF: University of Bergen, Allegaten 55, Bergen, 5007, Norway
AU: Connell, P H
AF: University of Valencia, P.O:Box 22085, Valencia, 46071, Spain
AU: Stadsnes, J
AF: University of Bergen, Allegaten 55, Bergen, 5007, Norway
AB: Based on TGF-measurements from BATSE it has been found that high energy photons (>300 keV) are observed earlier than low energy photons (25-50 keV), with an average of 240 μs. The explanation for this time dispersion has not yet been identified. Using a Monte Carlo simulation where the Compton scattering, pair production and absorption of X-rays are included, we find that the time dispersion, for most of the TGF, can be explained as a pure Compton effect, assuming a discrete TGF-production altitude. This is because the majority of low energy photons escaping the atmosphere are originally high energy photons that have experienced multiple Compton scattering and energy reduction. Each Compton scattering will make the photon's traveling path longer, which result in a longer traveling time. Our simulations show that the time delay increases as the TGF production altitude decreases, and as a satellite's nadir angle of measurements increases. The initial TGF spatial distribution at the producing altitude is also important for the time delay. If the TGF distribution is isotropic within a solid angle, a satellite measuring at angels inside this cone will hardly observe any time delay. These findings are supported by the BATSE measurements.
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting