EE 350 Radioscience Seminar
Professor Umran S. Inan
Date: Wednesday, March 09, 2005
Time: 4:15 PM – Refreshments at 4:00
b>Location: Sloan Mathematics
Center (Building 380), Room 380Y
Monte Carlo modelling of relativistic runaway electrons and terrestrial gamma-ray flashes
Dr. Nikolai Lehtinen
STAR Lab, Stanford University
The terrestrial gamma-ray flashes (TGF) were discovered by BATSE detector on Compton Gamma Ray Observatory satellite, which recorded a
total of ~76 of them. At present time, they are observed by RHESSI satellite at a rate of 10-20 per month. The TGF are observed in
regions with high lightning activity and many of them have been associated with lightning discharges. We investigate the hypothesis of TGF production by relativistic
runaway electrons accelerated by post-discharge electric field above thunderclouds. The runaway
electron avalanche process is studied using Monte Carlo simulations. The results include electron distributions and avalanche growth rates and depend on the values of
reduced electric and magnetic fields and the angle between them.
The calculated avalanche growth rate and electron drift velocities are applied to a fluid model of the avalanche above a thunderstorm, seeded by cosmic rays. We present
results of two-dimensional cylindrical and cartesian models, and compare levels and spectra of calculated gamma emissions with observations.
The RHESSI observations suggest existenceof runaway electron avalanche and TGF production at the geomagnetic equator. We discuss the problems with the avalanche being
strongly impeded by the geomagnetic field at high altitudes.