HR: 16:55h
AN: AE44A-05 INVITED    [Abstracts]
TI: What could cause terrestrial gamma-ray flashes?
AU: * Dwyer, J R
EM: jdwyer@fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences 150 W. University Blvd, Melbourne, FL 32901, United States
AB: Despite over a decade of research, the sources of Terrestrial Gamma-ray Flashes (TGFs) remain a mystery. Not only are the exact source locations unknown, the basic mechanism for producing the energetic electrons that emit the high-energy photons is still under active debate. When TGFs were first reported using data from the Burst and Transient Source Experiment (BATSE) on NASA's Compton Gamma-ray Observatory (CGRO), it was almost immediately suggested that the source was associated with sprites or other high altitude (>30 km) phenomena. However, new spectral measurements of TGFs by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite as well as detailed modeling of the gamma-ray propagation through the atmosphere indicate that the source altitudes are, in fact, much lower, between 15 and 21 km. Such altitudes are within the range of thunderstorm tops but are much too low for sprites. Because gamma-rays experience large attenuation in the atmosphere, such low source altitudes imply that the number of runaway electrons at the source must be very large, in excess of 10 to the power 16, which could produce measurable currents and changes in the electric charge moment. In this talk, possible source mechanisms of TGFs will be discussed, including runaway electron production through relativistic runaway electron avalanches acting on the cosmic-ray background and on extensive air showers, runaway electron production by the relativistic feedback mechanism, and runaway electron emission from lightning leaders and/or streamers.
DE: 2716 Energetic particles: precipitating
DE: 3300 ATMOSPHERIC PROCESSES
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3359 Radiative processes
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting