HR: 12:05h
AN: AE51B-06    [PDF]
TI: New x-ray observations of triggered lightning
AU: * Dwyer, J R
EM: dwyer@pss.fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Uman, M A
EM: uman@ece.ufl.edu
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AU: Rassoul, H K
EM: rassoul@pss.fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Rakov, V A
EM: rakov@ece.ufl.edu
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AU: Al Dayeh, M
EM: maldayeh@fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Caraway, L
EM: caraway78@yahoo.com
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Rambo, K J
EM: rambo@tec.ufl.edu
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AU: Jordan, D M
EM: jordan@ece.ufl.edu
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AU: Jerauld, J
EM: jjerauld@ufl.edu
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AU: Chrest, A
EM: achrest@fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Wright, B
EM: bwright@fit.edu
AF: Florida Institute of Technology, Department of Physics and Space Sciences, Melbourne, FL 32901 United States
AU: Smyth, C
EM: cadet003@hotmail.com
AF: University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 United States
AB: We report preliminary results from the x-ray observations of rocket-triggered lightning made in the summer of 2003 at the International Center for Lightning Research and Testing at Camp Blanding, FL. A total of 26 dart leader/return stroke sequences were observed, using eight NaI(Tl)/PMT detectors plus two identical control detectors with no scintillator. The detectors were enclosed in five thick aluminum boxes, designed to keep out RF noise, water and light, and placed between 5 m and 650 m from the lightning channels. X-rays were measured 0 - 100 microseconds just prior to the return strokes in 73 percent of these events, supporting earlier measurements of energetic radiation from triggered lightning. Using bronze collimators and attenuators, the emission was found to be composed of multiple, very brief bursts of x-rays with energies extending up to about 200 keV, with each burst typically lasting less than 1 microsecond. The x-ray emission was also observed to be spatially and temporally associated with the dart leaders, with the brightest bursts coming from the direction of the dart leader when it was within about 50 m of the ground. Finally, for one triggered lightning event, an intense burst of gamma-rays, lasting more than 300 microseconds, with energies up to 10 MeV was observed during the initial continuous current phase, associated with a large current pulse, from a distance of 650 m from the launcher. These x-ray observations suggest that copious numbers of runaway electrons are commonly produced during lightning, implying that the electric fields associated with some phases of lighting may be much stronger than previously thought. These results have important implications for the physics of lightning discharges.
DE: 3300 METEOROLOGY AND ATMOSPHERIC DYNAMICS
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3329 Mesoscale meteorology
DE: 3394 Instruments and techniques
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting