HR: 09:45h
AN: AE51A-07    [PDF]
TI: The Upward Directed Poynting Flux over a Thunderstorm
AU: * Farrell, W M
EM: william.farrell@gsfc.nasa.gov
AF: Laboratory for Extraterrestrial Physics, NASA/Goddard SFC, Greenbelt, 20771
AU: Goldberg, R A
AF: Laboratory for Extraterrestrial Physics, NASA/Goddard SFC, Greenbelt, 20771
AU: Blakeslee, R J
AF: Global Hydrology and Climate Center, NASA/Marshall SFC, Huntsville, 35805
AU: Cummer, S A
AF: Dept. of Computer and Electrical Engineering, Duke Univ., Durham, 27708
AU: Deschj, M D
AF: Laboratory for Extraterrestrial Physics, NASA/Goddard SFC, Greenbelt, 20771
AU: Mach, D M
AF: Global Hydrology and Climate Center, NASA/Marshall SFC, Huntsville, 35805
AU: Mitchell, J D
AF: Dept. of Electrical Engineering, Penn State Univ, State College, 16803
AU: Croskey, C L
AF: Dept. of Electrical Engineering, Penn State Univ, State College, 16803
AB: In August of 2002, NASA carried out the Altus Cumulus Electrification Study (ACES) to investigate the lightning/storm relationship, to quantify the storm electrical budget, and to validate the TRMM lightning sensor (LIS) data. The platform was General Atomic's Altus uninhabited aerial vehicle (UAV) which allowed long-duration, close-proximity monitoring of storms from their births to deaths. The platform carried a set of DC Field Mill sensors to measure electrostatic fields, AC electric and magnetic field sensors for deriving the Poynting flux, a Gerdien conductivity probe, optical sensors, and a flight payload data system. The data system collected low rate data, and also cloud be event-triggered into high rate mode for approximately 0.3 seconds about lightning strikes. During the month long mission, 11 scientific flights occurred yielding over 4300 high rate triggered events. An objective of this study was to determine the amount of upward radiated power into the middle atmosphere and ionosphere, and determine contribution of the radiated power to the global atmospheric electric circuit. In this work, we show upward Poynting flux measurements between 10 Hz -100 kHz from some specific thunderstorm overflights. We find that upward radiated powers from lightning strikes can be large. However, displacement currents are also comparatively large, suggesting that the radiation impedance above a thunderstorm is relatively low (~150 Ohms at 10 kHz). This radiation impedence is calculated as a function of frequency. The effect of the radiated power on the global circuit will be discussed.
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting