HR: 1340h
AN: AE23A-0837    [Abstracts]
TI: Dimensional Reduction: a Method for Retrieving Lightning Charge
AU: * Koshak, W J
EM: william.koshak@nasa.gov
AF: NASA Marshall Space Flight Center, 320 Sparkman Drive, Bldg. NSSTC, Huntsville, AL 35805 United States
AB: A method is introduced for retrieving the locations and magnitudes of charges deposited by a lightning flash using multiple ground-based electric field change measurements. The method, called Dimensional Reduction, reduces the number of unknowns in a discrete 2-charge model from the standard of eight (x, y, z, Q, x', y', z', Q') to just four (x, y, z, Q). This reduction is accomplished by analyzing "residual measurements" that are formed by subtracting from each ground-based electric field change the contribution due to the source (x, y, z, Q). Using an improved analytic solution to the four-parameter point charge model (or "Q-model") the residual measurements are inverted to find the associated "residual source." For flash charge depositions that look approximately like two arbitrary charges, the residual source will be modeled accurately when (x, y, z, Q) is accurate. Hence, one need only minimize a chi-squared goodness-of-fit that is a function of the four variables (x, y, z, Q), rather than one that is a function of the eight variables (x, y, z, Q, x', y', z', Q'). The accuracy of the method is assessed by inverting computer-simulated electric field changes produced from known charge sources (see related presentation by Murray et al., this session). The method is also applied to analyze real lightning electric field change data derived from the NASA Kennedy Space Center (KSC) and United States Air Force (USAF) Eastern Range (ER) ground-based field mill network. It is shown that the charge retrievals compare favorably with associated ancillary ground- and satellite- based lightning measurements.
DE: 3324 Lightning
DE: 3260 Inverse theory
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting