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A Multipole Expansion Method for Analyzing Lightning Field ChangesChanges in the surface electric field are frequently used to infer the locations and magnitudes of lightning-caused changes in thundercloud charge distributions. The traditional procedure is to assume that the charges that are effectively deposited by the flash can be modeled either as a single point charge (the Q model) or a point dipole (the P model). The Q model has four unknown parameters and provides a good description of many cloud-to-ground (CG) flashes. The P model has six unknown parameters and describes many intracloud (IC) discharges. In this paper we introduce a new analysis method that assumes that the change in the cloud charge can be described by a truncated multipole expansion, i.e., there are both monopole and dipole terms in the unknown source distribution, and both terms are applied simultaneously. This method can be used to analyze CG flashes that are accompanied by large changes in the cloud dipole moment and complex IC discharges. If there is enough information content in the measurements, the model can also be generalized to include quadrupole and higher order terms. The parameters of the charge moments are determined using a dme-dimensional grid search in combination with a linear inversion, and because of this, local minima in the error function and the associated solution ambiguities are avoided. The multipole method has been tested on computer-simulated sources and on natural lightning at the NASA Kennedy Space Center and U.S. Air Force Eastern Range.
Document ID
19990063842
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Koshak, William J.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Krider, E. Philip
(Arizona Univ. Tucson, AZ United States)
Murphy, Martin J.
(Arizona Univ. Tucson, AZ United States)
Date Acquired
August 19, 2013
Publication Date
April 27, 1999
Publication Information
Publication: Journal of Geophysical Research
Publisher: American Geophysical Union
Volume: 104
Issue: D8
ISSN: 0148-0227
Subject Category
Meteorology And Climatology
Report/Patent Number
Paper-1999JD900027
Funding Number(s)
CONTRACT_GRANT: NAG5-6461
CONTRACT_GRANT: NAG10-92
Distribution Limits
Public
Copyright
Other

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