HR: 0800h
AN: AE41A-0147    [Abstracts]
TI: A 3D Non-Grid-Point Dependent Lightning Scheme
AU: * Helsdon, J H
EM: john.helsdon@sdsmt.edu
AF: Institute of Atmospheric Sciences, SD School of Mines & Technology 501 E. St. Joseph St., Rapid City, SD 57701
AB: A new lightning scheme, for use in numerical storm models, has been developed. The scheme creates tortuous, branched lightning channels that propagate independent of the underlying model grid structure (a Lagrangian process). The scheme initiates a lightning flash in the high-field region based on the production by cosmic rays of random free electrons. The path of the lightning channel is determined by which cosmic-ray-generated electron can create the next 50-m channel segment in the shortest time under the influence of the ambient electric field, as well as the electric field produced by previous channel segments. When two electrons satisfy the "least-time" criterion, a branch is formed. Tortuousity angle criteria are imposed consistent with the observations of Hill (1968). Termination of the channel occurs when the potential difference between the conducting channel and the environment falls below a threshold. This presentation will show results from the lightning scheme used with a prescribed charge structure (main positive dipole with upper screening layer and lower positive charge center). One interesting result, so far, is that the scheme may offer an explanation as to how/why positive cloud-to-ground flashes can be produced from the core of normal polarity thunderstorms.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005