Abstract ATM-9407085 Thomson, Ewen M. University of Florida Title: The Physical Origin of Initial Discharge Processes in Lighting Transient electric fields have been recorded in a 800 Hz to 5 MHz bandwidth at four to five stations at Kennedy Space Center since October 1991. These fields are radiated from lighting and other electrical processes of a much smaller scale than lighting. The primary focus of this proposal is the analysis of these data to establish the physical origin of their sources, with an emphasis on the initial discharge processes in lighting and the initial lightings in a cell. According to recent theory that employs a transmission-line model, four electric field measurements on a sub-microsecond time scale can be processed to give the three-dimisional location, vector velocity, and peak current of an in-cloud source. Wideband electric fields pulses are associated with both step formation in streamers and the propagation of large current pulse downs ionized channels. The objective of the modeling is to characterize physically the sources of processes that previouly have been characterize only in terms of features of their electric field waveshapes. This will enable us to investigate the physical origin of processes that produce large microsecond-scale electric field pulses. Or particular importance are the sources of wideband electric field that occur in the initial stages of lighting, since these are most likely to reflect the pre-existing thunderstorm charge, and the initial lightings in a cell, since these are a manifestation of the thunderstorm charge generator. Our analysis will result in the physical characterization of the bipolar pulses that have been detected in the early stages of both intracloud and cloud-to-ground flashes, narrow bipolar pulses that may result from a discharge of much smaller extent than typical lighting, early stepped leader steps, and sources, and sources of fine structure in first return strokes.
