HR: 0800h
AN: AE31A-0031    [Abstracts]
TI: Assessing Patterns in the Surface Electric Field Prior to First CG Flashes and After Last CG Flashes in Air-Mass Thunderstorms
AU: Williams, D E
EM: vanillaice@ou.edu
AF: School of Meteorology University of Oklahoma, Suite 5900, National Weather Ctr 120 David L. Boren Blvd., Norman, OK 73072-7307,
AU: * Beasley, W H
EM: whb@ou.edu
AF: School of Meteorology University of Oklahoma, Suite 5900, National Weather Ctr 120 David L. Boren Blvd., Norman, OK 73072-7307,
AU: Hyland, P T
EM: pat.hyland@ou.edu
AF: School of Meteorology University of Oklahoma, Suite 5900, National Weather Ctr 120 David L. Boren Blvd., Norman, OK 73072-7307,
AB: In an effort to elicit patterns in the temporal and spatial evolution of the contours of surface electric field relevant to the occurrence of cloud-to-ground (CG) lightning, we have analyzed data from the network of 31 electric-field mills jointly operated by the John F. Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). To identify cases of interest, we used lightning ground-strike data, maps of in-cloud lightning discharges, rainfall data, and radar data. In particular, we have focused on two critical problems: 1) estimation of when and where the first CG flash in a storm might occur and 2) assessment of the likelihood of CG flashes occurring late in a storm after a long period without a CG flash. Our long-term goal is to understand the evolution of surface contours of electric field for periods of 30 minutes or more before the first flash of any kind and 30 minutes or more before and after the last flash of any kind. For practical reasons, we are reporting here on analysis of data for periods of 30 minutes before the first CG flash and 30 minutes after the last CG flash in each storm of interest. We have analyzed electric-field data from isolated air-mass convective storms that developed over KSC/CCAFS from late May through early September, 2004-2006. To identify thunderstorms that fit the air-mass, or "pop-up" criteria, we started by examining rainfall and CG lightning data, then looked at radar data. Then, for the storms selected, we performed a two-pass Barnes objective analysis on the electric-field data. Each analysis cycle resulted in one contour plot of 20-second averaged data, yielding 90 plots for each 30 minute interval, which we then animated. This resulted in 58 animations of the field contours prior to first CG flashes and 62 animations of the field contours after last CG flashes. Preliminary impressions from examinations of these cases suggest that the electric-field contours before the first flash exhibit a smooth transition from weak to strong gradient, but the strongest field just before the flash may occur up to several kilometers distant from the ground-strike point. Furthermore it appears that in several cases, the field remained strong throughout a broad area for relatively long periods after the last flash.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
DE: 3360 Remote sensing
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting