HR: 1340h
AN: AE33A-0191    [Abstracts]
TI: Duration and Extent of Large Electric Fields in a Thunderstorm Anvil After the Last Lightning Flash
AU: * Stolzenburg, M
EM: mstolzen@phy.olemiss.edu
AF: Department of Physics and Astronomy, University of Mississippi, University, MS 38677-1848 United States
AU: Marshall, T C
EM: marshall@olemiss.edu
AF: Department of Physics and Astronomy, University of Mississippi, University, MS 38677-1848 United States
AU: Krehbiel, P R
EM: krehbiel@ibis.nmt.edu
AF: Langmuir Laboratory for Atmospheric Research, Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, NM 87801 United States
AB: In 1999 we obtained a series of three complete soundings of electric field (E) through a large anvil. The soundings, acquired with balloons launched from Langmuir Laboratory in New Mexico, cover a 75-minute period during which the anvil moved northward and dissipated. Each of the balloons ascended through but near the edge of the radar-detectable anvil cloud. The later two soundings were made after the last lightning had occurred in the storm. The second balloon was launched 11 min after and 15 km distant from the closest part of the final lightning flash, and the third balloon was launched 28 min later. The first sounding in the series shows large electric field magnitudes (maximum 65 kV m$^{-1}$) and significant charge densities of both polarities (maximum positive charge density +2.5 nC m$^{-3}$) within and screening the anvil. There was little change in the maximum E values during the intervening 30 min between the first and second balloon flights, although the altitudes and densities of some charge regions were appreciably lower in the second sounding (maximum positive charge density +0.6 nC m$^{-3}$). The final balloon sounding was made through the visible, but optically less dense anvil cloud; maximum radar reflectivity along the track was 12 dBZ. There was essentially no enhanced E or net charge detected in this part of the anvil cloud. In this presentation we compare the location of the radar echo boundaries to the three anvil E soundings made near and through these boundaries. An estimate of the horizontal extent and duration of the charged regions within the anvil can be made from these data. For example, 30 min after the last lightning flash, we estimate that the interior positive charge region covered at least 130 km${^2}$, and 50 min after, it covered less than 50 km${^2}$. We also investigate the evolution of the screening layers and their location relative to the echo boundaries. These analyses should allow us to estimate the extent of potentially hazardous electric fields associated with an anvil after the last lightning flash.
DE: 3399 General or miscellaneous
DE: 3304 Atmospheric electricity
DE: 0320 Cloud physics and chemistry
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting