HR: 1340h
AN: AE23A-0845    [Abstracts]
TI: Potential Wells and Preliminary Breakdown in CG Flashes
AU: * Coleman, L
EM: leonidas@phy.olemiss.edu
AF: University of Mississippi, Department of Physics and Astronomy, University, MS 38655 United States
AU: Marshall, T C
EM: marshall@olemiss.edu
AF: University of Mississippi, Department of Physics and Astronomy, University, MS 38655 United States
AU: Stolzenburg, M
EM: mstolzen@phy.olemiss.edu
AF: University of Mississippi, Department of Physics and Astronomy, University, MS 38655 United States
AU: Winn, W P
EM: winn@loon.nmt.edu
AF: Langmuir Laboratory for Atmospheric Research, 237 Workman Center 801 Leroy Place, Socorro, NM 87801-4796 United States
AU: Krehbiel, P R
EM: krehbiel@ibis.nmt.edu
AF: Langmuir Laboratory for Atmospheric Research, 237 Workman Center 801 Leroy Place, Socorro, NM 87801-4796 United States
AU: Rison, W
EM: rison@arctic.nmt.edu
AF: Langmuir Laboratory for Atmospheric Research, 237 Workman Center 801 Leroy Place, Socorro, NM 87801-4796 United States
AU: Thomas, R J
EM: thomas@nmt.edu
AF: Langmuir Laboratory for Atmospheric Research, 237 Workman Center 801 Leroy Place, Socorro, NM 87801-4796 United States
AB: In this study, we explore the link between preliminary breakdown in CG flashes and the presence of potential wells associated with the lower positive charge of the storms which create the CG flashes. Because E is proportional to the first derivative of the electric potential, V, the presence of a one dimensional potential well can be inferred from a change in the polarity of the vertical component of E between two altitudes. In this study, the two altitudes are typically at ground and near the altitude of lightning initiation. The measurement of E at the ground is taken by ground field mills in the vicinity of the CG flash, and the measurement of E in the cloud is typically taken by a balloon borne electric field meter. When balloon measurements of E are not available, the altitude and behavior of the first few LMA detected radiation sources of the CG are used as a proxy for the altitude of large positive fields. The time between the first LMA detected radiation source and the first return stroke as detected by the NLDN or by fast antenna data is used as a proxy for determining the presence of preliminary breakdown. {\it Beasley et al.} [1983] studied 80 CG flashes from nine storms at the NASA Kennedy Space Center and found that the "durations of stepped leaders lie most frequently in the range of 6-20 milliseconds." They also found that preliminary breakdown, or "preliminary variation," lasted from 11 to 500 ms with a mean duration of 118 ms and a median duration of 65 ms. This study shows a strong correlation between the existence of potential wells associated with the lower positive charge of storms and delays of greater than 20 ms, the longest lifetime reported by {\it Beasley et al.} for the stepped leader, between flash initiation and the first return stroke. This result is consistent with a potential well influencing the propagation of the negative leader and causing preliminary breakdown. References: Beasley, W.H., M. A. Uman, and P.L. Rustan, Electric fields preceding cloud-to-ground lightning flashes, {\it J. Geophys. Res., 87}, 4883-902, 1983
DE: 3324 Lightning
DE: 3360 Remote sensing
DE: 3394 Instruments and techniques
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting