HR: 10:20h
AN: AE51B-01 INVITED     [PDF]
TI: Model Studies of Lightning in Thunderstorms
AU: * Mansell, E R
EM: mansell@ou.edu
AF: CIMMS/Univ. of Oklahoma, NSSL 1313 Halley Cir., Norman, OK 73069 United States
AU: Kuhlman, K
EM: kkuhlman@ou.edu
AF: CIMMS/Univ. of Oklahoma, NSSL 1313 Halley Cir., Norman, OK 73069 United States
AU: Ziegler, C L
EM: conrad.ziegler@noaa.gov
AF: Natl. Severe Storms Lab, 1313 Halley Cir., Norman, OK 73069 United States
AU: Straka, J M
EM: jstraka@ou.edu
AF: Univ. of Oklahoma/School of Meteor., 100 E. Boyd St., Norman, OK 73019 United States
AU: MacGorman, D R
EM: don.macgorman@noaa.gov
AF: Natl. Severe Storms Lab, 1313 Halley Cir., Norman, OK 73069 United States
AB: The OU/NSSL cloud-scale model has a microphysics package designed to treat a variety of convective events and has numerous noninductive graupel-ice charge separation schemes based on different laboratory results. Other features are a branched 3-D lightning scheme and a recently-added explicit treatment of small ion processes. Model results suggest that lower charge regions can be generated by either inductive or noninductive processes. Inductive graupel-droplet interactions were previously found to be able to generate a sufficiently strong lower positive charge region to cause negative cloud-to-ground ($-$CG) flashes to occur. However, the method used to diagnose ice crystal number concentration might underestimate the number of crystals at higher temperatures ($-15$--$0^{\circ}$C). If a minimum ice crystal concentration ($\sim 50$\,L$^{-1}$) is assumed, then the noninductive graupel-ice mechanism acting alone is able to generate a lower positive charge center, also leading to $-$CG flashes. The result indicates a need for a more detailed (and, it is hoped, more accurate) microphysical treatment of ice crystals in the model. A small Florida storm simulation used a 9 August 1991 sounding from CaPE. The modeled storm compares well with radar and electrical observations of storms on that day. The simulation produced IC and $-$CG lightning flashes. The warm rain process forms rain drops that freeze when they are carried by the updraft to $T<0^{\circ}$C. The frozen drops rime and separate charge via noninductive and/or inductive processes. The presence of large ice particles at low levels results in a rapid formation of a lower positive charge region and initially negative $E_{z}$ at the surface. The 29 June 2000 supercell storm observed during the STEPS field program has also been simulated. Both the observed and modeled storms had strong updrafts and midlevel rotation, produced many $+$CG lightning flashes, and had a strong correlation between updraft volume and total flash rate.
UR: http://www.cimms.ou.edu/~mansell/
DE: 3324 Lightning
DE: 3337 Numerical modeling and data assimilation
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting