HR: 10:35h
AN: AE42A-02    [Abstracts]
TI: Satellite Observations of Small Ice Crystals and Lightning
AU: * Sherwood, S C
EM: Steven.Sherwood@yale.edu
AF: Yale University, Dept. Geology and Geophysics PO Box 208109, New Haven, CT 06520-8109 United States
AU: Phillips, V T
EM: Vaughan.Phillips@noaa.gov
AF: Princeton University, Dept. of Geosciences, Princeton, NJ 08544-1003 United States
AU: Wettlaufer, J S
EM: john.wettlaufer@yale.edu
AF: Yale University, Dept. Geology and Geophysics PO Box 208109, New Haven, CT 06520-8109 United States
AU: Dash, G G
EM: dash@phys.washington.edu
AF: University of Washington, Dept. of Physics Box 351560, Seattle, WA 98195 United States
AB: Lightning is well known to require strong updrafts, but the reasons for this---and the charge transfer mechanism that produces electrification---have been the subject of intense debate. Here, pan-tropical satellite observations of lightning flash rate and near-infrared cloud scattering are used to show that lightning is facilitated by a broad ice size distribution that includes numerous, small ice particles in the upper part of the anvil. The abundance of small ice particles, rather than lofted graupel or supercooled water, appears to be the main control on lightning flash rate in tropical systems. We use an explicit microphysical cloud model to support our interpretation of the satellite data and to argue that enchanced CCN aerosol concentrations will generate the required particles, implicating aerosols in enhancing tropical lightning. Strong updrafts can also enhance CCN nucleation, helping to explain the observed correlation between updraft speed and electrification. We examine the implications of these empirical results for various microphysical charging mechanisms that have been examined in laboratory studies.
DE: 3324 Lightning
DE: 3360 Remote sensing
DE: 3374 Tropical meteorology
DE: 3314 Convective processes
DE: 0320 Cloud physics and chemistry
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting