Aerosol Influences on Tornado Genesis
David Lerach, Colorado State University, Fort Collins, CO; and B. Gaudet and W. R. Cotton
Simulations of an idealized supercell thunderstorm were performed to assess effects of increased aerosol concentrations acting as cloud condensation nuclei (CCN) and giant CCN (GCCN) on tornadogenesis. Initial background profiles of CCN and GCCN concentrations were set to represent a “clean” continental and an aerosol-polluted environment. Enhanced aerosol concentrations in the polluted simulation reduced both warm- and cold-rain processes within the rear flank downdraft (RFD) and forward flank downdraft (FFD), resulting in lower precipitation rates. A relatively weak cold pool was produced at the updraft-downdraft interface due to low evaporative cooling rates, providing a favorable environment for tornadogenesis, where the low-level mesocyclone and near-surface vorticity provided by the RFD-based gust front remained vertically-stacked. As a result, an EF-1 tornado formed in the polluted environment while the CLN case failed to produce such a vortex.
In summary, “other things being equal,” a polluted environment is more favorable for tornadogenesis. However, multiple factors control the strength of cold pools, including surface fluxes of heat and water vapor, dewpoint temperatures, storm-relative midlevel flow and entrainment, convective available potential energy (CAPE) and ice microphysics, particularly hail and raindrop size. Thus aerosol influences on tornado genesis may be hard to isolate as a causal factor in observations of tornado genesis.
Extended Abstract (332K)
Session 6, Air quality and climate change—II
Wednesday, 14 January 2009, 4:00 PM-5:30 PM, Room 127A
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