Wednesday, 26 January 2011
4E (Washington State Convention Center)
Intense dust storms occur frequently in the southwestern U.S. and northern Mexico during late Spring and Summer. Considerable circumstantial evidence exists suggesting that these major dust events can be causally related to the severity of supercell storm outbreaks in the Southern Plains. However this concept, first proposed by the late Edwin Danielsen, remains speculative. Past studies have shown that mineral dust has the ability to act as cloud condensation nuclei (CCN), giant CCN (GCCN), and ice nuclei (IN) at fairly low cloud supersaturations. This study attempts to investigate the potential indirect microphysical impacts of natural desert dust on supercell storms by numerically simulating a real storm event with the Regional Atmospheric Modeling System (RAMS) model in a nested-grid setup. During 15-16 April 2003, severe storms moved through northern Texas and Oklahoma, producing severe surface winds, large hail, and 11 tornadoes. The severe weather outbreak followed a major dust event originating from the Chihuahuan Desert, which transported a substantial amount of dust into the region prior to convection. Using sophisticated two-moment microphysics, a dust source and transport module, and allowing dust to realistically act as CCN, GCCN, and IN in the model, we perform an ensemble of simulations to assess possible dust-aerosol influences on the 15-16 April 2003 severe, tornadic storm outbreak. Analyses will focus on dust effects on hydrometeor formation and precipitation, cold-pool evolution, and resulting low-level supercell dynamics.
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