This research investigates the three primary cold pool buildup and destruction mechanisms identified in our earlier research on valley and basin cold pools and temperature inversions in the Rocky Mountains, the Colorado Plateau, and the Columbia Basin. The three mechanisms are: 1) differential temperature advection associated with traveling weather systems, 2) turbulent erosion at the top of the cold pool, and 3) cold pool mass buildup and removal by slope flows on the basin periphery. A bulk thermodynamics model guides the work, provides a mathematical basis for incorporating the mechanisms, and allows generalizations to other topographical situations. We believe that this model, while relatively simple, can be developed further to predict the timing of cold pool destruction and the rate of mass removal from the pool. Data sets from other basins and valleys may be used to generalize findings from the VTMX studies for use in other topographic and climate settings.
The RAMS mesoscale numerical model will also be used along with a Lagrangian particle dispersion code in a series of simulations to investigate mechanisms of cold pool buildup and destruction in idealized basins and for actual topography in the Salt Lake Basin. These simulations will be used to interpret the observations, to verify hypotheses and to provide further insight into physical mechanisms.
Two field studies are proposed for the Salt Lake Basin, one for diurnal cold pools (October 2000) and one for persistent multi-day wintertime cold pools (probably January 2002 or 2003). Both studies are designed with integrated meteorological and tracer study components. The first two inversion buildup and destruction mechanisms mentioned above will be studied using data from VTMX instrument arrays including radar profilers, RASSes, airsondes, radiosondes, and Doppler sodars in both case study and longer-term investigations. The third mechanism of inversion buildup and destruction will be investigated using an array of four tethered balloons and other instruments on an upslope cross section on the lower slopes of the Oquirrh Mountains on the southwest side of the Salt Lake Basin. This experiment site is a uniform low-angle slope that is above the basin inversion in late afternoon and evening but is normally covered by the basin inversion as it grows during the night. Perfluorocarbon tracer experiments will be run on this slope in conjunction with the tethersonde profiles to investigate hypotheses on the roles of up- and down-slope flows and boundary layer growth on cold pool evolution. Coupled mesoscale dynamics and Lagrangian particle dispersion models will be used to interpret the observations, verify hypotheses, and provide further insight into physical mechanisms.
The research is designed to lead to useful advances in knowledge of air pollution transport and diffusion in urban basins and valleys and in the ability to forecast cold pool buildup and breakup cycles. The persistent wintertime cold pool is identified as leading to particularly severe air pollution events in the western United States.
We invite other investigators to participate in our proposed research. We are especially interested in collaborations that would add instrumentation, insight, physical models, or numerical models to our planned investigations of boundary layer processes over the slopes during the morning and evening transition periods.
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