HR: 0830h
AN: A31C-0048    [PDF]
TI: Hydraulic Jumps, Waves and Other Flow Features Found by Modeling Stably-Stratified Flows in the Salt Lake Valley
AU: * Chen, Y
EM: yingchen@stanford.edu
AF: Stanford University, Environmental Fluid Mechanics Laboratory, Stanford, CA 94305-4020 United States
AU: Ludwig, F
EM: fludwig@stanford.edu
AF: Stanford University, Environmental Fluid Mechanics Laboratory, Stanford, CA 94305-4020 United States
AU: Street, R
EM: street@stanford.edu
AF: Stanford University, Environmental Fluid Mechanics Laboratory, Stanford, CA 94305-4020 United States
AB: The Advanced Regional Prediction System (ARPS) was used to simulate weak synoptic wind conditions with stable stratification and pronounced drainage flow at night in the vicinity of the Jordan Narrows at the south end of Salt Lake Valley. The simulations showed the flow to be quite complex with hydraulic jumps and internal waves that make it essential to use a complete treatment of the fluid dynamics. Six one-way nested grids were used to resolve the topography; they ranged from 20-km grid spacing, initialized by ETA 40-km operational analyses down to 250-m horizontal resolution and 200 vertically stretched levels to a height of 20 km, beginning with a 10-m cell at the surface. Most of the features of interest resulted from interactions with local terrain features, so that little was lost by using one-way nesting. Canyon, gap, and over-terrain flows have a large effect on mixing and vertical transport, especially in the regions where hydraulic jumps are likely. Our results also showed that the effect of spatial resolution on simulation performance is profound. The horizontal resolution must be such that the smallest features that are likely to have important impact on the flow are spanned by at least a few grid points. Thus, the 250 m minimum resolution of this study is appropriate for treating the effects of features of about 1 km or greater extent. To be consistent, the vertical cell dimension must resolve the same terrain features resolved by the horizontal grid. These simulations show that many of the interesting flow features produce observable wind and temperature gradients at or near the surface. Accordingly, some relatively simple field measurements might be made to confirm that the mixing phenomena that were simulated actually take place in the real atmosphere, which would be very valuable for planning large, expensive field campaigns. The work was supported by the Atmospheric Sciences Program, Office of Biological and Environmental Research, U.S. Department of Energy. The National Energy Research Scientific Computing Center (NERSC) provided computational time. We thank Professor Ming Xue and others at the University of Oklahoma for their help.
DE: 0399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting