On Rotors, Internal Waves and Hydraulic Jumps in Simulated Stably-Stratified Flows in Utah's Salt Lake Valley

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 the 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. Agreement between simulations and observations was qualitatively good, and usually quantitatively good as well. More flow features were resolved at finer spatial resolutions.

Five one-way nested grids were used to resolve the complex topography and flow features. A coarse ARPS model grid with horizontal spacing of 20 km was initialized by ETA 40-km operational analyses. Model outputs on that grid were input to finer grids with horizontal resolution of 5 km, 1 km, 250 m and 100 m via one-way nesting. The 250-m and 100-m grids have 200 vertically stretched levels up to a height of 20 km. The vertical spacing is 10 m at the surface, and 190 m at the uppermost level.

Our results showed that the stratified flow can be greatly altered by complex terrain. We present results that show that the flow over the Traverse Mountain barrier can induce wave motions in the lee, along with low-level rotor flow that is associated with internal waves and hydraulic jumps. The emphasis of the paper is on these interesting flow features.

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 provided computational time. We gratefully acknowledge Professor Ming Xue and others at the University of Oklahoma for their help.