Boundary layer effects on frontal interaction with topography
Powell, John H.
Williams, R. Terry
Peng, Melinda S.
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A hydrostatic, primitive equation model with frontogenetical deformation forcing is used to simulate the passage of cold fronts over a two-dimensional ridge. The model includes a K-theory planetary boundary layer (PBL) parameterization with implicitly defined diffusion coefficients. Numerical simulations are performed for synoptic-scale ridges of varying widths both with and without frontal forcing. These results are compared to simulations that do not include a PBL parameterization, similar to previous inviscid studies by Williams et al. Relative to the inviscid results, the PBL simulations produced reduced frontolysis on the upwind slope and reduced frontogenesis on the lee slope, resulting in significantly smaller frontogenetic variations over the mountain. This is caused by convergence forcing in the well-mixed layer offsetting the overall frontolytical forcing on the upwind slope, and greatly reduced lee side convergence forcing due to the PBL. In contrast to the inviscid results, the final downstream front is weaker in the mountain simulations than in the flat-topography control case when PBL effects are included. In all PBL simulations, gravity wave generation is greatly reduced and no lee side hydraulic jumps are observed. In general, the inclusion of a PBL into the model results in more realistic wind and temperature fields compared to the inviscid model simulations
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