11.8
Toward large-eddy simulations of strongly-stratified atmospheric boundary layers
Branko Kosovic, University of Colorado, Boulder, CO; and G. Poulos
An important application of large-eddy simulations (LES) is in development and improvement of atmospheric boundary layer (ABL) parameterizations used in large-scale models. While LES has been successfully used for studies of convective and weakly stable ABLs, a reliable LES of strongly-stratified ABLs has not been accomplished yet.
We use observations from the intense observational period (IOP) No. 9 during CASES99 experiment to initialize, and validate the results of our LES. IOP No. 9 corresponds to a clear-air, stably-stratified boundary layer (SBL) characterized by relatively weak flow conditions and moderate stability. This case was chosen because of relatively steady mesoscale conditions, and clearly defined features of a nocturnal ABL. Over the night a surface inversion of about 9C developed as well as a low level jet at 200m above the surface which reached maximum wind speed of 15 m/s.
We conduct a high-resolution, long-term LES of SBL that spans the entire night of the IOP. The numerical simulation domain is sufficiently large and the computational grid sufficiently fine to simultaneously resolve small-scale turbulence and internal gravity waves. Special attention is given to accurately representing interactions between gravity waves and shear associated with low-level jets and the conditions under which global intermittence occurs. The hypothesis that the failure of different models to capture global intermittence arise from their inability to account for nonlinear effects such as breaking gravity waves and Kelvin-Helmholtz billows is tested. We identify accurate modeling of subgrid dissipation and surface layer parameterizaton as possible obstacles on the path toward successful simulations of strongly stratified ABL characterized by global intermittence.
Session 11, Stable BLs - II
Thursday, 18 July 2002, 10:30 AM-12:30 PM
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