Mixing Processes in a Nocturnal Low-Level Jet: An LES Study

Abstract

A steady-state low-level jet observed in the Stable Atmospheric Boundary Layer Experiment in Spain-1998 (SABLES-98) campaign is simulated using a large-eddy simulation model. The radiation is taken into account since its contribution to the budget of the tendency of temperature is as important as the contribution of the turbulence in the surface layer. The resulting regime is a two-layer flow separated by a change of the temperature gradient at the level of maximum speed. The upper part has turbulence originated by shear production extending up to 3 times the height of wind maximum and of the same order of magnitude as in the layer below. The jet nose is seen by the model as a decoupling layer, and the use of passive scalars allows for the inspection of the amount of transport across it, which is very small. The lower layer is very sensitive to the surface boundary conditions, but the principal patterns in the upper layer do not change significantly. The runs are compared to the observations through mean profiles, time series, and probability density functions.