Large-eddy simulation of stable boundary layers: a case study

Recently, a new-generation tuning-free subgrid-scale (SGS) modeling approach, named "locally averaged scale-dependent dynamic" (LASDD) model, was developed and implemented to perform reliable large-eddy simulation (LES) of stable boundary layers. This model dynamically computes the Smagorinsky coefficient and the subgrid-scale Prandtl number based on the local dynamics of the resolved velocity and temperature fields. In idealized simulations, agreement between the statistics of the LES-generated turbulence and some well-established empirical formulations and theoretical predictions (e.g., the local scaling hypothesis) is remarkable. Moreover, in contrast to previous large-eddy simulations of stable boundary layers that have strong dependence on grid resolution, the simulated statistics obtained with the LASDD SGS model show relatively little resolution dependence.

In the present work, we investigate the capability of the LASDD SGS model in simulating a moderately stratified nocturnal boundary layer observed over the Southern High Plains of western Texas (June 2nd, 2004). During this night, over a period of 8 hours (from 04 to 12 UTC), two distinct low-level jet structures with wind maxima exceeding 16 ms-1 were observed. An extensive array of in-house monitoring systems (consisting of the West Texas Mesonet, a 200 m tall instrumented tower, and a boundary layer profiler) is effectively utilized to study this event in great detail, and to assess the performance of the newly proposed SGS model.