Abstract/Wyngaard ATM-9704740 Large-eddy simulation (LES) has become t he modeling method of choice in micrometeorological research. Nonetheless its performance in the surface layer suffers because of inadequate numerical resolution and heavy reliance on the precision of the subgrid-scale (SGS) model there. Until recently, little attention has been focused on these deficiencies in the surface layer, probably for two reasons. First, experimental limitations make it difficult to produce data for thorough testing of LES. No direct measurements of the resolvable-scale fields that LES predicts have been reported, for example. Second, the weaknesses of the traditional SGS models in the surface layer have not been documented in much detail. Measurements of resolvable- and subgrid-scale atmospheric turbulence in the atmospheric surface layer for the purpose of testing and improving SGS closures for LES are proposed here. Recent studies indicate major weaknesses of the widely used Smagorinsky SGS model near the surface. A new experimental technique is proposed whereby a lateral array of sensors is used to measure two-dimensionally filtered turbulence variables in the atmospheric surface layer. The preliminary studies presented here, which demonstrate the potential of the technique, will be extended in the proposed studies. Resolvable and SGS variables will be measured in the surface layer over a range of ABL states, from nearly neutral to highly convective, and shall be analyzed to study resolvable and subgrid-scale dynamics in detail. The resulting data and new physical insight will be coupled with parallel program using direct numerical simulation and LES data to provide the necessary impetus for the development of improved SGS models for surface-layer turbulence. The proposed program is part of a coordinated effort in a multi- disciplinary research group at the Penn State University directed at analysis and improvement of SGS modeling through combined numerical simulation and field measurement. The present studies will provide benchmark data for the development of remote sensing techniques for the measurement of filtered turbulence in the surface layer.
