The Cooperative Atmosphere-Surface Exchange Study field campaign, conducted near Wichita, Kansas, in October 1999 (CASES99) has provided a new data bank for boundary layer studies. In CASES99, the 60 m main tower was surrounded by a dozen smaller towers within a radius of 2 km, including five towers from the Army Research Laboratory (ARL). Although the field campaign was conducted over relatively flat terrain, the wind data from those tower measurements often show significant micro-scale wind heterogeneity. For example, the 30 minute mean surface winds can differ by 45 degrees in wind direction and by 50% in wind speed within a distance of several hundred meters. Such micro-scale wind heterogeneity is thought to be due primarily to local terrain effects.

A high resolution wind (HRW) model has been developed at ARL. This model is a two-dimensional, diagnostic atmospheric surface-layer model with a horizontal grid spacing of the order of 100 m over a domain about 5 by 5 km. It uses Gauss’ principle of least constraint and a direct variational relaxation method to adjust an initially uniform wind field to conform to constraints imposed by topography, mass conservation, and buoyancy forces. Using the CASES99 data, critical comparisons between the measured and the modeled winds have been carried out. The results of this study are presented, indicating how well the HRW model can explain such micro-scale wind heterogeneity as well as the limitations of the model.