The impact of the Wangara experiment

Abstract

Our understanding of the structure and dynamics of the atmospheric boundary layer (ABL) is often limited by a lack of experimental data. The voluminous amount of high quality data obtained from the Wangara Experiment (Clarke et al., 1971) has contributed greatly to meeting a long-standing need, particularly for data describing the ABL in middle latitudes over land. In the surface layer the measurements provided the basis for determination of the stability dependence of the dimensionless gradients Φ M and Φ H arising out of Monin-Obukhov similarity theory (Hicks, 1976). In the outer layer where the choice of scaling parameters is not unique, the data have been used to determine the stability dependence of the similarity functions A, B, and C, and the most appropriate choices of scaling parameters (e.g., Yamada, 1976). In addition, the experimental data give determinations of some of the fundamental constants of turbulent flow in the ABL, such as the Von Karman constant k = 0.41−0.41 (Hicks, 1969), and the neutral barotropic ABL similarity constants A 0=1.1 and B 0=4.3 (Clarke and Hess, 1974), where the subscript 0 indicates that the surface geostrophic wind was used as reference. Perhaps the greatest impact of the Wangara Experiment has been to provide a data bank which could be used to test numerical simulations of the ABL. This has been useful not only for the newly developed higher-order closure models, but also for one-layer integral models predicting the height of the mixed layer and the height of the nocturnal surface inversion layer. Lastly, the Wangara Experiment has pointed out some of the limitations and difficulties of obtaining accurate measurements of thermal winds, vertical velocity, acceleration terms, and representative spatially averaged fluxes. Microscale turbulence measurements outside the surface layer were not included in the Wangara Experiment and further experiments are needed to determine these statistics.