A popular means of turbulence closure in the geophysical fluid dynamics community is the Level 2.5 model of Mellor and Yamada (1982, hereafter MY82). Although the MY82 model has shown skill in a wide range of geophysical applications, its representation of pressure redistribution is relatively low order and as such is not generally used by the engineering community. Secondly, the determination of closure constants in the MY82 model is based on data measured in surface layers, whose conditions are not representative of the breadth experienced in the temporal and spatial evolution of many geophysical flows. An example of such a condition is one in which turbulence is detached from a lower level boundary layer, common in the nocturnal residual layer and in the marine atmospheric boundary layer. The apparent inconsistency between the above mentioned skill of the MY82 model and possible inaccuracies associated with its pressure redistribution parameterization and closure constant determination warrants a more detailed investigation into the subject than has been presented to this point.
The proposed conference report will present comparisons of Level 2.5 model solutions produced using the MY82, Isotropization of Production, and Launder, Reece & Rodi (1975) parameterizations for pressure redistribution. Comparisons will be made using different sets of closure constants to isolate the effect of the pressure redistribution parameterization. Results will be presented in non-dimensional form as contours of stability parameters SM and SH versus non-dimensional shear GM and stratification GH, similar to Fig. 3 in MY82. Guided by these non-dimensional behaviors, comparisons will be made of mean and turbulent structures within the atmospheric boundary layer predicted by the three models. Special attention will be paid to predictions of detached layers of atmospheric turbulence, guided by observations of Tjernstrom (1993)