Comparative Effects of Stability, Baroclinity and the Scale-Height Ratio on Drag Laws for the Atmospheric Boundary Layer

Abstract

The effects of baroclinity and the scale-height ratio on the drag laws of the planetary boundary layer (PBL) are examined theoretically and compared to those of stability. The similarity drag relations using surface geostrophic winds are found to be more sensitive to these parameters than the drag relations based on the layer-averaged winds. Since baroclinity can be more safely ignored in the latter, these are considered more suitable for parameterizing the PBL in general circulation models. The geostrophic drag relations based on the generalized similarity theory are used to explain (simulate) the observed increasing trend of the surface cross-isobar angle in going toward the equator. It is shown that this trend is partly due to the change in the scale-height ratio and partly due to baroclinity. Clarke and Mess (1975), on the other hand, have suggested that baroclinity is wholly responsible for this trend. It is shown here that baroclinity effects are very much exaggerated in their formulation.