The planetary boundary layer, capped by an inversion: extension to baroclinic and stable conditions

In a series of papers Garratt and Hess have shown that advanced models of the neutral, barotropic planetary boundary layer (PBL) overestimate the height of the PBL and underestimate the cross-isobaric angle over land. This leads to other discrepancies between predictions and observations, such as errors in the profile of the longitudinal stress component. Zilitinkevich and Esau attribute these discrepancies to the presence of a capping inversion, however recently Hess has shown that for flow over land the impact of the capping inversion on the PBL structure is small. In this paper sensitivity tests are carried out to assess the possibility that violations of the assumptions of neutral, barotropic conditions may be responsible. It is found that the effects of stable stratification and baroclinicity can both act to improve the agreement between predictions and observations, but for realistic values considering the effects separately, the impact is too small to give complete agreement. The discrepancies are probably due to a combination of violations of the assumptions of steady, horizontally homogeneous, neutral, barotropic flow. Alternatively, the assumption that the eddy viscosity is a scalar may be invalid. A tensor representation of the eddy viscosity would introduce more degrees of freedom, and allow the longitudinal and lateral components of the eddy viscosity to have different vertical profiles.