Baroclinicity and directional shear explain departures from the logarithmic wind profile*

Similarity and scaling arguments underlying the existence of a logarithmic wind profile in the atmospheric surface layer (ASL) invoke two simplistic assumptions of negligible Coriolis effects (no wind turning) and vertically-uniform pressure gradients (barotropic PBL). In this talk, we relax these oversimplifications to provide a more realistic representation of the ASL where the common occurrence of baroclinicity (height-dependent pressure gradients) and wind turning, traditionally treated as outer-layer phenomena, are accounted for in the ASL. The constant-stress ASL assumption is first replaced by a model for the Reynolds stress derived from the mean momentum equations to incorporate the cross-isobaric angle (directional shear) and a dimensionless baroclinicity parameter (geostrophic shear). This results in a model for the wind profile, obtained from first-order closure principles, correcting the log-law with an additive term that is linear in height and accounts for the combined effects of wind turning and baroclinicity. Both the stress and wind models agree well with a suite of large-eddy simulations in the barotropic and baroclinic ABL. The talk concludes with the potential applications and further developments of the model.