Effects of thermal winds on the structure and similarity of the atmospheric surface layer

Atmospheric surface layer (ASL) flows are often modeled as an analogue to the inertial region of wall flows, where Townsend’s attached eddy model predicts that the distance from the wall and friction velocity are the proper length/velocity scales for the active motion. Monin-Obukhov Similarity Theory (MOST) accounts for the effects of stratification through stability correction functions. However, field experiments have shown contradicting results regarding the similarity and scaling laws predicted by these theories. The work here examines the effects of thermal winds (geostrophic shear/baroclinicity) on ASL flows as a possible cause for such departures. A suite of large eddy simulations spanning a range of stability conditions, and strength and rotation of the height-dependent geostrophic velocity vector was designed to explore how baroclinicity modifies the local shear production in the ASL, leading to increased importance of turbulent and pressure transport, and hence stronger coupling with the outer-layer eddies. The mechanisms behind such changes are explored through the budgets of velocity and temperature variances, covariances, and heat fluxes to understand how turbulence is modified and to explain closure problems in field experiments and climate models.