Baroclinicity in stable atmospheric boundary layers: Characterizing turbulence structures and collapsing wind profiles via reduced models and large-eddy simulations

Baroclinicity is a common, while often overlooked, phenomenon in the atmospheric boundary layer (ABL) that significantly impacts mean wind and turbulence structures. It adds another layer of complexity to the much-studied stable barotropic ABLs by modulating the pressure gradient in height. Despite the prevalence of baroclinic and stable conditions in nature, our knowledge of their interacting effects on stratified ABL features is limited. The article aims to bridge this knowledge gap by systematically varying baroclinicity and stability using the large-eddy simulation (LES) technique. The results of 15 conducted LESs indicate that baroclinicity alters the Ekman spiral shape and the low-level jet's height in stable ABLs. Friction velocity, Obukhov length, shear production and the ABL height are highly influenced by baroclinicity in weakly stable ABLs, whereas they converge to a constant asymptote as the stability increases, independent of the baroclinicity regime. This is attributed to the strong turbulence destruction in very stable ABLs that decouples the surface from higher elevations where the baroclinicity effect is more significant. A reduced model for baroclinic wind profiles is developed and an analytical estimation of that for weakly baroclinic regimes is tested against LES results. Two rescaling methods in the inner and outer layers of stable baroclinic ABLs are used in a novel way to non-dimensionalize the wind profiles. The suggested approaches reasonably collapse baroclinic/barotropic stable wind profiles in all considered LES cases. This study's findings elucidate the underlying physics of baroclinic stable ABLs and are useful for characterizing the wind profiles in weather/climate models, field measurements, and various industrial applications.