Exploring the Impact of Baroclinicity and Stability on the Atmospheric Boundary Layer

A barotropic environment arises when density variations are only induced by pressure variations. On the other hand, in a baroclinic environment, density varies due to both pressure and temperature changes. Baroclinicity emerges whenever temperatures in the atmosphere vary on horizontal spatial scales commensurate with those of density and pressure. Such conditions occur quite often especially in mid-latitudes and across land-water or ice-water boundaries. However, despite observational evidence and theoretical support that point to the prevalence of baroclinic conditions, there has been a remarkably limited number of studies examining the impact of such conditions on the atmospheric boundary layer (ABL).

In this talk, we will bridge this gap by investigating the effects of baroclinic pressure gradients on mean and turbulence in the diabatic ABL. Large-eddy simulations were conducted where the direction of the baroclinicity, its strength, as well as the surface buoyancy flux are systematically varied to examine their interacting effects.

The simulations indicated that both weak and strong baroclinicity resulted in large departures from the barotropic cases, but the deviations were amplified by increasing the baroclinicity strength. The turbulent kinetic energy (TKE) budget is also drastically altered by baroclinicity. For example, some of the TKE profiles displayed a positive gradient in the z-direction (an increasing TKE with height). Baroclinicity also modulates the large turbulent structures in unstable ABLs. Furthermore, it increases mean shear rates in the outer ABL and may make the flow more neutral by decreasing the Richardson flux number, given a fixed surface buoyancy flux.