Krishan Chand

Vanderbilt University, November 7, 12:30 pm

Turbulent transport mechanisms in long-lived stable Ekman layers

A long-lived Ekman boundary layer is distinguished from its nocturnal counterpart by the presence of ambient stratification that is independent of surface cooling. We perform direct numerical simulations to investigate the turbulent structure of the stable Ekman boundary layer (SABL) under three distinct stratification regimes: surface cooling-dominated, ambient stratification-dominated, and a balanced regime with comparable contributions from both mechanisms. The results show that dominant ambient stratification induces unstable temperature characteristics that primarily affects the turbulent potential energy, while turbulent kinetic energy remains only weakly impacted. Analysis of the turbulent potential energy budget reveals an additional production term associated with ambient stratification, whereas the term linked to the mean temperature gradient transitions from a source to a sink, behaving more like a transport term. We further identify a three-tiered interaction structure governing energy transport: (1) between the mean flow and second-order statistics, (2) between second-order statistics and the turbulent potential energy budget, and (3) between turbulent kinetic and potential energies via turbulent heat flux, facilitating conservation of total turbulent energy. We also highlight the limitation of constant turbulent Prandtl number from the perspective of large-eddy simulations in long-lived Stable Ekman layer.