The Coriolis effects in parameterization of atmospheric turbulence and convection

Earth’s rotation can deflect turbulent momentum flux and anisotropy of turbulent kinetic energy. This Coriolis turbulent deflection is usually omitted in parameterization of atmospheric turbulence and convection. However, previous large-eddy simulations (LES) found that the nontraditional Coriolis terms (NCTs) can enhance vertical turbulent activity with prevailing easterly flow and suppress it with westerly flow. To parameterize this effect in the atmosphere, this study introduces the Coriolis terms to the Cloud Layers Unified By Binormals (CLUBB) parameterization of clouds and turbulence. We design three single-column benchmarks to test the implementation of the NCTs in CLUBB. First, assuming that all except the Coriolis terms vanish on the right-hand side of the prognostic equations of the second-order moments of velocity, we derive an analytical solution in which the anisotropy of the moments rotates back to the initial state with a certain period. Our CLUBB results match this analytic benchmark. Second, assuming dry and neutrally stratified atmosphere with constant geostrophic winds, our CLUBB and LES results suggest that the NCTs make the Ekman layer deeper with geostrophic easterlies but shallower with westerlies. Third, under realistic conditions for trade-wind shallow convection, our CLUBB results show that the cloud layer becomes shallower if we omit the NCTs or flip the geostrophic winds from easterly to westerly. These benchmarks not only validate the Coriolis terms in CLUBB but also form a model hierarchy that aids our understanding of the effects of the NCTs on turbulence and convection.