Comparison of the Atmospheric and Oceanic Boundary Layers During Convection and their Latitudinal Dependence

Abstract

The boundary layers of the atmosphere and the ocean are compared during convection, and their latitudinal dependence is investigated. The results are applied to examine the parameterization of the boundary layer depth in the K‐profile parameterization (KPP) model. The bulk Richardson number Rib varies excessively with time in the high‐latitude (HL) oceanic boundary layer (OBL) without unresolved shear Vt2, as a result of inertial oscillation. Inclusion of Vt2 is also necessary in the atmospheric boundary layer (ABL) to mitigate the large variation of Rib with wind stress. Stratification and velocity shear near the boundary layer height/depth are stronger and thicker at low latitudes (LLs), where the Ekman length scale is larger and the inertial time scale is longer. This enhanced shear makes the entrainment buoyancy flux larger at LL. Analysis of the turbulent kinetic energy (TKE) budget in the entrainment zone is carried out to explain the variation of Rib depending on the boundary layer and the latitude. This analysis shows that the TKE production in the entrainment zone is dominated by shear production at LL, but by the TKE flux at HL, and that Vt2 represents the contribution from the TKE flux to the entrainment zone. The enhancement of vertical TKE by Langmuir circulation (LC) does not depend on the latitude, but it decreases with depth faster at LL. The result suggests that the parameterization of the boundary layer depth in the KPP model should be different depending on whether it is the ABL or the OBL and depending on the latitude.