Testing the HBG model under strong stabilities: a SCM inter-comparison study using CCAM

The difficulty in simulating and modeling the stable Atmospheric Boundary-Layer (ABL) increases with stability. The GABLS-4 project is designed to address this challenge and study the ABL under strong stability (Ri>>1) through a series of inter-comparison studies of Land Surface Models (LSM), Single Column Models (SCM) and Large Eddy Simulations (LES). We have participated in the SCM inter-comparison of GALS-4 using the CSIRO's Cubic Conformal Atmospheric Model (CCAM). Three ABL parameterization schemes for stable conditions have been tested for this study: (1) the HBG model (Ri-based) proposed in Huang et al. (2013), (2) the Louis (1979) scheme and (3) a prognostic k-epsilon approach. The main difference of the HBG model from other Ri-based schemes is that the mixing length under stable conditions is not a corrected form based on its formulation under neutral conditions. Instead, the mixing length in the HBG model depends on Ri only under strongly stable conditions. In this talk, we will present how the HBG model is derived and parameterized based on a suite of LES runs under moderate and intermediate stabilities (Ri<=). Then, the performance of the HBG model in CCAM will be tested, and compared with other well-known turbulence closure schemes as well as with observation under strong stabilities.