Mixing in Very Stable Conditions

Recent extensive observations of the nocturnal boundary layer, such as taken in CASES99 (Poulos et al., 2001) and SABLE98 (Cuxart et al., 2000), have revealed important deficiencies in our ability to model the strongly stratified nocturnal boundary layer. Even with more or less continuous and relatively strong turbulence near the surface, the primary source of turbulence can be shear above the surface inversion layer (Mahrt, 1999; Mahrt and Vickers, 2002), often related to a low-level wind maximum (Cuxartet al., 2000; Banta et al., 2002, 2003). Consequently for the CASES99 data, mixing formulations with a z – less limit perform better than traditional parameterizations based on a definable boundarylayer depth (Mahrt and Vickers, 2003).