The Step-Mountain Eta Coordinate Model: Further Developments of the Convection, Viscous Sublayer, and Turbulence Closure Schemes

作者：Zavisă Janjić · 发表于：Monthly Weather Review · 年份：1994 · DOI：10.1175/1520-0493(1994)122<0927:tsmecm>2.0.co;2 · 被引用次数：3487 · 研究领域：Meteorological Phenomena and Simulations、Tropical and Extratropical Cyclones Research、Climate variability and models

The step-mountain eta model has shown a surprising skill in forecasting severe storms. Much of the credit for this should be given to the Betts and Miller (hereafter referred to as BM) convection scheme and the Mellor-Yamada (hereafter referred to as MY) planetary boundary layer (PBL) formulation. However, the eta model was occasionally producing heavy spurious precipitation over warm water, as well as widely spread light precipitation over oceans. In addition, the convective forcing, particularly the shallow one, could lead to negative entropy changes. As the possible causes of the problems, the convection scheme, the processes at the air-water interface, and the MY level 2 and level 2.5 PBL schemes were reexamined. A major revision of the BM scheme was made, a new marine viscous sublayer scheme was designed, and the MY schemes were retuned. The deep convective regimes are postulated to be characterized by a parameter called “cloud efficiency.” The relaxation time is extended for low cloud efficiencies and vice versa. It is also postulated that there is a range of reference equilibrium states. The specific reference state is chosen depending on the cloud efficiency. The treatment of the shallow cloud tops was modified, and the shallow reference humidity profiles are specified requiring that the entropy change be nonnegative. Over the oceans there are two layers: (a) a viscous sublayer with the vertical transports determined by the molecular diffusion, and (b) a layer above i...