EKMAN BOUNDARY LAYER DYNAMIC THEORIES

Based on the classical Ekman theory, a series of intermediate Ekman boundary layer models, which retain the nonlinear advective process while discard embellishments, have been developed with the intention to understand the complex nonlinear features of the Ekman boundary layer and its interaction with the free atmosphere. In this paper, the recent advances in the intermediate boundary-layer theoretical models are reviewed. Several intermediate models such as the Ekman-layer models incorporating geostrophic momentum approximation and Ekman momentum approximation, and the weak nonlinear Ekman layer model, and the nonlinear features of the Ekman layer illustrated by these models are a major theme. With inspection of the theoretical frameworks of the above motioned models, the physical meaning and the limitations of each intermediate model are discussed. It is found that the qualitative descriptions of the nonlinear features in Ekmanlayer made by the intermediate models are rather consistent though the details may be different. As the application of the intermediate models is concerned, the works applying the intermediate models to investigate the topographic boundary layer, frontogenesis and low-level frontal structures, and the boundary layer jet are summarized in this article. It is mainly focused on the dynamic characteristics of the Ekman layer and its effect on the low-level structure and circulation of the weather systems illustrated by the models. It is shown that the intermediate boundary-layer models have great potential in illustrating the low level structures of the weather and climate systems as they are coupled with the free atmospheric models. In addition, the important remaining scientific challenges and a prospectus for future research on the Ekman layer are also discussed.