Parameterization of sheared entrainment in a well-developed CBL. Part II: A simple model for predicting the growth rate of the CBL
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- 作者：Peng Liu ; Jianning Sun ; Lidu Shen
- 关键词：sheared convective boundary layer ; relative stratification parameter ; entrainment rate ; entrainment flux ratio ; convective velocity scale
- 刊名：Advances in Atmospheric Sciences
- 出版年：2016
- 出版时间：October 2016
- 年：2016
- 卷：33
- 期：10
- 页码：1185-1198
- 全文大小：621 KB
- 刊物主题：Atmospheric Sciences; Meteorology; Geophysics/Geodesy;
- 出版者：Springer Berlin Heidelberg
- ISSN：1861-9533
- 卷排序：33
文摘
Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model for predicting the growth rate of a well-developed and sheared CBL. The relative stratification, defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone, is found to be a function of entrainment flux ratio (Ae). This leads to a simple expression of the entrainment rate, in which Ae needs to be parameterized. According to the results in Liu et al. (2016), Ae can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL. The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations. Results indicate that the entrainment process is influenced by the dynamic effect, the interaction between mean shear and environmental stratification, and one other term that includes the Coriolis effect. These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL. This model is validated by outputs of LESs, and the results show that it performs satisfactorily. Compared with bulk models, this model does not need to solve a set of equations for the CBL. It is more convenient to apply in numerical models.