中尺度模式中的边界层特征量分析

Characteristic Quantity Analyese of Boundary Layer from Mesoscale Model

在中尺度数值天气预报模式ＭＭ４中， 用ｌｅｖｅｌ ３及Ｅ－ε－ｌ两种湍流闭合方法对原总体边界层参数化方案进行改进， 使得中尺度模式中可以直接输出有关湍流量， 并对地表通量参数化方案进行改进， 进而对不同下垫面如沙漠、 植被上的有关湍流量和边界层特征量进行分析， 研究中尺度系统中边界层结构的特征。本文主要从地表通量、 湍流交换系数、 湍流动能（ｑ２）、 温度脉动方差（ ２）及风温廓线等几个方面进行研究， 结果表明， 新方案能更好地反映边界层特征。

In mesoscale numerical weather predictionmodel (MM4), original bulk boundary layer parameterizations was improved by two turbulence closure schemes level 3 and %E－ε－ l%, so as to straightly output turbulence quantities in the mesoscale model. At the same time surface flux algorithm was also improved. Furthermore, we analyze turbulence quantities and boundary layer characteristic quantities on different underlying surfaces and study boundary layer structure characteristics in the mesoscale system. In this paper, we study surface flux, turbulence exchange coefficient, turbulent kinetic energy(q2), temperature fluctuation deviation( 2) and profiles of velocity and temperature. The results show that improved schemes can reflect characteristics of boundary layer well. For example, the sensible heat flux and the height of PBL have significant diurnal variation for various surfaces; the sensible heat flux over desert usually is larger than that over vegetation; the spatial and temporal variations of the eddy exchange coefficient are more close to the general law than original PBL scheme; usually the eddy kinetic energy increases with height near the surface, then decreases with height after the maximum value, is reached for unstable stratification but deceases with height monotonically for stable stratification the dissipation rate of the eddy kinetic energy and the variance of the fluctuating potential temperature usually decrease with height.