青藏高原高寒草甸的空气动力学粗糙度特征

The Characteristics of Aerodynamic Aoughness Length of Alpine Meadows on the Qinghai-Tibet Plateau

为认识高寒草甸下垫面的空气动力学粗糙度特征,利用阿柔冻融站的夏季观测资料,通过两种方法计算青藏高原高寒草甸的空气动力学粗糙度,并分析空气动力学粗糙度的日演变特征,探讨空气动力学粗糙度与大气动力因素之间的关系。结果显示,阿柔高寒草甸的夏季平均动力学粗糙度为0.026 m,白天和夜间的动力学粗糙度分别为0.033 m、0.019 m。从平均的日演变看,动力学粗糙度表现出明显的单峰型演变特征,峰值出现在中午至下午时段,这与大气动力特征的日变化密切相关。其次,动力学粗糙度线性相关于摩擦速度u,但两者的相关性受到风速u的影响,u越大则两者的线性关系越强,并且两者的拟合关系在高风速区间(3~6 m/s)保持较高的稳定性。而标准化变量u/u与动力学粗糙度之间存在负指数拟合关系,u/u与动力学粗糙度的关系相比于u或u更加稳定,并且u/u解释了空气动力学粗糙度60%左右的变化,可用于空气动力学粗糙度的参数化研究。

In order to understand the characteristics of aerodynamic roughness length of the underlying surface of alpine meadow,this paper uses two methods to calculate the aerodynamic roughness length of the Alpine Meadow over the Qinghai-Tibet Plateau based on the summer observations from the Arou freezing-thawing observation site.The diurnal evolution characteristic of aerodynamic roughness length is analyzed and the relationships are explored between aerodynamic roughness length and atmospheric dynamic factors.The results show that the summer average aerodynamic roughness length of Arou Alpine Meadow is 0.026 m,and the average values for daytime and night are 0.033 m and 0.019 m,respectively.In terms of the average diurnal evolution,the aerodynamic roughness length shows obvious unimodal characteristic,with the peak appearing during the noon and afternoon,which is closely related to the diurnal variation of atmospheric dynamics.Secondly,the correlation between aerodynamic roughness length and friction speed uis related to wind speed u.The larger the u is,the stronger the linear relationship between the two is,and the fitting relationship between the two is stable in the higher wind speed range(3-6 m/s).But the standardized variable u/uis negative exponentially related to aerodynamic roughness length,and the relationship between u/uand dynamic roughness is more stable than u or u,u/ucan explain about 60% of the change in aerodynamic roughness length,and can be used for parameterization.