藏南羊卓雍错湖面大气湍流特征观测分析

Observation of atmospheric turbulence characteristics over the Yamzhog Yumco,south Tibet

湍流运动是大气边界层的本质特征,是地表与大气之间能量和物质交换的主要方式.本文利用2016和2017年4-10月藏南羊卓雍错湖泊涡动观测资料,分析了湖面大气湍流方差和湍流特征量的统计和变化特征.结果表明:(1)不稳定层结下,三维风速分量和超声虚温、水汽密度、CO2密度的无量纲标准差随稳定度变化符合Monin-Obukhov相似理论的"1/3"或"-1/3"次幂律,垂直风速的拟合效果最好;稳定层结下,除CO2密度无量纲标准差与稳定度无明显关系外,其他量基本上满足相似性规律;中性条件下,以上物理量的无量纲标准差分别趋近常数:3.57、3.93、0.77、20.91、6.35和11.96.(2)水平方向平均湍流强度(0.60和0.58)大于垂直方向(0.13),三维方向湍流强度与平均风速的变化呈显著负相关,相关系数分别为-0.39、-0.42和-0.34.(3)湖面湍流动能随风速呈线性增长,增长率达0.45 m/s;近中性层结时湍流动能最大,层结越稳定或不稳定湍流动能均减小.(4)湖泊下午到傍晚动量输送较强,13:00-22:30时间段平均动量通量达0.091 kg/(m·s2);热量输送以潜热为主,潜热通量日平均值(77.3 W/m^2)是感热通量(14.6 W/m^2)的5.3倍,感热和潜热通量日变化峰值分别出现在5:30(22.4 W/m^2)和16:00(106.6 W/m^2).

Turbulent motion is the essential characteristic of atmospheric boundary layer,as well as the main pathway of atmospheric energy and mass transfer.The atmospheric turbulent variance and characteristic quantities are investigated over the Yamzhog Yumco based on eddy covariance data during April-October 2016 and 2017.The main results are summarized as follows.(1)The dimensionless standard deviations of velocity components,sonic temperature,vapor density,and CO 2 density varying with stability follow the law of"1/3"or"-1/3"fractional power of Monin-Obukhov Similarity Theory in unstable stratification,and the fitting effect of vertical speed is optimal.The dimensionless standard deviations of all physical quantities except CO 2 density,versus stability are also in agreement with the fractional power law in stable stratification.Under the near neutral stratification,these dimensionless standard deviations reach constants:3.57,3.93,0.77,20.91,6.35 and 11.96,respectively.(2)The horizontal turbulent intensities(on average,0.60 and 0.58)are larger than vertical turbulent intensity(0.13),and the variations of three-dimensional turbulent intensities with average wind speed show significant negative correlation with the coefficients of-0.39,-0.42 and-0.34,respectively.(3)Turbulent kinetic energy increases with wind speed with the rate of 0.45 m/s,and it displays stronger in near neutral stratification,while decreases when the atmosphere becomes stable or unstable.(4)Momentum flux is large during 13:00-22:30 with the average of 0.091 kg/(m·s^2).Latent heat flux,5.3 times higher than sensible heat flux with daily average value(14.6 W/m^2),plays a leading role in heat transportation.Sensible and latent heat flux reach maximum value at 5:30(22.4 W/m^2)and 16:00(106.6 W/m^2),respectively.