青藏高原总体输送系数的特征

CHARACTERISTICS OF BULK TRANSFER COEFFICIENTS OVER THE TIBETAN PLATEAU

利用中日亚洲季风机制合作研究计划设在西藏的 4个自动气象站（AWS）获得的5a多（199年7月～1998年12月）时次密集、观测连续的近地层梯度资料,以最小二乘法确定出相应站点各季节的地表粗糙度,并应用廓线-通量法计算了4站逐日的总体输送系数,分析了其随时间的变化特征。结果表明:青藏高原动量输送系数的多年平均值为3.53×10-3～4.99×10-3,热量输送系数为4.67×10-3～6.73×10-3,并且两种输送系数都存在明显的日变化和季节变化,部分站点还存在较明显的年际变化。另外,还讨论了总体输送系数与近地层大气层结稳定度、地表粗糙度以及地面风速等因子的关系,初步建立了可用常规气象站地面观测资料计算青藏高原总体输送系数的拟合公式。

On the basis of data from four sets of AWS installed in Tibet in the observational period of July 1993 to December 1998, according to PRC-Japan Asian Monsoon Cooperative Research Program, the seasonal surface roughness lengthes in each station are determined by the least square method, and the bulk transfer coefficients each day are estimated by using the profile-flux method. The results show that the five years' mean of the bulk transfer coefficient for momentum and heat is 3. 53×10-3 to 4. 99×10-3 and 4.67×10-3 to 6. 73×10-3, respectively. The diurnal and seasonal variations of the bulk transfer coefficients are obvious. In addition, the relationships between the bulk transfer coefficients, the atmospheric stability in the surface layer, surface roughness length and the surface wind velocity are analyzed. Moreover, a preliminary fitting formula for computing the bulk transfer coefficient of momentum using the routine data is also obtained.