陇中黄土高原半干旱区总体输送系数的特征

Characteristics of Bulk Transfer Coefficients over the Middle-Gansu Semi-Arid Region of Loess Plateau

利用在陇中黄土高原半干旱区2003年10月—2005年7月获得的近地层梯度观测资料,采用空气动力学法,计算了动量和感热总体输送系数。结果表明,陇中黄土高原半干旱区动量和感热总体输送系数均存在明显的日变化特征,夏季中午左右分别达到5.6×10-3和6.7×10-3。受下垫面植被的影响,在一年中呈现出双峰型特征,第一峰值出现在春小麦拔节—黄熟期,次高值出现在10月初。动量和感热总体输送系数平均值分别为2.9×10-3和3.1×10-3。当大气处于不稳定状态时,总体输送系数随着风速的增大而减小;相反当大气处于稳定状态时,随着风速的增大而增大。陇中黄土高原半干旱区的总体输送系数高于戈壁、平原草地和海洋下垫面的值,但低于青藏高原草地和城市下垫面的值。

Based on the gradient data in the near surface layer, which were observed over the middle- Gansu semi-arid region of Loess Plateau from October 2003 to July 2005, the bulk transfer coefficients for momentum and heat are estimated using the aerodynamic method. The results show that bulk transfer coefficients for momentum and heat appear obviously daily variations, and the maximum values are 5.6 ×10^-3 and 6.7 ×10^-3 , respectively around noon in summer. The largest mean values of bulk transfer coefficients occur in milky-ripening period of spring wheat, and the second largest values occur in the early October due to the effect of plants. Mean values of bulk transfer coefficients for momentum and heat are 2.9 ×10^-3 and 3.1 ×10^-3 , respectively during measurements period. Bulk transfer coefficients decrease with increasing wind speeds under unstable atmospheric condition, and increase with decreasing wind speeds un- der stable atmospheric condition. Moreover, bulk transfer coefficients over land surface of Loess Plateau are larger than those over land surface of Gobi, grassland in plain, ocean, and smaller than those over land surface of urban and grassland in Tibetan Plateau.