复杂地形条件下零平面位移和空气动力学粗糙度的计算——以珠海南亚热带常绿阔叶林地区为例

THE CALCULATION OF ZERO-PLANE DISPLACEMENT AND AERODYNAMIC ROUGHNESS LENGTH OF HETEROGENEOUS TERRAIN——With the Evergreen Broad-Leaf Forest in Zhuhai as an Example

空气动力学粗糙度和零平面位移是影响陆面过程的重要参数。以往对空气动力学粗糙度和零平面位移的计算往往针对均一程度较高的下垫面。以珠海南亚热带常绿阔叶林地区为例,探索了复杂地形下垫面空气动力学粗糙度和零平面位移的计算。用拟合法和粗糙元法计算了该地区下垫面的空气动力学粗糙度和零平面位移,并分析了两种方法的误差来源。计算结果表明,拟合法在这种复杂地形下的计算准确度并不理想,由于这种方法的代表范围较小,易受到周边地形影响而使测量结果不符合对数廓线的形式,从而得不到准确的结果。与拟合法相比,粗糙元法可以给出所计算下垫面的具体范围。粗糙元法计算结果的代表范围比拟合法大得多,因此,粗糙元法比拟合法更加能够反映的是该区域下垫面空气动力学粗糙度和零平面位移的总体情况。另外,粗糙元法可以计算那些因为风速资料不足无法用风速廓线直接加以计算的区域的空气动力学粗糙度和零平面位移。根据拟合法的计算结果,冬季315-45°范围内,z0=2.96m,d=22.48m;45-135°范围内,z0=1.26m,d=8.81m。春夏季315-45°范围内,z0=3.90m,d=27.00m;45-135°范围内,z0=1.51m,d=14.83m。根据粗糙元法的计算结果,东南西北四个方向1km×1km范围内z0分别为0.94m、1.28m、1.30m、2.08m;d分别为13.87m、18.79m、19.12m、30.61m。

Aerodynamic roughness length and zero-plane displacement are important parameters to influence on the land process. Most calculation before is only proper for the homogeneous underlying surface. The paper try to find a method to calculate the aerodynamic roughness length and the zero-plane displacement of heterogeneous underlying surface in the evergreen broad-leaf forest in Zhuhai. In the paper, we calculate the aerodynamic roughness length and the zero-plane displacement of the region with fitting method and roughness element method and analyze the error source of them. The results indicate ： the fitting method is not very accurate to the het- erogeneous region. Because the calculation with the method can only reflect a small range and the wind speed is easy to be influenced by the surrounding terrain, which lead the wind speed not satisfy the logarithmic profile, we may not get the accurate result. Compared to the fitting method, roughness element method can give a clear region where the result is calculated. The range reflected by roughness element method can be much larger than fitting method. So the method reflect the general condition better than fitting method. Moreover, the roughness element method can be used in the region lack of wind speed data. The calculation with the fitting method show that z0 =2. 96 m, d =22.48 m in 315 -45° range in winter; z0 = 1.26 m, d =8.81 m in 45 - 135° range in winter, z0 =3.90 m, d=27.00 m in 315 -45° range in summer; z0 = 1.51 m, d = 14. 83 m in 45 - 135° range in summer. The calculation with the roughness element method show that the values of z0 are 0. 94 m, 1.28 m, 1.30 m, 2.08 m and the values of d are 13.87 In, 18.79 m, 19. 12 m, 30.61 m in the east, west, south, north in 1 km × 1 km range.