森林冠层空气动力学参数的确定

Determination of Aerodynamic Parameters of Changbai Mountain ForestLIUHeping LIUShuhua (Department of Geophysics, Peking University, Beijing, 100871)

使用长白山阔叶红松林的风、温、湿梯度资料和超声风温仪测量的湍流资料，计算了长白山森林空气动力学粗糙度Ｚ０，零平面位移ｄ、冠层上动量曳力系数ＣＤ及水热曳力系数ＣＨ，并对ｄ和Ｚ０的计算方法做了误差分析。树高２６ｍ的长白山原始森林空气动力学粗糙度Ｚ０＝１．６ｍ，零平面位移ｄ＝１９．５ｍ。基于质量守恒原理来计算高植被下垫面的动力学粗糙度、零平面位移是目前较为精确和实用的方法。要想得到较精确的ｄ和Ｚ０，必须提高湍流通量ｕ′ｗ′和风廓线的测量精度，并确定合适的测量高度使得ｕ′ｗ′的测量和一点风速的测量在惯性副层内。在不稳定条件下，森林上空动量曳力系数ＣＤ，水热曳力系数ＣＨ与稳定度有较好的关系，近中性的平均代表值约为ＣＤ＝６．６×１０－３，ＣＨ＝６．４×１０－３。引入零平面位移ｄ后。

The aerodynamic roughnees length Z 0 , the zero plane displacement d , the momentum drag coefficient C D, water and heat drag coefficient C H are calculated by using turbulence data and wind, temperature profile data observed in Changbai Mountain forest. The causes of the error in the method of calculating d and Z 0 are also discussed. The method based on the mass conservation principle is a practical one to calculate the aerodynamic roughness lengthandzero plane displacement over tall vegetations. \ \ In Changbai Mountain forest, the roughness length Z 0 is about 1.6±0.25m and the zero plane displacement d is about 19.5±1.38 m. Drag coefficients C D and C H have a good relation with stability under unstable condition, and the average values of C D and C H are 6.6×10 -3 and 6.4×10 -3 in the neutral atmosphere, respectively.