森林冠层湍流结构的特征研究

Turbulence Structure Characteristics within and above Changbai Mountain Forest

使用长白山森林冠层上下得到的湍流及风、温、湿梯度资料，对长白山森林冠层的湍流结构作了较为详细的分析。结果表明，冠层内的风速分布遵循指数规律Ｕ（Ｚ）／Ｕ（ｈ）＝ｅｘｐ［α１（Ｚ／ｈ－１）］，且α１＝２．０５；冠层内的动量交换系数满足指数律：Ｋｍ（Ｚ）／Ｋｍ（ｈ）＝ｅｘｐ［α２（Ｚ／ｈ－１）］，且α２＝５．２；冠层上Ｚ／ｈ＝１．２３处，σｗ／Ｕ＊，σθ／θ＊与稳定度有很好的相关性；冠层上纵向湍流强度ｉｗ明显小于水平方向ｉｕ，ｉｖ，冠层内，由于大的叶面面积指数（ＬＡＩ），以及树冠、地面、树干的共同作用，使得ｉｕ，ｉｖ，ｉｗ十分接近且明显大于冠层上的值。冠层上下的惯性区湍流谱仍可用幂指数律描述，但斜率偏离－２／３方律，尤其在冠层内更为明显，谱曲线出现双峰现象，从资料及局地各向同性分析，冠层下的湍流并不遵从局地各向同性假设和Ｔａｙｌｏｒ冰冻假设。

Turbulence data and wind, temperature profile data are used to analyze turbulence structure within and above Changbai Mountain Forest. The normalized wind profiles within Changbai Mountain Forest is considered to be exponential: U(Z)/U(h) = exp [α 1(Z/h-1)] , where α 1 =2.05. The normalized momentum exchange coefficient within the canopy is proved to be exponential: K m(Z)/K m(h)= exp [α 2(Z/h-1)] , where α 2=5.2. Above the canopy the dimensionless standard deviations σ w/ U * and σ θ / θ * are strongly releated with stability. Above the canopy, the longitudinal and lateral turbulence intersity i u, i v have almost the same value but the vertical turbulence intensity i w is smaller than i u, i v because of the influence of the canopy. Within the canopy, i u, i v, i w are similar in magnitude but larger than those above the canopy because of the big LAI and the influence of the canopy, the ground and the trunk. The spectral densities of the velocity components in the inertial subrange still can be described by the way in the flat terrain but the slopes show that they are significantly more negative than -2/3 expecially within the canopy. In addition, the second peak of the spectrum within the canopy occurs and may be caused by wake turbulence generation. From the data and the locally isotropic analysis, Taylor′s frozen eddy hypothesis and locally isotropy are invalid within the canopy.