人工林冠层的湍流微气象特征

Turbulence micro-meteorological characteristics over the plantation canopy

利用涡动相关系统测定黄河小浪底森林生态系统定位研究站人工林在萌芽期(2015年3月15日至4月15日,春季)和叶片成型期(2015年7月15日至8月15日,夏季)的微气象数据,分析了冠层湍流微气象特征、湍流强度、湍流风速标准差和总体输送系数,旨在深入了解森林生态系统的微气象特征,为进一步研究能量平衡与物质交换提供工作基础.结果表明:冠层湍流谱在低频部分具有峰值频率,惯性副区具有明显的耗散趋势,基本符合-5/3规律.冠层结构对湍流强度影响明显,春季湍流旺盛时,风速小于3 m·s^(-1),而夏季时风速小于2m·s^(-1).湍流风速标准差符合1/3次幂相似规律,且水平方向比垂直方向的拟合效果好.冠层风速在u、v、w 3个方向分量的风速标准差与摩擦风速比值在春季为2.55、2.06和1.30,在夏季为2.61、2.45和1.21.总体输送系数随稳定度的增加而逐渐减小,在不稳定层结和稳定层结条件下可相差1~2个量级,冠层结构对各方向的湍流风速具有直接影响,从而改变物质能量在冠层的扩散方向.

Based on the eddy-covariance system monitoring during leaf germination（15^th March to 15^th April 2015） and leaf forming（15^th July to15^th August）,the turbulence characteristics,turbulence intensity,normalized standard variance of turbulent wind speed and bulk transfer coefficient over forest plantation canopy in the Xiaolangdi Ecosystem Location Research Station were analyzed,aiming to deepen the understanding of the micro-meteorological characteristics of the forest ecosystem and provide scientific basis for the further studies of energy balance and material exchange.Results showed that turbulence spectrum of the plantation had a peak frequency in the low frequency zone and the inertial subarea had an obvious dissipation tendency,which was basically in accordance with the law of-5/3. Turbulence intensity was significantly affected by canopy structure.When the turbulence was strong,the wind speed was less than 3 m·s^-1 in spring and less than 2 m·s^-1 in summer. Normalized standard variance of turbulent wind speed in horizontal direction was better than that in vertical direction,which conformed to the similarity law of 1/3 power. The ratio of normalized standard deviation and the friction velocity in u,v,w components of canopy wind speed was 2.55,2.06 and 1.30 in spring,2.61,2.45 and 1.21 in summer,respectively. The bulk transfer coefficient decreased with the increases of stability,with a difference of 1-2 orders of magnitude or more between unstable and stable conditions. Canopy structure had direct influence on the turbulence of the wind speed in each direction,and thereby changed the diffusion direction of the canopy material and energy.