Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest
Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest
复制标题
等龄松林粗糙度子层湍流通量的空间变化
DOI：
10.1023/a:1002079602069
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发表时间：
1999
影响因子：
4.3
通讯作者：
R. Oren
中科院分区：
文献类型：
--
作者：
G. Katul;C. Hsieh;D. Bowling;K. Clark;N. Shurpali;A. Turnipseed;J. Albertson;K. Tu;D. Hollinger;Bob Evans;B. Offerle;D. E. Anderson;D. Ellsworth;C. Vogel;R. Oren
对14m(=h)高的火炬松均匀林粗糙度亚层(RSL)湍流统计的空间变异性进行了实验研究。在1997年10月6日至10日期间，利用该站现有的7个步行塔，在离地面15.5米的高度测量了高频速度、温度、水蒸气和二氧化碳浓度。这七座塔之间至少相距100米。这项研究的目的是检验单塔湍流统计测量是否代表了均匀均匀管理的火炬松森林上方RSL湍流的流动特性，作为天然森林生态系统的最佳情景。密集的时空序列测量表明，纵向和垂直速度(σu，σw)和温度(σT)的标准差比垂直动量通量(u*2)和感热(H)的标准差更均匀。此外，与二氧化碳和水蒸气等其他标量实体的通量相比，测得的H在水平方向上更均匀。虽然通量的空间变异性很大(>；15%)，但这一独特的数据集证实了单塔测量代表了单点RSL湍流统计的典型结构，特别是通量-方差关系。讨论了推广RSL流动的“移动平衡”假设的意义。所有RSL流动变量的空间变异性在时间上不是恒定的，并且随空间平均摩擦速度u*变化很大，特别是当u*较小时。结果表明，与单点流量统计相比，由两点时间统计得到的流动特性，如相关函数，对叶面积密度的局部变化更为敏感。根据混合层理论预测的垂直速度积分时间尺度(IW)的倒数与组织结构到达频率(ū/h)之间的局部关系表现出对局部叶面积指数的依赖关系。还讨论了这些发现对RSL流量的测量和建模的更广泛的影响。
The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (σu, σw) and temperature (σT) are more planar homogeneous than their vertical flux of momentum (u*2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the ‘canonical’ structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the ‘moving-equilibrium’ hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (ū/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.