Turbulent transport of carbon dioxide and water vapor within a vegetation canopy during unstable conditions: Identification of episodes using wavelet analysis
Turbulent transport of carbon dioxide and water vapor within a vegetation canopy during unstable conditions: Identification of episodes using wavelet analysis
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不稳定条件下植被冠层内二氧化碳和水蒸气的湍流输送：使用小波分析识别事件
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
J. Albertson
中科院分区：
文献类型：
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作者：
T. Scanlon;J. Albertson
生物圈和大气之间的二氧化碳净交换是通过光合作用和呼吸作用相关的通量之间的差异来实现的。本文对比了影响这种交换的两条主要路径的湍流输运机制。利用在北卡罗来纳州杜克森林进行的一项实验的高频测量，将小波分析应用于二氧化碳和水汽浓度的时间序列，以(1)确定这些组分的净交换所涉及的主要涡旋大小，(2)解析从森林地面向大气间歇释放二氧化碳所涉及的涡大小和时间尺度，以及(3)将边界层湍流特征与土壤呼吸中富含二氧化碳的空气的输送联系起来。白天，当松林的光合作用和土壤呼吸作用活跃，蒸散作用发生时，富含二氧化碳和水蒸气的空气指示着来自森林地面的输送。因此，利用保留了时间域和频域信息的小波变换，从时间序列中识别并有条件地分析与这些传输事件相关的相干湍流结构。冠层和大气之间的主要通量携带涡旋直径约为63m，约为冠层高度的4倍。最有效地将富含二氧化碳的空气从树冠下方输送到大气中的涡流直径约为8米，约为树冠高度的一半。条件采样结果表明，大气中CO2和水汽的浓度与大气不稳定条件下的24小时时间序列中的湍流动能产生率有关。
The net exchange of CO 2 between the biosphere and atmosphere is realized as a difference between the fluxes associated with photosynthesis and respiration. This paper contrasts the turbulent transport mechanics of two dominant pathways affecting this exchange. Using high-frequency measurements from an experiment conducted at the Duke Forest in North Carolina, wavelet analysis is applied to time series of carbon dioxide and water vapor concentrations in order to (1) determine the dominant eddy sizes involved in the net exchange of these constituents, (2) resolve the eddy size and timescales involved in the intermittent release of CO 2 from the forest floor to the atmosphere, and (3) relate the boundary layer turbulent characteristics to the transport of air enriched in CO 2 from soil respiration. During the daytime hours, when photosynthesis and soil respiration are active in this pine forest and evapotranspiration is taking place, air enriched in both CO 2 and water vapor is indicative of transport from the forest floor. Thus the coherent turbulent structures associated with these transport events are identified and conditionally analyzed from the time series by wavelet transforms, which retain information in the time domain as well as the frequency domain. The dominant flux-carrying eddies between the canopy and atmosphere were approximately 63 m in diameter, about four times the height of the canopy. Eddies that were most effective in transporting air enriched in CO 2 from below the canopy to the atmosphere were found to be approximately 8 m in diameter, on the order of one half the canopy height. Conditional sampling shows that the prevalence of air enriched in both CO 2 and water vapor is related to the rate of turbulent kinetic energy production measured from 24 approximately half-hour time series corresponding to unstable atmospheric conditions.