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首页> 外文会议>25th Conference on Agricultural and Forest Meteorology and 12th Joint Conference on the Applications of Air Pollution Meteorology with Aamp;WMA and Fourth Symposium on the Urban Environment May 20-24, 2002 Norfolk, Virginia >SPECTRAL ANALYSES OF LONG-TERM MEASUREMENTS OF TURBULENT EXCHANGE OVER MIXED HARDWOOD FORESTS
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SPECTRAL ANALYSES OF LONG-TERM MEASUREMENTS OF TURBULENT EXCHANGE OVER MIXED HARDWOOD FORESTS

机译：硬木混交林湍流交换长期测量的谱分析

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摘要

It is well recognized that losses in measured eddy-covariance fluxes can be caused by path/line averaging, sensor separation, inadequate sensor frequency response, damping through tubes in closed-path gas analyzers, data processing, etc., (Moore, 1986). Previous studies using spectral methods have shown that corrections to measured fluxes range from a few to over 30% (Eugster & Senn 1995, Leuning & Judd 1996, Horst 1997, Massman 2000). The magnitudes of such flux losses in the higher frequency range could be on the same order as unaccounted lower frequency fluxes due to inadequate averaging time (Rissmann & Tetzlaff 1994, Sakai et al. 2001, Finnigan et al. 2002). Spectral methods used to correct the flux losses often require knowledge of the true spectra and cospectra, as well as the transfer functions (Moore, 1986; Massman, 2000). The most used spectral and cospectral models are those of Kaimal et al. (1972) and Wyngaard and Cote (1972) derived from observations over smooth surfaces and flat terrain. Sakai et al. (2001) indicated that the normalized cospectra of momentum and sensible heat in the roughness sublayer over forest canopies have nearly identical form in convective conditions. Here we examine spectra and cospectra charac-teristics to determine appropriate similarity forms of spectral and cospectral for subsequent applications. Then, we focus on the frequency loss of COz and water vapor fluxes due to damping through the long tubes, assuming this to be the major cause of frequency losses. Variations in the coefficients of damping function and the magnitudes of flux correction are also discussed. Data used here were collected at the UMBS (University of Michigan Biological Station in lower northern Michigan) AmeriFlux site. Eddy-covariance systems (CSAT-3 sonic anemometers and a LiCor-6262 closed path infrared gas analyzers) were installed at 34 m and 46 m. The mean tree height is 22 m and peak LAI is 3.5. Results are derived from over 2,400 hourly spectra and cospectra during June-August of 1999 and 2000 at 46 m. Similar analyses are to be performed for the MMSF (Morgan-Monroe State Forest in south central Indiana) site.
机译：众所周知，涡流-协方差通量的损失可能是由于路径/线路平均，传感器分离，传感器频率响应不足，闭路气体分析仪中的管道阻尼，数据处理等引起的（Moore，1986）。 。以前使用频谱方法进行的研究表明，对测得的通量的校正范围从几个到超过30％（Eugster＆Senn 1995，Leuning＆Judd 1996，Horst 1997，Massman 2000）。由于平均时间不足，在较高频率范围内的此类磁通损耗的幅度可能与未计及的低频通量的数量级相同（Rissmann＆Tetzlaff 1994，Sakai et al。2001，Finnigan et al。2002）。用来校正通量损耗的光谱方法通常需要了解真实的光谱和共谱以及传递函数（Moore，1986； Massman，2000）。最常用的光谱和共光谱模型是Kaimal等人的模型。 （1972年）以及Wyngaard和Cote（1972年）是从对光滑表面和平坦地形的观测中得出的。酒井等。 （2001年）表明，在对流条件下，森林冠层粗糙亚层中动量和显热的归一化共谱具有几乎相同的形式。在这里，我们检查光谱和共光谱特性，以确定光谱和共光谱的适当相似形式，以用于后续应用。然后，我们重点研究由于长管阻尼引起的COz和水蒸气通量的频率损失，假设这是造成频率损失的主要原因。还讨论了阻尼函数系数的变化和磁通校正的幅度。此处使用的数据是在UMBS（密歇根州北部下部的密歇根大学生物站）AmeriFlux站点收集的。涡度协方差系统（CSAT-3声波风速计和LiCor-6262闭路红外气体分析仪）安装在34 m和46 m处。平均树高为22 m，峰值LAI为3.5。结果来自1999年6月至8月以及2000年46 m时的超过2,400个小时光谱和共谱。将对MMSF（印第安纳州中南部的摩根-门罗州立森林）基地进行类似的分析。

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