...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Agricultural and Forest Meteorology >Random and systematic CO2 flux sampling errors for tower measurements over forests in the convective boundary layer
【24h】

Random and systematic CO2 flux sampling errors for tower measurements over forests in the convective boundary layer

机译：对流边界层内森林塔测量的随机和系统CO2通量采样误差

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

The perturbation timescale-dependences of the CO2 flux and the random flux sampling error are evaluated from eddy-covariance tower observations in the mid-day convective boundary layer over mid-latitude conifer forests. The perturbation timescale is the timescale used in the standard Reynolds decomposition to define mean and perturbations quantities. The random error due to inadequate sampling of the turbulence is estimated using two different approaches (traditional and daily-differencing). A fixed record length of 3.6 h (dyadic timescale) is used for all results, where the record length is the timescale over which the products of perturbations are averaged (flux averaging timescale). Long multiple-hour records are required to evaluate the sampling errors.When high temporal resolution flux estimates are of interest (e.g., sub-daily timescales), including incremental contributions to the flux from transport on timescales longer than 10 min cannot be justified based on the magnitude of the incremental increase in the random sampling error. That is, the additional flux obtained by increasing the perturbation timescale beyond 10 min is dominated by random sampling error. This result is supported by both the traditional and daily-differencing approaches. For a perturbation timescale of 30 min, the relative random error (random error divided by the flux) is 38% at the taller tower and 27% at the shorter tower, and increases with increasing perturbation timescale. The cost associated with reducing the random error by using the shorter 10 min perturbation timescale, compared to the standard practice of 30 min, is an increase in the systematic flux error from 3% to 7% (averaged over three sites). Such error, while systematic, may be small in comparison to other sources of uncertainty. The choice of the perturbation timescale, and the trade-offs between reducing systematic or random errors, may depend on the intended application of the flux data. When only longer term flux estimates (e.g., monthly or annual averages) are of interest the random sampling error tends to cancel because of the larger number of samples, and the perturbation timescale can be increased to further reduce the systematic flux error. (c) 2008 Elsevier B.V. All rights reserved.
机译：在中纬度针叶林中对流边界层的涡流-协方差塔观测中，评估了CO2通量的扰动时间尺度依赖性和随机通量采样误差。摄动时间标度是标准雷诺分解中用于定义均值和摄动量的时间标度。使用两种不同的方法（传统差分法和每日差分法）估计由于湍流采样不足而引起的随机误差。所有结果均使用固定的3.6 h记录长度（二进位时间标度），其中记录长度是扰动乘积平均的时间标度（通量平均时间标度）。需要长时间的长时间记录才能评估采样误差。当需要高时间分辨率通量估计值时（例如，子日时间尺度），包括基于大于10分钟的时间尺度的运输对通量的增量贡献，不能基于以下理由进行辩解随机采样误差的增量增加幅度。也就是说，通过增加摄动时间尺度超过10分钟而获得的额外通量主要由随机采样误差决定。传统和日常差分方法均支持此结果。对于30分钟的摄动时间尺度，相对较高的随机误差（随机误差除以通量）在较高的塔上为38％，在较短的塔上为27％，并且随着摄动时间尺度的增加而增加。与30分钟的标准做法相比，通过使用较短的10分钟扰动时间尺度来减少随机误差，与之相关的成本是系统通量误差从3％增加到7％（三个位置的平均值）。这种误差虽然是系统性的，但与其他不确定性来源相比可能很小。扰动时间尺度的选择以及减少系统误差或随机误差之间的权衡，可能取决于通量数据的预期应用。当仅关注较长期的通量估计（例如月或年平均）时，由于样本数量较大，随机采样误差趋于消除，因此可以增加扰动时间尺度以进一步减小系统通量误差。 （c）2008 Elsevier B.V.保留所有权利。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号