The Contribution of Variability of Lift-induced Upwash to the Uncertainty in Vertical Winds Determined from an Aircraft Platform
The Contribution of Variability of Lift-induced Upwash to the Uncertainty in Vertical Winds Determined from an Aircraft Platform
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升力引起的上洗流的变化对飞机平台确定的垂直风的不确定性的影响
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
P. Shepson
中科院分区：
文献类型：
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作者：
K. Garman;Phillip J. Wyss;M. Carlsen;James R. Zimmerman;B. Stirm;Thomas Q. Carney;R. Santini;P. Shepson
基于飞机的垂直通量测量填补了生物圈-大气交换研究空间领域的空白。为了获得有效的通量数据，必须确定与平均垂直风的偏差w′。当使用飞机平台时，流量测量会受到由飞机前方升力诱导的上洗引起的气流畸变的系统和随机误差的影响。虽然上洗通常被认为是一个恒定的量在用于计算通量的时期，它可以显着变化，在短期内（和长期）由于飞机升力的变化。这种上洗变化的特征对于通量测量是不可否认的重要性，特别是当需要实时计算w′时。在本文中，在上洗的变化进行了比较，从克劳福德等人的模型计算的上洗。（Boundary-Layer Meteorol，80：79-94，1996年），使用飞机长周期（长周期模式）自由振荡期间获得的数据。在自由振荡期间升力的周期性变化提供了一种理想的情况，在这种情况下，可以获得关于存在的上洗的飞行数据，以及测试上洗修正模型的能力。我们的研究结果表明，虽然该模型校正了大部分的平均上洗，上洗的时间尺度上，这是重要的通量测量可以有显着的变化。我们的研究结果表明，使用测得的载荷因子可以是一种容易实现的操作约束，以使由于飞机升力变化引起的上洗变化引起的w′的不确定性最小化。我们利用长周期数据，并根据通量测量布局中飞机姿态和空速的变化，估计由可变上洗引起的w的不确定性约为± 0.05 m s-1。
Aircraft-based vertical flux measurements fill a gap in the spatial domain for studies of biosphere–atmosphere exchange. To acquire valid flux data, a determination of the deviation from the mean vertical wind, w′, is essential. When using aircraft platforms, flux measurements are subject to systematic and random errors from airflow distortion caused by the lift-induced upwash ahead of the aircraft. Although upwash is typically considered to be a constant quantity over periods used for calculating fluxes, it can vary significantly over short (and longer) periods due to changes in aircraft lift. The characterization of such variations in upwash are of undeniable importance to flux measurements, especially when real-time computations of w′ are required. In this paper, the variability in upwash was compared to the calculated upwash from the model of Crawford et al. (Boundary-Layer Meteorol, 80:79–94, 1996) using data taken during a long-period (phugoid mode) free oscillation of the aircraft. The cyclic variation of lift during the free oscillation offers an ideal scenario in which to acquire in-flight data on the upwash that is present, as well as to test the capability of upwash correction models. Our results indicate that while this model corrects for much of the mean upwash, there can be significant variations in upwash on a time scale that is important to flux measurements. Our results suggest that use of the measured load factor could be an easily implemented operational constraint to minimize uncertainty in w′ due to changing upwash from changing aircraft lift. We estimate, using the phugoid data, and from variations in aircraft attitude and airspeed in flux-measurement configuration, that the uncertainty in w caused by variable upwash is approximately ± 0.05 m s−1.