Aircraft observations of the ekman layer during the joint air‐sea interaction experiment
Aircraft observations of the ekman layer during the joint air‐sea interaction experiment
复制标题
海空联合实验期间飞机对艾克曼层的观测
DOI：
--
复制
发表时间：
1985
期刊：
影响因子：
--
通讯作者：
S. Nicholls
中科院分区：
文献类型：
--
作者：
S. Nicholls
本文介绍了对海洋上空中纬度大气边界层进行观测研究的结果。这些数据主要是由作为联合海气相互作用实验（JASIN）的一部分的装有仪表的飞机获得的。
所选择的八个场合的研究的特点是小的表面浮力通量和条件被很好地描述为近中性和正压。在没有低水平反转的情况下，在每种情况下都观察到混合良好的埃克曼层，但限于约0.2u */f的深度。对水平梯度（包括压力）的精确测量，加上改进的风观测和湍流通量测量，使得能够在这一层的整个深度对动量平衡的每一项进行评估。这些条款被认为是相当密切的平衡，很好地描述了Ekman缩放，并与测量的湍流动能平衡的要求是一致的。后者表明，主要的切变产生项是在局部消散的，几乎没有输出到埃克曼层的上层，从而能够通过夹带而显著加深，尽管似乎只需要稍微增加不稳定性就可以改变这种平衡。这种边界层结构可能被观察到的条件的建议。各种系数的值用于计划有关的表面通量的平均数量（CD，CE，Cg，A，B）的推导和以前的测量结果进行比较。
谱分析表明，大部分的湍流运输被限制在一个独特的高波数区域，其特性作为Ekman层的深度和稳定性参数的函数而变化。这是叠加在较大规模的波动，不明显变化的埃克曼层内，因此，占主导地位的变化，在上部地区的小规模湍流的强度随高度强烈下降。
最后，这种解释的进一步影响进行了讨论，特别是参考热量和水蒸气平衡。这意味着从Ekman层中去除水蒸气是通过与云活动有关的转移来完成的，这标志着该层顶部湍流传输机制的重大变化。并讨论了这些结果与用不同方法同时得到的类似结果之间的关系。
Results are presented from an observational study of the mid-latitude atmospheric boundary layer over the sea. the data were obtained mainly by instrumented aircraft as part of the Joint Air-Sea Interaction Experiment (JASIN).
The eight occasions chosen for study are characterized by small surface buoyancy fluxes and the conditions are well described as near neutral and barotropic. In the absence of low-level inversions, a well-mixed Ekman layer is observed on each occasion but is limited to a depth of approximately 0.2u */f. Accurate measurements of horizontal gradients (including pressure) together with improved wind observations and turbulent flux measurements enabled each of the terms of the momentum balance to be evaluated throughout the depth of this layer. These terms were found to balance quite closely, were well described by Ekman scaling and were consistent with the requirements of the measured turbulent kinetic energy balance. the latter suggests that the main shear production terms are dissipated locally and that little is exported to upper levels in the Ekman layer to enable significant deepening by entrainment although only a slight increase in instability appears to be needed to alter this balance. Conditions in which such boundary layer structure might be observed are suggested. Values of various coefficients used in schemes for relating surface fluxes to mean quantities (CD, CE, Cg, A, B) are derived and compared with previous measurements.
Spectral analysis reveals that most of the turbulent transport is confined to a distinct high wavenumber region whose characteristics vary as a function of Ekman layer depth and stability parameters. This is superimposed on larger-scale fluctuations which do not vary appreciably within the Ekman layer and which therefore dominate the variances in the upper regions as the intensity of the smaller-scale turbulence decreases strongly with height.
Finally, further implications of this interpretation are discussed with particular reference to the heat and water vapour balance. These imply that removal of water vapour from the Ekman layer is accomplished by transfer related to cloud activity, marking a significant change in the mechanism of turbulent transport at the top of this layer. the relationship between these and similar results obtained concurrently by different methods is also discussed.