Understanding Physical Processes Represented by the Monin–Obukhov Bulk Formula for Momentum Transfer
Understanding Physical Processes Represented by the Monin–Obukhov Bulk Formula for Momentum Transfer
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DOI：
10.1007/s10546-020-00546-5
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发表时间：
2020-07
影响因子：
4.3
通讯作者：
Jielun Sun;E. Takle;O. Acevedo
中科院分区：
文献类型：
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作者：
Jielun Sun;E. Takle;O. Acevedo
用外场观测研究了用Monin-Obukhov体积动量公式表示的物理过程。我们讨论了能量最强的非局域、大尺度、相干湍流混合与传统上由K理论(类似于分子扩散)所代表的局域湍流混合之间的重要区别，特别是在考虑发展的表层层结的情况下。研究表明，无论风速如何，Monin-Obukhov整体公式中描述的水平均匀表层的中性态代表了一种特殊的中性态，例如，没有表面加热/冷却的表层。在这种情况下，Monin-Obukhov体积公式与至少30m高度的观测结果吻合得很好。由于近地层是分层的，无论是稳定的还是不稳定的，中性状态是通过最高能量的非局地相干涡旋通过机械产生的湍流混合实现的。观测到的(动量通量量级的平方根)与风速V之间的中性关系在任何高度都不同于Monin-Obukhov公式所描述的关系，但在离地面几米的范围内。Monin-Obukhov中性线关系与观测值的偏差随着高度的增加而增加，并导致整体公式的性能随高度的增加而恶化，这不能用稳定函数来补偿。在此基础上，还讨论了阻力系数的估计问题。
Physical processes represented by the Monin–Obukhov bulk formula for momentum are investigated with field observations. We discuss important differences between turbulent mixing by the most energetic non-local, large, coherent turbulence eddies and local turbulent mixing as traditionally represented by K-theory (analog to molecular diffusion), especially in consideration of developing surface-layer stratification. The study indicates that the neutral state in a horizontally homogeneous surface layer described in the Monin–Obukhov bulk formula represents a special neutrality regardless of wind speed, for example, the surface layer with no surface heating/cooling. Under this situation, the Monin–Obukhov bulk formula agrees well with observations for heights to at least 30 m. As the surface layer is stratified, stably or unstably, the neutral state is achieved by mechanically generated turbulent mixing through the most energetic non-local coherent eddies. The observed neutral relationship between(the square root of the momentum flux magnitude) and wind speedVat any height is different from that described by the Monin–Obukhov formula except within several metres of the surface. The deviation of the Monin–Obukhov neutrallinear relation from the observed one increases with height and contributes to the deteriorating performance of the bulk formula with increasing height, which cannot be compensated by stability functions. Based on these analyses, estimation of drag coefficients is discussed as well.