Turbulence Organization and Mean Profile Shapes in the Stably Stratified Boundary Layer: Zones of Uniform Momentum and Air Temperature
Turbulence Organization and Mean Profile Shapes in the Stably Stratified Boundary Layer: Zones of Uniform Momentum and Air Temperature
复制标题
DOI：
10.1007/s10546-022-00771-0
复制
发表时间：
2022-07
影响因子：
4.3
通讯作者：
M. Heisel;P. Sullivan;G. Katul;M. Chamecki
中科院分区：
文献类型：
--
作者：
M. Heisel;P. Sullivan;G. Katul;M. Chamecki
在稳定分层的行星边界层的最低部分中发现了涡旋的持续空间组织。该分析使用已发表的大涡流模拟（Sullivan 等人，J Atmos Sci 73(4):1815–1840, 2016）中的流动实现，稳定性范围从近中性到几乎无 z 分层。相干湍流结构可以很好地近似为一系列均匀动量区 (UMZ) 和均匀温度区 (UTZ)，它们由明显大于平均值的强梯度薄层隔开。这种模式产生阶梯状的瞬时流量剖面，其形状与长期平均产生的平均剖面不同。然而，楼梯组织的缩放比例与所得的平均轮廓密切相关。无论分层如何，薄梯度层上的速度和温度差异仍然与表面动量和热通量条件成比例。对于近中性和弱分层，UMZ 和 UTZ 的垂直厚度与地表以上的高度成正比，但随着稳定性的增加，UMZ 和 UTZ 的垂直厚度变得更薄且对高度的依赖性较小。因此，在中性条件下观察到的速度和温度对数平均分布的偏差主要是由于涡流尺寸随着分层的增加而减小，这是通过现有的动量和热量的莫宁-奥布霍夫相似关系凭经验捕获的。区域属性还用于解释湍流普朗特数的趋势，从而提供稳定分层条件下的涡流组织、平均轮廓和湍流扩散率之间的联系。
A persistent spatial organization of eddies is identified in the lowest portion of the stably stratified planetary boundary layer. The analysis uses flow realizations from published large-eddy simulations (Sullivan et al. in J Atmos Sci 73(4):1815–1840, 2016) ranging in stability from near-neutral to almost z-less stratification. The coherent turbulent structure is well approximated as a series of uniform momentum zones (UMZs) and uniform temperature zones (UTZs) separated by thin layers of intense gradients that are significantly greater than the mean. This pattern yields stairstep-like instantaneous flow profiles whose shape is distinct from the mean profiles that emerge from long-term averaging. However, the scaling of the stairstep organization is closely related to the resulting mean profiles. The differences in velocity and temperature across the thin gradient layers remain proportional to the surface momentum and heat flux conditions regardless of stratification. The vertical thickness of UMZs and UTZs is proportional to height above the surface for near-neutral and weak stratification, but becomes thinner and less dependent on height as the stability increases. Deviations from the logarithmic mean profiles for velocity and temperature observed under neutral conditions are therefore predominately due to the reduction in eddy size with increasing stratification, which is empirically captured by existing Monin–Obukhov similarity relations for momentum and heat. The zone properties are additionally used to explain trends in the turbulent Prandtl number, thus providing a connection between the eddy organization, mean profiles, and turbulent diffusivity in stably stratified conditions.