Surface Thermal Heterogeneities and the Atmospheric Boundary Layer: The Thermal Heterogeneity Parameter
Surface Thermal Heterogeneities and the Atmospheric Boundary Layer: The Thermal Heterogeneity Parameter
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DOI：
10.1007/s10546-020-00544-7
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发表时间：
2020-08
影响因子：
4.3
通讯作者：
F. Margairaz;E. Pardyjak;M. Calaf
中科院分区：
文献类型：
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作者：
F. Margairaz;E. Pardyjak;M. Calaf
尽管近年来计算技术取得了很大的进步，但数值天气预报模式在地表表现陆-气交换过程仍然是一个挑战。以前的研究调查的空间表面的不均匀性的影响已经被视为从湍流的角度来看，主要是假设存在的混合长度尺度以上的表面诱导的扰动建模使用一个特设的散装表面参数代表一个伪等效的表面条件。虽然这些类型的方法可以产生合理的结果，但它们无法解释修改平均流量的长期空间扰动。在这项工作中，表面热不均匀性和平均分辨流体动力学的特征尺度之间的相互作用进行了研究，为广泛的不稳定大气条件。热扩散通量，这自然出现作为一种手段，以占持续的时间平流通量产生的未解决的空间异质性，提供了一个量化的表面热异质性和大气边界层平均流量之间的相互作用。因此，他们也提供了一个确定性的方法，包括未解决的过程对平均流量的影响。我们引入一个新的无量纲数（即，非均匀性参数），该参数可用于识别非均匀性效应变得重要的流动条件和表面配置。非均匀性参数可以用来区分的情况下，高和低的色散通量的贡献的基础上的平均流量和热非均匀性的特点。这些结果表明，在弱地转强迫下，地面非均匀性的影响，应考虑在数值天气预报模式。
Representing land–atmosphere exchange processes at the ground surface of numerical-weather-prediction models remains a challenge in spite of the recent advances in computing. Previous studies investigating the effects of spatial surface heterogeneities have been viewed from a turbulence perspective, mostly assuming the existence of a blending length scale above which surface-induced perturbations are modelled using an ad hoc bulk surface parameter representing a pseudo-equivalent surface condition. While these types of approaches can generate reasonable results, they fail to account for the long-lasting spatial perturbations that modify the mean flow. In this work, the interactions between the characteristic scales of surface thermal heterogeneities and the mean resolved fluid dynamics are investigated for a broad range of unstable atmospheric conditions. Thermal dispersive fluxes, which naturally appear as a means to account for persistent-in-time advection fluxes generated by unresolved spatial heterogeneities, provide a quantification of the interaction between surface thermal heterogeneities and the atmospheric boundary-layer mean flow. Hence, they also provide a deterministic approach for including the effect of unresolved processes on the mean flow. We introduce a new non-dimensional number (i.e., the heterogeneity parameter) that can be used to identify the flow conditions and surface configurations in which heterogeneity effects become important. The heterogeneity parameter can be used to distinguish cases with high and low dispersive-flux contributions based on the mean flow and characteristics of the thermal heterogeneities. These results suggest that under weak geostrophic forcing, surface heterogeneity effects should be accounted for in numerical-weather-prediction models.