Surface Thermal Heterogeneities and the Atmospheric Boundary Layer: The Relevance of Dispersive Fluxes
Surface Thermal Heterogeneities and the Atmospheric Boundary Layer: The Relevance of Dispersive Fluxes
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DOI：
10.1007/s10546-020-00509-w
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发表时间：
2020-04
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
虽然计算能力的不断提高使数值天气预报模型的网格分辨率更加精细，但代表陆地-大气交换过程仍然具有挑战性。这部分是由于陆面异质性存在于所有空间尺度，其变异性不一定“平均”的大小减少。这里介绍的工作使用大涡模拟和分散通量的概念来量化表面的热不均匀（尺度约为大气边界层高度的10%），但均匀粗糙的影响。这些近典型的情况下，描述了在广泛的不稳定大气流动的非均匀标量输运。结果表明，存在一个政权的平均流量主要是由表面的热不均匀性。在这种情况下，色散通量的贡献可以占总感热通量的40%以上，在100米以上的地面和近地面约5-10%。这个结果是独立的空间分布的热不均匀性和弱依赖于平均时间用于定义的色散通量。此外，另一种制度存在的表面热不均匀性的影响被迅速混合和色散通量匹配的等效均匀表面上获得的。结果进一步说明了一种新的显热通量的同谱标度的存在，不同于传统的湍流同谱标度。我们相信，这些结果可能阐明的途径，为非典型的大气近地层开发新的参数化。
While the increasing availability of computational power is enabling finer grid resolutions in numerical-weather-prediction models, representing land–atmosphere exchange processes remains challenging. This partially results from the fact that land-surface heterogeneity exists at all spatial scales, and its variability does not necessarily ‘average’ out with decreasing size. The work presented here uses large-eddy simulations and the concept of dispersive fluxes to quantify the effects of a surface that is thermally inhomogeneous (with scales that are approximately 10% of the height of the atmospheric boundary layer), but uniformly rough. These near-canonical cases describe inhomogeneous scalar transport over a broad range of unstable atmospheric flows. Results illustrate the existence of a regime where the mean flow is mostly driven by the surface thermal heterogeneities. In this regime, the contribution of the dispersive fluxes can account for more than 40% of the total sensible heat flux at 100 m above the ground and about 5–10% near the surface. This result is independent of the spatial distribution of the thermal heterogeneities and weakly dependent on the averaging time used to define the dispersive fluxes. Additionally, an alternative regime exists where the effects of the surface thermal heterogeneities are quickly blended and the dispersive fluxes match those obtained over an equivalent homogeneous surface. Results further illustrate the existence of a new cospectral scaling for the dispersive sensible heat fluxes that differs from the traditional turbulence cospectral scaling. We believe that these results might elucidate pathways for developing new parametrizations for the non-canonical atmospheric surface layer.