Scalar Turbulence in Convective Boundary Layers by Changing the Entrainment Flux
Scalar Turbulence in Convective Boundary Layers by Changing the Entrainment Flux
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通过改变夹带通量来研究对流边界层中的标量湍流
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
I. Mazzitelli
中科院分区：
文献类型：
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作者：
A. Lanotte;I. Mazzitelli
采用警报涡模式模拟了无云对流边界层中标量输送的演变过程。由于地面释放的显热和浓度波动的微量气体在均匀的表面上发出的温度波动混合的不稳定的边界层内的湍流。在顶部，卷吸区的变化得到两种不同的情况：（i）温度反演强烈，穿过卷吸区的痕量气体增量很小，导致相对于地面排放的顶部通量很小;（ii）对流边界层顶部的温度逆温较弱，并且标量增量足够大，以实现朝向自由大气的浓度通量，该浓度通量抵消了表面通量。在这两种情况下，在一个简单的模型内获得的夹带通量的估计，并对数值数据进行测试。标量配置文件的演变进行了讨论，在不同的夹带表面通量比。结果表明，当边界层顶部的卷吸较弱时，温度场和痕量气体标量场有很强的相关性，特别是在边界层的下部。这意味着它们从最大到最小的空间尺度表现出相似的行为。然而，当夹带是强的，从表面移动，在运输的两个标量的差异出现。最后，它表明，独立的标量制度，温度场表现出更多的间歇性波动比微量气体。
Alarge-eddysimulationmodelisadoptedtoinvestigatetheevolutionofscalarstransportedbyatmospheric cloud-free convective boundary layer flows. Temperature fluctuations due to the ground release of sensible heat and concentration fluctuations of a trace gas emitted at the homogeneous surface are mixed by turbulence within the unstable boundary layer. On the top, the entrainment zone is varied to obtain two distinct situations: (i) the temperature inversion is strong and the trace gas increment across the entrainment region is small, yieldingto a small topflux with respect to the surface emission; (ii) the temperature inversionat the top of the convective boundary layer is weak, and the scalar increment large enough to achieve a concentration flux toward the free atmosphere that overwhelms the surface flux. In both cases, an estimation of the entrainment flux is obtained within a simple model, and it is tested against numerical data. The evolution of the scalar profiles is discussed in terms of the different entrainment‐surface flux ratios. Results show that, when entrainment at the top of the boundary layer is weak, temperature and trace gas scalar fields are strongly correlated, particularly in the lower part of the boundary layer. This means that they exhibit similar behavior from the largest down to the smallest spatial scales. However, when entrainment is strong, as moving from the surface, differences in the transport of the two scalars arise. Finally, it is shown that, independently of the scalar regime, the temperature field exhibits more intermittent fluctuations than the trace gas.