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首页> 外文期刊>Journal of the Atmospheric Sciences >MODELING ENTRAINMENT AND FINESCALE MIXING IN CUMULUS CLOUDS
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MODELING ENTRAINMENT AND FINESCALE MIXING IN CUMULUS CLOUDS

机译：积云建模诱因和最终混合

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A model used to study entrainment and mixing of thermodynamic properties in the stratus-topped boundary layer has been extended to represent these processes in cumulus clouds. The new model, called the ''explicit mixing parcel model'' (EMPM), depicts finescale internal structure of a rising thermal in a cumulus cloud using a 1D domain. The EMPM links the conventional parcel model, which has no internal structure, and multidimensional cloud models, which resolve cloud-scale structure produced by large eddies. In the EMPM, the internal structure evolves as a consequence of a sequence of discrete entrainment events and an explicit representation of turbulent mixing based on Kerstein's linear eddy model. In this version of the EMPM, subgrid-scale (eddy) diffusion is found to be adequate for representing the effects of the smallest turbulent eddies. In addition, a simple parameterization is used to determine the local condensation or evaporation rates. If the grid size is reduced so that the Kolmogorov scale is resolved and a droplet growth model is incorporated, the EMPM can predict the local microphysical environments of individual cloud droplets. To evaluate its entrainment parameterization, the EMPM was used to predict the bulk properties of Hawaiian cumulus cloud main turrets observed by aircraft. All of the quantities required by the EMPM except for the entrained blob size were obtained from the observations. Profiles of in-cloud means and variances of thermodynamic properties calculated by the EMPM for entrained blob sizes of 50 m, 100 m, and 200 m and by a parcel model with instantaneous mixing were compared to those observed. The observed mean conserved scalar profiles are reproduced by both mixing representations, but the observed mean liquid wirer mixing ratio and buoyancy profiles, all of the observed variance profiles, and the observed nonbuoyancy level are better reproduced by the EMPM. For entrained blob sizes of 100 m and 200 m, undiluted cloud base air reaches the inversion base in the EMPM, as was observed. These results indicate that the EMPM's entrainment parameterization is adequate for these cloud turrets, and that the characteristic entrained blob size is about 100 m. The model results also demonstrate that the finescale structure represented by the EMPM's 1D domain can be directly compared to high-frequency aircraft measurements. [References: 29]
机译：扩展了用于研究层状边界层中热力学性质的夹带和混合的模型，以表示积云中的这些过程。新模型称为“显式混合宗地模型”（EMPM），它使用一维域描绘了积云中上升的热量的精细内部结构。 EMPM链接了没有内部结构的常规宗地模型和多维云模型，该多维云模型解析了由大涡流产生的云规模结构。在EMPM中，内部结构是由于一系列离散夹带事件和基于Kerstein线性涡流模型的湍流混合的显式表示而演变而来的。在此版本的EMPM中，发现亚网格规模的（涡流）扩散足以代表最小的湍流涡流的影响。另外，使用简单的参数化来确定局部冷凝或蒸发速率。如果减小网格大小以解决Kolmogorov规模并合并液滴生长模型，则EMPM可以预测单个云滴的局部微物理环境。为了评估其夹带参数化，使用EMPM来预测飞机观测到的夏威夷积云主炮塔的体积特性。 EMPM所需的所有数量（夹带的斑点大小除外）均从观测中获得。将EMPM针对夹带的50 m，100 m和200 m的团块大小以及通过瞬时混合的包裹模型计算出的云中均值剖面和热力学性质的方差与观察到的相比较。观察到的平均守恒标量曲线可以通过两种混合表示来再现，但是观察到的平均液位混合比和浮力曲线，所有观察到的方差曲线和观察到的非浮力水平可以通过EMPM更好地再现。对于100 m和200 m的夹带斑点，未稀释的云层基础空气到达EMPM中的反演基础，如观察到的那样。这些结果表明，EMPM的夹带参数化对于这些云塔来说是足够的，特征性夹带斑点尺寸约为100 m。模型结果还表明，由EMPM的一维域表示的精细结构可以直接与高频飞机的测量结果进行比较。 [参考：29]

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