Abstract
In a convective scheme featuring a discretized cloud size density, the assumed lateral mixing rate is inversely proportional to the exponential coefficient of plume size. This follows a typical assumption of −1, but it has unveiled inherent uncertainties, especially for deep layer clouds. Addressing this knowledge gap, we conducted comprehensive large eddy simulations and comparative analyses focused on terrestrial regions. Our investigation revealed that cloud formation adheres to the tenets of Bernoulli trials, illustrating power-law scaling that remains consistent regardless of the inherent deep layer cloud attributes existing between cloud size and the number of clouds. This scaling paradigm encompasses liquid, ice, and mixed phases in deep layer clouds. The exponent characterizing the interplay between cloud scale and number in the deep layer cloud, specifically for liquid, ice, or mixed-phase clouds, resembles that of shallow convection, but converges closely to zero. This convergence signifies a propensity for diminished cloud numbers and sizes within deep layer clouds. Notably, the infusion of abundant moisture and the release of latent heat by condensation within the lower atmospheric strata make substantial contributions. However, this role in ice phase formation is limited. The emergence of liquid and ice phases in deep layer clouds is facilitated by the latent heat and influenced by the wind shear inherent in the middle levels. These interrelationships hold potential applications in formulating parameterizations and post-processing model outcomes.
摘要
在一个包含离散化云尺寸密度的对流方案中, 侧向混合速率被假设为与尺寸指数的指数系数成反比, 一般认为指数系数为1。然而, 由于固有的不确定性, 指数系数与1存在未知偏差, 特别对于深层云。为了填补这一知识空白, 本文进行了大涡模拟比较分析。研究结果表明, 云的形成遵循伯努利试验的原则, 云尺寸和云的数量之间呈现出幂律规律, 这一规律在深层云中同样适用, 且对于液态、冰态和混合相都成立。在液态、冰态或混合相云中, 云尺寸和数量之间的相互作用的指数与浅对流的类似, 但趋向于零, 这表明在深层云中云的数量倾向减少、尺寸增加。值得注意的是, 在下层大气层中丰富的湿度的注入和由凝结释放的潜热对深层云中液态云的生成做出了重要贡献。然而, 这种作用在冰相形成中是有限的。在深层云中, 液态和冰态的出现是由潜热促进的, 并受中层固有风切变的影响。这些相互关系在制定参数化和后处理模型结果方面具有潜在应用价值。
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Acknowledgements
This research was supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2019QZKK010203), the National Natural Science Foundation of China (Grant No. 42175174 and 41975130), the Natural Science Foundation of Sichuan Province (Grant No. 2022NSFSC1092), and the Sichuan Provincial Innovation Training Program for College Students (Grant No. S202210621009). The source code used in this study is WRF version 4.3 in LES mode. The WRF model can be downloaded at https://www2.mmm.ucar.edu/wrf/users/download/get_sources.html (WRF Users page). The code can be accessed by contacting Bangjun CAO (caobj1989@163.com). Bangjun CAO wrote the main manuscript text and Ziyuan ZHU prepared figures. Xianyu YANG and Jun WEN managed this project. All authors reviewed the manuscript. All authors agreed to participate and publish.
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Article Highlights
• Power-law scaling governs the relationship between cloud size and number in a deep layer, encompassing both liquid-and ice-phase clouds.
• The exponent characterizing the interplay between cloud scale and number implies a reduction in cloud number and size in the deep layer.
• Enhanced latent heat release along with mid-level wind shear increases the number and size of both liquid- and ice-phase deep layer clouds.
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Cao, B., Yang, X., Wen, J. et al. Large Eddy Simulation of Vertical Structure and Size Density of Deep Layer Clouds. Adv. Atmos. Sci. 41, 1629–1642 (2024). https://doi.org/10.1007/s00376-023-3134-2
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DOI: https://doi.org/10.1007/s00376-023-3134-2