Lagrangian and Eulerian Supersaturation Statistics in Turbulent Cloudy Rayleigh–Bénard Convection: Applications for LES Subgrid Modeling
Lagrangian and Eulerian Supersaturation Statistics in Turbulent Cloudy Rayleigh–Bénard Convection: Applications for LES Subgrid Modeling
复制标题
湍流多云瑞利-伯纳德对流中的拉格朗日和欧拉过饱和统计：LES 子网格建模的应用
DOI：
10.1175/jas-d-22-0256.1
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发表时间：
2023
影响因子：
3.1
通讯作者：
Shaw, Raymond A.
中科院分区：
文献类型：
--
作者：
Chandrakar, Kamal Kant;Morrison, Hugh;Shaw, Raymond A.
标量场和速度场的湍流波动对于云微物理过程至关重要，例如液滴激活和大小分布演变，因此可以影响云辐射强迫和降水形成。在Pi对流云室中直接数值模拟（DNS）中研究了湍流瑞利-巴姆纳德对流的拉格朗日和欧拉水汽、温度和过饱和度统计量，为大气模式参数化亚网格尺度波动提供了基础。提出了一种适用于晴天和阴天条件的水汽和温度方差、协方差和过饱和度方差的子网格模型。利用DNS数据对相变贡献进行了先验测试，结果表明该模型具有良好的性能。过饱和是温度和水蒸气的非线性函数，水蒸气和热量的相对外部通量（例如在夹带混合和相变过程中）影响湍流过饱和波动。虽然过饱和度具有与独立标量（温度和水蒸气）相似的自相关和结构功能，但过饱和度的自相关时间尺度不同。在无云的DNS中，相对标量通量使过饱和pdf比绝热情况下更少偏斜，在绝热情况下，它们高度负偏斜。液滴凝结改变了PDF形状响应：绝热情况下，PDF形状响应变为正偏态，而当侧壁相对通量较大时，PDF形状响应变为负偏态。在存在相对标量通量的情况下，凝结也增加了水蒸气和温度之间的相关性，但在绝热情况下则降低了相关性。这些相关性的变化抑制了非绝热情况下的过饱和变异性，而增加了绝热情况下的过饱和变异性。本文还讨论了使用拉格朗日随机方案进行亚网格微物理建模的意义。
Turbulent fluctuations of scalar and velocity fields are critical for cloud microphysical processes, e.g., droplet activation and size distribution evolution, and can therefore influence cloud radiative forcing and precipitation formation. Lagrangian and Eulerian water vapor, temperature, and supersaturation statistics are investigated in direct numerical simulations (DNS) of turbulent Rayleigh–Bénard convection in the Pi Convection Cloud Chamber to provide a foundation for parameterizing subgrid-scale fluctuations in atmospheric models. A subgrid model for water vapor and temperature variances and covariance and supersaturation variance is proposed, valid for both clear and cloudy conditions. Evaluation of phase change contributions through an a priori test using DNS data shows good performance of the model. Supersaturation is a nonlinear function of temperature and water vapor, and relative external fluxes of water vapor and heat (e.g., during entrainment-mixing and phase change) influence turbulent supersaturation fluctuations. Although supersaturation has autocorrelation and structure functions similar to the independent scalars (temperature and water vapor), the autocorrelation time scale of supersaturation differs. Relative scalar fluxes in DNS without cloud make supersaturation PDFs less skewed than the adiabatic case, where they are highly negatively skewed. However, droplet condensation changes the PDF shape response: it becomes positively skewed for the adiabatic case and negatively skewed when the sidewall relative fluxes are large. Condensation also increases correlations between water vapor and temperature in the presence of relative scalar fluxes but decreases correlations for the adiabatic case. These changes in correlation suppress supersaturation variability for the nonadiabatic cases and increase it for the adiabatic case. Implications of this work for subgrid microphysics modeling using a Lagrangian stochastic scheme are also discussed.