Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer
Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer
复制标题
DOI：
10.1175/2008mwr2582.1
复制
发表时间：
2009-03-01
影响因子：
3.2
通讯作者：
Zulauf, Mike
中科院分区：
文献类型：
--
作者：
Ackerman, Andrew S.;vanZanten, Margreet C.;Zulauf, Mike
层积边界层中的云水沉积和细雨是大涡模拟相互比较的焦点。本文是一个关于夜间层积云在干燥逆温下的理想化案例研究，其中嵌入了大量毛毛雨的开放细胞对流。使用了11个组的结果。两个模型解决了云粒子的尺寸分布问题，另一个模型对云水沉降和细雨过程进行了参数化处理。对于具有细雨和云水沉积的模拟集合，平均液态水路径(LWP)与测量结果非常稳定和一致，平均夹带率处于测量范围的低端，集合平均最大垂直风方差大约是测量的一半。平均而言，地面和云底的降水量较小，而降水蒸发速率较大。在模拟中加入毛毛雨降低了对流强度，增加了边界层层结，并降低了几乎所有模式的LWP。对于大多数模式来说，包括云水沉降在内，显著地减少了卷吸，降低了对流强度，并增加了LWP。在几乎所有的情况下，LWP对云水沉积的反应比对毛毛雨更强烈。强烈反对在模拟中忽略云水沉积，无论云底下是否存在降水。
Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.