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首页> 外文期刊>Journal of the Atmospheric Sciences >PBL stratiform cloud inhomogeneities thermally induced by the orography: A parameterization for climate models
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PBL stratiform cloud inhomogeneities thermally induced by the orography: A parameterization for climate models

机译：地形热诱发的PBL层状云非均匀性：气候模型的参数化

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This paper proposes a parameterization for use in climate models of the orographic variance and associated thermal circulation's impact on the macroscopic behavior of planetary boundary layer (PBL) stratiform clouds. Orographically induced inhomogeneities in the PBL cloud field can significantly alter the area-averaged cloud-radiative properties and consequently the PBL evolution. Current climate models do not include this effect. The design of the parameterization is based on a systematic set of experiments in which a cloud system resolving model (CSRM) explicitly simulates the diurnally varying interactions between PBL clouds and the orography for a variety of configurations. Analyses of the results suggest that the orographic effect on PBL clouds is parameterizable to a large extent due to a quasi equilibrium between cloud-radiative, turbulent, and mesoscale processes. Parameterizability holds in the range of parameters for which stratiform clouds play a dominant role in the PBL dynamics (cloud fraction similar to0.5 or larger). A statistical parameterization of the liquid water path (LWP) spatial distribution in the PBL is formulated as a function of its mean state. The component of the LWP distribution not captured by the parameterization is mostly associated with a hysteresis effect in the PBL height and decreases with increasing orographic variance. The LWP distribution is characterized by an exponentially decaying function that describes the patchy clouds and a bell-shaped function that describes the solid cloud decks. Orographic variance impacts cloud fraction and the relative area cover of the patchy and solid clouds, mainly by reducing the incidence of the latter, while the characteristic horizontal scale of the orography has little influence on PBL cloudiness. [References: 68]
机译：本文提出了一种参数化方法，可用于地形变异和相关热循环对行星边界层（PBL）层状云宏观行为的影响的气候模型中。 PBL云场中的地形诱发的不均匀性会显着改变面积平均的云辐射特性，并因此改变PBL的演化。当前的气候模型不包括这种影响。参数化的设计基于一组系统的实验，在该实验中，云系统解析模型（CSRM）明确模拟了PBL云和地形对于各种配置的日变化交互作用。对结果的分析表明，由于云辐射过程，湍流过程和中尺度过程之间的准平衡，对PBL云的地形影响在很大程度上是可参数化的。可参数化性处于参数范围内，对于这些参数，层状云在PBL动力学中起着主要作用（云分数等于或大于0.5）。将PBL中的液态水路径（LWP）空间分布的统计参数化表示为其平均状态的函数。参数化未捕获的LWP分布的分量主要与PBL高度中的滞后效应相关，并且随着地形方差的增加而减小。 LWP分布的特征是描述斑块云的指数衰减函数和描述实心云层的钟形函数。地形变异主要通过减少斑块云和实心云的发生率来影响云分数和相对面积覆盖，而地形学的特征水平尺度对PBL云度几乎没有影响。 [参考：68]

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