A modified formulation of fractional stratiform condensation rate in the NCAR Community Atmospheric Model (CAM2)
A modified formulation of fractional stratiform condensation rate in the NCAR Community Atmospheric Model (CAM2)
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DOI：
10.1029/2002jd002523
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发表时间：
2003-01
影响因子：
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通讯作者：
Minghua Zhang;Wuyin Lin;C. Bretherton;J. Hack;P. Rasch
中科院分区：
文献类型：
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作者：
Minghua Zhang;Wuyin Lin;C. Bretherton;J. Hack;P. Rasch
[1]本文介绍了一个修正的公式，层状凝结率与云量的社区大气模式版本2（CAM 2）。介绍了云量变化与凝结水总量变化的关系式。再加上诊断云的关系，代表亚网格尺度的相对湿度的变化，形成一个封闭的系统来计算冷凝率。因此，新公式消除了Rasch和Kristjansson [1998]预报云方案中的两个闭合假设。它还扩展了Sundqvist [1978]方案，包括对流性的凝结物的平流和对流性的消散对云量分数的影响。通过大气辐射测量计划的数据和CAM2的全球模式模拟，本制剂和Rasch和Kristjansson方案之间的比较。结果表明，相对于Rasch和Kristjansson方案，新的公式产生更少的云和对流层略暖，从而减少了原来的冷偏差，在美国国家大气研究中心（NCAR）社区气候模式（CCM）。尽管新公式对模式气候的总体影响很小，但修改导致模式中云量变化、凝结率和云水变化的处理更加一致。
[1] This paper describes a modified formulation of stratiform condensation rate associated with fractional cloudiness in the Community Atmospheric Model Version 2 (CAM2). It introduces an equation to link cloudiness change with the variation of total condensate. Together with a diagnostic cloud relationship that represents subgrid-scale variability of relative humidity, a closed system is formed to calculate the fractional condensation rate. As a result, the new formulation eliminates the two closure assumptions in the Rasch and Kristjansson [1998] prognostic cloud scheme. It also extends the Sundqvist [1978] scheme by including the influence of convective detrainment and advection of condensates on the fractional cloudiness. Comparison is made between the present formulation and the Rasch and Kristjansson scheme by using data from the Atmospheric Radiation Measurement Program and through global model simulations with CAM2. It is shown that relative to the Rasch and Kristjansson scheme, the new formulation produces less clouds and a slightly warmer troposphere, thus reducing the original cold bias in the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM). Even though the overall impact of the new formulation on the model climate is small, the modifications lead to more consistent treatments of fractional cloudiness change, condensation rate, and cloud water change in the model.