SimCloud version 1.0: a simple diagnostic cloud scheme for idealized climate models
SimCloud version 1.0: a simple diagnostic cloud scheme for idealized climate models
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DOI：
10.5194/gmd-2020-402
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发表时间：
2020-12
影响因子：
5.1
通讯作者：
Qun Liu;M. Collins;P. Maher;S. Thomson;G. Vallis
中科院分区：
文献类型：
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作者：
Qun Liu;M. Collins;P. Maher;S. Thomson;G. Vallis
抽象的。本研究提出了一种用于大气环流模型 (GCM) 的简单诊断云方案 (SimCloud)，该方案具有适度的复杂性，并且在描述其对可调参数的依赖性方面是透明的。构成该计划核心的大尺度云是根据相对湿度来诊断的。此外，通常在副热带海洋上大陆西海岸附近发现的海洋低层云，很大程度上取决于逆温强度的函数。基于比湿度的简单函数的“冻干”调整也可用于减少极地地区的过度云偏差。其他云属性，例如云滴的有效半径和云液态水含量，被指定为温度的简单函数。所有这些功能都是用户可配置的。云方案在 Isca 中实现，Isca 是一个建模框架，旨在支持构建不同复杂程度的 GCM，但可以轻松适应其他 GCM。使用该方案对现实大陆进行的模拟通常会捕获观测到的云分数结构和云辐射效应（CRE）及其季节变化。具体来说，显式低云方案通过增加云分数和云水路径改进了东部副热带海洋上空短波CRE的模拟。冻干调整缓解了极地地区特别是冬季的长波 CRE 偏差。然而，与观测相比，热带地区的长波CRE和温带地区的短波CRE仍然太强。然而，这种简单的云方案为在理想化模型框架中检查云对气候的影响提供了合适的基础。
Abstract. A simple diagnostic cloud scheme (SimCloud) for general circulation models (GCMs), which has a modest level of complexity and is transparent in describing its dependence on tunable parameters, is proposed in this study. The large-scale clouds, which form the core of the scheme, are diagnosed from relative humidity. In addition, the marine low stratus clouds, typically found off the west coast of continents over subtropical oceans, are determined largely as a function of inversion strength. A “freeze-dry” adjustment based on a simple function of specific humidity is also available to reduce an excessive cloud bias in polar regions. Other cloud properties, such as the effective radius of cloud droplet and cloud liquid water content, are specified as simple functions of temperature. All of these features are user-configurable. The cloud scheme is implemented in Isca, a modeling framework designed to enable the construction of GCMs at varying levels of complexity, but could readily be adapted to other GCMs. Simulations using the scheme with realistic continents generally capture the observed structure of cloud fraction and cloud radiative effect (CRE), as well as its seasonal variation. Specifically, the explicit low-cloud scheme improves the simulation of shortwave CREs over the eastern subtropical oceans by increasing the cloud fraction and cloud water path. The freeze-dry adjustment alleviates the longwave CRE biases in polar regions, especially in winter. However, the longwave CRE in tropical regions and shortwave CRE over the extratropics are both still too strong compared to observations. Nevertheless, this simple cloud scheme provides a suitable basis for examining the impacts of clouds on climate in idealized modeling frameworks.