Evaluating the Representation of Tropical Stratocumulus and Shallow Cumulus Clouds As Well As Their Radiative Effects in CMIP6 Models Using Satellite Observations
Evaluating the Representation of Tropical Stratocumulus and Shallow Cumulus Clouds As Well As Their Radiative Effects in CMIP6 Models Using Satellite Observations
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使用卫星观测评估热带层积云和浅积云在 CMIP6 模型中的表示及其辐射效应
DOI：
10.1029/2022jd038437
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
R. Pincus
中科院分区：
文献类型：
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作者：
Nina Črnivec;Grégory Cesana;R. Pincus
热带海洋上空的低云将很大一部分太阳辐射反射回太空，从而使地球降温，然而，在前几代气候模型中，这种现象的模拟效果很差。本研究的主要目的是利用卫星观测，在参加CMIP6的最新气候模式的一个子集中评估海洋热带低云的表现及其在大气顶部的辐射效应。我们致力于以体制为导向的模式验证，从而引入一种定性的方法来区分层积云(SC)和浅积云(Cu)。新的SC-Cu分类在概念上的优势是基于云的属性，而不是依赖于对云控制因素的模型响应。我们发现，CMIP6模式低估了热带海洋SC区和Cu区的低云量。对云偏差的更详细的研究表明，大多数CMIP6模式低估了SC的相对出现频率(RFO)，而高估了铜的RFO。我们进一步证明，CMIP6模式中的热带低云量仍然太亮。以体制为导向的验证是改进物理过程参数的基础，这些物理过程决定了SC和Cu的云量和辐射影响，目前的气候模型仍然错误地描述了这两个因素。
Low clouds over tropical oceans reflect a great proportion of solar radiation back to space and thereby cool the Earth, yet this phenomenon has been poorly simulated in several previous generations of climate models. The principal aim of the present study is to employ satellite observations to evaluate the representation of marine tropical low clouds and their radiative effect at the top of the atmosphere in a subset of latest climate models participating in CMIP6. We strive for regime‐oriented model validation and hence introduce a qualitative approach to discriminate stratocumulus (Sc) from shallow cumulus (Cu). The novel Sc‐Cu categorization has a conceptual advantage of being based on cloud properties, rather than relying on a model response to a cloud‐controlling factor. We find that CMIP6 models underestimate low‐cloud cover in both Sc‐regions and Cu‐regions of tropical oceans. A more detailed investigation of cloud biases reveals that most CMIP6 models underestimate the relative frequency of occurrence (RFO) of Sc and overestimate RFO of Cu. We further demonstrate that tropical low cloudiness in CMIP6 models remains too bright. The regime‐oriented validation represents the basis for improving parameterizations of physical processes that determine the cloud cover and radiative impact of Sc and Cu, which are still misrepresented in current climate models.