Important Ice Processes Are Missed by the Community Earth System Model in Southern Ocean Mixed‐Phase Clouds: Bridging SOCRATES Observations to Model Developments
Important Ice Processes Are Missed by the Community Earth System Model in Southern Ocean Mixed‐Phase Clouds: Bridging SOCRATES Observations to Model Developments
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DOI：
10.1029/2022jd037513
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发表时间：
2023-02
期刊：
影响因子：
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通讯作者：
Xi Zhao;Xiaohong Liu;S. Burrows;P. DeMott;M. Diao;G. McFarquhar;S. Patade;V. Phillips;G. Roberts;K. Sanchez;Yang Shi;Meng Zhang
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作者：
Xi Zhao;Xiaohong Liu;S. Burrows;P. DeMott;M. Diao;G. McFarquhar;S. Patade;V. Phillips;G. Roberts;K. Sanchez;Yang Shi;Meng Zhang
全球气候模式（GCM）在模拟南大洋云相态和云辐射效应方面遇到了困难。一些新一代的GCM预测混合相云中的液体太多，冰太少。这种对云相的错误描述导致SO上空云的负反馈较弱，气候敏感性较高。基于南大洋云辐射和气溶胶传输实验研究期间获得的观测数据的模型比较，本研究解决了一个关键的不确定性，在社区地球系统模型第2版（CESM 2）云相，即冰的形成在原始远程SO云。结果表明，海雾有机气溶胶（SSOAs）是SO上空最重要的冰核粒子（INPs）类型，其浓度比沙尘INPs高1个数量级。二次产冰（SIP）包括霜裂、雨滴破碎和冰-冰碰撞破碎，如CESM 2中所实现的，是云温度大于−20°C的中等冷云中的主要产冰过程。SIP将云内冰数浓度（Ni）提高了1-3个数量级，并预测了更多的混合相（发生率从15%增加到21%），与观测结果更一致。这项研究强调了准确地代表云相的原始远程SO的重要性，通过考虑冰成核的SSOA和SIP过程，这是目前大多数GCM云微物理参数化失踪。
Global climate models (GCMs) are challenged by difficulties in simulating cloud phase and cloud radiative effect over the Southern Ocean (SO). Some of the new‐generation GCMs predict too much liquid and too little ice in mixed‐phase clouds. This misrepresentation of cloud phase in GCMs results in weaker negative cloud feedback over the SO and a higher climate sensitivity. Based on a model comparison with observational data obtained during the Southern Ocean Cloud Radiation and Aerosol Transport Experimental Study, this study addresses a key uncertainty in the Community Earth System Model version 2 (CESM2) related to cloud phase, namely ice formation in pristine remote SO clouds. It is found that sea spray organic aerosols (SSOAs) are the most important type of ice nucleating particles (INPs) over the SO with concentrations 1 order of magnitude higher than those of dust INPs based on measurements and CESM2 simulations. Secondary ice production (SIP) which includes riming splintering, rain droplet shattering, and ice‐ice collisional fragmentation as implemented in CESM2 is the dominant ice production process in moderately cold clouds with cloud temperatures greater than −20°C. SIP enhances the in‐cloud ice number concentrations (Ni) by 1–3 orders of magnitude and predicts more mixed‐phase (with percentage occurrence increased from 15% to 21%), in better agreement with the observations. This study highlights the importance of accurately representing the cloud phase over the pristine remote SO by considering the ice nucleation of SSOA and SIP processes, which are currently missing in most GCM cloud microphysics parameterizations.