The Impact of Resolving Subkilometer Processes on Aerosol‐Cloud Interactions of Low‐Level Clouds in Global Model Simulations
The Impact of Resolving Subkilometer Processes on Aerosol‐Cloud Interactions of Low‐Level Clouds in Global Model Simulations
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DOI：
10.1029/2020ms002274
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发表时间：
2020-11
影响因子：
6.8
通讯作者：
C. Terai;M. Pritchard;P. Blossey;C. Bretherton
中科院分区：
文献类型：
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作者：
C. Terai;M. Pritchard;P. Blossey;C. Bretherton
亚千米过程对气溶胶-云相互作用(ACI)的物理过程至关重要，但在全球模式模拟中一直依赖于参数设置。因此，我们在超参数社区大气模式(UPCAM)中报告了ACI的强度，UPCAM是一个多尺度气候模式，它使用粗略的外部分辨率嵌入具有足够分辨率(水平250米，垂直20米)的显式云分辨模式，以准分辨亚千米涡旋。为了研究对ACIS的影响，将UPCAM的模拟与一个水平分辨率为4公里的较粗的多尺度模式进行了比较。UPCAM产生的云滴数密度(ND)和云液态水路径(LWP)值高于较粗的模式，但与观测值相比同样可信。我们的分析集中在北半球(20-50°N)海洋，那里的气溶胶历史上增加幅度最大。我们在两个模型中发现了来自ACI的整体辐射强迫的相似之处，但这掩盖了根本上的差异。在UPCAM中，LWP增加的辐射强迫较弱，而ND增加的强迫较大。令人惊讶的是，较弱的LWP增加并不是由于雨云LWP增加较弱，而是非雨云LWP增加较弱和UPCAM雨云比例较小共同作用的结果。这意味着，随着全球建模朝着比风暴分辨率网格更精细的方向发展，以降水的存在和对降水基线概率的良好观测约束为条件的ACI统计数据的细微差别模型验证将成为更严格的约束和更好的概念理解的关键。
Subkilometer processes are critical to the physics of aerosol‐cloud interaction (ACI) but have been dependent on parameterizations in global model simulations. We thus report the strength of ACI in the Ultra‐Parameterized Community Atmosphere Model (UPCAM), a multiscale climate model that uses coarse exterior resolution to embed explicit cloud‐resolving models with enough resolution (250 m horizontal, 20 m vertical) to quasi‐resolve subkilometer eddies. To investigate the impact on ACIs, UPCAM's simulations are compared to a coarser multiscale model with 4 km horizontal resolution. UPCAM produces cloud droplet number concentrations (Nd) and cloud liquid water path (LWP) values that are higher than the coarser model but equally plausible compared to observations. Our analysis focuses on the Northern Hemisphere (20–50°N) oceans, where historical aerosol increases have been largest. We find similarities in the overall radiative forcing from ACIs in the two models, but this belies fundamental underlying differences. The radiative forcing from increases in LWP is weaker in UPCAM, whereas the forcing from increases in Nd is larger. Surprisingly, the weaker LWP increase is not due to a weaker increase in LWP in raining clouds, but a combination of weaker increase in LWP in nonraining clouds and a smaller fraction of raining clouds in UPCAM. The implication is that as global modeling moves toward finer than storm‐resolving grids, nuanced model validation of ACI statistics conditioned on the existence of precipitation and good observational constraints on the baseline probability of precipitation will become key for tighter constraints and better conceptual understanding.