Cloud condensation nuclei (CCN) numbers derived from CAMS reanalysis EAC4 (Version 1)

Project: Quantifying aerosol-cloud-climate effects by regime - The goal of QUAERERE (Latin for researching) is a reliable, observations-based, global quantification of aerosol indirect effects, which would also imply a constraint on climate sensitivity and thus climate predictions. This goal is now reachable combining recent advances in different disciplines: (i) a decade-long satellite dataset involving retrievals of the relevant quantities is now available, complemented by a complete aerosol dataset from a new reanalysis; (ii) on the basis of high-resolved numerical weather prediction models, which include parameterisations of aerosol cycles and cloud-precipitation microphysics, cloud-system resolving simulations at a regional scale are now possible; reliable simulations beyond idealised cases are thus possible. These tools are complemented by comprehensive global climate models and reference ob servations from ground-based sites. The problem in aerosol-cloud-climate effects is in its complexity: Various processes counteract each other, and large spatiotemporal variability of clouds buffers the forcing effects. QUAERERE proposes a two-fold divide-and-conquer approach to this complex problem: (i) aerosol-cloud-climate effects will be investigated by regime; this allows to circumvent the problem of aerosol-cloud-climate effects being buffered when averaging over different regimes; and (ii) by investigating individual terms contributing to the aerosol-cloud-climate effects separately; this allows to analyse individual statistical relationship in satellite observations and model results consistently, and to perform model sensitivity studies for cause-effect attribution. QUAERERE is funded by European Research Council (Call ERC-2012-StG, PE10, FP7 ideas starting grant 306284). Summary: Determining concentrations of cloud condensation nuclei (CCN) is one of the first steps in the chain in analysis of cloud droplet formation, the direct microphysical link between aerosols and cloud droplets, a process key for aerosol-cloud interactions (ACI). However, due to sparse coverage of in-situ measurements and difficulties associated with retrievals from satellites, a global exploration of their magnitude, source, temporal and spatial distribution cannot be easily obtained. Thus, a better representation of CCN is one of the goals for quantifying ACI processes and achieving uncertainty reduced estimates of their associated radiative forcing. Here, we introduce a new CCN dataset which is derived based on aerosol mass mixing ratios from the latest Copernicus Atmosphere Monitoring Service (CAMS) reanalysis (RA: EAC4) in a diagnostic model that uses CAMSRA aerosol properties and a simplified kappa-Köhler framework suitable for global models. Acknowledgement: Generated using Copernicus Atmosphere Monitoring Service information [2003-2021]. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains. The source data is downloaded from the Copernicus Atmosphere Monitoring Service (CAMS) Atmosphere Data Store (ADS) (https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-reanalysis-eac4?tab=overview).项目：按模态量化气溶胶-云-气候效应——QUAERERE（拉丁语意为“研究”）的目标是基于观测数据，对气溶胶间接效应进行可靠的全球量化，这同时也将为气候敏感性乃至气候预测提供约束。 这一目标如今可通过整合多学科的最新进展得以实现：其一，目前已拥有覆盖十年时长的卫星数据集，包含相关物理量的反演结果，并辅以来自全新再分析资料的完整气溶胶数据集；其二，依托包含气溶胶循环与云-降水微物理参数化方案的高分辨率数值天气预报模式，如今已可开展区域尺度的云系统解析模拟，从而能够实现脱离理想工况的可靠模拟。上述研究工具还可辅以全面的全球气候模式以及来自地面观测站点的参考观测数据。 气溶胶-云-气候效应的研究难点在于其复杂性：各类过程相互抵消，而云的强时空变异性会缓冲辐射强迫效应。对此，QUAERERE提出了双管齐下的分治策略来攻克这一复杂难题：其一，按模态开展气溶胶-云-气候效应研究，以此规避在不同模态间平均时气溶胶-云-气候效应被缓冲的问题；其二，单独拆解贡献于气溶胶-云-气候效应的各个分项进行研究，如此便可一致性地分析卫星观测与模式结果中的个体统计关系，并开展模式敏感性研究以实现因果归因。 QUAERERE项目由欧洲研究委员会（European Research Council）资助（资助编号：ERC-2012-StG、PE10、FP7创意启动基金306284）。 **摘要**：云凝结核（Cloud Condensation Nuclei，CCN）浓度的测定是云滴形成分析链条中的首要环节之一，而云滴形成是气溶胶与云滴之间直接的微物理关联，也是气溶胶-云相互作用（Aerosol-Cloud Interactions，ACI）的关键过程。然而，由于原位观测的覆盖范围有限，且卫星反演存在诸多难点，目前尚难以获取其全球尺度的浓度量级、来源及时空分布特征。因此，更精准地表征云凝结核，是量化气溶胶-云相互作用过程、降低相关辐射强迫估算不确定性的核心目标之一。本研究基于最新的哥白尼大气监测服务（Copernicus Atmosphere Monitoring Service，CAMS）再分析资料（RA: EAC4）中的气溶胶质量混合比，借助采用CAMSRA气溶胶特性与适配全球模式的简化κ-Köhler框架的诊断模型，构建了全新的云凝结核数据集。 **致谢**：本研究使用了2003-2021年的哥白尼大气监测服务相关信息。欧洲委员会与欧洲中期天气预报中心（ECMWF）均不对基于其所提供的哥白尼信息或数据的任何使用行为承担责任。原始数据下载自哥白尼大气监测服务大气数据商店（ADS）：https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-reanalysis-eac4?tab=overview。