Environmental effects on aerosol–cloud interaction in non-precipitating marine boundary layer (MBL) clouds over the eastern North Atlantic
Environmental effects on aerosol–cloud interaction in non-precipitating marine boundary layer (MBL) clouds over the eastern North Atlantic
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DOI：
10.5194/acp-22-335-2022
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发表时间：
2022-01
影响因子：
6.3
通讯作者：
Xiaojian Zheng;B. Xi;Xiquan Dong;Peng Wu;T. Logan;Yuanzu Wang
中科院分区：
文献类型：
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作者：
Xiaojian Zheng;B. Xi;Xiquan Dong;Peng Wu;T. Logan;Yuanzu Wang
抽象的。在北大西洋东部（ENA）海洋上，选择了20个非降水性单层海洋边界层（MBL）层云和层积云个例，使用2016-2018年期间能源部大气辐射测量（ARM）设施的地基测量来研究环境变量对气溶胶-云相互作用（ACIr）的影响。ACIr代表在分层水汽环境中，云滴有效半径re相对于0.2%过饱和云凝结核（NCCN，0.2%）数浓度变化的相对变化。随着云下边界层可降水量（PWVBL）条件的增加，ACIr值在-0.01到0.22之间变化，这表明在足够的水汽供应下，re对云凝结核的负荷更敏感，这是由于与较高的Nc和PWVBL相关的增强的凝结增长和合并过程的综合效应。主成分分析表明，在选定的情况下，最显着的模式是共同变化的MBL条件的特征在于湍流动能（TKEw）的垂直分量，去耦指数（Di），和PWVBL。ACIr的环境效应出现后，数据分层到不同的TKEw制度。ACIr值，在较低和较高PWVBL条件下，从低TKEw到高TKEw制度增加一倍以上。这可以解释的事实，即较强的边界层湍流保持一个良好的混合MBL，加强云微物理特性和云下CCN和水分来源之间的联系。在水汽充足和云凝结核含量较低的情况下，主动合并过程使云滴谱变宽，从而导致云滴谱的增大。云凝结核的活化增强和云下云凝结核含量增加引起的云滴凝结增长都能有效地降低re，共同表现为ACIr的增加。本研究探讨了环境影响的ACIr评估的重要性，并提供了观测的限制，未来的模式评估气溶胶-云的相互作用。
Abstract. Over the eastern North Atlantic (ENA) ocean, a total of 20 non-precipitating single-layer marine boundary layer (MBL) stratus and stratocumulus cloud cases are selected to investigate the impacts of the environmental variables on the aerosol–cloud interaction (ACIr) using the ground-based measurements from the Department of Energy Atmospheric Radiation Measurement (ARM) facility at the ENA site during 2016–2018. The ACIr represents the relative change in cloud droplet effective radius re with respect to the relative change in cloud condensation nuclei (CCN) number concentration at 0.2 % supersaturation (NCCN,0.2 %) in the stratified water vapor environment. The ACIr values vary from −0.01 to 0.22 with increasing sub-cloud boundary layer precipitable water vapor (PWVBL) conditions, indicating that re is more sensitive to the CCN loading under sufficient water vapor supply, owing to the combined effect of enhanced condensational growth and coalescence processes associated with higher Nc and PWVBL. The principal component analysis shows that the most pronounced pattern during the selected cases is the co-variations in the MBL conditions characterized by the vertical component of turbulence kinetic energy (TKEw), the decoupling index (Di), and PWVBL. The environmental effects on ACIr emerge after the data are stratified into different TKEw regimes. The ACIr values, under both lower and higher PWVBL conditions, more than double from the low-TKEw to high-TKEw regime. This can be explained by the fact that stronger boundary layer turbulence maintains a well-mixed MBL, strengthening the connection between cloud microphysical properties and the below-cloud CCN and moisture sources. With sufficient water vapor and low CCN loading, the active coalescence process broadens the cloud droplet size spectra and consequently results in an enlargement of re. The enhanced activation of CCN and the cloud droplet condensational growth induced by the higher below-cloud CCN loading can effectively decrease re, which jointly presents as the increased ACIr. This study examines the importance of environmental effects on the ACIr assessments and provides observational constraints to future model evaluations of aerosol–cloud interactions.