Source attribution of cloud condensation nuclei and their impact on stratocumulus clouds and radiation in the south-eastern Atlantic
Source attribution of cloud condensation nuclei and their impact on stratocumulus clouds and radiation in the south-eastern Atlantic
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DOI：
10.5194/acp-2022-43
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发表时间：
2022-01
影响因子：
6.3
通讯作者：
H. Che;P. Stier;D. Watson‐Parris;H. Gordon;L. Deaconu
中科院分区：
文献类型：
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作者：
H. Che;P. Stier;D. Watson‐Parris;H. Gordon;L. Deaconu
抽象的。大西洋东南(海)上空的半永久性层积云可以作为区域和全球气候系统的“空调”。气溶胶和云的相互作用在这一地区变得很重要，并可能导致负辐射效应，部分抵消温室气体的正辐射强迫。气溶胶影响云性质的一个重要途径是作为云凝结核(CCN)。本文利用英国地球系统模式研究了海洋中CCN的来源(大气过程和排放源)，以及云滴数密度(CDNC)、云液态水路径(LWP)和辐射强迫对这些来源的响应。总体而言，总核化(二元核化)是海洋边界层CCN0.2%的最重要来源，年平均贡献CCN0.2%的50%。在排放源方面，人为排放(能源、工业、农业等)对海洋边界层年平均CCN0.2%的贡献最大，其次是BB。而在自由对流层，BB成为大气中碳碳的主要来源，占年平均值的%。不同来源的气溶胶对CDNC的贡献与它们对海洋边界层内CCN0.2%的贡献是一致的，总成核是CDNC的最主要来源。在排放量方面，人为来源也是CDNC年平均排放量的最大贡献者，紧随其后的是BB。BB对CDNC的贡献比其对CCN0.2%的贡献更显著，这主要是因为BB气溶胶还可以通过短波吸收的辐射效应增加最大过饱和度，从而增加CDNC。对于显示CDNC增加的气溶胶来源，它还显示由于自动转换减少而导致LWP的增加。BB气溶胶由于吸收作用，可以增强现有的逆温，减少亚饱和空气的夹带，导致LWP进一步增加。结果表明，BB对LWP的贡献仅次于全成核。这些发现表明，从排放源的角度来看，BB不是海洋边界层内CCN的主要来源。然而，由于它的吸收作用，它对云的贡献增加了(与CDNC的人为源大致相同，而对LWP的人为源更多)，突出了它对云的辐射效应的关键作用。对气溶胶辐射效应的研究表明，BB气溶胶总体上表现为正的辐射强迫(与气溶胶-辐射相互作用相关的辐射强迫)，但由于其对云的影响(主要是吸收效应)，其净有效辐射强迫仍然是负的。通过量化不同来源对气溶胶和云性质的影响，为了解气溶胶来源对海洋卷积云和海洋辐射的影响提供了一个框架。
Abstract. The semi-permanent stratocumulus clouds over the South-eastern Atlantic Ocean (SEA) can act as an “air conditioners” to the regional and global climate system. The interaction of aerosols and clouds become important in this region, and can lead to negative radiative effects, partially offsetting the positive radiative forcing of greenhouse gases. A key pathway of aerosols affecting cloud properties is by acting as cloud condensation nuclei (CCN). In this paper, we use the United Kingdom Earth System Model to investigate the sources of CCN (from atmospheric processes and emission sources) in the SEA, and the response of cloud droplet number concentration (CDNC), cloud liquid water path (LWP), and radiative forcing to those sources. Overall, total nucleation (binary nucleation) is the most important source of CCN0.2 % in the marine boundary layer, contributing an annual average of 50 % of CCN0.2 %. In terms of emission sources, anthropogenic emissions (from energy, industry, agriculture, etc.) contribute the most to the annual average CCN0.2 % in the marine boundary layer, followed by BB. In the free troposphere, however, BB becomes the dominant source of CCN0.2 %, accounting for 64 % of the annual average. The contribution of aerosols from different sources to CDNC is consistent with their contribution to CCN0.2 % within the marine boundary layer, with total nucleation being the most important source of CDNC overall. In terms of emissions, anthropogenic sources are also the largest contributors to the annual average of CDNC, closely followed by BB. The contribution of BB to CDNC is more significant than its increase to CCN0.2 %, mainly because BB aerosol also can increase CDNC by enhancing the maximum supersaturation through the radiative effect of shortwave absorption. For an aerosol source that shows an increase in CDNC, it also shows an increase in LWP resulting from a reduction in autoconversion. BB aerosol, due to the absorption effect, can enhance existing temperature inversions and reduce the entrainment of sub-saturated air, leading to a further increase in LWP. As a result, the contribution of BB to LWP is second only to total nucleation. These findings demonstrate that BB is not the dominant source of CCN within the marine boundary layer from an emission source perspective. However, its contribution to clouds increases due to its absorption effect (about the same as anthropogenic sources for CDNC and more than anthropogenic sources for LWP), highlighting the crucial role of its radiative effect on clouds. The results on the radiative effects of aerosols show that BB aerosol exhibits an overall positive RFari (radiative forcing associated with aerosol-radiation interaction), but its net effective radiative forcing remains negative due to its effect on clouds (mainly by absorbing effect). By quantifying aerosol and cloud properties affected by different sources, this paper provides a framework to understand aerosol sources effects on the marine cirrocumulus clouds and radiation in the SEA.