Aerosol properties and their influences on low warm clouds during the Two-Column Aerosol Project
Aerosol properties and their influences on low warm clouds during the Two-Column Aerosol Project
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DOI：
10.5194/acp-19-9515-2019
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发表时间：
2019-02
影响因子：
6.3
通讯作者：
Jianjun Liu;Zhanqing Li
中科院分区：
文献类型：
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作者：
Jianjun Liu;Zhanqing Li
抽象的。从2012年夏季开始，在马萨诸塞州科德角的双柱气溶胶计划现场活动中收集了12个月的测量数据，用来研究气溶胶的物理、光学和化学性质及其对热力(即对流层低稳定度)条件对云发展的影响。研究了不同主导气团条件下气溶胶负荷与云性质的关系、第一间接效应(FIE)的大小以及FIE对不同气溶胶成分的敏感性。气溶胶数浓度(Na)的季节变化与气溶胶光学性质(即散射系数、σS和柱状气溶胶光学厚度)的变化不一致。研究发现，有机物对小颗粒的贡献很大。这一贡献在颗粒生长过程中有所下降。在气溶胶浓度较低的情况下，液态水路径(LWP)和液滴有效半径(DER)随LTS的增加而显著增大，而在气溶胶浓度较高的条件下，LWP和DER变化不大，表明气溶胶显著减弱了云发展对LTS的依赖。LWP和DER从低到高的减少在稳定的环境中更大，这表明稳定条件下的云比不稳定条件下的云更容易受到气溶胶扰动的影响。高的气溶胶负荷减弱了DER随LWP增加而增加的趋势，而强化了云光学厚度(COD)随LWP增加而增加的趋势，从而改变了云性质之间的相互依赖关系。在大陆和海洋气团条件下，高气溶胶负荷均可显著增加COD，降低LWP和DER，使其分布变窄。在大陆气团条件下估计的FIE的大小在0.07±0.03到0.26±0.09之间，平均值为0.16±0.03，并且随着LWP的增加有增加的趋势。有机物含量较低的气溶胶的FIE值大于有机物含量较高的气溶胶的FIE值。这意味着，由主要含有无机物的气溶胶颗粒为主的地区上空的云比以有机气溶胶颗粒为主的地区上空的云更容易受到气溶胶扰动的影响，从而导致更大的气候强迫。
Abstract. Twelve months of measurements collected during the Two-Column Aerosol Project field campaign at Cape Cod, Massachusetts, which started in the summer of 2012, were used to investigate aerosol physical, optical, and chemical properties and their influences on the dependence of cloud development on thermodynamic (i.e., lower tropospheric stability, LTS) conditions. Relationships between aerosol loading and cloud properties under different dominant air-mass conditions and the magnitude of the first indirect effect (FIE), as well as the sensitivity of the FIE to different aerosol compositions, are examined. The seasonal variation in aerosol number concentration (Na) was not consistent with variations in aerosol optical properties (i.e., scattering coefficient, σs, and columnar aerosol optical depth). Organics were found to have a large contribution to small particle sizes. This contribution decreased during the particle growth period. Under low-aerosol-loading conditions, the liquid water path (LWP) and droplet effective radius (DER) significantly increased with increasing LTS, but, under high-aerosol-loading conditions, LWP and DER changed little, indicating that aerosols significantly weakened the dependence of cloud development on LTS. The reduction in LWP and DER from low- to high-aerosol-loading conditions was greater in stable environments, suggesting that clouds under stable conditions are more susceptible to aerosol perturbations than those under more unstable conditions. High aerosol loading weakened the increase in DER as LWP increased and strengthened the increase in cloud optical depth (COD) with increasing LWP, resulting in changes in the interdependence of cloud properties. Under both continental and marine air-mass conditions, high aerosol loading can significantly increase COD and decrease LWP and DER, narrowing their distributions. Magnitudes of the FIE estimated under continental air-mass conditions ranged from 0.07±0.03 to 0.26±0.09 with a mean value of 0.16±0.03 and showed an increasing trend as LWP increased. The calculated FIE values for aerosols with a low fraction of organics are greater than those for aerosols with a high fraction of organics. This implies that clouds over regions dominated by aerosol particles containing mostly inorganics are more susceptible to aerosol perturbations, resulting in larger climate forcing, than clouds over regions dominated by organic aerosol particles.