Numerical simulations of aerosol radiative effects and their impact on clouds and atmospheric dynamics over southern West Africa
Numerical simulations of aerosol radiative effects and their impact on clouds and atmospheric dynamics over southern West Africa
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DOI：
10.5194/acp-18-9767-2018
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发表时间：
2018-07-11
影响因子：
6.3
通讯作者：
Vogel, Bernhard
中科院分区：
文献类型：
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作者：
Deetz, Konrad;Vogel, Heike;Vogel, Bernhard
西非南部（SWA）正在经历与空气污染大幅增加相关的快速和重大的社会经济变化。然而，大气污染物，特别是气溶胶颗粒对该地区天气和气候的影响几乎没有得到探讨。在这项研究中，区域尺度模式框架COSMO-ART应用于2016年7月2-3日的夏季风过程研究，以评估气溶胶对云和大气动力学的直接和间接影响。该建模研究得到了2016年6月至7月DACCIWA项目（西非动态气溶胶化学云相互作用）广泛实地活动期间获得的观测数据的支持。如以前的研究所示，观察到沿海锋在白天发展，并在晚上向内陆传播（大西洋流入）。增加COSMO-ART中的气溶胶量导致传播速度降低，锋位移为10-30 km，夜间低空急流减弱。这与与近地面加热减少有关的过程的微妙平衡有关：（1）由于陆地-海洋温度对比度降低，因此局部压力梯度降低，气流减速，（2）有利于锋面向内陆推进的湍流减少，以及（3）通过对流边界层的延迟开始，延迟1-2小时的层云到积云转变。在一个新的概念模型中，大西洋流入的空间变化和层积云过渡的时间变化是协同作用的。我们假设一个负反馈的层积云过渡的大西洋流入增加气溶胶。结果表明，辐射作为关键球员的气溶胶通过气溶胶直接效应和Twomey效应对SWA大气动力学的影响，而降水的影响很小。
Southern West Africa (SWA) is undergoing rapid and significant socioeconomic changes associated with a massive increase in air pollution. Still, the impact of atmospheric pollutants, in particular that of aerosol particles, on weather and climate in this region is virtually unexplored. In this study, the regional-scale model framework COSMO-ART is applied to SWA for a summer monsoon process study on 2-3 July 2016 to assess the aerosol direct and indirect effect on clouds and atmospheric dynamics. The modeling study is supported by observational data obtained during the extensive field campaign of the project DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) in June-July 2016. As indicated in previous studies, a coastal front is observed that develops during daytime and propagates inland in the evening (Atlantic inflow). Increasing the aerosol amount in COSMO-ART leads to reduced propagation velocities with frontal displacements of 10-30 km and a weakening of the nocturnal low-level jet. This is related to a subtle balance of processes related to the decrease in near-surface heating: (1) flow deceleration due to reduced land-sea temperature contrast and thus local pressure gradient, (2) reduced turbulence favoring frontal advance inland and (3) delayed stratus-to-cumulus transition of 1-2 h via a later onset of the convective boundary layer. The spatial shift of the Atlantic inflow and the temporal shift of the stratus-to-cumulus transition are synergized in a new conceptual model. We hypothesize a negative feedback of the stratus-to-cumulus transition on the Atlantic inflow with increased aerosol. The results exhibit radiation as the key player governing the aerosol affects on SWA atmospheric dynamics via the aerosol direct effect and the Twomey effect, whereas impacts on precipitation are small.