Large simulated radiative effects of smoke in the south-east Atlantic
Large simulated radiative effects of smoke in the south-east Atlantic
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DOI：
10.5194/acp-18-15261-2018
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发表时间：
2018-10-24
影响因子：
6.3
通讯作者：
Carslaw, Ken S.
中科院分区：
文献类型：
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作者：
Gordon, Hamish;Field, Paul R.;Carslaw, Ken S.
2016年8月，在对流允许和全球分辨率下，使用HadGEM气候模式对Ascension岛附近热带南大西洋1200 x 1200 km（2）区域进行了为期10天的案例研究。在模拟期间，来自非洲的生物质燃烧烟雾进入该地区并混合到云层中。在Ascension岛，这场烟雾事件是2016年火灾季节最强烈的。感兴趣的区域是在4公里的分辨率模拟，没有参数化的对流计划。模拟由全球模型驱动并与全球模型进行比较。这是第一次，英国化学和气溶胶模式（UKCA）包括在一个区域模式与预测气溶胶数浓度平流从全球模式在该地区的边界。火灾排放增加总气溶胶负担的一个因素的3.7和云滴数浓度的一个因素的3，这是与中分辨率成像分光仪观测。在区域模式中，逆温高度减少了高达200米时，包括烟雾。烟雾也影响降水，在一定程度上取决于模型的微物理。微物理和动力学的变化导致的液态水路径的增加60克（-2），相对于一个模拟无烟雾气溶胶，在污染期间平均。这种增长是不确定的，在全球模型中较小。这主要是由于辐射驱动的动力学变化，而不是降水抑制气溶胶。在5天的污染期内，烟雾的直接辐射效应为+11.4Wm（-2），半直接辐射效应为-30.5Wm（-2），间接辐射效应为-10.1Wm（-2）。我们的结果表明，辐射效应是敏感的模式的结构（全球与区域）和降雨自动转换的参数化。此外，我们模拟了一个液态水路径，与卫星观测结果相比，平均偏高22%，这导致了对域平均气溶胶直接效应和气溶胶对云的影响的高估计。有了这些注意事项，我们模拟了整个区域的大净冷却，为-27.6Wm（-2）。
A 1200 x 1200 km(2) area of the tropical South Atlantic Ocean near Ascension Island is studied with the HadGEM climate model at convection-permitting and global resolutions for a 10-day case study period in August 2016. During the simulation period, a plume of biomass burning smoke from Africa moves into the area and mixes into the clouds. At Ascension Island, this smoke episode was the strongest of the 2016 fire season. The region of interest is simulated at 4 km resolution, with no parameterised convection scheme. The simulations are driven by, and compared to, the global model. For the first time, the UK Chemistry and Aerosol model (UKCA) is included in a regional model with prognostic aerosol number concentrations advecting in from the global model at the boundaries of the region. Fire emissions increase the total aerosol burden by a factor of 3.7 and cloud droplet number concentrations by a factor of 3, which is consistent with MODIS observations. In the regional model, the inversion height is reduced by up to 200m when smoke is included. The smoke also affects precipitation, to an extent which depends on the model microphysics. The microphysical and dynamical changes lead to an increase in liquid water path of 60gm(-2) relative to a simulation without smoke aerosol, when averaged over the polluted period. This increase is uncertain, and smaller in the global model. It is mostly due to radiatively driven dynamical changes rather than precipitation suppression by aerosol. Over the 5-day polluted period, the smoke has substantial direct radiative effects of +11.4Wm(-2) in the regional model, a semi-direct effect of -30.5 Wm(-2) and an indirect effect of -10.1Wm(-2). Our results show that the radiative effects are sensitive to the structure of the model (global versus regional) and the parameterization of rain autoconversion. Furthermore, we simulate a liquid water path that is bi-ased high compared to satellite observations by 22% on average, and this leads to high estimates of the domain-averaged aerosol direct effect and the effect of the aerosol on cloud albedo. With these caveats, we simulate a large net cooling across the region, of -27.6Wm(-2).