Coupling aerosol-cloud-radiative processes in the WRF-Chem model: Investigating the radiative impact of elevated point sources
Coupling aerosol-cloud-radiative processes in the WRF-Chem model: Investigating the radiative impact of elevated point sources
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DOI：
10.5194/acp-9-945-2009
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发表时间：
2009-01-01
影响因子：
6.3
通讯作者：
Fast, J. D.
中科院分区：
文献类型：
--
作者：
Chapman, E. G.;Gustafson, W. I., Jr.;Fast, J. D.
利用WRF-Chem社区模式研究了北美东北部地区夏季气溶胶强迫和云-气溶胶相互作用的局部和区域高架点源的影响。利用现有模块模拟了气溶胶对入射太阳辐射的直接影响，将气溶胶的大小和化学成分与气溶胶光学特性联系起来。间接影响进行了模拟，通过增加一个预测处理的云滴数和添加模块，激活气溶胶粒子形成云滴，模拟水相化学，并将两个时刻的处理云水（云水质量和云滴数）降水和现有的辐射计划。因此，在修改后的模型中创建了完全交互式的反馈，气溶胶影响云滴数量和云辐射特性，云通过水过程，湿清除和气相相关的光解过程改变气溶胶的大小和组成。基线模拟与观测结果的比较表明，该模型捕捉到了气溶胶光学厚度（AODs）的一般时间周期，并在适当的时间和地点产生了与观测相当厚度的云。该模型高估了SO2混合比和PM2.5质量，但再现了观测到的SO2硫酸盐气溶胶比例的范围，这表明大气氧化过程导致气溶胶硫酸盐形成的模型中捕获。将基线模拟与敏感性模拟进行比较，在敏感性模拟中，将模型层以上的所有排放量设置为零，从而消除烟囱排放。两个模拟之间的气溶胶和云相关属性的瞬时，特定地点的差异可能是相当大的，因为去除地表以上的排放源影响云在建模域中形成的时间和地点。当在空间上最好的分辨率模式域（其范围对应于一个单一的全球气候模式网格单元的典型大小）和时间超过三天的分析期间，总降雨量的敏感性模拟增加了31%，在基线模拟。在灵敏度模拟中形成的光学薄云（任意定义为光学深度小于1的云）较少。域平均AOD从基线模拟中的0.46下降到灵敏度模拟中的0.38。由地表上方点源排放的初级颗粒物和气溶胶前体物产生的额外气溶胶的总体净效应是平均白天下沉短波辐射的域平均减少5 Wm（-2）。
The local and regional influence of elevated point sources on summertime aerosol forcing and cloud-aerosol interactions in northeastern North America was investigated using the WRF-Chem community model. The direct effects of aerosols on incoming solar radiation were simulated using existing modules to relate aerosol sizes and chemical composition to aerosol optical properties. Indirect effects were simulated by adding a prognostic treatment of cloud droplet number and adding modules that activate aerosol particles to form cloud droplets, simulate aqueous-phase chemistry, and tie a two-moment treatment of cloud water (cloud water mass and cloud droplet number) to precipitation and an existing radiation scheme. Fully interactive feedbacks thus were created within the modified model, with aerosols affecting cloud droplet number and cloud radiative properties, and clouds altering aerosol size and composition via aqueous processes, wet scavenging, and gas-phase-related photolytic processes. Comparisons of a baseline simulation with observations show that the model captured the general temporal cycle of aerosol optical depths (AODs) and produced clouds of comparable thickness to observations at approximately the proper times and places. The model overpredicted SO2 mixing ratios and PM2.5 mass, but reproduced the range of observed SO2 to sulfate aerosol ratios, suggesting that atmospheric oxidation processes leading to aerosol sulfate formation are captured in the model. The baseline simulation was compared to a sensitivity simulation in which all emissions at model levels above the surface layer were set to zero, thus removing stack emissions. Instantaneous, site-specific differences for aerosol and cloud related properties between the two simulations could be quite large, as removing above-surface emission sources influenced when and where clouds formed within the modeling domain. When summed spatially over the finest resolution model domain (the extent of which corresponds to the typical size of a single global climate model grid cell) and temporally over a three day analysis period, total rainfall in the sensitivity simulation increased by 31% over that in the baseline simulation. Fewer optically thin clouds, arbitrarily defined as a cloud exhibiting an optical depth less than 1, formed in the sensitivity simulation. Domain-averaged AODs dropped from 0.46 in the baseline simulation to 0.38 in the sensitivity simulation. The overall net effect of additional aerosols attributable to primary particulates and aerosol precursors from point source emissions above the surface was a domain-averaged reduction of 5Wm(-2) in mean daytime downwelling shortwave radiation.