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首页> 外文期刊>Atmospheric chemistry and physics >Aerosol size-dependent below-cloud scavenging by rain and snow in the ECHAM5-HAM
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Aerosol size-dependent below-cloud scavenging by rain and snow in the ECHAM5-HAM

机译：ECHAM5-HAM中降雨和降雪对气溶胶尺寸依赖性的低于云层的清除

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摘要

Wet deposition processes are highly efficient in the removal of aerosols from the atmosphere, and thus strongly influence global aerosol concentrations, and clouds, and their respective radiative forcings. In this study, physically detailed size-dependent below-cloud scavenging parameterizations for rain and snow are implemented in the ECHAM5-HAM global aerosol-climate model. Previously, below-cloud scavenging by rain in the ECHAM5-HAM was simply a function of the aerosol mode, and then scaled by the rainfall rate. The below-cloud scavenging by snow was a function of the snowfall rate alone. The global mean aerosol optical depth, and sea salt burden are sensitive to the below-cloud scavenging coefficients, with reductions near to 15% when the more vigorous size-dependent below-cloud scavenging by rain and snow is implemented. The inclusion of a prognostic rain scheme significantly reduces the fractional importance of below-cloud scavenging since there is higher evaporation in the lower troposphere, increasing the global mean sea salt burden by almost 15%. Thermophoretic effects are shown to produce increases in the global and annual mean number removal of Aitken size particles of near to 10%, but very small increases (near 1%) in the global mean below-cloud mass scavenging of carbonaceous and sulfate aerosols. Changes in the assumptions about the below-cloud scavenging by rain of particles with radius smaller than 10 nm do not cause any significant changes to the global and annual mean aerosol mass or number burdens, despite a change in the below-cloud number removal rate for nucleation mode particles by near to five-fold. Annual and zonal mean nucleation mode number concentrations are enhanced by up to 30% in the lower troposphere with the more vigourous size-dependent below-cloud scavenging. Closer agreement with different observations is found when the more physically detailed below-cloud scavenging parameterization is employed in the ECHAM5-HAM model.
机译：湿式沉积过程在从大气中去除气溶胶方面非常高效，因此会强烈影响全球气溶胶浓度，云量及其各自的辐射强迫。在这项研究中，在ECHAM5-HAM全球气溶胶-气候模型中实施了针对雨雪的物理详细尺寸相关的低于云的清除参数设置。以前，在ECHAM5-HAM中通过雨水清除云层以下只是气溶胶模式的函数，然后根据降雨率进行缩放。积雪清除云层以下仅是降雪速度的函数。全球平均气溶胶光学深度和海盐负荷对云层以下的清除系数敏感，如果实施了更强的大小相关的雨雪清除云层以下的措施，则减少了近15％。由于低层对流层中的蒸发量更高，因此将预测性降雨方案包括在内大大降低了清除云层以下部分的重要性，使全球平均海盐负担增加了近15％。结果表明，热泳效应使Aitken尺寸颗粒的全球和年平均去除量增加了近10％，但对碳质和硫酸盐气溶胶的全球平均低于云量的清除作用却有很小的增加（接近1％）。尽管半径小于10 nm的尘埃清除率发生了变化，但关于半径小于10 nm的粒子被雨水冲刷而清除云层的假设的变化不会导致全球和年度平均气溶胶质量或数量负担发生任何重大变化。成核模式的颗粒接近五倍。在对流层较低的地方，年度活动和区域平均成核模式数浓度增加了多达30％，而对大小的依赖则取决于云层下的清除。当在ECHAM5-HAM模型中采用物理上更详细的云下清除参数化方法时，会发现与不同观察结果更一致。

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