The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model
The relationship between aerosol and cloud drop number concentrations in a global aerosol microphysics model
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DOI：
10.5194/acp-9-4131-2009
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发表时间：
2009-06
影响因子：
6.3
通讯作者：
K. Pringle;K. Carslaw;D. Spracklen;G. Mann;M. Chipperfield
中科院分区：
文献类型：
--
作者：
K. Pringle;K. Carslaw;D. Spracklen;G. Mann;M. Chipperfield
抽象的。将云滴数(CDN)与气溶胶数或质量联系起来的经验关系通常被用来计算用于气候强迫评估的CDN的全球场。在这项工作中，我们使用硫酸盐和海盐气溶胶的分段全球模式和机械气溶胶激活方案来探索这种方法的局限性。我们发现，由于气溶胶尺寸分布形状的不同，给定的气溶胶数浓度会产生很大范围的CDN浓度。在全球尺度上，CDN对尺度分布的依赖导致预测的CDN(对于给定的气溶胶数)存在区域偏差。气溶胶数和CDN之间的经验关系通常来自区域数据，但适用于整个全球。在一个类似的过程中，我们导出了气溶胶数与CDN之间的区域“相关关系”，并将这些区域关系应用于全球尺度上的CDN计算。区域CDN-气溶胶关系对CDN的全球平均百分误差为20%~26%，约为上升速度加倍引起的CDN全球平均百分变化率的一半。然而，在南大洋、北极和持续层积云地区，当使用北大西洋的气溶胶-CDN相关关系时，误差高达25%-75%。这些地区产生的CDN浓度(对于给定的气溶胶数值)比全球统一经验关系预测的要高得多。不同地区的CDN-气溶胶数关系对气溶胶变化的敏感性也有很大差异。CDN随粒子数变化的幅度为4倍。持续性层积云云处理区的CDN对气溶胶数的变化特别敏感。因此，很可能低估了这些重要地区的间接影响。
Abstract. Empirical relationships that link cloud droplet number (CDN) to aerosol number or mass are commonly used to calculate global fields of CDN for climate forcing assessments. In this work we use a sectional global model of sulfate and sea-salt aerosol coupled to a mechanistic aerosol activation scheme to explore the limitations of this approach. We find that a given aerosol number concentration produces a wide range of CDN concentrations due to variations in the shape of the aerosol size distribution. On a global scale, the dependence of CDN on the size distribution results in regional biases in predicted CDN (for a given aerosol number). Empirical relationships between aerosol number and CDN are often derived from regional data but applied to the entire globe. In an analogous process, we derive regional "correlation-relations" between aerosol number and CDN and apply these regional relations to calculations of CDN on the global scale. The global mean percentage error in CDN caused by using regionally derived CDN-aerosol relations is 20 to 26%, which is about half the global mean percentage change in CDN caused by doubling the updraft velocity. However, the error is as much as 25–75% in the Southern Ocean, the Arctic and regions of persistent stratocumulus when an aerosol-CDN correlation relation from the North Atlantic is used. These regions produce much higher CDN concentrations (for a given aerosol number) than predicted by the globally uniform empirical relations. CDN-aerosol number relations from different regions also show very different sensitivity to changing aerosol. The magnitude of the rate of change of CDN with particle number, a measure of the aerosol efficacy, varies by a factor 4. CDN in cloud processed regions of persistent stratocumulus is particularly sensitive to changing aerosol number. It is therefore likely that the indirect effect will be underestimated in these important regions.