Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM
Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM
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为什么大气环流模型高估了气溶胶云寿命效应？
DOI：
10.5194/acp-17-21-2017
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发表时间：
2017
影响因子：
6.3
通讯作者：
J. Penner
中科院分区：
文献类型：
--
作者：
Cheng Zhou;J. Penner
抽象的。基于观测的研究表明，气溶胶云寿命效应或云液态水路径（LWP）随气溶胶载量增加而增加可能在气候模式中被高估。在这里，我们模拟浅暖云2011年5月27日在南部大平原（SGP）的测量站点建立的能源部（DOE）的大气辐射测量（ARM）计划，使用单柱版本的全球气候模型（社区大气模型或CAM）和云解析模型（CRM）。CAM模拟的LWP随气溶胶负荷的增加而显著增加，而CRM模拟的LWP则不随气溶胶负荷的增加而显著增加。云滴数增加时，自转换率的大幅度下降是导致CAM中LWP增加的原因。在CRM中，自动转换率也降低了，但这被云顶附近云滴蒸发的增加所抵消甚至超过，导致LWP的总体下降。我们的研究结果表明，气候模式需要包括云顶生长和蒸发/凝结过程对云滴数浓度的依赖性。
Abstract. Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 27 May 2011 at the southern Great Plains (SGP) measurement site established by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) program using a single-column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near the cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.