基于层积云飞机观测资料评估气溶胶间接效应

利用2009年4、5月美国浅薄低云观测项目(RACORO)的层积云飞机观测资料,使用两种方法对气溶胶间接效应进行了估算:根据云滴数浓度定义的值(AIE_n)和根据有效半径定义的值(AIE_s)。AIE_n几乎都比AIE_s大,尤其在中等含水量条件下。理论推导表明,AIE_n与AIE_s的偏差应与气溶胶对云滴谱离散度的影响有关,即离散度效应。当AIE_n加上离散度效应后,数值与AIE_s十分接近,证实了理论预期。离散度效应对气溶胶间接效应的贡献主要为抵消作用,这种抵消作用在中等含水量时最大,当含水量为0.24 g/m~3时达到37%左右。该研究成果增强了对气溶胶-云相互作用的理论认识,将有助于增强对模式和观测中气溶胶间接效应的准确评估。

Evaluation of aerosol indirect effect based on aircraft observations of stratocumulus

By considering the aircraft observational data of the stratocumulus obtained during the Routine AAF (Atmospheric Radiation Measurement(ARM) Aerial Facility) Clouds with Low Optical Water Depths(CLOWD) Optical Radiative Observations(RACORO) field operation that was accomplished in April and May 2009,two approaches were adopted in order to estimate the aerosol incidental effects.The first effect was estimated by considering the cloud drop concentration(AIE_n),while the second effect was estimated by considering the effective radius(AIE_s).It was observed that the AIE_n always owned the higher value in comparison with AIE_s,and this alteration was more projecting especially at moderate liquid water content.Theoretical derivation established on the base of deviation between AIE_n and AIE_s indicated that the dispersion of cloud droplet spectrum influentially related to the effect of aerosol in the consideration of the dispersion effect.It was observed that when the dispersion effect increased the value of evaluated AIE_n come closer to the evaluated value of AIE_s,and the happening of this corresponds authenticated the theoretical expectations.The contribution of the dispersion effect in the consideration of the aerosol indirect effect was the leading offset effect,which owned the largest value at moderate liquid water content,and it was observed that when liquid water content is 0.24 g/m³ then its corresponding percentage was about 37%.The consequences of this research enhance the theoretical understanding of the aerosol-cloud interaction and it can be concluded that it could be helpful asset to improve the accurate assessment of the aerosol indirect effect in models and observations.