Analysis of the Condensational Growth in Marine Stratocumulus During the Second Aerosol Characterization Study

云是负责将阳光反射回太空的主要大气成分，因此是决定地球气候的关键组成部分。在气候变化中，云量或云成分的变化与大气中温室气体的增加一样重要。例如，由许多微小液滴组成的云比具有相同含水量但液滴更少和更大的云反射性更强。水滴形成于称为云凝结核（CCN）的水溶性气溶胶颗粒上。不同气团的气溶胶数量差别很大，这取决于地面类型、地面附近的风速以及与自然或人为颗粒物来源的接近程度。在气溶胶和气候之间的联系中，一个重要的环节是云滴形成和生长的凝结过程。这个项目的目的是提高我们对不同类型气团中气溶胶数量与其上形成的液滴浓度之间关系的理解。该方法利用了第二次气溶胶表征实验（ACE-2）期间飞机收集的数据，这是1997年夏天在特内里费岛北部进行的一个国际实地项目。云底以下空气中CCN的测量值将与云中测量的微滴浓度进行比较，以确定根据已知气溶胶特征预测浓度的程度。CCN的航空测量没有标准化，分析的一个重要部分将是几种不同仪器测量的CCN的比较，以指定观测的实验不确定度。通过与辐射传输和数值模拟方面的专家合作，分析结果将应用于气溶胶对云反射率和降水发展的影响问题。这项研究将为我们理解气溶胶、云层和气候之间的复杂关系提供比现在更坚实的基础。

Clouds are the main atmospheric constituent responsible for reflecting sunlight back to space, and thus are a crucial component in determining the climate of Earth. Changes in cloudiness or cloud composition can be as important an element in climate change as the increase in greenhouse gases in the atmosphere. For example, a cloud consisting of many tiny droplets is more reflective than a cloud having the same water content but with fewer and larger droplets. The droplets form on water-soluble aerosol particles called cloud condensation nuclei (CCN). Different air masses have widely different populations of aerosols, depending on the surface type, the wind speed near the ground, and the proximity to natural or anthropogenic sources of particulate matter. An important link in the connection between aerosols and climate is the condensation process by which cloud droplets form and grow. The purpose of this project is to improve our understanding of the relationship between the aerosol populations in different types of air masses and the concentration of droplets that form on them. The approach makes use of data collected by aircraft during the Second Aerosol Characterization Experiment (ACE-2), an international field program conducted north of the Island of Tenerife in the summer of 1997. Measurements of CCN in the air below cloud base will be compared with droplet concentrations measured in the clouds to determine the extent to which the concentration can be predicted on the basis of known aerosol characteristics. Airborne measurements of CCN are not standardized, and an important part of the analysis will be a comparison of CCN measured by several different instruments to specify the experimental uncertainty of the observations. Results of the analysis will be applied to the questions of aerosol effects on cloud reflectivity and precipitation development through collaboration with specialists in radiative transfer and numerical modeling. The study will provide a more solid foundation than we now have for understanding the complex relationships between aerosols, clouds, and climate.