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

云是大气的主要组成部分，负责将阳光反射回太空，因此是决定地球气候的关键组成部分。云量或云组成的变化对气候变化的影响可能与大气中温室气体的增加一样重要。例如，由许多微小水滴组成的云比水含量相同但水滴更少、更大的云的反射率更高。这些水滴形成在称为云凝结核(CCN)的水溶性气溶胶颗粒上。不同的气团具有非常不同的气溶胶种群，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。气溶胶和气候之间联系的一个重要环节是云滴形成和生长的凝结过程。该项目的目的是增进我们对不同类型气团中的气溶胶种群与其上形成的液滴浓度之间的关系的了解。该方法利用了飞机在第二次气溶胶特性实验(ACE-2)期间收集的数据，该实验是1997年夏天在特内里费岛北部进行的一项国际实地计划。云底以下空气中CCN的测量将与云中测量的液滴浓度进行比较，以确定根据已知的气溶胶特征可以预测浓度的程度。CCN的空中测量没有标准化，分析的一个重要部分将是比较几种不同仪器测量的CCN，以明确观测的实验不确定度。分析结果将通过与辐射传输和数值模拟方面的专家协作，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、云和气候之间的复杂关系提供比我们现在更坚实的基础。

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.