Converting AOT to CCN for Studying the Impact of Aerosol on Cloud and Precipitation

气溶胶通过以多种方式改变云的特性来影响气候系统，并且具有高度的不确定性。利用10年来大气辐射测量(ARM)对大平原南部(SGP)站点各种气溶胶和气象量的地面测量，发现了气溶胶浓度、云高度和降雨频率之间的密切关系。为了将研究从单一地点扩展到气溶胶类型有限的地方，我们将分析全球地面气溶胶机器人网络(AERONET)的气溶胶数据，以及匹配的卫星反演的云和降水产品，以进一步调查各种气溶胶和气象条件对云和降水的影响。虽然AERONET提供了最可靠和最一致的气溶胶光学厚度(AOT)的反演，但与云的形成、发展和降水更直接相关的是云集中核(CCN)。以前的许多研究使用AOT作为CCN的替代，因为AOT的观察比CCN的要多得多。这两个量描述了不同的气溶胶属性，因此有必要彻底了解它们之间的关系，这是目前缺乏的。本研究的目的是：1)调查影响AOT和CCN关系的因素，如环境相对湿度(RH)、气溶胶粒子的粒度分布和吸湿性；2)通过考虑主要影响因素，建立更稳健的AOT-CCN关系，并将其应用于AERONET AOT数据，以获得更好的AERONET站点CCN的估计；3)将估计的CCN数据与来自CloudSat的卫星云和降水数据进行匹配，以研究气溶胶对云和降水的影响。这项研究将利用AERONET、野外实验和卫星飞行任务的广泛测量。任务1和任务2将依赖于在世界许多地区开展的实地活动中收集的气溶胶特性、环境气象条件和CCN的测量。将考察许多因素，如空气质量、颗粒大小分布、可溶分数等，并将评估它们对气溶胶光学和吸湿性的影响。知识优势：1)综合分析气溶胶性质和环境对气溶胶辐射和微物理效应的影响；2)气溶胶和大气环流的关系得到改善，将使广泛可用的气溶胶对云和降水的影响从地面和星载传感器扩展到研究气溶胶对云和降水的影响，就像许多人所做的那样，但没有对它们的关系进行严格的调查；3)进一步调查和了解不同气象条件下气溶胶对不同类型气溶胶在全球尺度上的云和降水的影响。广泛影响：1)随着对AOT-CCN关系的了解和理解的加深，模型者将更了解和更有动力地探索使用全球卫星AOT产品来填补目前在研究气溶胶对全球气候影响方面的空白；2)这项研究将为本科生和研究生以及博士后提供测量气溶胶、数据分析和建模的跨学科培训机会；3)这项研究将对云物理、大气化学、气候和环境课程的教学产生直接影响。

Aerosols affect the climate system by changing cloud characteristics in many ways and with a high degree of uncertainty. Using 10 years' worth of Atmospheric Radiation Measurement (ARM) ground-based measurements of a variety of aerosol and meteorological quantities at the Southern Great Plains (SGP) site, robust relationships were found between aerosol concentration, cloud height and rain frequency. To extend the study from a single location with limited types of aerosols, we will analyze world-wide surface Aerosol Robotic Network (AERONET) aerosol data, together with matched satellite-retrieved cloud and precipitation products, to further investigate the impact of all kinds of aerosols and meteorological conditions on clouds and precipitation. While the AERONET provides the most reliable and consistent retrievals of aerosol optical thickness (AOT), it is cloud concentration nuclei (CCN) that is more directly related to cloud formation, development and precipitation. Many previous studies used AOT as a proxy for CCN, because there are much more observations of AOT than those of CCN. These two quantities describe different aerosol attributes so a thorough understanding of their relationship is warranted, which is lacking at present.The objectives of this research are to:1) investigate factors that influence the relationship between AOT and CCN, such as ambient relative humidity (RH), the particle size distribution and hygroscopic properties of aerosol particles;2) develop more robust AOT-CCN relationships by accounting for major influencing factors and apply them to AERONET AOT data to obtain better estimates of CCN at AERONET sites;3) match estimated CCN data with satellite cloud and precipitation data from CloudSat to study the impact of aerosols on cloud and precipitation.The study will make use of extensive measurements from AERONET, field experiments, and satellite missions. Tasks 1 and 2 will rely on measurements of aerosol properties, ambient meteorological conditions and CCN collected in field campaigns conducted in many parts of the world. Numerous factors will be examined, such as air mass, particle size distribution, soluble fraction, etc., and their influences on both optical and hygroscopic properties of aerosols will be assessed. Intellectual merit:1) A comprehensive analysis of how AOT and CCN are affected by aerosol properties and the ambient environment that have been most widely employed for studying aerosol radiative and microphysical effects;2) The improved relationship between AOT and CCN will enable the extension of widely available AOT from ground-based and space-borne sensors to study the impact of aerosols on cloud and precipitation, as many have done but without rigorous investigation of their relationship;3) Further investigation and understanding of the impact of aerosols on cloud and precipitation on global scales for different types of aerosols under diverse meteorological conditions.Broad impacts:1) With an improved knowledge and understanding of the AOT-CCN relationship, modelers would be better informed and motivated to explore the use of global satellite AOT products to fill the void currently present in studying the impacts of aerosols on global climate;2) The research will provide interdisciplinary training opportunities in measuring aerosols, data analysis, and modeling for undergraduate and graduate students and postdoctoral fellows;3) This study will have an immediate impact on the teaching of cloud physics, atmospheric chemistry, climate and environmental courses.