Ice Nuclei and Ice Initiation in Mid-latitude Clouds in Springtime: Background and Dust-Affected

该项目侧重于增进对冰成核的了解，这是导致降水并影响冷云辐射特性的最基本过程之一。对云中冰的形成过程缺乏了解，导致对降水生产进行模拟的能力存在很大的不确定性。此外，最不为人所知的气溶胶气候效应之一是冷云特性的改变，即“冰的间接效应”。由于缺乏关于能够在与对流层中上层有关的条件下形成冰的粒子浓度的观测数据，这种影响的量化受到了阻碍。近年来在各种环境中使用连续流动扩散箱收集的冰核数据有助于阐明冰的间接效应。这些数据表明，矿物尘埃作为非均质冰核(IN)的一个重要但高度可变的来源具有重要意义。通过这项研究，将扩大相对不受扰动的背景对流层IN的数据库，并将在多尘气团中量化沙尘颗粒浓度、IN浓度以及对冷云形成和微物理的影响之间的关系。具体地说，IN测量将与两个基于飞机的测量计划相关联，其目标包括调查波浪云、中层云、孤立的积云和卷云中的冰形成。这两个实验分别是ICE-L(云中冰实验层云)和PACDEX(太平洋沙尘实验)。在该研究小组在以前研究中开发的方法的基础上，将在飞行计划的背景下使用特定的采样程序来调查冰的形成过程，并将IN测量与云中的冰晶体浓度联系起来。此外，将利用全球气溶胶输送模型的辅助测量和指导，测量成冰颗粒的成分，浓度和成分都将与气溶胶来源有关。这两项实地研究都特别强调评估春季从亚洲到美国的长距离沙尘输送对云形成和性质的影响。预计结果将为混合相云和冰相云的数值模式模拟提供信息并加以改进。该项目的学术价值在于对直接影响冷云特性和间接影响气候的气溶胶的重要亚群的理解有望得到改善。实地研究的参与提供了一个前所未有的机会，可以确认和加强对云中冰的形成以及与自然或人造来源的气溶胶粒子的联系的了解。这项工作将产生更广泛的影响，包括促进研究生教育和培训，加强研究基础设施，在新的机载平台上测试新的测量能力，以及通过与数值建模人员合作，将结果应用于全球气候变化问题。一名研究生和博士后研究员将参加实地实验，这将涉及来自多所大学和一个国家研究中心的不同学科的科学家之间的合作。最后，这些数据对于全球变化中悬而未决的问题和人类活动对气候的影响至关重要。预计这项研究的研究将得到广泛的应用，如人类活动对云形成的影响的全球研究，以及云解析和全球模式中改进的参数化的发展。

This project focuses on advancing understanding of ice nucleation, one of the most basic processes leading to precipitation and impacting the radiative properties of cold clouds. Poor understanding of ice initiation processes in clouds results in large uncertainties in the ability to model precipitation production. Furthermore, one of the least understood postulated climate effects of aerosols is the modification of cold-cloud properties, the "ice indirect effect". Quantification of this effect is hampered by the lack of observational data on concentrations of particles capable of initiating ice formation at conditions relevant to the mid-to-upper troposphere. Data on ice nucleation collected using continuous flow diffusion chambers in a variety of settings in recent years have contributed to elucidation of the ice indirect effect. These data have indicated the importance of mineral dust as a significant, but highly variable, source of heterogeneous ice nuclei (IN). Through this research, the database on relatively unperturbed background tropospheric IN will be expanded and, in dust-laden air masses, relationships between dust particle concentrations, IN concentrations, and impacts on cold cloud formation and microphysics will be quantified. Specifically, IN measurements will be made in association with two aircraft-based measurement programs having objectives that include the investigation of ice initiation in wave clouds, mid-level layer clouds, isolated cumuli and cirrus clouds. These experiments are ICE-L (Ice in Clouds Experiment - Layer clouds) and PACDEX (PACific Dust Experiment). Building on methodologies developed in previous studies by this research group, specific sampling procedures will be used within the context of flight plans to investigate ice formation processes and to relate IN measurements to ice crystal concentrations in clouds. Further, the compositions of ice nucleating particles will be measured and both concentrations and compositions will be related to aerosol sources, using supporting measurements and guidance from global aerosol transport models. Both field studies have a particular emphasis on evaluating the impact on cloud formation and properties of long-range dust transport from Asia to the U.S. in Spring. Results are expected to inform and improve numerical model simulations of mixed- and ice-phase clouds. The intellectual merit of the project lies in the expected improvement in understanding the important sub-population of aerosols that affect cold cloud properties directly and climate indirectly. Participation in the field studies offers an unprecedented opportunity to confirm and augment understanding of ice initiation in clouds and links to aerosol particles of natural or manmade origin. This work will have broader impacts through promoting graduate education and training, enhancing research infrastructure, testing new measurement capabilities on a new airborne platform, and through collaboration with numerical modelers, application of results toward global climate change issues. A graduate student and post-doctoral researcher will participate in the field experiments, which will involve collaborations amongst scientists in different disciplines from multiple universities and from a national research center. Finally, these data are of critical importance to unresolved issues in global change and climate impacts of anthropogenic activities. It is expected that the research of this research will find broad applications as diverse as global studies of the effects of human activities on cloud formation and development of improved parameterizations in cloud resolving and global models.