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

该项目的重点是推进对冰核的理解，这是导致降水和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了解不多，导致模拟降水产生的能力存在很大的不确定性。此外，气溶胶的一个最不为人所知的气候效应是冷云特性的改变，即“冰间接效应”。由于缺乏在对流层中上部相关条件下能够引发结冰的粒子浓度的观测数据，对这种影响的量化受到阻碍。近年来，在各种环境中使用连续流扩散室收集的冰成核数据有助于阐明冰的间接效应。这些数据表明矿尘的重要性，作为一个重要的，但高度可变的，来源的异质冰核（IN）。通过这项研究，相对未受干扰的背景对流层IN的数据库将得到扩展，在充满灰尘的空气质量，尘埃粒子浓度之间的关系，IN浓度，冷云形成和微物理的影响将被量化。具体而言，IN测量将与两个基于飞机的测量计划相关联，其目标包括调查波云、中层云、孤立积云和卷云中的冰的形成。这些实验是ICE-L（云中冰实验-层状云）和PACDEX（太平洋尘埃实验）。在该研究小组以前研究中开发的方法的基础上，将在飞行计划范围内使用特定的取样程序，以调查冰的形成过程，并将IN测量与云中冰晶浓度联系起来。此外，冰成核颗粒的成分将被测量，浓度和成分将与气溶胶源相关，使用全球气溶胶传输模型的支持测量和指导。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尘埃输送对云形成和特性的影响。预计结果将为混合云和冰相云的数值模型模拟提供信息和改进。该项目的智力价值在于预期将增进对直接影响冷云特性和间接影响气候的气溶胶重要亚群的了解。参与实地研究提供了一个前所未有的机会，以确认和扩大对云中冰的形成以及与自然或人为来源的气溶胶颗粒的联系的了解。这项工作将通过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，并通过与数值模拟人员的合作，将结果应用于全球气候变化问题，产生更广泛的影响。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和人类活动的气候影响方面尚未解决的问题至关重要。预计这项研究的研究将发现广泛的应用，如全球研究人类活动对云形成的影响，以及云解析和全球模型中改进参数化的发展。

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.