Droplet Nuclei and Condensed Water Content in Mixed-Phase Clouds

这项资助支持Twohy博士参与AIRS II项目（第二联盟结冰研究），这是美国、加拿大和欧洲机构和机构的合作，受到飞机结冰这一重要实际问题的激励。AIRS实地项目计划在2003-2004年冬季进行，基地设在加拿大蒙特利尔北部的Mirabel机场，地面观测网和地面遥感设备将在那里部署。图伊博士和她的同事们将在俄亥俄州克利夫兰的国家科学基金会C-130飞机上负责云的微物理观测。主要的科学目标是解释在可能含有冰晶的云层中，过冷液滴区域能够形成并继续存在的环境。C-130将配备测量云的含水量和冰含量的设备；冰晶：冰晶的浓度、大小、习性和密度；造冰核的浓度；云凝结核（CCN）的活动谱；以及项目区域内的气溶胶颗粒的浓度和特征以及目标云形成的上游空气中的气溶胶颗粒的浓度和特征。图伊博士将负责两种仪器，逆流虚拟冲击器（CVI）和云分光仪和冲击器（CSI）。CVI是一种安装在机身上的仪器，它对直径在8到50微米之间的云滴和冰晶进行取样和测量，并蒸发水分，留下残留的颗粒，这些颗粒可以被分析，以确定云滴和冰晶形成的核的大小和组成。CSI是一种安装在机翼上的新型仪器，可以测量每单位体积云的冷凝水质量、液滴大小分布和颗粒残留。这些仪器提供的数据，当与云外测量的气溶胶和CCN进行比较时，将表明哪些气溶胶参与了云的形成，它们在云中混合的程度，以及理论在多大程度上能够根据CCN活性谱预测水滴大小分布。将特别注意大型过冷液滴，因为这是飞机结冰的主要原因。该研究不仅有助于从根本上认识过冷云的微观物理结构，而且有助于提高航空安全水平。

This grant supports the participation of Dr. Twohy in the AIRS II project (second Alliance Icing Research Study), a collaboration of American, Canadian, and European agencies and institutions motivated by the important practical problem of aircraft icing. The AIRS field program is scheduled for the winter of 2003-2004 and based at Mirabel Airport, north of Montreal, Canada, where a surface observing network and ground-based remote-sensing equipment will be located. Dr. Twohy and her colleagues will be responsible for cloud microphysical observations aboard the NSF C-130 aircraft operating out of Cleveland, Ohio. The main scientific objective is to explain the circumstances by which regions of supercooled drops can form and continue to exist in clouds that may also contain ice crystals. The C-130 will be equipped for measuring the water content and ice content of clouds; the concentration, size, habit, and density of ice crystals; the concentration of ice-forming nuclei; the activity spectrum of cloud condensation nuclei (CCN); and the concentration and characteristics of aerosol particles both within the project area and in the air upstream of where the clouds of interest form. Dr. Twohy will be in charge of two instruments, a counterflow virtual impactor (CVI) and a cloud spectrometer and impactor (CSI). The CVI is a fuselage-mounted instrument that samples and sizes cloud droplets and ice crystals between about 8 and 50 micrometers in diameter and evaporates the water, leaving residual particles that can be analyzed to determine the size and composition of the nuclei on which the droplets and crystals formed. The CSI is a new, wing-mounted instrument that measures the mass of condensed water per unit volume of cloud, the droplet-size distribution, and the particle residue. The data provided by these instruments, when compared with the aerosols and CCN measured just outside the cloud, will indicate which of the aerosols participated in cloud formation, the extent to which they were mixed into the cloud, and the degree to which theory enables the prediction of the drop-size distribution on the basis of the CCN activity spectrum. Special attention will be given to large supercooled drops, because these are a major cause of aircraft icing. The research contributes not only to the fundamental understanding of the microphysical structure of supercooled clouds but also to the advancement of aviation safety.