Supercooled Large Drop Formation by Ultragiant Particles in Wintertime Stratiform Clouds during the Second Alliance Icing Research Study (AIRS II)

题目：冬季层状云中超大粒子形成的过冷大液滴。这项资助支持Lasher-Trapp博士参与AIRS II项目（第二联盟结冰研究），该项目是由美国、加拿大和欧洲的机构和机构合作开展的，主要研究飞机结冰的重要实际问题。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，地面观测网络和地面遥感设备将在那里部署。拉舍-特拉普博士和她的同事将在美国国家科学基金会的C-130飞机上负责云的微物理观测，该飞机将从俄亥俄州克利夫兰起飞。主要的科学目标是解释在冰晶可能存在的情况下，过冷云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。Lasher-Trapp博士将使用各种光学和撞击粒子传感器来确定“超巨型”粒子（UGP）的浓度、大小和组成（固体或液体）——这些粒子的等效球形直径大于约10微米。人们知道，在温度过高而不含冰的云中，这种粒子有时通过凝聚-凝聚过程在雨的形成中发挥作用，但在含有冰晶或过冷水的云中，它们还没有被系统地研究过，甚至没有被观察到。据推测，UGP可能解释了最近报道的冬季云层中大于50微米的过冷雨滴的观测结果——大到足以成为飞机结冰的主要原因。计划在AIRS II上进行测量，将提供从小于10微米到0.6毫米的颗粒的信息。将对这些数据进行分析，以确定云外测量的UGP浓度与云内大型过冷液滴的浓度之间是否存在对应关系。如果是这样的话，UGP的存在可以解释为什么过冷液滴即使在可能冻结的过冷温度下也能长得很大，或者，如果冰晶也存在，当晶体从蒸汽中扩散长大时，液滴会蒸发。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。

AbstractATM-0312439Lasher-Trapp, SoniaPurdue UniversityTitle: Supercooled Large Drop Formation by Ultragiant Particles in Wintertime Stratiform Clouds During AIRS IIThis grant supports the participation of Dr. Lasher-Trapp 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 2003-04 and based at Mirabel Airport, north of Montreal, Canada, where a surface observing network and ground-based remote-sensing equipment will be located. Dr. Lasher-Trapp 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 cloud can form and continue to exist though ice crystals may also be present. 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. Lasher-Trapp will work with various optical and impaction particle sensors to determine the concentration, sizes, and composition (solid or liquid) of "ultragiant" particles (UGP) - those with equivalent spherical diameters greater than about 10 micrometers. Such particles are known sometimes to play a part in the formation of rain by the condensation-coalescence process in clouds that are too warm to contain ice, but they have not been systematically studied or even observed in clouds containing ice crystals or supercooled water. It has been conjectured that UGP may account for recently reported observations of supercooled drops larger than 50 micrometers in wintertime clouds - drops large enough to be a major cause of aircraft icing. Measurements are planned in AIRS II that will provide information on particles ranging from smaller than 10 micrometers up to 0.6 mm. The data will be analyzed to determine if there is a correspondence between the concentration of UGP measured outside of the cloud and the concentration of large supercooled drops within. If so, the presence of UGP may explain how supercooled drops can grow to large size even at the supercooled temperatures where they might be expected to freeze or, if ice crystals are also present, to evaporate as the crystals grow by diffusion from the vapor. The research contributes not only to the fundamental understanding of the microphysical structure of supercooled clouds but also to the advancement of aviation safety.