Quantification of the secondary ice production mechanisms: droplet shattering on freezing vs. droplet-ice collision

二次冰生成机制的量化：冷冻时液滴破碎与液滴-冰碰撞

• 批准号: 386137169
• 负责人: Dr. Susan Hartmann
• 金额: --
• 依托单位: IMK - Atmosphärische Aerosolforschung (IMK- AAF)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/386137169?language=en
• 关键词: Quantification; secondary; ice; production; mechanisms

Reliable modeling of cloud processes for weather predictions and climate change projections requires a sound understanding of the ice formation in mixed-phase clouds. However, ice crystal concentrations measured in-situ are often found to exceed the concentration of ice nucleating particles by many orders of magnitude. This discrepancy motivates the atmospheric research community to search for Secondary Ice Production (SIP) mechanisms, i.e., processes producing additional ice particles by e.g. fragmentation of existing ice particles or during droplet freezing events. In a collaborative effort between the Leibniz-Institute for Tropospheric Research (TROPOS) in Leipzig and the Institute of Meteorology and Climate Research of Karlsruhe Institute of Technology (KIT), we plan to investigate two proposed SIP mechanisms: production of secondary ice particles caused by (A) droplet-ice collisions (rime-splintering) and (B) splintering of freezing droplets. These two SIP mechanisms have been suggested to be of particular relevance in mixed-phase clouds.The main objectives of the proposed project will be: (1) to develop a new experimental set-up, the Ice Droplet splintEring and Fragmentation eXperiment (IDEFIX), for investigating secondary ice particle production via (A) and (B), (2) to identify the physical mechanisms of SIP via high speed video observations of the SIP events, (3) to quantify the number of secondary ice particles produced by both mechanisms as a function of temperature, droplet size and impact velocity for mechanism (A) and droplet size and droplet composition for mechanism (B), and (4) to develop parameterizations for both SIP mechanisms (A) and (B). These parameterizations will be applied by external collaborators for SIP representation in cloud microphysics resolving models.The development of IDEFIX will benefit from the long-standing expertise of both collaboration partners: expertise in droplet/ice particle nucleation, growth and evaporation in a well-defined thermodynamic controlled system and the detection of those hydrometeors contributed by TROPOS team and expertise in high-speed video observation of freely suspended freezing droplets contributed by KIT team. The modular design of IDEFIX will allow both collaboration partners to use their respective on-site capabilities for module development and then combine the experimental efforts in a series of measuring campaigns conducted at TROPOS site.

为天气预报和气候变化预估建立云过程的可靠模型，需要对混合相云中冰的形成有充分的了解。然而，原位测量的冰晶浓度经常超过冰成核粒子的浓度许多个数量级。这种差异促使大气研究界寻找二次制冰（SIP）机制，即通过现有冰粒破碎或液滴冻结事件产生额外冰粒的过程。在莱比锡莱布尼茨对流层研究所（TROPOS）和卡尔斯鲁厄理工学院气象与气候研究所（KIT）的合作努力下，我们计划研究两种提出的SIP机制：由(a)液滴与冰碰撞（白霜碎裂）和(B)冷冻液滴碎裂引起的二次冰颗粒的产生。这两种SIP机制被认为与混合相云特别相关。拟议项目的主要目标是：(1)建立一个新的实验装置，冰滴分裂和破碎实验（IDEFIX），用于研究通过(a)和(B)产生的二次冰颗粒；(2)通过高速视频观测SIP事件来确定SIP的物理机制；(3)量化两种机制产生的二次冰颗粒数量作为温度的函数。机制(A)的液滴尺寸和撞击速度，机制(B)的液滴尺寸和液滴组成，以及(4)为SIP机制(A)和(B)建立参数化。这些参数化将由外部合作者应用于云微物理解析模型中的SIP表示。IDEFIX的开发将受益于双方合作伙伴长期以来的专业知识：在一个定义良好的热力学控制系统中液滴/冰粒成核、生长和蒸发方面的专业知识，以及TROPOS团队提供的水成体表物的检测，以及KIT团队提供的自由悬浮冷冻液滴的高速视频观察方面的专业知识。IDEFIX的模块化设计将允许双方合作伙伴利用各自的现场能力进行模块开发，然后将实验工作结合在TROPOS现场进行的一系列测量活动中。