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

为天气预报和气候变化预测建立可靠的云过程模型需要对混合相云中的冰形成有充分的了解。然而，原位测量的冰晶浓度经常被发现超过冰成核颗粒的浓度许多数量级。这种差异促使大气研究界寻找二次冰产生（SIP）机制，即，通过例如现有冰粒的碎裂或在液滴冻结事件期间产生额外冰粒的过程。 在莱比锡的莱布尼茨对流层研究所（TROPOS）和卡尔斯鲁厄理工学院（KIT）的气象和气候研究所之间的合作努力中，我们计划调查两个拟议的SIP机制：（A）液滴-冰碰撞（雾凇分裂）和（B）冻结液滴分裂所造成的二次冰粒的产生。这两个SIP机制被认为在混合相云中特别相关。拟议项目的主要目标是：（1）开发一种新的实验装置，冰滴剪切和碎裂实验（IDEFIX），用于研究通过（A）和（B）的二次冰粒产生，（2）通过对SIP事件的高速视频观测来识别SIP的物理机制，（3）量化由两种机制产生的作为温度的函数的二次冰粒的数量，机制（A）的液滴尺寸和冲击速度以及机制（B）的液滴尺寸和液滴组成，以及（4）开发SIP机制（A）和（B）的参数化。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的开发将受益于两个合作伙伴的长期专业知识：在液滴/冰粒成核方面的专业知识，在一个定义明确的热力学控制系统中的生长和蒸发，以及TROPOS团队和在高由KIT团队提供的自由悬浮的冷冻液滴的快速视频观察。IDEFIX的模块化设计将允许合作伙伴使用各自的现场能力进行模块开发，然后将联合收割机的实验工作结合在TROPOS现场进行的一系列测量活动中。

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.