Experimental and numerical investigation of collision induced and spontaneous raindrop breakup for forecasting and nowcasting of precipitation

碰撞诱发和自发雨滴破裂的实验和数值研究，用于降水预报和临近预报

• 批准号: 431120337
• 负责人: Dr. Axel Seifert
• 金额: --
• 依托单位: Deutscher Wetterdienst (DWD)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/431120337?language=en
• 关键词: Experimental; numerical; investigation; collision; induced

The raindrop size distribution (RSD) is a fundamental parameter used for the description and analysis of precipitation. The evolution of the RSD is primarily affected by coalescence and breakup of colliding drops, as well as by spontaneous breakup of very large raindrops. The number of experimental studies on the fragment size distribution (FSD) after breakup of drops under well-controlled near-atmospheric conditions is so far very limited in literature. In the proposed study we will conduct dedicated laboratory experiments in the Mainz vertical wind tunnel on collision induced and spontaneous breakup of raindrops of sizes from 1 to 6 mm. The Mainz vertical wind tunnel is a world-wide unique facility in which single raindrops and cloud particles can be freely suspended in a vertical air stream without wall contacts or tethered. This physically represents the situation when drops are floating in or falling out from a cloud at their terminal velocities. The wind tunnel experiments are augmented by novel detection and imaging methods allowing the accurate determination of fragment sizes after raindrop breakup. The results from the breakup experiments will extend the existing data base; this will help to validate or falsify different existing FSD parameterizations utilized in cloud models. Therefore, an important objective of this study is to derive an improved parameterization for the FSD of collision induced and spontaneous breakup based on the results from the laboratory experiments. The novel parameterizations will be implemented in a spectral-bin cloud microphysical scheme and in a Monte Carlo super-droplet approach. Both methods guarantee mass conservation of the drops. In a first step they will be incorporated in a box and in a 1D rain shaft model to understand how breakup affects the behavior and evolution of the RSD. These process studies will also allow a first comparison of the shape of the simulated RSD with field observations. Finally, the new parameterizations will be applied in 3D cloud models. 3D simulations represent the interaction between dynamics and cloud microphysics in a realistic way and, thus, allow to assess the impact of breakup processes on precipitation and the rainfall rate. To improve the reliability of precipitation forecasting is of increasing importance as extreme precipitation events are propagating.

雨滴谱是描述和分析降水的基本参数。RSD的演变主要受碰撞水滴的合并和分裂，以及非常大的雨滴的自发分裂。在近大气条件下，液滴破碎后的碎片尺寸分布（FSD）的实验研究数量非常有限。在拟议的研究中，我们将进行专门的实验室实验在美因茨垂直风洞碰撞诱导和自发的雨滴的大小从1到6毫米的分裂。美因茨垂直风洞是一个世界范围内的独特设施，其中单个雨滴和云粒子可以自由地悬浮在垂直气流中，没有墙壁接触或拴系。这实际上代表了水滴以其终端速度漂浮在云中或从云中落下的情况。风洞实验增加了新的检测和成像方法，使雨滴破碎后的碎片大小的准确测定。破裂实验的结果将扩展现有的数据库，这将有助于验证或证伪云模型中使用的不同的现有FSD参数化。因此，本研究的一个重要目标是从实验室实验的结果的基础上获得一个改进的参数化的碰撞诱导和自发破碎的FSD。新的参数化将在光谱箱云微物理方案和蒙特卡罗超级液滴方法中实现。这两种方法都保证了液滴的质量守恒。在第一步中，他们将被纳入一个盒子和一个一维雨井模型，以了解破碎如何影响RSD的行为和演变。这些过程研究也将允许模拟RSD的形状与现场观察的第一次比较。最后，新的参数化将应用于3D云模型。3D模拟以现实的方式代表了动力学和云微物理学之间的相互作用，因此，可以评估分裂过程对降水和降雨率的影响。随着极端降水事件的传播，提高降水预报的可靠性变得越来越重要。