Numerical Study of the Riming Growth of Graupel

霰粒生长的数值研究

• 批准号: 0729898
• 负责人: Pao-Kuan Wang
• 金额: $ 51.43万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-02-01 至 2013-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0729898&HistoricalAwards=false
• 关键词: Numerical; Study; Riming; Growth; Graupel

The growth of ice particles by riming is one of the central problems in cloud physics and has great impacts on many other atmospheric processes. This is the dominant process that forms graupel and hail. It occurs in deep convective clouds and it influences the further development of such clouds due to its thermodynamic and dynamic effects. It is also one of the most important processes leading to the electrification of thunderclouds. Quantitative knowledge of this process is necessary for accurate weather and climate predictions. Despite the critical importance of the riming growth process, there are only limited field and laboratory experimental data on riming growth available, and only very simplistic theoretical treatments of the process. In order to increase understanding of the process, a numerical study will be conducted on the growth of ice particles by accreting supercooled droplets, starting from a pristine ice crystal and following its growth to become a graupel. Two numerical models will be developed, one for simulating the fall behavior of the falling ice particles while accreting droplets (hence changing its shape); the other for determining the collision efficiency of the supercooled droplet hitting the ice particle. The first model involves solving numerically the relevant Navier-Stokes equations to obtain the flow field around the falling particle. Using these flow fields, solutions will be found to the equations of motion of supercooled droplets around the falling ice particle so as to determine their trajectories and hence their collision efficiency. Computations of the ventilation coefficients of the falling rimed particles will be performed as well. These numerical models will be used to perform computations to determine the collision efficiencies for a wide range of ice crystal/droplet size combinations and atmospheric conditions. This will yield an extensive data set of quantitative collisional growth rates of graupel in different conditions. The intellectual merit of the proposed work is that the results from this study will fill a large gap in available knowledge in this fundamental area of cloud physics and provide necessary quantitative information on how the riming growth process operates in clouds. Such information can be used to design better graupel riming parameterizations for use in storm-scale numerical models to understand better the convective cloud dynamics. It can also be used by larger scale weather/climate models to improve their large scale precipitation parameterizations. The experience gained and the numerical flow fields obtained from this study also will also be useful for the future study of ice-ice collisional growth. The broader impacts of the results of the study include their use to enhance our capability to predict weather and climate evolution through the use of numerical prediction models. The research activity will help train graduate students and young scientists who will contribute to atmospheric science research. The research results will be disseminated in scientific journals, meetings, and public lectures so that wider audience becomes aware of them. Recent research results are regularly incorporated into survey-level courses (aiming at college freshmen) by the principal investigator. They convey to the younger generation the excitement of scientific discoveries and their great contributions to society.

霜化作用下的冰粒增长是云物理学的核心问题之一，对许多其他大气过程有着重要的影响。这是雹、雹形成的主要过程。它发生在深对流云中，由于其热力学和动力学效应，它影响着深对流云的进一步发展。它也是导致雷暴云带电的最重要过程之一。这一过程的定量知识对于准确的天气和气候预测是必要的。 尽管起霜生长过程至关重要，但关于起霜生长的现场和实验室实验数据非常有限，而且对该过程的理论处理也非常简单。 为了加深对这一过程的理解，将对冰粒的增长进行数值研究，即从原始冰晶开始，然后增长成为<$球，使过冷液滴增长。 将开发两个数值模型，一个用于模拟下落的冰粒的下落行为，同时吸积液滴（从而改变其形状）;另一个用于确定过冷液滴撞击冰粒的碰撞效率。第一个模型涉及数值求解相关的Navier-Stokes方程，以获得下落颗粒周围的流场。利用这些流场，将找到下落冰粒周围过冷液滴运动方程的解，以确定它们的轨迹，从而确定它们的碰撞效率。还将计算落下的有边颗粒的通风系数。这些数值模型将用于计算，以确定大范围的冰晶/液滴尺寸组合和大气条件下的碰撞效率。这将产生一个广泛的数据集的定量碰撞增长率在不同的条件下。所提出的工作的智力价值是，这项研究的结果将填补云物理学这一基本领域现有知识的巨大空白，并提供必要的定量信息，如何在云中运行的riming增长过程。这些信息可以用来设计更好的<$球成霜参数化，用于风暴尺度的数值模式，以更好地了解对流云动力学。它也可以用于更大尺度的天气/气候模式，以改善其大尺度降水参数化。本研究所获得的经验和数值流场也将对未来冰-冰碰撞增长的研究有所帮助。研究结果的更广泛影响包括通过使用数值预测模型来提高我们预测天气和气候演变的能力。该研究活动将有助于培养为大气科学研究做出贡献的研究生和年轻科学家。研究成果将在科学期刊、会议和公开讲座中传播，以便更广泛的受众了解它们。首席调查员定期将最新研究成果纳入调查级课程（针对大学新生）。他们向年轻一代传达科学发现的兴奋和他们对社会的巨大贡献。