Dryline Dynamics

干线是两种不同气团之间的地面边界，这两种气团经常在春季和初夏出现在美国中南部。在这条线的东部是相对较浅的凉爽潮湿的海洋气团，而在西部是较深的温暖干燥的大陆气团。这种中尺度现象很重要，因为它通常与恶劣天气（破坏性风、冰雹和龙卷风）的发生有关。雷暴倾向于沿干线及其以东发展。干旱线通常在白天向东移动几百公里，然后在夜间向西逆行。干线的日变化使恶劣天气的预报成为一项重大挑战。本研究的目的是模拟干线的结构和位置的日变化。基本的方法是将干线视为浅层海洋气团的西部边缘。该气团的动力学将首先使用一种简化的数值模型进行研究，即浅水模型。将确定模型干线对质量、动量和热强迫的敏感性，并与现有理论进行比较。然后，气团的板状混合层模型将得到发展，以更准确地表示主要的热力学过程。建模工作的改进包括二维研究和扩展到多个气团。这种使用介于解析理论和复杂的中尺度数值模型之间的中等复杂性模型的理论方法应该能够捕捉基本的物理现象，并提供对干线动力学的洞察。研究结果将有助于更好地了解干旱线，并有助于预测恶劣天气。＊＊＊

9729631 Bannon The dryline is the surface boundary between two distinct air masses that frequently inhabit the south central United States in Spring and early Summer. To the east of the line lies a relatively shallow cool moist maritime air mass and to the west a deeper warm dry continental air mass. This mesoscale phenomenon is significant because it is often linked to the occurrence of severe weather (damaging winds, hail and tornadoes). Thunderstorms tend to develop along and to the east of the dryline. The dryline often migrates several hundred kilometers to the east during the day and then retrogrades westward during the night. This diurnal evolution of the dryline helps make the forecasting of severe weather a major challenge. The purpose of this research is to model the diurnal evolution in structure and position of the dryline. The fundamental approach is to treat the dryline as the western edge of a shallow layer maritime air mass. The dynamics of this air mass will first be studied using a simplified numerical model know as the shallow water model. The sensitivity of the model dryline to mass, momentum, and thermal forcings will be ascertained and compared with existing theories. A slab mixed- layer model of the air mass will then be developed to more accurately represent the major thermodynamic processes. Refinements of the modeling effort include two dimensional studies and an extension to multiple air masses. This theoretical approach of using models of intermediate complexity between analytic theory and sophisticated mesoscale numerical models should be able to capture the essential physics and provide insight into the dynamics of the dryline. The results of the research should provide a better understanding of the dryline and help the forecasting of severe weather. ***