Dynamics of Heavy Precipitation over Mesoscale Mountains

更好地预测山区的洪水已被确定为美国跨部门天气研究计划的一个高优先级研究领域。 根据该奖项，首席研究员（PI）将进行数值和观测研究，旨在提高对中尺度地形降雨和洪水的科学理解。 将使用的数据集是在国际中尺度高山方案期间收集的数据集。 以下问题将得到解决：1。大气稳定度和山脉的几何形状对地形引起的中尺度对流系统的形成和传播有什么影响？2.造成地形性暴雨或洪水的基本因素是什么？3.对流层上部高位涡（PV）气团或槽如何与来自北非的深层温暖沙漠空气相互作用，从而在阿尔卑斯山形成强烈的地形降雨或洪水？为了解决第一个问题，PI假设对流系统的传播是由上游弗劳德数和垂直的水分通量是由阿尔卑斯山凹的几何形状在意大利的马焦雷湖地区增强。 PI然后将进行一系列涉及不同大气不稳定性和山脉几何形状的数值敏感性实验。 该研究将分析雷达、风廓线仪和卫星数据，以验证数值模型结果，并增加对潜在动力学的理解。关于第二个问题，假设产生地形暴雨或洪水的基本成分是：降水效率高，低空急流的存在，陡峭的山脉，有利的山脉几何形状，天气系统引起的强烈垂直运动，地形引起的对流系统移动缓慢。 为了验证这一假设，PI将对MAP案例以及历史上的阿尔卑斯山和美国洪水事件进行天气和中尺度分析，以探索这些成分之间的相对重要性和关系。为了解决第三个问题，PI假设对流层上部的高PV空气团或槽有助于从海洋输送深层潮湿空气，增强南方低空急流，与地形强迫上升运动同相的高空辐散有利于深对流的发展。 通过数值模拟试验和资料分析，对这一假说进行了探讨，并对控制地形降水的重要因素进行了深入的研究。 这可能会导致改善山区山洪暴发和其他降水预报。

Better prediction of flooding in mountainous terrain has been identified as a high priority research area under the interagency U.S. Weather Research Program. Under this award, the Principal Investigator (PI) will perform numerical and observational studies aimed at improving scientific understanding of mesoscale orographic rainfall and flooding. The data set to be used is that collected during the international Mesoscale Alpine Programme (MAP). The following questions will be addressed:1. What are the effects of atmospheric stability and mountain geometry on the formation and propagation of orographically induced mesoscale convective systems?2. What are the basic ingredients for producing orographic heavy rainfall or flooding?3. How do upper-tropospheric high potential vorticity (PV) air masses or troughs interact with deep warm desert air from North Africa to develop heavy orographic rainfall or flooding in the Alps?To address the first question, the PI hypothesizes that propagation of convective systems is controlled by the upstream Froude number and the vertical moisture flux is enhanced by the Alpine concave geometry in the Lago Maggiore area of Italy. The PI will then perform a series of numerical sensitivity experiments involving different atmospheric instabilities and mountain geometry. The research will analyze radar, wind profiler, and satellite data to verify numerical model results and increase understanding of the underlying dynamics.With respect to the second question, it is hypothesized that the basic ingredients for producing orographic heavy rainfall or flooding are: high precipitation efficiency, the presence of low-level jet, a steep mountain, favorable mountain geometry, strong vertical motion induced by the synoptic system, and slow movement of the orographically induced convective system. To test this hypothesis, the PI will produce synoptic and mesoscale analyses of MAP cases as well as historical Alpine and US flooding events to explore the relative importance and relationship between these ingredients.To address the third question, the PI hypothesizes that an upper-tropospheric high PV air mass or trough helps transport deep moist air from the ocean, enhances the southerly low-level jet, and induces upper-level divergence in phase with the orographically forced upward motion, which is favorable for the development of deep convection. Numerical simulation experiments and data analysis will be conducted to explore this hypothesis.Successful completion of this research will provide insights into the important factors that control orographic precipitation. This potentially could lead to improved flash flood and other precipitation forecasts in mountainous terrain.