Orographic Effects on Precipitating Cloud Systems

对地形降水过程的广泛了解对于暴雨、洪水和恶劣天气的预报至关重要。 地球上大多数降水都与锋面系统、对流风暴或热带气旋有关。 当风暴发生在山脉附近或上空时，这些风暴的降水会增强、重新分布和集中。 这项研究试图促进对所有三种类型风暴的这些影响的理解。 研究工作将以若干实地活动中现有但尚未充分利用的数据集为基础。 采用若干最新冰相微物理方案进行的高分辨率模型模拟将补充实地观测研究。 该研究利用合作来促进对不同山脉（阿尔卑斯山，瀑布，加拿大海岸山脉，内华达州山脉、安第斯山脉、喜马拉雅山脉和台湾中部山脉）。对于锋面系统通过山脉，这项研究将测试假设的降水增强建议的地图和改进II现场程序，并确定这些想法是否适用于风暴在不同的山脉附近。特别是，从雪V10的数据将被用来确定存在和分离流的特性，伴随剪切，并在加拿大西海岸的山区设置的山谷流。 比较阿尔卑斯山脉、海岸山脉和内华达州山脉的数据，将用于确定这些层中的湍流是否具有开尔文-亥姆霍兹波的特定形式。 将通过对接近安第斯山脉的锋面进行模式模拟，探索由障碍射流形成的解耦层的发展。对于对流系统，我们将研究的触发和下游发展的强对流系统的低层气流对山脉的冲击和增强的中尺度对流系统通过大山的结果。 触发机制将在安第斯区域通过模型模拟和数据分析加以审查。该模型将测试的假设，即地形沉降举行了深对流的覆盖潮湿的低层湿射流，直到射流打破了盖撞击山麓。模式将检验造山带对流向中尺度系统的下游演变。将通过模拟2010年喜马拉雅山莱赫洪水案例来检验经过陡峭地形的中尺度对流系统的增强。 在热带气旋方面，将分析台风莫拉克（2009）的雷达资料，该台风在地形增强的情况下造成了毁灭性的洪灾。 我们将探讨的假设，暖雨增长是至关重要的增强，模型模拟将测试的结果。智力价值：这项研究的结果将提高山区的作用，影响整个地球仪的基本理解。 该研究将使用现有但未开发的实地活动数据集和最新版本的高分辨率数值预报模型，以检查发生在所有主要风暴类型（锋面，对流风暴和热带气旋）的降水过程，当它们发生在山脉附近或上方时。 更广泛的影响：改善对山脉如何影响降水的观测和理解，将有助于改善对严重洪水、冰雹、龙卷风和大风的预测。 本研究调查的风暴已造成数百人伤亡和巨大的财产损失，研究将包括调查其对人类的影响。

A broad understanding of orographic precipitation processes is vital to the forecasting of heavy rain, floods, and severe weather. Most precipitation on earth occurs in connection with frontal systems, convective storms, or tropical cyclones. The precipitation of these storms is enhanced, redistributed and concentrated when the storms occur near or over mountains. This study tries to advance understanding of these effects, for all three types of storms. The research effort will be based on existing but not fully exploited datasets from several field campaigns. High-resolution model simulations with several of the latest ice-phase microphysical schemes will supplement the field observation studies. The study leverages collaborations to facilitate examination of a range of storm types near different mountain ranges (Alps, Cascades, Canadian Coast Mts., Sierra Nevada, Andes, Himalayas, and Taiwan Central Mts.).For frontal systems passing over mountain ranges, this research will test hypotheses of precipitation enhancement suggested by the MAP and IMPROVE II field programs and determine if these ideas have applicability to storms in the vicinities of diverse mountain ranges. In particular, data from SNOW-V10 will be used to determine the existence and characteristics of decoupled flows, accompanying shear, and down-valley flows in the mountain setting of the Canadian western coast. Comparison of data from Alps, Coast Mountains, and Sierra Nevada range will be used to determine whether the turbulence in these layers has the specific form of Kelvin-Helmholtz waves. The development of decoupled layers by barrier jet formation will be explored by model simulation of fronts approaching the Andes. For convective systems, we will examine the triggering and downstream development of intense convective systems as a result of the impingement of low-level flow on mountains and the enhancement of mesoscale convective systems passing over large mountains. The triggering mechanism will be examined with model simulations and data analysis in the Andean region. The modeling will test the hypothesis that orographic subsidence holds back the deep convection by capping of the moist low-level moist jet until the jet breaks the cap by striking a foothill. Downstream evolution of the orogenic convection into a mesoscale system will be examined with the model. The enhancement of a mesoscale convective system passing over steep terrain will be examined by simulating the 2010 Leh flood case over the Himalayas. The precipitation mechanisms in the orographically triggered and modified convective systems will be examined using radar data from operational and research radars in Taiwan.For tropical cyclones, Taiwan radar data will be analyzed for Typhoon Morakot (2009), which caused devastating flooding when its rain was orographically enhanced. We will explore the hypotheses that warm-rain growth was crucial to the enhancement, and model simulations will test the results.Intellectual merit: The results of this study will improve basic understanding of the role of mountains in affecting all major precipitation systems across the globe. The research will use existing but unexploited field campaign datasets and the latest versions of high-resolution numerical forecast models to examine the precipitation processes occurring in all major storm types (fronts, convective storms, and tropical cyclones) when they occur near or over mountains. Inclusion of all major storm types and examination over geographically separated mountain ranges will achieve generality.Broader impacts: Improved observations and understanding of how mountains affect precipitation will lead to improved prediction of severe flooding, hail, tornadoes, and winds. The storms investigated in this study have caused hundreds of casualties and great property damage, and the research will incorporate investigation of their human impacts.