Mesoscale Airflow over Mountains: Wave Drag and Orographic Precipitation

山脉对天气和气候有深远的影响。这个项目将研究山脉和大气之间相互作用的两个重要方面。第一个努力将是研究山脉对气流施加的阻力如何在大气中的不同垂直水平之间分配，以及这种阻力如何反馈到更大规模的气流中。第二项工作将研究山脉增加降水和干燥空气向下流动的方式。智力上的优点：当气流遇到山障时，可能会在山障的上方和下游形成“山波”，低层气流可能会被阻挡并改道绕过山体两侧。这些扰动的规模太小，无法在全球天气和气候模式中解决，但它们对必须参数化的大范围流动产生了重要的拖累。这个项目将试图将这种参数化建立在更坚实的理论基础上，并通过高分辨率数值模拟的分析来确定对地形阻力的大尺度响应。尽管山区的降水在很大程度上是由大尺度天气系统的幕式通过所驱动的，但关于孤立脊与此类系统相互作用的典型理论研究尚未开展，部分原因是难以同时对复杂的大、小尺度气流进行建模。我们将利用计算能力和模式架构的进步来研究大范围抬升和降水与地形强迫的更局部化上升之间协同作用的本质。这种相互作用可能会产生比之前简单上坡流动模拟中产生的更强烈的降水。背风处干燥空气的强度和下游分布也将被确定，并与水平均匀跨山气流强迫的模型所建议的结果进行比较。更大的影响：两名研究生将因他们的研究和专业发展而获得NSF奖的支持。研究结果应该有助于改进大型模式中低层重力波阻力的参数化，这些模式对全球天气预报和许多气候研究至关重要。地形降水是世界上许多文明的主要水源。通过更好地了解当大范围天气系统经过地形时降水是如何增加的，我们可以为水资源管理者和水文学家提供指导，他们试图在当前气候下保持供水，并为未来中纬度暴风雨可能发生的变化的影响进行规划。

Mountains exert a profound influence on the weather and climate. This project will investigate two important aspects of the interaction between mountains and the atmosphere. The first effort will be to examine how the drag exerted by mountains on an air stream is distributed among different vertical levels in the atmosphere and how that drag feeds back on the larger scale flow. The second effort will examine the way that mountains enhance precipitation and dry the air downstream.Intellectual Merit:When an air stream encounters a mountain barrier, "mountain waves" may be set up above and downstream of the barrier and the low-level flow may be blocked and diverted around the flanks of the mountain. These disturbances are too small in scale to be resolved in global weather and climate models, but they produce an important drag on the large-scale flow that must be parameterized. This project will attempt to place such parameterizations on a firmer theoretical footing and also determine the large-scale responses to orographic drag through the analysis of high-resolution numerical simulations.Although the precipitation over mountains is largely driven by the episodic passage of large-scale weather systems, prototypical theoretical studies of the interactions of an isolated ridge with such systems have not yet been undertaken, due in part to the difficulty of simultaneously modeling complex large and small-scale flows. We will take advantage of advances in computing power and model architecture to investigate the nature of the synergistic interactions of the large-scale lifting and precipitation with the more localized ascent forced by the topography. Such interactions are likely to generate more intense precipitation than that produced in previous simulations of simple upslope flows. The strength and downstream distribution of the dry air in the lee will also be determined and compared to that suggested by models forced by horizontally uniform cross-mountain flows.Broader Impacts:Two graduate students will be supported under this NSF award for their research and professional development. Research results should help improve the parameterization of low-level gravity wave drag in large-scale models essential for global weather forecasting and much climate research. Orographic precipitation is a key source of water for many of the world's civilizations. By developing a better understanding of how precipitation is enhanced when large-scale weather systems pass over topography, we can provide guidance to water resource managers and hydrologists trying to maintain water supplies in the current climate and planning for the effect of possible future shifts in mid-latitude storminess.