Mesoscale Airflow over Mountains: Wave Drag and Orographic Precipitation

山脉对天气和气候有着深远的影响。该项目将研究山脉与大气之间相互作用的两个重要方面。第一项工作将是研究山脉对气流施加的阻力如何分布在大气中不同垂直高度上，以及该阻力如何反馈到更大规模的气流上。 第二项工作将研究山脉增强降水并使下游空气干燥的方式。智力成果：当气流遇到山脉屏障时，可能会在屏障的上方和下游形成“山波”，低层气流可能会被阻挡并在山的侧面​​周围转向。这些扰动的规模太小，无法在全球天气和气候模型中解决，但它们对必须参数化的大规模流动产生了重要的阻力。 该项目将尝试将此类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分析来确定对地形阻力的大规模响应。尽管山区降水主要是由大规模天气系统的间歇性变化驱动的，但尚未对孤立山脊与此类系统相互作用的原型理论研究进行研究，部分原因是同时模拟复杂的大尺度和小尺度流的困难。我们将利用计算能力和模型架构的进步来研究大规模抬升和降水与地形迫使的局部上升之间协同相互作用的本质。这种相互作用可能会产生比之前简单的上坡流模拟中产生的降水更强烈的降水。 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所产生的模型所建议的进行比较。更广泛的影响：两名研究生将获得国家科学基金会奖的支持，以进行他们的研究和专业发展。 研究成果应有助于改善大型模型中低层重力波阻力的参数化，这对全球天气预报和许多气候研究至关重要。地形降水是世界许多文明的重要水源。通过更好地了解大规模天气系统经过地形时降水如何增强，我们可以为水资源管理者和水文学家提供指导，帮助他们在当前气候下维持供水，并规划中纬度暴风雨未来可能变化的影响。

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.