Mesoscale Airflow over Mountains: Wave Drag and Orographic Precipitation

山脉对天气和气候有着深远的影响。本项目将调查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在大气中不同的垂直高度上分布，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如何增加降水和干燥下游的空气。智力优势：当气流遇到山脉障碍物时，障碍物的上方和下游可能会产生“山波”，低空气流可能会被阻挡并转向山脉两侧。这些扰动的尺度太小，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尺度流动产生了重要的阻力。 本计画将尝试将这些参数化建立在更坚实的理论基础上，并透过高解析度数值模拟分析，来决定大尺度地形拖曳的反应。虽然山区的降水主要是由大尺度天气系统的间歇性通过所驱动，但孤立脊与这些系统相互作用的原型理论研究尚未展开，部分原因是难以同时模拟复杂的大规模和小规模流动。我们将利用计算能力和模式架构的进步来研究大规模提升和降水与地形迫使的更局部化上升的协同相互作用的性质。这种相互作用可能会产生更强烈的降水比在以前的模拟简单的上坡流。 还将确定背风面干燥空气的强度和下游分布，并与水平均匀跨山流迫使的模型所建议的强度和下游分布进行比较。更广泛的影响：两名研究生将获得该NSF奖项的研究和专业发展支持。 研究结果应有助于改进全球天气预报和许多气候研究所必需的大尺度模型中的低层重力波阻力参数化。地形降水是世界上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人员和水文学家提供指导，以保持当前气候下的供水，并为未来中纬度风暴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.