Numerical Modeling of Mesoscale Airflow over Mountains

在主要山脉附近进行准确的天气预报是一个极其困难的气象问题。大尺度天气系统和山区之间的相互作用常常产生复杂的中尺度天气模式。由于缺乏对复杂地形中尺度环流的物理过程的理解，预测这些天气模式发展的努力受到限制。此外，中尺度地形效应也通过重力波阻力作用影响全球环流。全球尺度模式中重力波阻力参数化的误差被认为是扩展范围预报误差的主要来源。在先前支持的关于该主题的研究中，首席研究员发现，垂直传播的山波似乎不像以前认为的那样对底层地形的不对称性敏感。利用自由滑移条件，他发现最大背风坡风对地形的不对称性也不敏感。然而，当考虑表面摩擦时，对地形的敏感性增强了，但最大风速的主要调节因素似乎是背风坡的陡峭度。首席研究员将继续这条研究路线，最终目标是改善山区附近地区的天气预报，并改进扩展范围的预报和气候模型。主要集中在：研究复杂三维地形下的气流，重点研究有和没有山隙的山障以及孤立的山峰；地形强迫重力波动量通量及其与重力波阻力大尺度气流相互作用的研究。

Accurate weather forecasting in the vicinity of major mountain ranges is an extremely difficult meteorological problem. Interactions between large-scale weather systems and mountainous regions often spawn complex mesoscale weather patterns. Efforts to forecast the development of these weather patterns are limited by deficiencies in understanding of the physical processes governing mesoscale circulations in complex terrain. Additionally, mesoscale orographic effects also influence the global circulation through the action of gravity wave drag. Errors in the parameterization of gravity wave drag in global scale modes are believed to be a major source of error in extended range forecasts. Under previously supported research on this topic the Principal Investigator has found that vertically propagating mountain waves appear to be not as sensitive to the asymmetry of the underlying terrain as previously thought. Using free slip conditions, he has found that maximum lee slope winds also are not sensitive to asymmetry of the terrain. When surface friction is included, however, sensitivity to terrain is enhanced, but the primary regulator of maximum winds appears to be the steepness of the lee slope. The Principal Investigator will continue this line of research with the ultimate goal of improving weather forecasts for locations in the vicinity of mountains and to improve extended range forecasts and climate models. The major areas of concentration are: investigation of airflow in complex three-dimensional topography with emphasis on mountain barriers with and without mountain gaps, and isolated mountain peaks; study of momentum fluxes in orographically forced gravity waves and the interactions of these waves with the larger scale flow through gravity wave drag.