Structure and Evolution of Intermountain Cyclones

天气系统及其伴随的降水往往受到复杂地形的深刻影响。对地形影响的了解有些有限，部分原因是在这些地区很难获得观测结果。首席调查员将调查有助于山间气旋和相关冬季风暴发展和演变的过程。山间气旋通常发展或增强到内华达山脉的背风处，这是一个频繁发生气旋的地区，并可能在内华达州、犹他州和邻近各州产生破坏性的风和雪。它们也是科罗拉多气旋发生的前兆，并最终影响锋面和降水的演变到落基山脉的背风。研究的目标是确定(1)天气尺度、地形和非绝热过程如何影响山间气旋的发展和演变，(2)像内华达山脉这样的主要山障如何改变锋面结构和动力学，以及(3)上游山障上方的气团转换如何影响水汽输送和下游地形降水。该项目将包括观测分析和数值模拟。来自中西部合作网络的高密度地面观测，来自WSR 88D雷达网的雷达观测，以及来自加利福尼亚州、内华达州、爱达荷州和犹他州的风廓线数据将被用来描述所观测到的选定山间气旋的中尺度结构和演变。MM5和天气研究和预报(WRF)模式的理想化和真实数据模拟将被用来检验大尺度、地形和非绝热对气旋发生的贡献，确定内华达山脉和大盆地山脉如何改变锋面的结构和动力学，并量化主要地形障碍上的气流期间的水汽通量、源和汇。该项目是利用高密度地面观测和高分辨率数值模拟对山间气旋演变进行的第一次全面研究。以前开发的地形修改的气旋发生理论的相关性将在一个与阿尔卑斯山和落基山脉背风区明显不同的地区进行评估，此前的大多数研究都集中在那里。此外，还将首次描述内华达山脉对下游锋面演变和水汽输送的影响。更广泛的影响包括改善西部山区的天气和气候预报，将研究成果纳入本科生和研究生教育，以及指导研究生。

Weather systems and their accompanying precipitation are often profoundly affected by complex terrain. Knowledge of the influence of orography is somewhat limited, partially because observations in these regions are difficult to obtain. The Principal Investigator will investigate the processes contributing to the development and evolution of intermountain cyclones and associated winter storms. Intermountain cyclones typically develop or intensify to the lee of the Sierra Nevada, a region of frequent cyclogenesis, and can produce damaging winds and snowfall over Nevada, Utah, and adjoining states. They are also precursors for Colorado cyclogenesis, and ultimately affect the evolution of fronts and precipitation to the lee of the Rockies.The objectives of the research are to determine (1) how synoptic scale, orographic, and diabatic processes influence the development and evolution of intermountain cyclones, (2) how major mountain barriers like the Sierra Nevada modify frontal structure and dynamics, and (3) how moisture transport and downstream orographic precipitation are impacted by air mass transformation over upstream mountain barriers.The project will involve observational analysis and numerical modeling. High-density surface observations from the MesoWest cooperative networks, radar observations from the WSR 88D radar network, and wind profiler data from California, Nevada, Idaho, and Utah will be used to describe the observed mesoscale structure and evolution of selected intermountain cyclones. Idealized and real-data simulations by the MM5 and Weather Research and Forecast (WRF) models will be used to examine large-scale, orographic, and diabatic contributions to cyclogenesis, determine how the Sierra Nevada and Great Basin ranges alter the structure and dynamics of fronts, and quantify water vapor fluxes, sources, and sinks during airflow over major topographic barriers.The project represents the first comprehensive study of intermountain cyclone evolution to employ high-density surface observations and high-resolution numerical simulations. The relevance of previously developed orographically modified cyclogenesis theories will be evaluated in a region that is markedly different from the lee of the Alps and Rockies, where most prior studies have been focused. Also for the first time, the impact of the Sierra Nevada on downstream frontal evolution and moisture transport will be described. Broader impacts include improved weather and climate prediction over the intermountain west, integration of research results into undergraduate and graduate education, and the mentoring of graduate students.