Orographic Precipitation Processes over the Wasatch Mountains during the Intermountain Precipitation Experiment (IPEX)

要改进美国西部的定量降水预报，需要在几个领域取得进展，包括了解地形降水事件期间的动力和微物理过程，以及地形引起的环流和降水微物理的数值模拟和参数化。地形诱导的流场和地形降水过程之间的相互作用仍然知之甚少，地形降水的测量和预测是一项重大的科学挑战。在狭窄和陡峭的山脉上尤其如此，例如西部山区，那里的业务数值天气预报模式的定量降水预报技能大大低于美国其他地区。研究的主要目标是(1)促进西部山区地形降水过程的基本知识，重点是犹他州北部的瓦萨奇山脉；(2)验证和改进中尺度模式的性能和复杂地形地区的定量降水预报。该项目将利用2000年2月在犹他州北部举行的一项主要实地计划--山间降水实验(IPEX)期间收集的数据。在综合方案执行期间收集的专门数据集包括机载多普勒雷达和微物理观测、两个移动多普勒雷达收集的地面雷达观测以及高分辨率地面和高空观测。这些数据集将被用来研究控制瓦萨奇山脉降水分布的因素，包括上游阻塞效应对迎风的增强以及山波结构对背风面溢流的影响。这些目标与美国天气研究计划(USWRP)的定量降水预报重点直接相关。该项目的结果也将对包括2002年冬奥会举办地盐湖城在内的西部地区产生积极的科学和社会经济效益。教育方面的好处包括犹他大学研究生的参与，以及将项目数据集和调查结果用于课堂教学。

Improvement in quantitative-precipitation forecasts over the western United States requires advances in several areas including the understanding of dynamical and microphysical processes during orographic precipitation events and the numerical simulation and parameterization of orographically-induced circulations and precipitation microphysics. The interaction between terrain-induced flow fields and orographic precipitation processes remains poorly understood, and the measurement and prediction of orographic precipitation is a major scientific challenge. This is particularly true over narrow and steeply sloped mountain ranges, such as those of the Intermountain West, where the quantitative precipitation forecast skill of operational numerical weather prediction models is substantially lower than in other regions of the United States.The primary objectives of the research are (1) to advance fundamental knowledge of orographic precipitation processes over the Intermountain West, with an emphasis on the Wasatch Mountains of northern Utah; (2) to validate and improve mesoscale model performance and quantitative precipitation forecasts over regions of complex terrain. The project will utilize data collected during the Intermountain Precipitation Experiment (IPEX), a major field program held in northern Utah during February 2000. Specialized data sets collected during IPEX include airborne Doppler-radar and microphysical observations, ground-based radar observations collected by two mobile Doppler radars, and high resolution surface and upper-air observations. These data sets will be used to examine factors controlling the distribution of precipitation across the Wasatch Mountains, including windward enhancement by upstream blocking effects and the influence of mountain-wave structure on lee-side spillover.These objectives are directly related to the quantitative-precipitation forecasting focus of the U.S. Weather Research Program (USWRP). Results from the project will also have positive scientific and socio-economic benefits for the West, including Salt Lake City, host of the 2002 Winter Olympics. Educational benefits include the participation of graduate students from the University of Utah and the use of project data sets and findings for classroom instruction.