Average and Variability Characteristics of Orographic Precipitation at Multiple Scales

南阿尔卑斯山的中尺度高山项目（MAP）（1999）和华盛顿和俄勒冈的观测验证试验微物理参数化改进（IMPROVE）（2000和2001）两个主要野外项目在地形降水机制方面取得了许多新发现。本研究将利用MAP和IMPROVE（国家气象局业务数据集）中获得的特殊观测数据，以及与中尺度模式输出的比较，建立并扩展有关地形降水微物理和动力学的几个关键结果。从MAP和IMPROVE数据集的分析中出现的一个重要主题是地形降水在空间和时间上的多尺度变异性。对于2公里尺度，地形上的阻塞流和非阻塞流的三维降水模式不同。小尺度降水特征向上游发展，向山区漂移。与此同时，其他被地形锁定的小尺度特征也在发展。在山上流动的航空包裹经常会穿过彼此的路径，扰乱热力学和微物理性质。研究的第一部分将建立在这些发现的基础上，通过检查几个冬季运行的国家气象局WSR-88D雷达和来自华盛顿州南部和俄勒冈州北部降水事件的高空探测。降水模式、频率、时空变化以及与沿海和喀斯喀特山脉的关系将以一种便于与合作首席研究员提供的区域中尺度模式输出进行客观比较的方式进行表征。对MAP数据集的分析揭示了在大范围降水强度范围内数百米尺度上的微物理变化，以及0℃以上和0℃以下的吸积对地形降水中观测到的高降水效率的重要性。对IMPROVE数据集的分析表明，小尺度对流翻转是降水增强的机制之一。研究的第二部分将扩展和完善这些结果。未解决的关键问题涉及小尺度对流翻转的频率以及小尺度垂直空气运动和降水强度联合变率的细节。从现有数据集对垂直指向雷达和降水测量的分析将侧重于集合特性方面的小尺度变率特征。知识价值：改进定量降水预报是美国天气研究计划的一项主要倡议。本研究将评估基于MAP和IMPROVE研究的新的地形降水机制概念模式的适用性。将评估对垂直空气运动的亚网格尺度变化进行参数化的潜在需求。所开发的方法将有助于未来使用作战雷达数据集来常规评估预测模型的性能。更广泛的影响：结果将与区域业务预测界以及相关课程的研讨会和客座讲座分享。该项目将包括一名研究生和一名本科生研究助理的教育和培训。

Two major field programs, the Mesoscale Alpine Programme (MAP) (1999) in the southern Alps and the Improvement of Microphysical PaRameterization through Observational Verification Experiment (IMPROVE) (2000 and 2001) in Washington and Oregon have yielded many new findings regarding orographic precipitation mechanisms. This research will build on and extend several key results regarding the microphysics and dynamics of orographic precipitation using special observations obtained in the MAP and IMPROVE, National Weather Service operational data sets, and comparisons with mesoscale model output. An important theme emerging from the analysis of the MAP and IMPROVE data sets is the variability of orographic precipitation over multiple scales in space and time. For scales 2 km, different three-dimensional patterns of precipitation occur in blocked versus unblocked flow over terrain. Small-scale precipitation features develop upstream and drift toward the mountains. Simultaneously, other small-scale features develop that are locked to terrain. Air parcels flowing over mountains often cross each other's paths, scrambling both sets of thermodynamic and microphysical properties. The first component of the research will build on these findings by examining several winter seasons of operational National Weather Service WSR-88D radar and upper-air soundings from precipitation events in southern Washington and northern Oregon. Precipitation patterns, their frequency, variability in space and time, and relationships to the coastal and Cascade mountain ranges will be characterized in a manner to facilitate objective comparison to regional mesoscale model output supplied by a collaborating Principal Investigator. Analyses of the MAP data sets have revealed microphysical variability at the scale of hundreds of meters within a wide range of precipitation intensities as well as the importance of accretion both above and below the 0 degree C level to the high precipitation efficiencies observed in orographic precipitation. Analyses of the IMPROVE data sets indicate small-scale convective overturning as a mechanism of precipitation enhancement. The second component of the research will extend and refine these results. Key unanswered questions relate to the frequency of small-scale convective overturning and the details of the joint variability of small-scale vertical air motions and precipitation intensity. Analysis of vertically pointing radar and precipitation measurements from existing data sets will focus on characterization of small-scale variability in terms of ensemble properties. Intellectual merit: Improvement of quantitative precipitation forecasting is a major initiative of the U.S. Weather Research Program. This research will evaluate the applicability of the new conceptual models of orographic precipitation mechanisms derived from MAP and IMPROVE studies. The potential need for parameterizations of sub-grid scale variability of vertical air motion will be evaluated. Methods developed will facilitate future use of operational radar data sets to routinely evaluate forecast model performance. Broader impacts: Results will be shared with the regional operational forecast community as well as within seminars and guest lectures for relevant courses. The project will involve the education and training of a graduate student and an undergraduate research assistant.