Average and Variability Characteristics of Orographic Precipitation at Multiple Scales

阿尔卑斯山南部的中尺度阿尔卑斯山计划(MAP)(1999年)和华盛顿和俄勒冈州通过观测验证实验改进微物理参数化(MAPE)(2000年和2001年)这两个主要的野外计划在地形降水机制方面取得了许多新的发现。这项研究将利用地图和改进图中获得的特殊观测、国家气象局业务数据集以及与中尺度模式输出的比较，在地形降水微观物理和动力学方面的几个关键成果的基础上并加以扩展。对地图和改进后的数据集进行分析后得出的一个重要主题是地形降水在空间和时间上在多个尺度上的可变性。对于2公里尺度，在地形上阻塞和非阻塞流动中出现不同的三维降水模式。小尺度降水特征向上游发展，向山区漂移。同时，还会开发出受地形限制的其他小比例要素。在山脉上流动的气团经常相互交叉，扰乱了热力学和微观物理性质。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雷达和华盛顿南部和俄勒冈州北部降水事件的高空探测。将描述降水模式、其频率、在空间和时间上的变化以及与沿海和喀斯喀特山脉的关系，以便与合作首席调查员提供的区域中尺度模式结果进行客观比较。对地图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的微物理可变性，以及0摄氏度上下的吸积对在地形降水中观察到的高降水效率的重要性。对改进后的数据集的分析表明，小尺度对流翻转是降水增强的一种机制。这项研究的第二部分将扩展和提炼这些结果。尚未回答的关键问题涉及小规模对流翻转的频率，以及小规模垂直空气运动和降水强度联合变化的细节。对现有数据集的垂直指向雷达和降水量测量结果的分析将侧重于从集合属性的角度描述小规模可变性的特征。智力优势：改进定量降水预报是美国天气研究计划的一项主要倡议。这项研究将评估从MAP衍生的新的地形降水机制概念模式的适用性，并改进研究。将对垂直空气运动的次网格尺度可变性的潜在需要进行评估。所开发的方法将有助于今后使用作战雷达数据集来例行评估预报模型的性能。更广泛的影响：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成果。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.