Orographic Enhancement of Precipitation in Mid-latitude Baroclinic Waves

地形对中纬度斜压波降水的增强作用

• 批准号: 0221843
• 负责人: Robert Houze
• 金额: $ 83.08万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-09-01 至 2006-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0221843&HistoricalAwards=false
• 关键词: Orographic; Enhancement; Precipitation; Mid; latitude

The goal of this research is to advance understanding of the orographic modification of precipitation systems as they pass over major mountain ranges. The study will integrate data from two recent field programs: the Mesoscale Alpine Programme (MAP), conducted over the European Alps in 1999, and the second phase of the Improvement of Microphysical PaRameterization through Observational Verification Experiment (IMPROVE II), conducted over the Oregon Cascades in 2001. Data in both projects was collected from a variety of airborne and ground-based advanced weather radars. This collection of radars was effective at indicating the predominant precipitation mechanisms over the windward slopes in both projects. In MAP, mobile Dopplers provided further information in deep valleys hidden from the view of fixed site radars. In IMPROVE II the University of Washington Convair aircraft collected ice particle samples aloft, while ground observers collected ice particle samples at the crest of the Cascades.The tentative conceptual model of orographic precipitation enhancement inferred from the data collected in MAP suggests that coalescence of drops below the 0 degree C level and riming that generates graupel, just above the 0 degree C level, are key processes in producing particles that fall out quickly on the windward slopes. This process seems to work best in unblocked flow over the terrain, i.e., when the flow is strong and weakly stable, so it possesses the energy required to rise directly over the barrier. The process works even better when the flow up the terrain is slightly unstable, so that embedded convective cells can form and accelerate the coalescence and graupel-forming processes over the first large windward peak of terrain. Preliminary analysis of the new IMPROVE II data set suggests that similar processes are at work over the Cascades.The empirical conceptual models will guide the critical evaluation of high resolution numerical model runs for the MAP and IMPROVE II storms. Numerical model output provides a database which will be evaluated for consistency with the MAP and IMPROVE II empirical models of orographic enhancement. The numerical models also will be run for select cases to obtain finer spatial resolution and more details on the microphysical processes taking place in the model. The radar data will provide dynamical constraints on the model results and the data will be examined for consistency with the model-simulated microphysical fields. Improvements to the numerical models will help to advance the forecasting of precipitation and runoff in mountainous regions.

这项研究的目的是提高认识的地形修改降水系统，因为他们通过主要山脉。 这项研究将综合最近两个实地方案的数据：1999年在欧洲阿尔卑斯山上空进行的中尺度阿尔卑斯山方案（MAP）和2001年在俄勒冈州瀑布上空进行的通过观测验证实验改进微物理参数化的第二阶段（IMPROVE II）。这两个项目的数据都是从各种机载和地面先进气象雷达收集的。 在两个项目中，雷达的收集有效地指示了迎风坡上的主要降水机制。 在MAP中，移动的多普勒雷达提供了隐藏在固定雷达视野之外的深谷中的进一步信息。 在IMPROVE II中，华盛顿大学的康维尔飞机在高空收集了冰粒样本，而地面观察员在瀑布顶部收集了冰粒样本。根据MAP收集的数据推断的地形降水增强的初步概念模型表明，0摄氏度以下的水滴聚合和刚好在0摄氏度以上产生的雾凇，是产生颗粒的关键过程，这些颗粒迅速落在迎风坡上。 这个过程似乎在地形上的畅通流中效果最好，即，当流动是强稳定的和弱稳定的时，因此它具有直接上升越过障碍物所需的能量。 当沿地形向上的气流稍微不稳定时，这一过程的效果甚至更好，因此嵌入的对流单体可以形成，并加速地形第一个大型迎风峰上方的合并和雹粒子形成过程。 对新的IMPROVE II数据集的初步分析表明，瀑布上也存在类似的过程。经验概念模型将指导MAP和IMPROVE II风暴高分辨率数值模型运行的严格评估。 数值模型输出提供了一个数据库，将评估该数据库与MAP和IMPROVE II地形增强经验模型的一致性。 数值模型还将在选定的情况下运行，以获得更精细的空间分辨率和模型中发生的微物理过程的更多细节。 雷达数据将提供对模型结果的动力学约束，并将检查数据与模型模拟的微物理场的一致性。 数值模式的改进将有助于提高山区降水和径流的预报水平。