Numerical and Observational Study of Secondary Potential Vorticity (PV) Banners and Wakes in the Alps

本研究的重点是观测分析和数值模拟的多个剪切线和尾流和相关的位涡（PV）异常（横幅）下游的高度不规则的山区地形。 这项研究的目的是量化不同尺度和制度的地形强迫，并确定这种强迫对观测到的中尺度天气现象在一个主要山脉附近的影响。 首席研究员将利用最近完成的中尺度阿尔卑斯山方案（MAP）期间收集的观测数据，MAP期间收集的大量数据集提供了迄今为止关于主要山脉附近气流时空结构的最详细文件。在这项研究中，从选定的MAP密集观测期（IOPs）的观测数据将被用来执行风场和热力学场的分析，并重建相应的PV横幅下风向的阿尔卑斯山。 每一个分析的情况下，将进行数值模拟，以审查中尺度模式的能力，再现观测在高的时间和空间精度。 模拟工作的目标是：（1）重建所选MAP IOP期间观测到的PV异常;（2）评价现有的地形PV生成和动态演化理论;以及（3）研究模型模拟PV场对不同参数化的敏感性（特别是，边界层表示和次网格尺度地形学）以推荐最佳参数化。对主要急流、地形涡旋和下坡风暴的气候位置和强度以及它们发展的条件范围有了更好的了解，将有利于减少恶劣天气现象对经济的负面影响。 这些知识可实际应用于确定桥梁位置、预防强风地区的道路事故、避免与横跑道强风有关的航空危险以及预测污染事件和对流的开始和结束等问题。

This research focuses on the observational analysis and numerical simulations of multiple shearlines and wakes and the associated potential vorticity (PV) anomalies (banners) downstream of a highly irregular mountain topography. The goal of the study is to quantify different scales and regimes of orographic forcing and to determine effects such forcing has on observed mesoscale weather phenomena in the proximity of a major mountain range. The Principal Investigator will take advantage of the observational data collected during the recently completed Mesoscale Alpine Program (MAP).The extensive data sets collected during the MAP provide the most detailed documentation to date of the spatial and temporal structure of airflow in the vicinity of a major mountain range. In this study, the observational data from selected MAP Intensive Observation Periods (IOPs) will be used to perform analysis of the wind and thermodynamic fields and to reconstruct corresponding PV banners downwind of the Alps. Each analyzed case will be numerically simulated in order to scrutinize mesoscale model's ability to reproduce observations at high temporal and spatial accuracy. The objectives of the modeling work are to (1) reconstruct the observed PV anomalies during the selected MAP IOPs; (2) evaluate existing theories of orographic PV generation and dynamic evolution; and (3) investigate sensitivities of the model simulated PV field to different parameterizations (especially, boundary-layer representation and the subgrid scale orography) in order to recommend the optimal parameterizations.Improved knowledge of climatological positions and strengths of major jets, orographic vortices and downslope windstorms, and the range of conditions under which they develop, will be beneficial in decreasing the negative economic impact of severe weather phenomena. Such knowledge has practical application to problems such as the determination of bridge locations, prevention of road accidents in severe wind zones, avoidance of aviation hazards related to strong cross-runway winds and forecasting of the onset and termination of pollution episodes and convection.