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

本文研究了高度不规则山地地形下游多条剪切线和尾迹及其相关的位涡（PV）异常（旗）的观测分析和数值模拟。这项研究的目的是量化地形强迫的不同尺度和制度，并确定这种强迫对主要山脉附近观测到的中尺度天气现象的影响。首席研究员将利用最近完成的中尺度高山计划（MAP）收集的观测数据。在MAP期间收集的大量数据集提供了迄今为止主要山脉附近气流时空结构的最详细文件。在本研究中，将利用MAP密集观测期（IOPs）的观测数据进行风场和热力学场分析，并重建相应的阿尔卑斯下风PV旗。每个分析的案例都将进行数值模拟，以便仔细检查中尺度模式在高时空精度下再现观测结果的能力。建模工作的目标是：(1)在选定的MAP IOPs期间重建观测到的PV异常；(2)评价现有的地形光伏发电和动态演化理论；(3)研究模型模拟PV场对不同参数化（特别是边界层表示和亚网格尺度地形）的敏感性，以推荐最佳参数化。提高对主要急流、地形涡旋和下坡风暴的气候位置和强度的认识，以及它们发展的条件范围，将有助于减少恶劣天气现象对经济的负面影响。这些知识可应用于实际问题，例如确定桥梁位置、预防强风地区的道路交通事故、避免与强横跑道风有关的航空危害，以及预测污染事件和对流的开始和结束。

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.