Modulation of Airflow Within Complex Terrain by Moist Processes

该项目旨在更好地理解和量化在持续降雨下主要河谷湿排水流新提出的概念所涉及的物理过程。这一现象背后的可能机制是由于降水颗粒的融化和蒸发冷却造成的空气沉降。下沉的空气集中在河谷中，起到空气排水的作用。由此产生的下山谷气流可以在相反方向的湿空气流下发展，湿空气流被抬升到形成降水的地形屏障上。在该项目中进行的分析主要集中在：(a)深入评估在中尺度高山计划（MAP）期间在欧洲阿尔卑斯山南侧主要河谷收集的地面和机载多普勒雷达和热力学数据；(b)湿排水流现象的数值模拟和数值实验，以描述这种现象发生的条件，并评估对地形降水形成机制的潜在反馈。本研究的重点是潮湿过程对山谷内空气流动的影响，补充了在干燥（晴朗天空）条件下山谷气流的大量工作。所提出的分析将有助于更好地定义湿排水流动的新概念，并评估这种流动现象与从局部（山谷）尺度到地形障碍和更大尺度的动态和微物理过程的相关性。该研究与MAP密切相关，主要研究复杂地形对降水形成和洪水的中尺度影响。MAP被认为是一个综合的基础研究项目，直接应用于数值中尺度天气预报领域。高山地区以及世界上许多其他主要山脉的地形降水机制是洪水、滑坡和泥石流灾害的重要因素。

This project seeks to better understand and quantify the physical processes involved in the newly proposed concept of wet drainage flow in major river valleys under sustained rainfall. The suggested mechanism behind this phenomenon is air subsiding as a result of cooling from melting and evaporation of precipitation particles. The subsiding air concentrates in river valleys, which act as air drainage. The resulting down-valley flow can develop underneath an opposite-directed flow of moist air that is lifted onto the topographic barrier in which precipitation is formed.The analyses to be carried out during this project are focused on (a) in-depth evaluation of ground-based and airborne Doppler radar and thermodynamic data collected in major river valleys on the south side of the European Alps during the Mesoscale Alpine Program (MAP), and (b) numerical simulation of the wet drainage flow phenomenon and numerical experimentation to delineate the conditions under which this occurs and evaluate a potential feedback to orographic precipitation formation mechanisms.This research is focused on the effect of moist processes on the flow of air within valleys, complementing substantial work performed on airflow in valleys under dry (clear sky) conditions. The proposed analyses will help to better define the new concept of wet drainage flow and assess the relevance of this flow phenomenon to dynamic and microphysical processes ranging from the local (valley) scale to the topographic barrier and larger scales. The research is tightly knitted to MAP, which is focused on exploring the mesoscale effects of complex topography on precipitation formation and flooding. MAP is conceived as an integrated program of basic research with direct applications in the realm of numerical mesoscale weather prediction. Orographic precipitation mechanisms in the Alpine region, as well as many other major mountain ranges around the world, are an important element of flooding, landslide and debris flow hazards.