Understanding extreme precipitation processes at the weather-climate interface

极端降水是一个特别严重的社会危害。观测到的大气温度和水汽的长期增加有利于极端降水事件的发生，这些极端降水事件越来越频繁、持续时间越来越长，并产生更大的降水率。理解和预测这些极端事件是具有挑战性的科学问题，这些问题在我们不断变化的气候中变得越来越重要。科学界面临的一个特别重要的挑战是，如何理解极端降水持续时间远长于与个别天气系统相关的一两天时间尺度的过程。在一个特定的地点，这种极端降水通常会持续数天或数周。因此，这些状态的时间尺度延伸到天气-气候界面的次季节范围。本研究的长期目标是提高科学界对造成亚季节气候的持续极端降水机制的认识和预测。我们在实现这些结果方面的成功将为加强对与次季节变率及其相关的极端天气相关的过程的理解提供重大进展。这项研究最直接的短期目标包括对有利于极端降水的热力学和动力环境进行严格的诊断分析。以气团形式存在的热力环境调节着降水速率。动力环境通过产生持续的上升运动和长时间的水汽供应来促进极端降水。正是降水率和持久性的综合影响促成了极端降水状态。我们试图了解将热带气团输送到北美高纬度地区，特别是加拿大的大气河流的作用。这些河流通常与持续的极端降水有关。此外，我们打算研究气旋和反气旋在产生驱动北美极端降水的大气河流中的作用。我们的研究计划将包括与中尺度天气和区域气候模拟小组的合作，目的是将我们的研究成果应用于改善极端降水的预测。我们打算定期与这些建模小组会面，目的是提出与本研究相关的适当科学目标。参与本研究项目的学生将有机会与来自麦吉尔大学大气与海洋科学系各个分支学科的教职员工和学生同事，以及在学术界、政府和私营部门工作的蒙特利尔大气科学家的更大社区进行互动和合作。

Extreme precipitation is a particularly significant societal hazard. The observed secular increases in atmospheric temperature and water vapor favor extreme precipitation events that are increasingly frequent, longer in duration, and generate larger precipitation rates. Understanding and forecasting such extreme events are challenging scientific problems that are becoming ever more consequential in our changing climate. A particularly important challenge to the scientific community is understanding the processes of extreme precipitation persisting for periods considerably longer than the one-two day time scales associated with individual weather systems. Such regimes of extreme precipitation often persist for several days, or weeks, in a given location. The time scales of these regimes therefore extend into the sub-seasonal range at the weather-climate interface. The long-term objective of this research is to provide the scientific community with improved understanding and forecasting of persistent extreme precipitation regimes contributing to the sub-seasonal climate. Our success in achieving these outcomes will provide significant progress towards an enhanced understanding of processes associated with sub-seasonal variability, and its associated extreme weather. The most immediate short-term objectives of this research include rigorous diagnostic analyses of the thermodynamic and dynamic environments favoring extreme precipitation. The thermodynamic environment, in the form of air mass, modulates the precipitation rate. The dynamical environment contributes to extreme precipitation by generating sustained upward motion and a long-lived moisture supply. It is the combined effects of precipitation rate and persistence that contribute to an extreme-precipitation regime. We seek to understand the role of atmospheric rivers that transport tropical air masses into the higher latitudes of North America, particularly Canada. These rivers are often associated with persistent extreme precipitation. Additionally, we intend to examine the role of cyclones and anticyclones in producing the atmospheric rivers driving North American extreme precipitation. Our research program will include collaborations with mesoscale-weather and regional-climate modeling groups, with the objective of applying our research results to improving forecasts of extreme precipitation. We intend to meet regularly with these modeling groups with the objective of posing appropriate scientific objectives related to this research. The students supervised in this research program will have opportunities for interactions and collaborations with faculty and student colleagues from a rich variety of sub-disciplines within the Department of Atmospheric and Oceanic Sciences, McGill University, and in the larger community of Montreal-based atmospheric scientists working in academia, government, and the private sector.