Assessment of connections between atmospheric planetary waves and extreme rainfall events

NERC：安娜惠特福德：NE/S 007512/1极端降雨事件被认为会造成重大的社会经济损失和生命损失，因为强降雨可能产生危险的洪水，特别是在小的陡峭集水区和城市地区。这些极端降雨事件是由当地和区域尺度上的热力学（与温度有关）和动力学（与大气环流有关）共同驱动的。虽然近年来的研究已经揭示了很多关于极端降雨的热力学驱动因素，但我们仍然对动力学驱动因素知之甚少（Westra等人，2014年）。这些动态驱动因素的范围从非常大的行星尺度大气波（罗斯贝波）到非常局部化的小尺度对流。在这个项目中，我们专注于大尺度大气驱动因素，特别是Rossby波和极端降雨事件之间的关系。这些大规模的大气波在以前的研究中已经被证明是极端热浪事件和5至7天极端降雨事件的驱动因素。这些连接发生在匿名高振幅波和非常缓慢移动（准静止）波（Petoukhov等人，2013; Wolf等人，2018; Kornhuber等人，2019年）。因此，我们的目标是确认这些联系是否也发生在较短的多日（3天或更短）极端降雨事件中，然后调查是否也与每日和亚每日极端事件有关。中纬度波导是发生在大气中的高空风（喷流）的窄带，可以有效地将Rossby波捕获在波导的纬度带内。已经发现中纬度波导与异常高的准定常波活动和极端热事件一起发生（Petoukhov等人，2013;白色，2019），这表明它们对有利于异常Rossby波发展的条件的发展产生了影响。这个项目的目的是确定是否相同的波导- Rossby波协会是目前极端降雨事件。一旦确定了Rossby波和极端降雨之间的任何联系，我们将使用季节到亚季节气候预测模型的输出和Rossby波指数来研究是否有可能根据Rossby波活动在季节时间尺度上预测极端降雨事件的发生。支持异常RW发展的条件在频率上增加（Petoukhov等人，2013; Kornhuber等人，2019年）。与此同时，由于全球变暖，极端降雨的强度和频率增加的证据（Trenberth等人，2003年）表明，我们迫切需要了解这些破坏性事件背后的驱动因素。因此，提高我们对异常RWs如何影响极端降雨的理解对于提高我们预测和准备这些事件以及任何相关洪水的能力至关重要。该项目最终将为这一理解提供关键的研究成果，其结果将有助于提高我们预测未来极端事件频率的能力。该项目的成果可能对保险业以及地方和国家政府机构（如英国环境署）产生巨大的积极影响。能够在季节到次季节的基础上预测这些破坏性极端事件可能发生的时间，将使保险公司和地方政府能够实施计划和战略，帮助在这些事件发生之前做好准备，从而提高复原力并减轻任何由此产生的洪水的负面社会经济影响

NERC:Anna Whitford:NE/S007512/1Extreme rainfall events are recognised as causing significant socioeconomic damage and loss of life as the intense rainfall can generate dangerous floods, particularly in small steep catchments and urban areas. These extreme rainfall events are driven by a combination of thermodynamic (linked to temperature) and dynamic (linked to atmospheric circulation) forces on both local and regional scales. While research in recent years has revealed much about the thermodynamic drivers of extreme rainfall, there is still much we do not know about the dynamical drivers (Westra et al., 2014). These dynamic drivers range from very large, planetary scale atmospheric waves (Rossby waves) down to very localised small-scale convective currents. In this project we are focussing on the large-scale atmospheric drivers, in particular the relationships between Rossby waves and extreme rainfall events. These large-scale atmospheric waves have been shown in previous studies to be drivers of extreme heatwave events and also of 5 to 7-day extreme rainfall events. These connections occur for both anonymously high amplitude waves and also for very slow-moving (quasi-stationary) waves (Petoukhov et al., 2013; Wolf et al., 2018; Kornhuber et al., 2019). We therefore aim to confirm whether these connections also occur for shorter multi-day (3 days and less) extreme rainfall events and then investigate whether there are also connections to daily and sub-daily extreme events. Midlatitude waveguides are narrow bands of high altitude wind (jets) which occur in the atmosphere and can effectively trap the Rossby waves within the latitude band of the waveguide. Midlatitude waveguides have been found to occur in conjunction with anomalously high quasi-stationary wave activity and extreme heat events (Petoukhov et al., 2013; White, 2019), suggesting they have an influence on the development of conditions conducive to anomalous Rossby wave development. This project aims to identify whether the same waveguide - Rossby wave associations are present for extreme rainfall events. Once any connections between the Rossby waves and extreme rainfall have been identified, we will use output from seasonal to subseasonal climate forecast models and Rossby wave indices to investigate whether it is possible to produce forecasts of extreme rainfall event occurrence on seasonal timescales based on the Rossby wave activity.It has been shown that, due to climate change, the conditions which support the development of anomalous RWs have increased in frequency (Petoukhov et al., 2013; Kornhuber et al., 2019). At the same time, the evidence for increases in the intensity and frequency of extreme rainfall due to global warming (Trenberth et al., 2003) indicates we urgently need to understand the drivers behind these damaging events. Therefore, improving our understanding of how anomalous RWs effect extreme rainfall is vital to enhance our ability to forecast and prepare for these events and any associated flooding. This project would ultimately provide a key piece of research towards this understanding and the results will help improve our ability to project future extreme event frequency. The outcomes of this project could have large positive impacts for the insurance industry and for local and national government agencies e.g. the UK Environment Agency. Being able to forecast on a seasonal to sub-seasonal basis, when these damaging extreme events may occur would allow insurers and local governments to implement plans and strategies to help prepare before these events occurred, thereby increasing resilience and mitigating the negative socioeconomic impacts of any resulting flooding