The motivation of our study is to provide forecasters and users complementary guidance and tools to identify and predict atmospheric conditions that could lead to life-threatening flash floods. Using hourly and sub-hourly rainfall datasets, proximity radiosondes, ERA5 reanalysis of extreme rainfall events in the UK during 2000–2020, and case studies in 2021, we observe a three-layered atmospheric structure, consisting of Moist Absolute Unstable Layers (MAULs) embedded in a conditional unstable layer sandwiched between a stable upper layer and a near-stable low layer. Based on our analysis, we propose a conceptual model to describe the atmospheric properties of a ‘rainfall extreme’ environment, with a particular focus on the thermodynamics associated with sub-hourly rainfall production processes. We then set this model within a wider framework to describe the precursor synoptic and mesoscale environments necessary for sub-hourly rainfall extremes in the mid-latitudes. We show that evolution of the Omega block and Rex Vortex couplet provides the optimal environmental conditions for sub-hourly rainfall extremes. These results provide the potential to develop a ‘4-stage’ warning system to assist in the identification and forecasting of life threatening short-duration extreme rainfall intensities and flash floods.

中文翻译：

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用于理解和预测危及生命的极端降雨的新概念模型


我们研究的动机是为预报员和用户提供补充指导和工具，以识别和预测可能导致危及生命的山洪的大气条件。使用每小时和次小时降雨数据集、邻近无线电探空仪、对 2000-2020 年英国极端降雨事件的 ERA5 重新分析以及 2021 年的案例研究，我们观察到由潮湿绝对不稳定层 (MAUL) 组成的三层大气结构嵌入在夹在稳定上层和近稳定低层之间的条件不稳定层中。根据我们的分析，我们提出了一个概念模型来描述“降雨极端”环境的大气特性，特别关注与每小时降雨量产生过程相关的热力学。然后，我们将该模型设置在更广泛的框架内，以描述中纬度地区亚小时降雨极端事件所需的前兆天气和中尺度环境。我们表明，欧米茄块和雷克斯涡对的演化为每小时以下的极端降雨提供了最佳环境条件。这些结果提供了开发“四阶段”预警系统的潜力，以协助识别和预测危及生命的短期极端降雨强度和山洪。