Did the 2022 strong polar vortex make serial extratropical cyclone clustering more likely? (StratClust)

温带风暴或气旋是影响西欧的最具破坏性的自然灾害。当几个强烈风暴在短时间内影响一个特定地区时，就会发生连续的气旋聚集，这可能导致巨大的社会影响，如洪水、强风造成的破坏和生命风险。2022年2月，英国和爱尔兰受到一连串温带风暴的严重影响：达德利、尤尼斯和富兰克林。这些风暴造成了破纪录的阵风，可悲的是造成了多人伤亡。气象预报员将尤妮斯风暴描述为“十年一遇”的风暴。识别和量化导致这段时间强烈暴风雨天气的因素对于了解未来的天气危害非常重要。一个潜在的因素是平流层极地涡旋——在地球表面上方25公里处环绕北极的一圈强风——这几乎是2022年2月有记录以来最强的一次。极地涡旋已被证明会影响地表天气和气候，但它以前并没有与温带风暴的聚集联系起来。StratClust将验证的假设是，异常强烈的极地涡旋创造了有利于多种北大西洋强烈风暴发展的环境条件。为了解决这一假设，StratClust将分析来自最先进的数值预测系统的分季节预报，并执行定制的“归因”实验，以分离和量化平流层对地面天气的影响，并将其与其他因素分开。StratClust的研究结果将首次提供有关2022年2月异常极地涡旋条件是否导致英国和爱尔兰极端天气的信息。StratClust将作为一项试点研究，通过与世界气候研究计划（SNAPSI）的一个国际项目合作，将吸引其他国际建模小组进行类似的归因实验，从而生成2022年2月的分季节预测的新社区数据集，并为进一步研究提供机会。

Extratropical storms, or cyclones, are the most damaging natural hazard affecting western Europe. Serial clustering of cyclones occurs when several intense storms affect one specific region in a short period, which can lead to large societal impacts such as flooding, damage from strong winds and risk to life. In February 2022, the UK and Ireland were severely impacted by a succession of extratropical storms: Dudley, Eunice and Franklin. These storms caused record breaking wind gusts and sadly led to multiple deaths and injuries. Storm Eunice was described by weather forecasters as a 'once in a decade' storm. Identifying and quantifying the factors that caused this period of intense stormy weather is important for understanding future weather hazards. One potential contributor was the stratospheric polar vortex - a band of strong winds encircling the North pole around 25 km above Earth's surface - which was nearly the strongest on record in February 2022. The polar vortex has been shown to affect surface weather and climate, but it has not previously been connected to clustering of extratropical storms. The hypothesis that StratClust will test is that the unusually strong polar vortex created environmental conditions that favoured the development of multiple intense North Atlantic storms. To address this hypothesis, StratClust will analyse subseasonal forecasts from state-of-the-art numerical prediction systems and perform bespoke 'attribution' experiments to isolate and quantify the impact of the stratosphere on surface weather and separate it from other factors. The outcomes from StratClust will provide the first information about whether the exceptional polar vortex conditions in February 2022 contributed to the extreme weather in the UK and Ireland. StratClust will serve as a pilot study which, through collaboration with an international project as part of the World Climate Research Programme (SNAPSI), will engage other international modelling groups to perform similar attribution experiments, thereby generating a new community dataset of subseasonal forecasts for February 2022 and opportunities for further research.