A global climatology of sting-jet cyclones

冬季风暴，正式称为中纬度或热带外气旋，是中纬度地区的主要自然灾害。尽管风力较弱，但它们造成的破坏程度与飓风一样大，因为它们的长锋面可以拖到1000多公里。破坏可能来自极端的风、雨和风暴潮，而具有异常强风的风暴通常被称为风暴。自2015年以来，英国气象局已经命名了所有影响英国的风暴，这些风暴有可能导致黄色或红色天气预警，以改善对即将到来的潜在危险天气的沟通；通常每年大约会发生7次命名的风暴（以及更多未命名的风暴）。自2004年对1987年“十月大风暴”的观测结果进行重新研究以来，已经在影响英国的一些最具破坏性的中纬度气旋中发现了刺状喷气机。据报道，此次风暴造成的损失为63亿美元（以2012年的价值为基准）。刺状喷流是一种连续的气流，从云头内部持续几个小时下降，云头是一种云带，在强气旋的中心向极地倾斜。这些喷流不同于其他寿命更长、规模更大、特征更明显的近地表风喷流。虽然它们的风足迹通常只有50-100公里宽，但它们可以导致不同的区域出现异常强烈的近地表风和破坏性阵风。自首次发现刺状急流以来，我们对刺状急流动力学的理解已经有了很大的进步，但主要是通过对穿越北大西洋影响欧洲西北部的气旋的案例研究进行分析。最近发表了一宗起源于地中海的刺痛喷气式飞机活动的个案，但其他中纬度地区没有发表的个案，发表的气候学只涵盖北大西洋。尽管如此，没有已知的物理原因说明为何刺状喷流不应在其他海洋盆地上发展，而且与刺状喷流相关的大气不稳定类型已被证明在中纬度海洋上广泛存在。该项目将产生第一个刺状急流气旋的全球气候学，并描述这些气旋与不含刺状急流的气旋之间的差异。我们将在再分析数据中对气旋进行识别和跟踪，并应用刺射环境前兆工具。再分析数据提供了过去天气和气候的最完整的代表，是通过将观测与使用一致的现代天气预报模式重新运行的天气预报混合而产生的。刺状喷流的瞬态、相对小尺度性质以及与其产生相关的大气不稳定类型意味着它们只能用非常高分辨率的模式来表示（即，运动方程在空间上紧密分离的点上求解），这些模式通常在数据周期和/或区域性质上是有限的。前驱工具的设计目的是在多年的全球数据集中诊断有利于刺状射流形成的环境条件，例如再分析，这些数据集的分辨率太粗，无法表示刺状射流。这项工作将利用项目组成员以前的工作来开发前体，最近，提高其计算效率，作为在气象局实施的预测工具的一部分（它应用于实时预测输出），以及从最新的ECMWF再分析得出的气旋路径的可用性，ERA5（从1979年至今）。这些创新意味着全球气候学现在是可行的。由此产生的气候学结果将揭示刺流在南半球、北太平洋、北大西洋和欧洲大陆的存在和频率。本研究将为全面评估当前和未来几年刺射气旋的影响铺平道路。

Winter storms, formally called mid-latitude or extra-tropical cyclones, are a major natural hazard in the midlatitudes. They can cause as much damage as hurricanes, despite somewhat weaker winds, due to their long fronts that can trail for more than 1000 km. Damage can come from extreme wind, rain and storm surge, and storms with exceptionally strong winds are often called windstorms. Since 2015 the Met Office has named all storms impacting the UK that have the potential to cause an amber or red weather warning to improve the communication of impending potentially dangerous weather; typically about 7 named storms (and many more unnamed storms) occur each year. Sting jets have been identified in some of the most damaging mid-latitude cyclones that have affected the UK since their first identification in 2004 from a re-examination of observations of the 1987 Great October Storm. The damage caused by this storm is indicated by the reported insured loss of $6.3bn (indexed to 2012 values). Sting jets are coherent airflows that descend over a few hours from within the cloud head, a band of cloud that hooks poleward around the centre of intense cyclones. These jets are distinct from the other longer-lived, broader-scale and much better characterised near-surface wind jets. While their wind footprints are typically just 50-100 km across, they can lead to distinct regions of exceptionally strong near-surface winds, and damaging gusts. Our understanding of the dynamics of sting jets has advanced considerably since their first identification, but mostly through analysis of case studies of cyclones crossing the North Atlantic to affect northwest Europe. A single case of sting-jet activity originating in the Mediterranean has recently been published, but no published cases exist for other mid-latitude regions and published climatologies only cover the North Atlantic. Despite this, there are no known physical reasons why sting jets should not develop over other oceanic basins and the type of atmospheric instability associated with sting jets has been shown to be widespread over the mid-latitude oceans. This project will produce the first global climatology of sting-jet cyclones and characterise the differences between these cyclones and cyclones that do not contain sting jets. We will apply a sting-jet environmental precursor tool to cyclones identified and tracked in reanalysis data. Reanalysis data provide the most complete representation of past weather and climate and are generated by blending observations with weather forecasts rerun using a consistent modern weather forecast model. The transient, relatively small-scale nature of sting jets and the type of atmospheric instability associated with their generation mean that they can only be represented by models with very high resolution (i.e., the equations of motion are solved at points that are closely separated in space) which are typically limited in data period and/or regional in nature. The precursor tool is designed to diagnose environmental conditions conducive to sting jet formation in multi-decadal, global datasets, such as reanalyses, that have too coarse resolution to represent sting jets.This work will exploit previous work by members of the project team to develop the precursor and, more recently, improve its computational efficiency as part of work to implement it at the Met Office as a forecast tool (it is applied to forecast output in real time), as well as the availability of cyclone tracks derived from the latest ECMWF reanalysis, ERA5 (which is available from 1979 to the present day). These innovations mean that a global climatology is now feasible. The resulting climatology will reveal the presence and frequency of sting jets over the southern hemisphere, North Pacific, and North Atlantic oceans, and continental Europe. This research will pave the way to a comprehensive evaluation of the impact of sting-jet cyclones in present and future years.