A global climatology of sting-jet cyclones

Lead Research Organisation: University of Reading
Department Name: Meteorology


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.


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