A global climatology of sting-jet cyclones
Lead Research Organisation:
University of Reading
Department Name: Meteorology
Abstract
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.
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.
Organisations
| Description | Sting jets have been identified in several of the most damaging mid-latitude cyclones impacting northwest Europe. In contrast to the major long-lived cyclone wind jets, sting jets can lead to regions of exceptionally strong near-surface winds, and particularly damaging gusts, over just a few hours and with much smaller wind "footprints". Research to date has focused exclusively on cyclones crossing the North Atlantic, although there are no known physical reasons why sting jets should not develop over other oceanic basins. We have produced the first global climatology of sting-jet cyclones, revealing their presence and frequency over all major extratropical ocean basins and characterising differences between these cyclones and those that do not contain sting jets. A sting jet precursor diagnostic has been applied to more than 10,000 tracked cyclones, the most intense (top 10% in terms of maximum intensity) cyclones with a warm secluded core in midlatitude regions globally, using over 40 years of data from the ERA5 reanalysis (a long time series consistent gridded dataset including meteorological variables). The applicability of this diagnostic, which identifies the type of convective instability in the cyclone required for sting jets in the appropriate part of the cyclone, outside of the North Atlantic region in which its use has been previously validated has been tested and refined by evaluating its behaviour for a set of "notable storms". Cyclones with sting jet precursors are found to occur over the North Pacific and Southern Ocean, as well as over the North Atlantic, though they are more prevalent in the Northern Hemisphere (37% of assessed cyclones) compared to the Southern Hemisphere (20%). Sting jet precursor cyclones have distinct characteristics to those cyclones without the precursor in terms of their average track, composite structure and intensity. In particular they have stronger near surface winds, both in the reanalysis dataset and in an independent blended observation dataset. These differences evidence the climatological consequences of strong cloud processes on cyclone characteristics with implications for how cyclone intensity will change under global warming. |
| Exploitation Route | Open questions remaining following this research include (i) why cyclones with sting jet precursors (SJP) are far less prevalent in the Southern Hemisphere than in the Northern Hemisphere and the consequence of this difference for the presence of sting jets, (ii) whether sting-jet cyclones occur beyond the mid-latitude region considered here (in particular in the Mediterranean region), and (iii) the relationship between the presence (and magnitude) of the SJP, the presence of sting jet(s), and enhanced surface winds due to sting jet(s) in cyclones. It is anticipated that the databases generated here of cyclones with and without SJP will enable case study and other analyses to be performed to address some of these questions. Finally, a bi-product of this study is a database of intense warm-seclusion cyclones (and an efficient algorithm for their objective identification). While outside the scope of this study, interesting questions can be addressed using this database linked to conceptual models of cyclone development. We are working to make these databases publicly available. |
| Sectors | Environment |
| Title | Warm-seclusion identification in cyclones |
| Description | A new algorithm to objectively identify extratropical cyclones with a warm seclusion. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2023 |
| Provided To Others? | No |
| Impact | This tool has enabled us to more efficiently assess the likelihood of sting jets in extratropical cyclones by limiting our analysis to those cyclones that have a warm seclusion and so can have a sting jet. |