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Sting jet

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Diagram of fronts and airstreams associated with an extratropical cyclone in the Northern Hemisphere as viewed from above
Horizontal structure
Diagram of fronts and airstreams associated with an extratropical cyclone in the Northern Hemisphere as viewed from an oblique angle
Vertical structure
Airstreams associated withexplosively developingextratropical cyclones. A sting jet (marked as "SJ" ) may develop within thefrontal fracture regionas the cyclone reaches its mature stage.

Asting jetis a narrow, transient andmesoscaleairstream that descends from themid-troposphereto the surface in someextratropical cyclones.[1]When present, sting jets produce some of the strongest surface-level winds in extratropical cyclones and can generate damagingwind gustsin excess of 50 m/s (180 km/h; 110 mph).[2][3][4]Sting jets are short-lived, lasting on the order of hours,[5]and the area subjected to their strong winds is typically no wider than 100 km (62 mi), making their effects highly localised. Studies have identified sting jets in mid-latitude cyclones primarily in the northern Atlantic and western Europe, though they may occur elsewhere. The storms that produce sting jets have tended to follow theShapiro–Keyser modelof extratropical cyclone development. Among these storms, sting jets tend to form following storm's highest rate of intensification.

Sting jets were first formally identified in 2004 byKeith Browningat theUniversity of Readingin an analysis of thegreat storm of 1987,though forecasters have known of its effects since at least the late 1960s.[6]The sting jet emerges from within the end of an extratropical cyclone's cloud head – a hook-shaped region of cloudiness near thecentre of low pressure– and accelerates as it descends to the surface. Multiple mechanisms explaining why sting jets form and why they accelerate during descent;frontolysis,the release ofconditional symmetric instability,andevaporative coolingare often cited as influences on sting jet evolution. The presence of these factors can be used to forecast the jets themselves as sting jets are too small to be resolved by mostglobally-spanning weather models.The speed of the winds brought to the surface by a sting jet is dependent on thestabilityof the atmosphere within thelayer of air near the surface.Sting jets can produce multiple areas of damaging winds, and a single cyclone can produce multiple sting jets.

Climatology and structure

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See also:List of sting jet cyclones
Satellite image of a large extratropical cyclone
TheGreat Storm of 1987was the first storm for which a sting jet was identified.

Sting jets are roughly 10–20 km (6–12 mi) wide and last 3–4 hours.[7]They are characterised in part by their mid-tropospheric origin and the acceleration of descending air, and are distinct from the low-tropospheric airstreams accompanying the cold and warm conveyor belts ofextratropical cyclones.[8][9]Sting jets constitute one possible mechanism through which high winds can be produced in extratropical cyclones without being directly caused byatmospheric convection.[10]

Not all mid-latitude cyclones produce sting jets; in most cases, the strong surface winds found in extratropical cyclones are produced by the cold and warm conveyor belts.[9]One analysis suggested that 39–49% of the strongest extratropical cyclones in theNorth Atlanticexhibit them.[11]Nearly a third of the most intense windstorms affecting theUnited Kingdomfrom 1993 to 2013 produced sting jets.[12]Within the North Atlantic, cyclones developing sting jets tend to follow commonstorm tracksand originate south of50°N,suggesting a potential influence of warm and moist air on sting jet formation.[13][14]Sting jet development also appears more likely forexplosively intensifyingstorms.[15]Atmospheric reanalysisdata suggest that sting jets are more common over water than over land,[13]but sting jets can develop entirely over continental land.[16]Theincreased moistureassociated withclimate changemay amplify theatmospheric instabilitiesthat support sting jet development, potentially increasing the proportion of extratropical cyclones with sting jets and their intensities.[17][18][19]The frequency of extremewindstormsand sting jets overall may also increase with climate change;[20]one study assessed a 60% increase in the occurrence of conducive conditions for sting jet development over the North Atlantic by 2100 ifRCP8.5is assumed.[21]

Explanatory diagram showing the stages of the Shapiro–Keyser model
Cyclones exhibiting sting jets have tended to develop in accordance with theShapiro–Keyser model.

Sting jet-producing cyclones typically follow the evolution envisaged by theShapiro–Keyser model.[22]In the four-stage model, a frontal fracture – a discrete separation of thecold frontfrom the low-pressure centre – occurs during the development of an extratropical cyclone as the cold front moves perpendicular to the warm front.[23][6]In Shapiro–Keyser storms, the temperature contrast initially associated with thewarm frontwraps around the low-pressure centre, forming aback-bent frontas the cyclone reaches its mature stage;[22]the most damaging extratropical cyclones exhibit these developmental signatures.[24]A hook-shapedcloud headaligned with the back-bent front is characteristic of storms producing sting jets.[3]The sting jet originates equatorward of the cyclone centre at the end of the back-bent front and near the tip of the cloud head following the frontal fracture stage of the Shapiro–Keyser model.[22][3]This tends to occur following the storm's fastest intensification and prior to the storm's peak intensity.[25]MeteorologistKeith Browningat theUniversity of Readingformally identified sting jets in a paper published in 2004 analysing the intense winds associated with theGreat Storm of October 1987.[26]His coinage of "sting jet" paid homage to the pioneering work of Norwegian meteorologists in the mid-20th century who likened the area of strong winds at the end of back-bentocclusionsin storms affectingNorwayto the "poisonous tail" of ascorpion.[22]

Sting jets may result in the clearing of clouds in theplanetary boundary layerevident onsatellite imagerypast the tip of the cloud head.[2]Shallow arc- or chevron-shapedstratiform cloudsin an extratropical cyclone's dry slot may also accompany sting jets,[27]and some of these cloud features may contribute directly to sting jet intensity.[28]However, conclusive identification of sting jets requires confirmation of the presence of a descending airstream,[2]and detection can be difficult with routine meteorological observations.[26]Most identifications of sting jets have been derived from the outputsnumerical weather models.[29]Sting jets have been diagnosed inseveral windstormsover the eastern North Atlantic and western Europe, including the 1987 storm.[30][31]Research into sting jets outside of the northern Atlantic has been limited,[31]with case studies primarily focusing onEuropean windstormsaffecting theBritish Isles.[16]Nonetheless, the observed conditions that facilitate sting jet development are not unique to the northern Atlantic.[13]Sting jets may occur in northern Pacific windstorms,[32]but may be less significant forPacific Northwest windstorm.[33]The first aerial in situ observations of a sting jet were taken inCyclone Friedhelmin 2011 as part of the Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) field campaign.[30]

Development

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Illustration of an archetypal extratropical cyclone path and affected areas
Idealised depiction of the trajectory of anextratropical cycloneand its swathes of strong winds. The narrow sting jet emerges during the storm's fastest intensification period.

Sting jets emanate from the cloud head and descend into the corridor of dry air associated with mid-latitude cyclones.[3]The descending air begins in the mid-levels of the troposphere, between the 600hPaand 800 hPapressure levels.[8]The mechanisms that cause the initial descent of air and the acceleration of winds in the sting jet are not well-established,[1]with studies finding both supporting and refuting evidence for proposed mechanisms.[16]These qualities of sting jets may be influenced by bothsynoptic scaleandmesoscaleprocesses.[31]Sting jets descend from the mid-troposphere at a rate of roughly 10 cm/s (0.33 ft/s), reaching the surface over the course of several hours.[34]The descent may be triggered by strongfrontolysisequatorward of the cyclone centre.[1]Warm air initially brought into the cyclone by the warm conveyor belt descends upon reaching the frontolytic region, providing one possible process through which sting jets develop. This region of frontolysis associated with the back-bent front is unique to Shapiro–Keyser storms.[34]The appearance of banded structures in the cloud head associated with sloped circulations with alternating regions of ascending and descending air – possibly indicative of the release ofconditional symmetric instability(CSI) – may also play a direct role in sting jet development, with air sinking in one of the cloud head downdraughts.[35]The presence of filamentary cloud bands in the cloud head, separated by one or more cloud-free regions, indirectly suggests the possible presence of sting jets. TheMet Officehas used the appearance of bands in cloud heads to operationally forecast sting jets.[36]The slanted nature of the sting jet has also been observed inwind profilerobservations.[37]The release of symmetric instability – a form of inertial instability independent of moisture – may also be implicated in sting jet formation.[38]

Illustration of processes that may contribute to sting jets.
Multiple atmospheric processes may contribute to sting jet formation and intensification

Sting jets do not derive their high wind speeds from thejet streamin the upper troposphere.[39]Instead, the air associated with the sting jet initially bears lowermomentumin the mid-troposphere and accelerates as it descends.[1]The sting jet's rate of descent depends on theinstabilityof the troposphere,[40]which in turn may be influenced by the local behaviour ofwater vapour,such as throughevaporative coolingor the release of CSI.[1]Both of these processes may influence sting jet intensification in different phases.[41]The reduction in stability from evaporative cooling or fluxes of heat and moisture from the surface may enable faster vertical motions.[2]Water from showers associated with sloped updraughts within the cloud head or from higher clouds may fall into regions of descent,[35][6]evaporating and cooling the air as the sting jet moves into the dry frontal fracture zone.[42]The evaporating cooling can result in the decreasedpotential temperatureand increasedspecific humiditycharacteristic of air in sting jets;[35]the increased density of the cooled air relative to the surrounding environment forces it to descend.[7]Alternatively, the acceleration of winds in the sting jet may be due to air encountering strongerpressure gradientswhile descending and rotating about thelow pressure centre,[1][43]and damaging sting jet winds may be achievable without enhancement from evaporative cooling or CSI release.[44]In the Northern Hemisphere, the strongest pressure gradients in a Shapiro–Keyser cyclone are often in the southwestern part of the cyclone where sting jets are found.[45]

Air carried by the sting jet descends rapidly from the mid-troposphere.[35]The trajectory of a sting jet follows a sloped path of constantwet-bulb potential temperature.[8]Once it reaches theplanetary boundary layer,atmospheric convectionandturbulent mixingwithin that layer brings the high momentum associated with the accelerated airstream to the surface, generating the intense surface winds associated with sting jets.[35]The degree to which sting jet air reaches the surface is dependent on the stability of the boundary layer.[31]Compared to other regions in mid-latitude cyclones, the frontal-fracture region into which sting jets descend is more neutrally stable to convection, enabling strong gusts to more efficiently reach the surface.[46]Destabilisation of the air at the top of the boundary layer may also prompt sting jet descent.[47]However, the boundary layer stability may be sufficiently high in some cases to prevent the descending sting jet from reaching the surface.[31]The imprint of sting jets may be evident as a locally intense region of surface wind speeds, though such maxima may arise from the combination of both sting jets and the cold air wrapping around alow-pressure area(thecold conveyor belt).[2]While the sting jet originates above the cold conveyor belt, it may descend to the surface ahead of the tip of the cold conveyor belt to produce a distinct region of intense winds,[5]or augment the pre-existing winds in the cold conveyor belt;[17]both circumstances may occur during a cyclone's lifecycle.[48]The swath of damaging winds produced by sting jets is narrower than 100 km (62 mi) in width.[46]Multiple sting jets may be simultaneously present within a cyclone, and a single sting jet may produce multiple wind maxima.[30]

Forecasting and modelling

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Plots of a modeled extratropical cyclone
The presence of DSCAPE in cloud heads may signal sting jet development.

The features of extratropical cyclones observable on satellite imagery and ascribable to sting jets are only evident when sting jets are imminent or already in progress. Longer range forecasts of sting jets rely on gauging whether or not the broader environmental conditions favour the development of a Shapiro–Keyser cyclone.[49]Sting jets can be reproduced inatmospheric models,but sufficiently high spatial resolution is necessary to resolve the mesoscale sting jet.[50]The horizontal spacing of model grid cells must be smaller than about 10–15 km (6.2–9.3 mi) to depict sting jets, and finer resolutions are needed to resolve localised details.[51]These can be used by forecasters; however, the scale of sting jets is near the limits of the resolution of longer-range globalnumerical weather predictionmodels, makingensemble forecastingthrough the use of their explicit appearance in global model outputs impractical.[49]Difficulties withparameterisingthe planetary boundary layer also lead to difficulties with depicting sting jets in computer models.[25]

As a proxy for direct modelling of sting jets, the relationship between CSI and sting jets may be leveraged to identify "sting jet precursors": properties of cyclones likely to generate sting jets.[49]The potential for CSI to enhance the descent of sting jets is quantified by downdraught slantwiseconvective available potential energy(DSCAPE), which measures the theoretical maximumkinetic energythat a descendingair parcelmay attain while remainingsaturatedand conservinggeostrophicabsolute momentum.[52][a]A method for identifying sting jet precursors in low-resolution data was published inMeteorological Applicationsin 2013, proposing that precursors featured high DSCAPE (exceeding 200 J kg−1) for air parcels descending from the mid-troposphere within the frontal fracture zone and less than 80 percentrelative humidity.[54]Bsed on this algorithm, the University of Reading developed a forecasting aid in use by the Met Office highlighting sting jet precursors based on the presence of sufficiently high DSCAPE in the cloud head of modelled cyclones.[52]

See also

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Notes

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  1. ^Geostrophic absolute momentum is defined as,whereis the component ofgeostrophic windperpendicular to the temperature gradient,is theCoriolis parameter,andis the position along acoordinate axisaligned with the temperature gradient, such thatincreases in the direction of warmer air.[53]

References

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  1. ^abcdefSchultz & Browning 2017,pp. 63–64.
  2. ^abcdeSchultz & Browning 2017,p. 65.
  3. ^abcdBaker 2009,p. 143.
  4. ^Gliksman et al. 2023,p. 2174.
  5. ^abClark & Gray 2018,p. 967.
  6. ^abcMartínez-Alvarado, Weidle & Gray 2010,p. 4055.
  7. ^abSlawson, Nicola (18 February 2022)."What is a 'sting jet'? Scientists warn of repeat of 1987 phenomenon".The Guardian.Retrieved18 December2023.
  8. ^abcBaker, Gray & Clark 2014,p. 97.
  9. ^abGray et al. 2021,p. 369.
  10. ^Knox et al. 2011,p. 63.
  11. ^Schultz & Browning 2017,pp. 64.
  12. ^"What is a sting jet?".MetMatters.Royal Meteorological Society.
  13. ^abcClark & Gray 2018,p. 964.
  14. ^Martínez-Alvarado et al. 2012,p. 7.
  15. ^Hart, Gray & Clark 2017,p. 5468.
  16. ^abcEisenstein, Pantillon & Knippertz 2020,p. 187.
  17. ^abMartínez‐Alvarado et al. 2018,p. 1.
  18. ^Knippertz, Pantillon & Fink 2018.
  19. ^Little, Priestley & Catto 2023,p. 1.
  20. ^Manning et al. 2022,p. 2402.
  21. ^Catto et al. 2019,p. 413.
  22. ^abcdSchultz & Browning 2017,p. 63.
  23. ^Clark & Gray 2018,p. 945.
  24. ^Browning 2004,p. 375.
  25. ^abHewson & Neu 2015,p. 10.
  26. ^abClark & Gray 2018,p. 944.
  27. ^Browning & Field 2004,p. 287.
  28. ^Browning et al. 2015,p. 2970.
  29. ^Clark & Gray 2018,p. 953.
  30. ^abcClark & Gray 2018,p. 950.
  31. ^abcdeClark & Gray 2018,p. 966.
  32. ^Pichugin, Gurvich & Baranyuk 2023,p. 1.
  33. ^Mass & Dotson 2010,p. 2526.
  34. ^abSchultz & Sienkiewicz 2013,pp. 607–611.
  35. ^abcdeBaker 2009,p. 144.
  36. ^Clark & Gray 2018,p. 952.
  37. ^Parton et al. 2009,p. 663.
  38. ^Clark & Gray 2018,p. 961.
  39. ^Clark & Gray 2018,p. 965.
  40. ^Baker, Gray & Clark 2014,p. 96.
  41. ^Volonté, Clark & Gray 2018,p. 896.
  42. ^Gray et al. 2011,p. 1499.
  43. ^"The Sting Jet".Training module on Cyclogenesis.EUMeTrain. 2020.Retrieved18 December2023.
  44. ^Smart & Browning 2014,p. 609.
  45. ^Clark & Gray 2018,p. 958.
  46. ^abClark & Gray 2018,p. 963.
  47. ^Rivière, Ricard & Arbogast 2020,p. 1819.
  48. ^Martínez-Alvarado et al. 2014,p. 2593.
  49. ^abcGray et al. 2021,p. 370.
  50. ^Coronel et al. 2016,p. 1781.
  51. ^Clark & Gray 2018,p. 955.
  52. ^abGray et al. 2021,pp. 370–371.
  53. ^Schultz & Schumacher 1999,p. 2712.
  54. ^Martínez‐Alvarado et al. 2013,pp. 52–53.

Sources

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