Sting jet

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explosively developing extratropical cyclones. A sting jet (marked as "SJ") may develop within the frontal fracture region
as the cyclone reaches its mature stage.

A sting jet is a narrow, transient and mesoscale airstream that descends from the mid-troposphere to the surface in some extratropical cyclones.[1] When present, sting jets produce some of the strongest surface-level winds in extratropical cyclones and can generate damaging wind gusts in 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 the Shapiro–Keyser model of 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 by

evaporative cooling are 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 most globally-spanning weather models. The speed of the winds brought to the surface by a sting jet is dependent on the stability of the atmosphere within the layer 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

See also: List of sting jet cyclones
Great Storm of 1987
was 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 of extratropical cyclones.[8][9] Sting jets constitute one possible mechanism through which high winds can be produced in extratropical cyclones without being directly caused by atmospheric 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.

RCP8.5 is assumed.[21]

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

Sting jet-producing cyclones typically follow the evolution envisaged by the

Great 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-bent occlusions in storms affecting Norway to the "poisonous tail" of a scorpion.[22]

Sting jets may result in the clearing of clouds in the

Cyclone Friedhelm in 2011 as part of the Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) field campaign.[30]

Development

Illustration of an archetypal extratropical cyclone path and affected areas
Idealised depiction of the trajectory of an extratropical cyclone and 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.

pressure 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 both synoptic scale and mesoscale processes.[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 strong frontolysis equatorward 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 of conditional 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. The Met Office has 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 in wind profiler observations.[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 the

specific humidity characteristic 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 stronger pressure gradients while descending and rotating about the low 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 constant wet-bulb potential temperature.[8] Once it reaches the planetary boundary layer, atmospheric convection and turbulent mixing within 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 a low-pressure area (the cold 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

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 in atmospheric 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 global numerical weather prediction models, making ensemble forecasting through the use of their explicit appearance in global model outputs impractical.[49] Difficulties with parameterising the 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.

relative 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

Notes

  1. ^ Geostrophic absolute momentum is defined as , where is the component of geostrophic wind perpendicular to the temperature gradient, is the
    Coriolis parameter
    , and is the position along a
    coordinate axis
    aligned with the temperature gradient, such that increases in the direction of warmer air.[53]

References

  1. ^ a b c d e f Schultz & Browning 2017, pp. 63–64.
  2. ^ a b c d e Schultz & Browning 2017, p. 65.
  3. ^ a b c d Baker 2009, p. 143.
  4. ^ Gliksman et al. 2023, p. 2174.
  5. ^ a b Clark & Gray 2018, p. 967.
  6. ^ a b c Martínez-Alvarado, Weidle & Gray 2010, p. 4055.
  7. ^ a b Slawson, Nicola (18 February 2022). "What is a 'sting jet'? Scientists warn of repeat of 1987 phenomenon". The Guardian. Retrieved 18 December 2023.
  8. ^ a b c Baker, Gray & Clark 2014, p. 97.
  9. ^ a b Gray 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. ^ a b c Clark & Gray 2018, p. 964.
  14. ^ Martínez-Alvarado et al. 2012, p. 7.
  15. ^ Hart, Gray & Clark 2017, p. 5468.
  16. ^ a b c Eisenstein, Pantillon & Knippertz 2020, p. 187.
  17. ^ a b Martínez‐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. ^ a b c d Schultz & Browning 2017, p. 63.
  23. ^ Clark & Gray 2018, p. 945.
  24. ^ Browning 2004, p. 375.
  25. ^ a b Hewson & Neu 2015, p. 10.
  26. ^ a b Clark & Gray 2018, p. 944.
  27. ^ Browning & Field 2004, p. 287.
  28. ^ Browning et al. 2015, p. 2970.
  29. ^ Clark & Gray 2018, p. 953.
  30. ^ a b c Clark & Gray 2018, p. 950.
  31. ^ a b c d e Clark & Gray 2018, p. 966.
  32. ^ Pichugin, Gurvich & Baranyuk 2023, p. 1.
  33. ^ Mass & Dotson 2010, p. 2526.
  34. ^ a b Schultz & Sienkiewicz 2013, pp. 607–611.
  35. ^ a b c d e Baker 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. Retrieved 18 December 2023.
  44. ^ Smart & Browning 2014, p. 609.
  45. ^ Clark & Gray 2018, p. 958.
  46. ^ a b Clark & Gray 2018, p. 963.
  47. ^ Rivière, Ricard & Arbogast 2020, p. 1819.
  48. ^ Martínez-Alvarado et al. 2014, p. 2593.
  49. ^ a b c Gray et al. 2021, p. 370.
  50. ^ Coronel et al. 2016, p. 1781.
  51. ^ Clark & Gray 2018, p. 955.
  52. ^ a b Gray 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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