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Sting Jet

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Category: Weather Weather
Content source: SKYbrary About SKYbrary
Content control: SKYbrary About SKYbrary
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Tag(s) Weather Phenomena

Description

A Sting Jet is a meteorological phenomenon, a type of low-level jet stream, associated with some rapidly developing mid-latitude storms. The term sting jet describes the storm's most damaging winds, which sometimes reach speeds of more than 100 kts. The name refers to the shape the cloud pattern takes, as shown on satellite imagery. As it wraps around the centre of an area of low pressure, it takes on the appearance of a scorpion's tail. Although the strongest winds occur for only a short period of time in a very small area, perhaps only 30 miles across, they can cause significant damage and risk to life.

The "Sting at the end of the tail"

Definition

"The Sting Jet is defined as a coherent airflow that descends from mid‐levels inside the cloud head into the frontal‐fracture region of a Shapiro-Keyser cyclone over a period of a few hours leading to a distinct region of near‐surface stronger winds. It lies above the Cold Conveyor Belt (CCB) during some stage of its life, but, at least in some cases, descends to reach the top of the boundary layer ahead of the CCB. Strong near‐surface wind speeds and gusts may or may not result from a Sting Jet depending on boundary‐layer processes. It is not attributed to a specific mechanism in this definition.

Sting Jets do not, in all cases, accelerate beyond the tip of the CCB, so may not always form a distinct peak in speed at the surface, though it seems likely that, in this case, the SJ may still enhance the impact of the CCB."[1]

Formation

Extratropical cyclones develop along fronts that separate warm air from cold air. In the Northern Hemisphere, the counterclockwise circulation of these lows pulls warm air northward ahead of the storm and cold air southward behind hit. In the Southern Hemisphere, where lows rotate clockwise, warm air, this time from the north (and southward), still occurs ahead of the storm with cold air from the south behind it again (going northward). Extra-tropical cyclones are often associated with strong winds. The warm air flow ahead of the storm is known to meteorologists as the Warm Conveyor Belt (WCB) and can be associated with concentrated strong southerly winds - a warm jet (WJ). Conversely, the cold air flow is called the Cold Conveyor Belt (CCB) and can also be associated with a “cold jet” (CJ). Wind speeds exceeding 50 knots can occur over a fairly large area with both jets. When moisture is available, lifting with the low and associated fronts produces clouds and [{Precipitation|precipitation]]. The cloud pattern is clearly revealed by satellite imagery. The initial front is depicted by a line of clouds. As the cyclone develops, its circulation will produce a bulge or ball of clouds on the west side of the front. Strong cyclones will pull in dry air from aloft to the west and generate a cloudless dry slot feature. This can wrap around the storm, finally producing almost a question mark appearance.

Researchers at the University of Reading, led by Professor Keith Browning, reanalysing the violent extratropical storm that caused significant damage over southern England 1-16 October 1987, identified an even smaller scale flow with the most damaging winds in the same general region as the cold jet but apparently a separate feature. The mesoscale flow was shown to be emanating from the evaporating tip of the hooked cloud head on the southern flank of the cyclone. It is thought that a zone of strong winds, originating from within the mid-tropospheric cloud head of an explosively deepening depression, are enhanced further as the "jet" descends for reasons that are not yet clear. Sting jets were first observed in oceanic storms of the eastern North Atlantic. The damage produced by the October 1987 storm prompted a closer examination of that event and other similar cyclones. There was no physical reason why sting jets couldn’t occur in other regions and indeed, they have been noted in the Bering Sea and elsewhere. However, few other high latitude regions have heavily populated areas which could be affected like Western Europe.

Schematic depicting the nature of and causes of European windstorms. From https://dx.doi.org/10.3402/tellusa.v67.27128

Forecasting

Sting Jets are difficult to forecast because of their relatively small size, and the way each individual low-pressure system develops. However, there are tell-tale signs in weather models that are now able to spot cores of very strong winds.

It is also possible to spot the Sting Jet developing on satellite images, as the end of the cold conveyor is marked by a hook-shaped cloud with a point at the end. There are also types of satellite images that show the amount of water vapour, made up of light and dark shades. The darker the shade the less water vapour there is. Around the sting jet there are often dark fingers of air stretching out, indicating sinking air that can bring strong winds down to the surface.

Related Articles

Further Reading

References

  1. ^ Sting jets in extratropical cyclones: a review, Clark & Gray, Quarterly Journal of the Royal Meteorological Society, Volume 144, Issue 713 April 2018 Part B Pages 943-969.