What is a sting jet?
You may have noticed the term ‘sting jet’ used when describing deep Atlantic cyclones and windstorms over the British Isles and Ireland and parts of northern central Europe. Sting jets are associated with the strongest and most damaging windstorms, and cause extremely severe hurricane-force winds. What is a sting jet and how does it form?
What is a sting jet?
A sting jet is a relatively localized jet of rapidly descending cold air inside a deep extratropical cyclone. It affects a small region, compared to th size of the cyclone and lasts only several hours. Destructive winds of over 150 km/h have been attributed to sting jets.
How a sting jet forms
A typical extratropical cyclone consists of two frontal system: the warm front and the cold front. Strong flow, called conveyor belts form ahead of both fronts. A strong flow of cold air develops into the cyclone ahead of the warm front, called the cold conveyor belt. Behind the cold front, cool and dry air flows into the cyclone, forming the dry intrusion.
The cold conveyor belt brings cold, moist air towards the centre of the cyclone, bringing with it precipitation – rain and snow. The dry intrusion brings cool, dry air into the cyclone. As the precipitation from the cold conveyor belt falls into the dry air of the dry intrusion, it evaporates and further cools the air through evaporative cooling.
All this is happening at altitudes up to about 3-4 km. The cooled air is denser than the surrounding air and it descends rapidly to the surface, producing even stronger winds within the intense wind field of the cyclone. The entire region of this cooled, accelerated air is narrow, forming a jet – a sting jet.
The term sting jet comes from its appearance in satellite imagery: they form banded cloud heads, strongly curved into the cyclone – producing the appearance of a scorpion’s tail and stinger. The cloud bands terminate quite sharply, the effect of evaporation in the dry air of the dry intrusion.
Satellite analysis of post-tropical storm Ophelia on October 16, 2017. Notice the branches of “banded cloud head” pushed towards the SW Ireland, indicating that the sting jet structure is likely developed. Source: EUMETSAT
Not every deep extratropical cyclone develops a sting jet; in fact, sting jets are rare events. They have so far been confirmed on less than 10 cyclones over western and central Europe. The Great Storm of 1987 produced a sting jet with wind gusts peaking at 217 km/h (recorded at Pointe Du Roc, Grancille, France). Cyclone Oratia (Tora in Norway) in late October and early November of 2000 produced winds gusting up to 176 km/h (Camaret-sur-Mer, France). More recently storm Ulli produced winds up to 172 km/h in Ijmuiden, the Netherlands (early January 2012).
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