A sting jet is a narrow, transient and mesoscale airstream that descends from the mid-troposphere to the surface in some extratropical cyclones. 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). Sting jets are short-lived, lasting on the order of hours, 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 a storm's highest rate of intensification. Sting jets were first formally identified in 2004 by Keith Browning at the University of Reading in an analysis of the great storm of 1987, though forecasters have known of their effects since at least the late 1960s. The sting jet emerges from within the end of an extratropical cyclone's cloud head – a hook-shaped region of cloudiness near the centre of low pressure – and accelerates as it descends to the surface. Multiple mechanisms explain why sting jets form and why they accelerate during descent; frontolysis, the release of conditional symmetric instability, and 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
Sting jets are roughly 10–20 km (6–12 mi) wide and last 3–4 hours. 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. Sting jets constitute one possible mechanism through which high winds can be produced in extratropical cyclones without being directly caused by atmospheric convection. 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. One analysis suggested that 39–49% of the strongest extratropical cyclones in the North Atlantic exhibit them. Nearly a third of the most intense windstorms affecting the United Kingdom from 1993 to 2013 produced sting jets. Within the North Atlantic, cyclones developing sting jets tend to follow common storm tracks and originate south of 50°N, suggesting a potential influence of warm and moist air on sting jet formation. Sting jet development also appears more likely for explosively intensifying storms. Atmospheric reanalysis data suggest that sting jets are more common over water than over land, but sting jets can develop entirely over continental land. The increased moisture associated with climate change may amplify the atmospheric instabilities that support sting jet development, potentially increasing the proportion of extratropical cyclones with sting jets and their intensities. The frequency of extreme windstorms and sting jets overall may also increase with climate change; one study assessed a 60% increase in the occurrence of conducive conditions for sting jet development over the North Atlantic by 2100 if RCP8.5 is assumed.
… excerpt ends here. Continue reading the full article.
