May 14, 2012
Sting jets are common in North Atlantic windstorms
Sting jets can be responsible for strong surface winds in parts of extratropical cyclones that would otherwise be relatively calm. Now a team from the University of Reading, UK, and Monash University, Australia, have found that up to a third of the 100 strongest North Atlantic winter storms in recent years could have contained the phenomena.
"Our paper presents the first assessment of the prevalence and characteristics of the most devastating type of winter storm to affect north-west Europe," Oscar Martínez-Alvarado told environmentalresearchweb. "This class of European windstorms is characterized by a descending jet of air that can result in strong, localized surface winds and wind gusts in a region of the storm not normally associated with strong surface winds. This descending jet is called [a] sting jet because of its location at the tip of the cloud head, which resembles a scorpion's tail because of its hooked shape."
According to Martínez-Alvarado, the findings show that there are "new recognized sources of strong winds" and they are "not rare". He believes scientists, policy-makers and those responsible for emergency response should take this into consideration when planning response strategies.
The team reckons that sting jets are a relatively generic feature of North Atlantic cyclones. The Great Storm of 1987 that devastated southeast England was unusual both in its path over populated areas and in its sting jet's exceptional strength, they say. Other storms have been unusual only in their path over northwest Europe, which enabled their identification as sting-jet storms: the strength of their sting jets does not appear to have been out of the ordinary.
"The existence of sting jets was fully recognized by Keith Browning (then at Reading) in 2004 in an analysis of the infamous Great Storm of October 1987," explained Martínez-Alvarado. "Since then many individual storms have been studied. These studies answered questions about the structure and potential causes of sting jets, but they were unable to answer other questions such as where or how frequently they occur."
The problem was that computational limitations prevented existing long-term data sets for storms from containing information on sting jets. So Martínez-Alvarado and colleagues developed a way of inferring the presence of sting jets in 20-years' worth of atmospheric data produced by the European Centre for Medium-Range Weather Forecasts (ECMWF).
"From [previous case] studies we concluded that there was a relationship between the presence of a certain kind of atmospheric instability and the occurrence of sting jets," said Martínez-Alvarado. "In those studies we also found that this instability is actually present in the type of storm data sets available even if actual sting jets were not. We took the next step by joining these results together and exploring a long time series in full."
Many questions remain about the structure of storms. "In a current project, DIAMET (DIAbatic influences on Mesoscale structures in ExTratropical storms), involving the collaboration of several universities in the UK and the Met Office, we are undertaking a huge effort to try to find out more about these storms," said Martínez-Alvarado. "This project not only involves numerical modelling and analysis but also in-situ measurements using a research aircraft to fly through interesting weather systems. In fact, on 8 December last year we were 'lucky' enough to fly through a storm that seems to have produce a sting jet."
A separate project is planned to assess how sting jets in cyclones may change in a future changing climate.
The team reported its work in Environmental Research Letters (ERL).
About the author
Liz Kalaugher is editor of environmentalresearchweb.