The normal flow of air high up in the atmosphere over the equator, known as the quasi-biennial oscillation, was seen to break down earlier this year. These stratospheric winds are found high above the tropics, their direction and strength changes in a regular two- to three-year cycle which provides forecasters with an indication of the weather to expect in Northern Europe. Westerly winds are known to increase the chance of warm and wet conditions, while easterlies bring drier and colder weather.
Scientists from NCAS at the University of Oxford and the Met Office were part of an international team that observed the unusual behaviour in February, noticing a reversal of the expected pattern in the winds. This same team then identified the reason why.
The quasi-biennial oscillation is a regular feature of the climate system. On average, these equatorial eastward and westward winds alternate every 28 to 29 months, making them very predictable in the long term. The team's findings published in Science this week, show that this unexpected change in wind direction was caused by atmospheric waves in the Northern Hemisphere.
Dr Scott Osprey, an NCAS scientist at the University of Oxford, said: "The recent disruption in the quasi-biennial oscillation was not predicted, not even one month ahead. If we can get to the bottom of why the normal pattern was affected in this way, we could develop more confidence in our future seasonal forecasts."
Prof Adam Scaife, Head of Long-range Forecasting at the Met Office and Honorary Visiting Professor at the University of Exeter, said: "This unexpected disruption to the climate system switches the cycling of the quasi-biennial oscillation forever. And this is important as it is one of the factors that will influence the coming winter."
A return to more typical behaviour within the next year is forecast, though scientists believe that the quasi-biennial oscillation could become more susceptible to similar disruptions as the climate warms.
Later this month international research groups will meet in Oxford to discuss the origins and implications of this event.
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The paper "An unexpected disruption of the atmospheric Quasi-Biennial Oscillation" is published in Science today. For copies of the paper, interviews, images or further information, contact Scott M Osprey on +44(0)1865 282434 or email Scott.Osprey@physics.ox.ac.uk
Key facts
- In February 2016 the quasi-biennial oscillation, a regular feature of the climate system, broke down from its regular pattern.
- The eastward winds in the upper atmosphere unexpectedly reversed to a westward direction
- Seasonal forecasts did not predict the disruption, despite the quasi-biennial oscillation being the most predictable long term atmospheric variation after the annual cycle
- The quasi-biennial oscillation varies every 28 to 29 months on average, and has known impacts on surface weather and climate
- As the climate warms in future, similar disruptions to the quasi-biennial oscillation could become more frequent
Further information
About lead author: Scott M Osprey, NCAS Scientist, University of Oxford
The paper "An unexpected disruption of the atmospheric Quasi-Biennial Oscillation" is published in Science today. For copies of the paper, interviews, images or further information, contact Scott M Osprey on +44(0)1865 282434 or email Scott.Osprey@physics.ox.ac.uk
Department of Physics, University of Oxford
The Department of Physics at the University of Oxford is one of the largest physics departments in the world, employing about 500 people alongside around 650 undergraduate and 330 graduate students, and with an annual research income of about £25m. The department was judged to have the highest proportion of 4* (world leading) research of any UK physics department in the most recent Research Excellence Framework. www2.physics.ox.ac.uk
National Centre for Atmospheric Science
The National Centre for Atmospheric Science (NCAS) is a world leader in atmospheric science, a multi-million pound research centre, funded by the Natural Environment Research Council (NERC). NCAS carries out research in climate science, atmospheric composition and air quality, physics of the atmosphere (including hazardous and extreme weather) and provides the UK community with state-of-the-art technologies and scientific facilities for observing and modelling the atmosphere, including a world-leading research aircraft. http://www.ncas.ac.uk
Met Office
The Met Office Hadley Centre for Climate Science and Services provides world-class guidance on the science of climate change and is the primary focus in the UK for climate science. Its work is, in part, jointly funded by BEIS (Department for Business, Energy and Industrial Strategy) and DEFRA (Department for Environment, Food and Rural Affairs). http://www.metoffice.gov.uk/climate-guide/science/science-behind-climate-change/hadley
Department of Mathematics and Computer Science, University of Exeter
The University of Exeter is a Russell Group university that combines world-class research with very high levels of student satisfaction. Exeter has over 21,000 students and is one of the global top 100 universities according to the Times Higher Education World University Rankings 2015-16, positioned 93rd. Exeter is also ranked 7th in The Times and The Sunday Times Good University Guide 2016 and 11th in the Guardian University Guide 2017. In the 2014 Research Excellence Framework (REF), the University ranked 16th nationally, with 98% of its research rated as being of international quality. Exeter was named The Times and The Sunday Times Sports University of the Year 2015-16, in recognition of excellence in performance, education and research. Exeter was The Sunday Times University of the Year 2012-13.
The University will launch its flagship Living Systems Institute in 2016, a world-class, interdisciplinary research community that will revolutionise the diagnosis and treatment of diseases. This follows recent investments of more than £350 million worth of new facilities across its campuses in recent years; including landmark new student services centres - the Forum in Exeter and The Exchange on the Penryn Campus in Cornwall, together with world-class new facilities for Biosciences, the Business School and the Environment and Sustainability Institute. http://www.exeter.ac.uk
International Pacific Research Center, University of Hawai'i iprc.soest.hawaii.edu
Canadian Centre for Climate Modelling and Analysis, University of Victoria http://www.cccma.ec.gc.ca
Journal
Science