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AO Index | AMOC Index | ENSO | EPO Index | MEIv2 Index | NAO Index | PDO Index | PNA Index | QBO Index | Teleconnection Monthly Summary

1950's | 1960's | 1970's | 1980's | 1990's | 2000's | 2010's | 2020's

ENSO and Snowfall Earth | 1960's | 1970's | 1980's | 1990's | 2000's | 2010's | 2020's

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The Quasi-Biennial Oscillation is one of the most remarkable phenomena in the Earth's atmosphere. High above the equator, in the stratosphere, strong zonal winds blow in a continuous circuit around the Earth. At a given altitude, the winds might start as westerlies, but over time they weaken and eventually reverse, becoming strong easterlies. Looking at different heights, we see that the peak amplitude of the westerly winds migrates slowly downwards, with the zone of easterly winds coming behind it also migrating downwards. When the winds approach the base of the stratosphere, at around 80 hPa, they dissipate. New bands of zonal winds appear in the mid-stratosphere, at around 10 hPa, to replace the bands which migrate downwards. At any one time, there is one region of easterlies and one region of westerlies. The whole cycle progresses at a fairly (but not entirely) uniform rate, taking on average 26 months to return to the starting state.

Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found. At the 30mb level, with regards to monthly mean zonal winds, the strongest recorded easterly was 29.55 m/s in November 2005, while the strongest recorded westerly was only 15.62 m/s in June 1995.

Effects of the QBO include mixing of stratospheric ozone by the secondary circulation caused by the QBO, modification of monsoon precipitation, and an influence on stratospheric circulation in northern hemisphere winter (mediated partly by a change in the frequency of sudden stratospheric warmings). Eastward phases of the QBO often coincide with more sudden stratospheric warmings, a weaker Atlantic jet stream and cold winters in Northern Europe and eastern USA whereas westward phases of the QBO often coincide with mild winters in eastern USA and a strong Atlantic jet stream with mild, wet stormy winters in northern Europe. In addition, the QBO has been shown to affect hurricane frequency during hurricane seasons in the Atlantic and research has also been conducted investigating a possible relationship between ENSO (El Nino Southern Oscillation) and the QBO.


The images below show the impacts that negative QBO's have had on Winter temperatures.

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