Quasi-biennial oscillation
The quasi-biennial oscillation (QBO) is a quasi-periodic
Quasiperiodicity is the property of a system that displays irregular periodicity. Periodic behavior is defined as recurring at regular intervals, such as "every 24 hours". Quasiperiodic behavior is a pattern of recurrence with a component of unpredictability that does not lend itself to precise...

Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

 of the equatorial
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

Zonal and meridional
The terms zonal and meridional are used to describe directions on a globe. Zonal means "along a latitude circle" or "in the west–east direction"; while meridional means "along a meridian" or "in the north–south direction"....

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

 between easterlies and westerlies in the tropical stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.621372736649807 mi) per month until they are dissipated at the tropical tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...

. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

 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.


The QBO was discovered in the 1950s, but its cause remained unclear for some time. Rawinsonde soundings showed that its phase was not related to the annual cycle
Annual cycle
In geosciences, an annual cycle is the part of a measured quantity's fluctuation that is attributed to Earth's changing position in orbit over the course of the year. Such quantities might be influenced directly or indirectly In geosciences, an annual cycle is the part of a measured quantity's...

, as is the case for all other stratospheric circulation patterns. In the 1970s it was recognized by Richard Lindzen
Richard Lindzen
Richard Siegmund Lindzen is an American atmospheric physicist and Alfred P. Sloan Professor of Meteorology at the Massachusetts Institute of Technology. Lindzen is known for his work in the dynamics of the middle atmosphere, atmospheric tides and ozone photochemistry. He has published more than...

 and James Holton that the periodic wind reversal was driven by atmospheric wave
Atmospheric wave
An atmospheric wave is a periodic disturbance in the fields of atmospheric variables which may either propagate or not . Atmospheric waves range in spatial and temporal scale from large-scale planetary waves to minute sound waves...

s emanating from the tropical troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

 that travel upwards and are dissipated in the stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 by radiative cooling
Radiative cooling
Radiative cooling is the process by which a body loses heat by thermal radiation.- Earth's energy budget :In the case of the earth-atmosphere system it refers to the process by which long-wave radiation is emitted to balance the absorption of short-wave energy from the sun.The exact process by...

. The precise nature of the waves responsible for this effect was heavily debated; in recent years, however, gravity wave
Gravity wave
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media which has the restoring force of gravity or buoyancy....

s have come to be seen as a major contributor.


Effects of the QBO include mixing of stratospheric ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

 by the secondary circulation
Secondary circulation
A secondary circulation is a circulation induced in a rotating system. For example, the primary circulation of Earth's atmosphere is zonal. If however a parcel of air, that moves in a purely zonal direction, is accelerated or decelerated zonally, the Coriolis force will add a meridional component...

 caused by the QBO, modification of monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...

 precipitation, and an influence on stratospheric circulation in northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

 winter (the sudden stratospheric warmings).

Observation of the QBO with weather balloons

The FU Berlin
Free University of Berlin
Freie Universität Berlin is one of the leading and most prestigious research universities in Germany and continental Europe. It distinguishes itself through its modern and international character. It is the largest of the four universities in Berlin. Research at the university is focused on the...

 supplies a QBO data set that comprises rawinsonde observations from Canton Island, Gan
Gan may refer to:-Computing and telecommunications:*.gan, the file extension for documents created by GanttProject*Generic Access Network formerly known as Unlicensed Mobile Access *Global Area Network- Mythology :...

, and Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...

. The plot below shows the QBO during the 1980s.

Further reading

  • Andrews, D.G., J.R. Holton, and C.B. Leovy, 1987: Middle Atmosphere Dynamics. Academic Press, 489pp.
  • Baldwin, M.P. et al., 2001: The Quasi-Biennial Oscillation. Rev. Geophys., 39, 179–229.

External links

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