Quasi-biennial oscillation
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The quasi-biennial oscillation (QBO) is a
quasiperiodic 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 unpred ...
oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
of the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
ial zonal
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
between easterlies and westerlies in the tropical
stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...
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 per month until they are dissipated at the tropical
tropopause The tropopause is the atmospheric boundary that demarcates the troposphere from the stratosphere; which are two of the five layers of the atmosphere of Earth. The tropopause is a thermodynamic gradient-stratification layer, that marks the end of ...
. Downward motion of the easterlies is usually more irregular than that of the westerlies. The
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
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.


Theory

In 1883, the eruption of Krakatoa led to visual tracking of subsequent volcanic ash in the stratosphere. This visual tracking led to the discovery of easterly winds between 25 and 30 km above the surface. The winds were then called the Krakatau easterlies. In 1908, data balloons launched above
Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
in Africa recorded westerly winds in the stratospheric levels of the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
. These findings, at the time, were thought to contradict the 1883 findings. However, the winds that would become known as the QBO were discovered to oscillate between westerly and easterly in the 1950s by researchers at the UK
Meteorological Office The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...
. The cause of these QBO winds remained unclear for some time.
Radiosonde A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calcula ...
soundings showed that its phase was not related to the
annual cycle An annual cycle refers to a set of changes or events that uniformly, or consistently, take place at the same time of year. In biology, the annual cycle for plants and animals details behavioral and chemical changes that take place as the seasons ...
, as is the case for many other stratospheric circulation patterns. In the 1970s it was recognized by Richard Lindzen and
James Holton James Reed Holton (1938–2004) was a professor of atmospheric sciences at the University of Washington. He was a specialist on atmospheric dynamics, and the author of the atmospheric science textbook ''An Introduction to Dynamic Meteorology''. He ...
that the periodic wind reversal was driven by
atmospheric wave An atmospheric wave is a periodic disturbance in the fields of atmospheric variables (like surface pressure or geopotential height, temperature, or wind velocity) which may either propagate ('' traveling wave'') or not (''standing wave''). Atmos ...
s emanating from the tropical
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
that travel upwards and are dissipated in the
stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air ...
by
radiative cooling In the study of heat transfer, radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation. Radiative cooling ha ...
. The precise nature of the waves responsible for this effect was heavily debated; in recent years, however,
gravity wave In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere ...
s have come to be seen as a major contributor and the QBO is now simulated in a growing number of climate models.


Effects

Effects of the QBO include mixing of stratospheric
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
by the
secondary circulation In fluid dynamics, a secondary circulation or secondary flow is a weak circulation that plays a key maintenance role in sustaining a stronger primary circulation that contains most of the kinetic energy and momentum of a flow. For example, a tro ...
caused by the QBO, modification of
monsoon A monsoon () is traditionally 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 annual latitudinal oscil ...
precipitation, and an influence on stratospheric circulation in
northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
winter (mediated partly by a change in the frequency of
sudden stratospheric warmings A sudden stratospheric warming (SSW) is an event in which the polar stratospheric temperature rises by several tens of kelvins (up to increases of about 50 °C (90 °F)) over the course of a few days. The warming is preceded by a slowin ...
). Easterly 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 westerly 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. Research has also been conducted investigating a possible relationship between ENSO (
El Niño–Southern Oscillation El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea te ...
) and the QBO.


Observation of the QBO with weather balloons

The
Free University of Berlin The Free University of Berlin (, often abbreviated as FU Berlin or simply FU) is a public research university in Berlin, Germany. It is consistently ranked among Germany's best universities, with particular strengths in political science and t ...
supplies a QBO data set that comprises radiosonde observations from
Canton Island Canton Island (also known as Kanton or Abariringa), previously known as Mary Island, Mary Balcout's Island or Swallow Island, is the largest, northernmost, and , the sole inhabited island of the Phoenix Islands, in the Republic of Kiribati. It i ...
,
Gan The word Gan or the initials GAN may refer to: Places *Gan, a component of Hebrew placenames literally meaning "garden" China * Gan River (Jiangxi) * Gan River (Inner Mongolia), * Gan County, in Jiangxi province * Gansu, abbreviated ''Gā ...
, and
Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Peninsula, borde ...
. The plot below shows the QBO during the 1980s.


Recent observations

The first significant observed deviation from the normal QBO since its discovery in early 1950s was noted beginning in February 2016 when the transition to easterly winds was disrupted by a new band of westerly winds that formed unexpectedly. The lack of a reliable QBO cycle deprives forecasters of a valuable tool. Since the QBO has a strong influence on the
North Atlantic Oscillation The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...
and thereby north European weather, scientists speculated that the coming winter could be warmer and stormier in that region.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
scientists have been researching to test if the extremely strong
El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date L ...
event of 2015/16,
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, or some other factor might be involved. They are trying to determine if this is more of a once in a generation event, or if this is a sign of the changing climate.


See also

*
North Atlantic oscillation The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...


References


Further reading

* *


External links


The Berlin QBO data series
(1953–) {{Climate oscillations Tropical meteorology Atmospheric dynamics Regional climate effects Climate oscillations