The quasi-biennial oscillation (QBO) dominates the variability of the equatorial stratosphere (∼16–50 km) and is easily seen as downward propagating easterly and westerly wind regimes, with a variable period averaging approximately 28 months. From a fluid dynamical perspective, the QBO is a fascinating example of a coherent, oscillating mean flow that is driven by propagating waves with periods unrelated to that of the resulting oscillation. Although the QBO is a tropical phenomenon, it affects the stratospheric flow from pole to pole by modulating the effects of extratropical waves. Indeed, study of the QBO is inseparable from the study of atmospheric wave motions that drive it and are modulated by it. The QBO affects variability in the mesosphere near 85 km by selectively filtering waves that propagate upward through the equatorial stratosphere, and may also affect the strength of Atlantic hurricanes. The effects of the QBO are not confined to atmospheric dynamics. Chemical constituents, such as ozone, water vapor, and methane, are affected by circulation changes induced by the QBO. There are also substantial QBO signals in many of the shorter-lived chemical constituents. Through modulation of extratropical wave propagation, the QBO has an effect on the breakdown of the wintertime stratospheric polar vortices and the severity of high-latitude ozone depletion. The polar vortex in the stratosphere affects surface weather patterns, providing a mechanism for the QBO to have an effect at the Earth's surface. As more data sources (e.g., wind and temperature measurements from both ground-based systems and satellites) become available, the effects of the QBO can be more precisely assessed. This review covers the current state of knowledge of the tropical QBO, its extratropical dynamical effects, chemical constituent transport, and effects of the QBO in the troposphere (∼0–16 km) and mesosphere (∼50–100 km). It is intended to provide a broad overview of the QBO and its effects to researchers outside the field, as well as a source of information and references for specialists. The history of research on the QBO is discussed only briefly, and the reader is referred to several historical review papers. The basic theory of the QBO is summarized, and tutorial references are provided.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999RG000073

The quasi-biennial oscillation

After defining the terms commonly used in reporting volcanic eruptions and noting previous approaches to assessment of their magnitudes, this study proceeds to examine aspects of importance, or possible importance, to meteorology―principally the dust veils created in the atmosphere, particle sizes and distribution, heights, fall speeds and atmospheric residence times. Later sections deal with spread of the dust by the atmospheric circulation and the direct effects apparent upon radiation, surface temperature and extent of ice in the polar regions. These effects, as well as various crude measures of the total quantity of solid matter thrown up, are used to arrive at numerical assessments of volcanic eruptions in terms of a dust veil index (d. v. i.). The latitude of origin of the dust (latitude of the volcano) receives some attention, and apparently affects the course of development of the atmospheric circulation over the three or four years following, at least in the case of great eruptions (d. v. i. > 100 over one hemisphere). Effects upon the extent of ice on the polar seas may be of somewhat longer duration, and thereby influence the atmospheric circulation over a longer period of years, since there seems to be some association with the cumulative d.v.i. values when successive great eruptions occur with only few years between. The time distribution of volcanic dust since the last Ice Age, and since a. d. 1500, are indicated in as much detail as the evidence permits. Some associations with changes of climate are suggested, but it is clear that volcanic dust is not the only, and probably not the main, influence in this. The appendices give a chronology of eruptions (including those which it seems possible to dismiss as regards any effect on world weather or climate) and a chronology of d. v. i. values. A third appendix displays by means of graphs the variation of some circulation parameters in January and July in the region of northwest Europe over the years immediately following forty of the greatest eruptions since 1680.

Volcanic dust in the atmosphere; with a chronology and assessment of its meteorological significance

Zonal mean temperature, pressure, zonal wind and geopotential height as functions of latitude

The Quasi-Biennial Oscillation in the Northern Hemisphere Lower Stratosphere

We have used a variety of satellite, ground-based, and in situ observations to construct a climatology of the semiannual oscillation (SAO) of the tropical middle atmosphere. The sources of data include rocketsonde observations of winds and temperature, MF radar wind observations, and observations of winds and temperatures made from space by the High Resolution Doppler Imager (HRDI) and the Solar Mesosphere Explorer (SME). These data sets provide a generally consistent picture of the SAO, of the relationship between its stratospheric and mesospheric manifestations, and of its apparent modulation by the stratospheric quasi-biennial oscillation (QBO). In agreement with earlier studies, we find that the first cycle of the stratospheric SAO (which begins with the stratopause easterly phase in northern winter) is stronger than the second cycle (beginning with the easterly phase in southern winter). Similar behavior is apparent in the mesosphere, where the easterly phase is stronger during the first cycle than during the second cycle. HRDI and MF radar are capable of observing the seasonal cycle well into the lower thermosphere. Data from these two sources indicate that a strong SAO is present up to about 90 km, giving way above this altitude to time mean easterly winds with a weak semiannual variation. Between 105 and 110 km, HRDI data indicate the presence of a westerly wind layer with almost no seasonal variation. Apparent modulation of the stratospheric SAO by the QBO is found in rocketsonde data, while HRDI and MF radar observations suggest a correlation between the QBO and the easterly phase of the mesospheric SAO. We discuss the implications of these observations for the wave processes that drive the SAO.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JD00207

Climatology of the semiannual oscillation of the tropical middle atmosphere

The observed variability patterns of monthly mean zonal winds over an 11-year period, from 80°N–70°S and from 20–65 km, are explained in terms of component patterns of a long-term mean, quasi-biennial, annual and semi-annual periodic variations. Interannual variations are displayed by monthly mean height-time sections for each of eleven years, and Northern Hemisphere–-Southern Hemisphere differences are seen from 11-year mean, latitude-month sections for each 10 km. An 11-year mean, height-month section at the equator shows the transition of the easterly regime at low levels to a westerly one at highest levels. Summer easterlies extend from equator to pole, from 30 to 50 km, but winter westerlies extend from equator to about 70° only at 60 km. Also, only at 60 km are there westerlies from pole to pole during the equinoxes. The stronger Southern Hemisphere westerly circulation of the troposphere is found to extend to at least 40 km, and possibly to 60 km. Southern summer easterlies are the same as...

Variations of Stratospheric Zonal Winds, 20-65 km, 1961-1971.

Daily data at 16 stations along five latitudes from 13°N. to 33°S. were carefully examined at the 50-, 100-, and 500-mb. levels for evidence of longitudinal phase progression of the quasi-biennial oscillation (QBO). At 50 mb. there is evidence of west to east progression although there are many irregularities and much uncertainty. The phase dates differ by days at low latitudes. At 100 and 500 mb., it appears that the QBO originates in tropical America and progresses both eastward and westward, occurring last in the Indian Ocean. The progression time ranges from 1 to 2 yr. At 500 and 100 mb., however, a cellular phase progression in possible due to the difficulty of identifying corresponding waves with a very meager network. It appears now that the QBO may not be simultaneous in longitude and that its speed and even direction of propagation, like its other properties, may very from cycle to cycle. The analysis is being expanded to other levels and latitudes to obtain better continuity in followin...

Variation with longitude of the quasi-biennial oscillation1,,2

The semiannual wave in zonal wind shows two maximums in amplitude (at 50 km at 10°S and at 65 km near 60°N), arranged along an axis sloping upward from south to north. The amplitude of the wave at each maximum is near 30 m/sec. The tropic maximum appears to be south of the equator.

Semiannual variation in zonal wind from 20 to 65 kilometers at 80°N–10°S

The 10.7-cm solar radio flux is considered to be highly correlated with solar extreme ultraviolet radiation, thermospheric temperatures, sunspots, and the 27-day and 11-year solar cycles. To investigate the possibility of ultraviolet radiation being a cause of the quasi-biennial oscillation in tropical stratospheric winds and temperatures, the daily values of 10.7-cm flux were subjected to a non-linear, curve-fitting analysis to determine the major component sinusoidal frequencies of the time series. No evidence was found for a period near 26 months; hence, to the extent that extended ultraviolet 10-cm flux relationship is valid, ultraviolet insolation does not appear to vary with a quasi-biennial oscillation.

The 10.7-cm Solar Flux and the 26-Month Oscillation

Monthly-mean zonal wind data from approximately 200 rawin stations have been filtered to remove the annual and shorter period variations. Data from 1950–1964 for levels from 700 to 7 mb were analysed. The primary variation is the quasi-biennial oscillation of the equatorial stratosphere and its extension to higher latitudes. There is much greater variability with longitude and time of the weak quasi-biennial oscillation at higher latitudes than observed in the equatorial stratosphere. However, as the vertical and meridional phase progression patterns of the oscillations in both troposphere and stratosphere are systematic, these properties are probably real. The main fluctuations can frequently be traced from the surface to at least 35 km except in the middle latitudes of the Northern Hemisphere where the stratospheric variations often do not appear related to those of the troposphere. The most organized phase progressions with latitude are the apparent opposite ones observed in the stratosphere and troposphere of the Northern Hemisphere. Prior to 1960, well-defined poleward progression is observed in the troposphere (300 mb), while weaker Equatorward progression is evident in the stratosphere (30 mb). In 1961 the pattern reverses, with poleward progression at 30 mb and Equatorward progression at 300 mb. In the tropical stratosphere during the years 1960–1961, the quasi-biennial oscillation was characterized by unusually low amplitude, short-period fluctuations.

A global analysis of the variability of the quasi-biennial oscillation

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