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

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Abstract
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.

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