On the variation in period and amplitude of the quasi-biennial oscillation in the equatorial stratosphere, 1951-85

Abstract The quasi-biennial variation in zonal-wind period and amplitude is examined for Balboa and Ascension at 50, 30 and 10 mb, and for Singapore at 50 and 30 mb, through July 1985. The increase in zonal-wind period following the Agung eruption in 1963 is shown to be due almost entirely to an increase in west-wind half period at 50 mb but east-wind half period at 10 mb. There have been average correlation coefficients of 0.96 and 0.71 between zonal-wind half periods at 50 mb and the next downcoming half period of opposite phase at 10 mb. There is little indication of a relation between zonal-wind period or amplitude and equatorial sea-surface temperature (El Nino), and the nearly inverse relation between zonal-wind period and sunspot number is not significant at the 5% level taking into account serial correlations. The 30 mb west-wind amplitude was relatively large at Balboa and small at Ascension after Agung, but there is little evidence of an appreciable change in amplitude or period following the EX...