Long-Term Variations in the Quasi-Biennial Oscillation
of the Equatorial Stratospheric Wind

A. N. Gruzdev and V. A. Bezverkhnii

Oboukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevskii per. 3, Moscow, 109017 Russia

Received June 24, 1998; in final form, December 22, 1998

Abstract—Variations in the period of the quasi-biennial oscillation (QBO) of the zonal equatorial (3° S–1.5° N)
stratospheric wind are analyzed at the 70-, 50-, 40-, 30-, 20-, 15-, and 10-hPa isobaric surfaces during the period
1953–1997. Specifically, wavelet-transform, high-resolution spectral, and circle-map analyses are made. Dif-
ferent approaches indicate that the equatorial wind QBO at the above stratospheric levels are mainly manifested
in the form of two predominant regimes with periods of 2 and 2.5 years, which alternate leading to long-term
variations in the QBO period. At the upper stratospheric levels, the QBO amplitude also varies with variations
in the period (it increases with the period). Transitions between the regimes are rather abrupt. The two periods
are in a fractional ratio to an annual period (with ratios of the corresponding frequencies to the annual frequency
of 1/2 and 2/5), which testifies to the synchronization between the QBO and the annual cycle. In addition to the
main QBO periods, annual and semiannual periods, as well as periods of 20.8 and 8.6 months, which corre-
spond to oscillations with combination frequencies, are also revealed in wind-speed spectra. The combination
frequencies are equal to the difference and sum of the annual-cycle frequency and the main QBO frequencies.
Hypothetical conceptual mechanisms for the existence of the two noted QBO periods are discussed.

Pleiades Publishing home page | journal home page | top

If you have any problems with this server, contact webmaster.