REVIEWS OF GEOPHYSICS, VOL. 39, NO. 2, PAGES 179–229, 2001

The Quasi-Biennial Oscillation

M. P. Baldwin

NorthWest Research Associates, Inc., Bellevue, Washington.

L. J. Gray

Rutherford Appleton Laboratory, Oxon, England, United Kingdom.

T. J. Dunkerton

NorthWest Research Associates, Inc., Bellevue, Washington.

K. Hamilton

International Pacific Research Center and Department of Meteorology, University of Hawaii, Honolulu, Hawaii.

P. H. Haynes

Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, England, United Kingdom.

W. J. Randel

National Center for Atmospheric Research, Boulder, Colorado.

J. R. Holton

Department of Atmospheric Sciences, University of Washington, Seattle, Washington.

M. J. Alexander

NorthWest Research Associates, Colorado Research Associates Division, Boulder, Colorado.

I. Hirota

Department of Geophysics, Kyoto University, Kyoto, Japan.

T. Horinouchi

Radio Atmospheric Science Center, Kyoto University, Uji, Japan.

D. B. A. Jones

Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.

J. S. Kinnersley

Qwest, Seattle, Washington.

C. Marquardt

GeoForschungsZentrum Potsdam, Potsdam, Germany.

K. Sato

National Institute of Polar Research, Arctic Environment Research Center, Tokyo, Japan.

M. Takahashi

Center for Climate System Research, University of Tokyo, Tokyo, Japan.

Abstract

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.

Citation: Baldwin, M. P., et al. (2001), The Quasi-Biennial Oscillation, Rev. Geophys., 39(2), 179–229.

Copyright 2001 by the American Geophysical Union.