The Influence of the Equatorial Quasi-Biennial Oscillation on the Global Circulation at 50 mb

Abstract

Monthly mean Northern Hemisphere 50 mb geopotential heights for a 16-year period (1962-77) are composited with respect to the phase of the equatorial quasi-biennial oscillation (QBO). The observed zonal mean geopotential height at high latitudes is significantly lower during the westerly phase of the equatorial QBO than during the easterly phase in all months composited. For this 16-year sample we find that in early winter (November-December) the amplitude of planetary wavenumber 1 is nearly 40% stronger during the easterly phase of the equatorial QBO. In late winter (January-March) the amplitude of planetary wavenumber 2, on the other hand, is nearly 60% stronger during the westerly phase of the equatorial QBO. Data from an additional 6-year sample show a similar wavenumber 1 signal during the November-December period. However, an additional 4-year sample does not support our conclusions concerning wavenumber 2 during the January-March period. Composites based on zonal wind data from a longitudi... Abstract Monthly mean Northern Hemisphere 50 mb geopotential heights for a 16-year period (1962-77) are composited with respect to the phase of the equatorial quasi-biennial oscillation (QBO). The observed zonal mean geopotential height at high latitudes is significantly lower during the westerly phase of the equatorial QBO than during the easterly phase in all months composited. For this 16-year sample we find that in early winter (November-December) the amplitude of planetary wavenumber 1 is nearly 40% stronger during the easterly phase of the equatorial QBO. In late winter (January-March) the amplitude of planetary wavenumber 2, on the other hand, is nearly 60% stronger during the westerly phase of the equatorial QBO. Data from an additional 6-year sample show a similar wavenumber 1 signal during the November-December period. However, an additional 4-year sample does not support our conclusions concerning wavenumber 2 during the January-March period. Composites based on zonal wind data from a longitudi...