The Quasi-Biennial Oscillation in the Northern Hemisphere Lower Stratosphere

Abstract

Monthly mean Northern Hemisphere geopotential heights and temperatures on the 10, 30, 50, 100, and 300mb surfaces for a 16 year period (1962-1977) are composited with respect to the phase of the equatorial quasi-biennial oscillation (QBO) at 50mb for the winter months (November-March). The composited fields show zonally symmetric seesaw oscillations in both heights and temperatures with negative (positive) anomalies in polar regions and positive (negative) anomalies in midlatitudes during the westerly (easterly) phase of the equatorial QBO.
Latitude-height cross sections of the zonal mean geostrophic wind for the 10-300mb layer indicate that during the westerly (easterly) phase of the equatiorial QBO at 500mb the polar night jet is stronger (weaker) than normal and the ttopospheric midlatitude jet is slightly weaker (stronger) than normal.
Similar composites for zonal wavenumbers 1 and 2 and composites of the Eliassen-Palm flux show some indication of a QBO in stratospheric planetary waves, but the signal is surprisingly small considering the large amplitude QBO in the polar night jet.