The influence of the equatorial QBO on the Northern Hemisphere winter circulation of a GCM

The influence of a simulated equatorial quasi-biennial oscillation (QBO) on the Northern Hemisphere winter was studied by analyzing output data from a general circulation model (GCM). The differences between the 7-50 hPa equatorial QBO phases of the January-March (JFM) averaged zonal wind composite exhibit a weaker polar-night jet during the easterly phase of the equatorial QBO and a stronger polar-night jet in the westerly phase. The Eliassen-Palm flux of planetary waves is stronger and more convergent in the high latitude stratosphere for the easterly phase, while it exhibits similar characteristics in the mid latitude stratosphere during the westerly phase. These results are nearly consistent with observed results. Zonal wind deceleration anomalies are located slightly north of the zonal wind anomalies. It is likely that the JFM time-mean zonal wind anomalies develop from the small zonal wind anomalies during the early winter and propagate northward with time. The anomaly pattern in the troposphere coupled with that in the stratosphere reveals a tripole structure among equatorial, middle, and high latitudes, similar to the North Atlantic oscillation (NAO) pattern.