Mechanisms for the extra-tropical QBO phenomenon

Associated with the equatorial Quasi-Biennial Oscillation is an extratropical QBO oscillation in tracer transport and dynamics which extends from the subtropics to the polar regions in both hemispheres. It is further found to be synchronized with the winter seasons. Previous studies have attempted to explain the extratropical QBO phenomenon using a single mechanism. Closer examination of the tracer and dynamical data, and numerical model results appears to reveal two mechanisms, one operating from the subtropics to the midlatitudes of the winter hemisphere, and a separate mechanism local to the mid to high latitudes. By combining both mechanisms, we are able to simulate successful a coherent QBO over the whole globe and for all seasons.