The Quasi-Biennial Oscillation and Feedback Processes in the Atmosphere-Ocean-Earth System

Abstract

Recent investigations indicate that the quasi-biennial oscillation (QBO) in stratospheric winds may be related to variations in the tropospheric circulation in middle and high latitudes. Although the QBO was noticed years ago in a number of worldwide atmospheric phenomena, it is still not well understood. A logical question arises as to whether the oscillation might be a result of the annual forcing by the solar heating, since it is well known that in some nonlinear systems subharmonic oscillations can be produced of order one-half the frequency of the exciting force. A conceptual model is presented to show how a two-year oscillation could be produced by a negative feedback process acting on a two-state system, i.e., winter and summer states. Even for a relatively weak biennial oscillation with stochastic elements involved, the results show that rather strong links must exist in the chain or feedback loop, indicating potential predictability for periods of six months or more. Support for the concept is provided by the analysis of monthly mean observations of the 50 mb zonal winds at Balboa (9°N, 80°W) f man September 1950 to October 1976. It is clear that the transitions from an easterly to westerly mode (and vice versa) and the duration of a particular mode are closely related to the annual cycle.