A MECHANISM FOR THE LOW-FREQUENCY VARIABILITY OF THE MIDLATITUDE TROPOSPHERE

Low-frequency variability of the zonal-mean zonal wind in long runs of a simplified global circulation model is dominated by bands of wind a nomaly which originate in the tropics and propagate slowly poleward wi th speeds of 0-2 m s(-1). Such propagation could be the result of the interaction between the zonal-wind anomaly and an equatorward flux of Rossby-wave activity originating in middle or high latitude. A barotro pic weakly nonlinear model of this process has been derived. It sugges ts propagation of zonal-wind anomalies similar to those produced in th e global circulation model, and leads to comparable propagation speeds .