1. Large Scale Rossby waves amplifying and breaking as they approach weak ambient flow in the subtropics Potential Vorticity (PV) @ 350K

2. Latitudinal PV gradient: restoring mechanism for Rossby waves - waveguide Red=isentropic sfc Black=iso-PV sfc Blue=zonal wind speed PV @ 350K

3. INTERANNUAL VARIABILITY EL NINO LA NINA

4. PWB along the Stratospheric Vortex PV on the 1100K surface for February 1999 Abatzoglou and Magnusdottir, Quarterly Journal of the Royal Meteorological Society (in prep)

5. 1.Poleward reflection near breaking level drives waves toward high- latitudes 2.Wave convergence decelerates mean flow; critical line established 3.Further vertical wave propagation is effectively trapped below critical line. 4.Waves converge onto progressively lower levels of the atmosphere, critical line descent (“downward propagation”). Wave Propagation Wave-mean flow interaction Latitude EP flux convergence mean flow deceleration Critical line Dynamical Mechanism