Large Scale Rossby waves amplifying and breaking as they approach weak ambient flow in the subtropics

Potential Vorticity (PV) @ 350K

Latitudinal PV gradient: restoring mechanism for Rossby waves - waveguide

Red=isentropic sfcBlack=iso-PV sfcBlue=zonal wind speed

PV @ 350K

INTERANNUAL VARIABILITY

EL NINO

LA NINA

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)

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 PropagationWave-mean flow interaction

Latitude

EP flux convergence mean flow deceleration

Critical line

Dynamical Mechanism