Rossby wavepacket propagation in a zonally-varying basic flow

Rossby wavepacket propagation in a zonally-varying basic Row is examined with a barotropic model in connection with the critical layer. A number of experiments are conducted by systematically changing the longitude of forcing, to analyze interactions between the zonally-varying flow and a Rossby-wave packet. A particular form of wave-activity flux applicable to zonally-varying basic Rows is used to illustrate the propagation patterns. Several reflection patterns are found and their mechanism, which is different from those currently proposed, is discussed. The present numerical results show that the wavepacket propagation slows down in the weak wind region and that vorticity anomalies are advected by the anticyclonic basic flow. Vorticity anomalies associated with Rossby waves, in turn, influence the intensity of a subtropical anticyclonic flow in the basic state. The present numerical results are compared with an observed vorticity overturning in the upper troposphere and wave amplification near the jet exit region obtained in a linear numerical study.