Rossby wavepacket propagation in a zonally-varying basic flow

Abstract

Rossby wavepacket propagation in a zonally-varying basic flow is examined with a barotropicmodel in connection with the critical layer. A number of experiments are conducted by systematicallychanging the longitude of forcing, to analyze interactions between the zonally-varyingflow and a Rossby-wave packet. A particular form of wave-activity flux applicable to zonallyvaryingbasic flows is used to illustrate the propagation patterns. Several reflection patterns arefound and their mechanism, which is different from those currently proposed, is discussed. Thepresent numerical results show that the wavepacket propagation slows down in the weak windregion and that vorticity anomalies are advected by the anticyclonic basic flow. Vorticity anomaliesassociated with Rossby waves, in turn, influence the intensity of a subtropical anticyclonicflow in the basic state. The present numerical results are compared with an observed vorticityoverturning in the upper troposphere and wave amplification near the jet exit region obtainedin a linear numerical study.