Mechanisms for Wave Packet Formation and Maintenance in a Quasigeostrophic Two-Layer Model

Abstract

Abstract A quasigeostrophic, two-layer, β-plane channel model is used to investigate the dynamics of baroclinic wave packets. A series of experiments are performed in which an unstable flow is maintained by lower-level Ekman friction and radiative relaxation toward a temperature profile that corresponds to a broad parabolic upper-level jet. The final statistically steady state achieved in each experiment is found to depend on the magnitude of the hyperdiffusivity ν0 and the supercriticality, which is controlled by β. The most important qualitative difference in such states between experiments is found to be the degree to which a waveguide in the upper level is found to develop. The mechanism for this upper-level waveguide development is the mixing effect of the eddies at the flanks of the jet, which leads to a strong potential vorticity gradient at the center of the channel, with well-mixed regions to the north and south. Two distinct regimes with different qualitative behavior are observed and illustrate...