Wave Structure and Evolution In Baroclinic Flow Regimes

Abstract

AbstractA uniform potential vorticity model, modified by two Ekman layers of different strengths, is used to study analytically and numerically the structure and evolution of strongly nonlinear, baroclinic waves. the model consists of a single zonal wave with its lowest two meridional modes, and of the mean flow correction with its lowest four meridional modes. Each meridional mode consists of a baroclinic and a barotropic pattern.Travelling steady waves, amplitude vacillation and structural vacillation are found in the model. Steady waves are energetically balanced between baroclinicity and Ekman dissipation through nonlinearity. In a typical amplitude vacillation, the wave potential energy vacillates with time, via the interference of nonlinear barotropic and baroclinic patterns of the lowest meridional mode of the wave. In a typical structural vacillation, the distribution of wave kinetic energy in the meridional direction vacillates with time, via interference of the lowest two nonlinear meridional modes of the wave. the results are qualitatively consistent with those observed in annulus experiments. the mechanisms of amplitude and structural vacillations may be responsible for blocking in middle and high latitudes.