Baroclinic generation of planetary transient and stationary waves from forced stationary waves

Abstract

The linear instability of forced stationary waves in a baroclinic zonal flow is examined with a two‐level quasi‐geostrophic beta plane model. Realistic zonal topography and diabatic forcings produce a steady state solution of planetary‐scale stationary waves. Baroclinic instability of the forced waves gives rise to transient perturbation modes of planetary zonal scale and a preferred meridional scale of about twice the radius of deformation. One of the dominant planetary modes is stationary and resembles the observed stationary wave pattern. In the steady state model this form can be obtained only for certain values of the meridional scale of the forcings. It is suggested that this stationary mode could contribute to the time average stationary wave distribution. Applications to blocking are also considered. Interference of stationary and quasi‐stationary modes can apparently produce regional as well as global blocking patterns.