Stationary Rossby-wave propagation in a baroclinic atmosphere

Observational studies of teleconnections in both solsticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies. These have been interpreted using barotropic Rossby-wave theory, and simulated using stationary forcing in barotropic models linearized about 300 hPa flows. In this paper the relevant propagation behaviour is investigated using a baroclinic model with three-dimensional, climatological basic states. Time integrations are performed using localized thermal forcing as a wavemaker. The propagation results are qualitatively very similar to those obtained with the barotropic model, though there are quantitative differences. The westerly jets still act as strong waveguides. The shorter wavelengths and smaller wave-activity speeds found with the baroclinic model are generally in better agreement with observation. Propagation into and hom the upper tropospheric equatorial westerlies in the east Pacific, propagation across North America and propagation from Europe across the Arabian Gulf are all found. The extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions. Barotropic models can only represent such behaviour if the basic state reflects the near-equatorial upper tropospheric zonal wind structure.