Bifurcation in Eddy Life Cycles: Implications for Storm Track Variability

By analyzing a number of very high resolution, nonhydrostatic experiments of baroclinic lifecycles, it was concluded that the intensity of the near-surface baroclinic development influences the upper-level wave to such an extent that it could produce cyclonic or anticyclonic wave breaking. Since the final jet position is equatorward or poleward, the position depends on whether the waves break cyclonically or anticyclonically, respectively. The low-level baroclinicity plays a very important role in the outcome of the wave and feedback to the mean circulation. Using a shallow water model the hypothesis that the intensity of the eddy forcing from the lower layers of the atmosphere can have a profound effect on the disturbances of the upper layers is tested. From these experiments the following is concluded. For weak intensities, the strong effective beta asymmetries due to the earth’s sphericity produce anticyclonic wave breaking and a poleward shift of the zonal jet will occur. For moderate forcing, anticyclonic wave breaking occurs and consequently, as before, a poleward shift of the zonal jet will occur. However, there is an important distinction between weak and moderate forcing. In the latter case, the eddy anticyclonic centers are very intense. The influence of the two anticyclones produces a difluence field that will strain the cyclonic vortex along the SW–NE direction. Consequently, the meridional vorticity flux y9z9 is positive in the north and negative in the