ABRUPT CHANGE OF QUASI-GEOSTROPHIC FLOW FORCED BY OROGRAPHY AND DIABATIC HEATING

A low-order spectral model is used to study abrupt change of quasi-geostrophic current forced by both orography and diabatic heating. In certain parametric combinations, along with the gradual change of external thermal forcing, it is found that abrupt changes of both the spectral coefficient and the locations of the westerly jet stream can be stimulated. Introducing the orography into the model results in a change of the parametric range in which the multiple equilibrium states in flow patterns exist and the shift of the parametric critical points at which the abrupt change of the locations of westerly jet streams is created, as well as increase of the wave components of the equilibrium flow patterns. The aspects of simulated "South Branch" jet streams are more similar to the observational fact in the presence of both the orography and the diabatic heating than those in the case of the heating forcing.