Evolution mechanism of the western Pacific subtropical high

Abstract

To surmount the deficiency in studying the multiple equilibrium states in the atmosphere motion with highly truncated spectral method, the trigonometric functions for describing the prototypical 500 hPa height fields and the outgoing long wave radiation (OLR) fields are retrieved respectively for the northward bias and the southward bias years of the western Pacific subtropical high with corresponding observational data and the optimum subset retrieval method for four factors. Then the evolution mechanism of the western Pacific subtropical high is studied by means of multiple equilibrium state theory. The results show that the cause of inducing the abnormal location of the western Pacific subtropical high is differences in the early external thermal forcing, which evoke different waveforms in atmosphere. If the early meridional and zonal external thermal forcing differences are stronger, there are wave-mean flow and wave-wave interactions between the response waveforms in atmosphere. In such a case, the western Pacific subtropical high shifts northward obviously. On the contrary, when the early meridional and zonal external thermal forcing differences are weaker, there is no wave-mean flow interaction between the response waveforms in atmosphere, and accordingly the position of the western Pacific subtropical high oscillates with the external thermal forcing oscillation, and is on the south of normal.