Catastrophe and Mechanism Analyses of Multiple Equilibria in the Western Pacific Subtropical High System Based on Objective Fitting of Spatial Basis Functions

Abstract

Abstract Scholars have been showing great interest in revealing the mechanisms that govern the activities of the western Pacific subtropical high (WPSH). However, the problem currently remains unresolved. In this paper, a new model is developed to reveal the dynamical mechanism of the WPSH abnormal activities. Variables in the partial differential vorticity equations based on latent heat flux are separated in space and time using Galerkin methods. To overcome three deficiencies of the traditional highly truncated spectral method, spatial basis functions are reconstructed from observation field time series based on a combination of empirical orthogonal function decomposition and genetic algorithm. Based on the atmospheric vorticity equation, nonlinear ordinary differential equations of the WPSH can be obtained using an objective spatial basis function. Moreover, dynamical characteristics and actions, such as bifurcation and catastrophe induced by latent heat flux factors, are analyzed. Results show that the latent heat flux field in the Indian Ocean and the Bay of Bengal region determines the formation and rupture of the WPSH (such as the “double ridge” phenomenon). The enhancements of land–sea heating contrast and latent heat flux field in the South China Sea lead to WPSH abnormal activities and WPSH circulation anomalies, such as subtropical high northward jump and rapid westward extension. Linked with the real weather phenomena and the diagnostic analysis of the previous studies, the credibility of the bifurcation and catastrophe analysis is confirmed. This work documents new areas of research on the evolution mechanism of the WPSH under the action of latent heat flux from the view of chaotic dynamics.