Principal Modes in Linear Coupled Air-sea System of Tropical Pacific and Their Association with ENSO
热带太平洋线性海气耦合系统的主模与ENSO

By using a tropical Pacific coupled air-sea model with an oceanic surface boundary layer,including the linear atmospheric and oceanic dynamics and linearized SST prognostic equation about non-uniform climatic states, the characteristic period and stability of principal modes in the linear coupled air-sea system and their association with ENSO are investigated by solving the eigenvalue problem within realistic ranges of climate background states and parameters. Results show that the quasi biennial (QB) oscillation is the most unstable mode of the linear coupled air sea system and only the QB mode displays ENSO-like horizontal structure. Therefore, as an intrinsic mode of coupled air-sea system, the QB mode would be fundamental for full understanding of mechanism responsible for ENSO cycle. Moreover, the relationship between the QB mode and the mean annual cycle, and the influence of the QB mode in determining the time scales of ENSO variability are also discussed in this paper.