ABSTRACT

    The variability of El Niño-La Niña events was analyzed in a low-dimensional phase space, a concept derived from dynamic system theory. The space-time extended EOFs derived from the observed monthly mean SST field over tropical Pacific were used as the basis of the phase space that describes the time evolution of ENSO signals. It was shown that the essential features of the ENSO variability, such as the irregular oscillation, the phase locking to the annual cycle, and the interdecadal changes in its propagation and onset, can be effectively represented by a three-dimensional phase space. The typical El Niño-La Niña life cycle is four years with its mature phases in boreal winter. The intensity of the ENSO signal within one life cycle is closely linked to the frequency of its occurrence (onset). The interdecadal variability of the ENSO signals is characterized by both the intensity and the frequency of occurrence, displaying an irregularity with the gross feature comparable to the regime behavior and intermittency of some low-dimensional chaotic systems.