Tropical Pacific Decadal Oscillation in Subsurface Ocean Temperature

Tropical Pacific Decadal Oscillation in Subsurface Ocean Temperature

This study utilizes a new monthly-assimilated sea temperature and analyzes trend and decadal oscillations in tropical Pacific 100-200 m subsurface ocean temperature (SOT) from 1945 to 2005 on the basis of the harmonic analysis and Empirical Orthogonal Function (EOF) methods. Significant cooling trends in the SOT in the tropical western Pacific were found over this 60-year period. The first EOF of the SOT in tropical Pacific displays an ENSO-like zonal dipole pattern on decadal time scale, and we considered this pattern in subsurface ocean temperature the tropical Pacific decadal oscillation (TPDO). Our analysis suggests that TPDO is closely correlated with the Pacific decadal oscillation (PDO) in the surface sea temperature (SST). The correlation coefficient between the indices of TPDO and PDO is +0.81 and reaches a maximum of +0.84 when TPDO lags behind PDO by 2 months. Therefore, a change of TPDO is likely related to the variation of PDO. The long-term change in TPDO best explains decadal warming in the tropical eastern Pacific SST and implies potential impact on the weakening of East Asian summer monsoons after the late 1970s.