Oceanic dynamics associated with ENSO in affecting the SST variation in the Western Pacific / Philippine Sea sector

During the warm phase of El Niño-Southern Oscillation (ENSO), sea surface temperature (SST) in the western Pacific/Philippine Sea sector exhibits anomalous cooling. Compared to the warm anomalies in the eastern Pacific, the magnitude of the cooling is relatively small (0.2-0.7C), yet the impact on the regional climate is significant. It is found that the correlation between the interannual variations of net heat flux and SST tendency is weak in the tropical western Pacific, and that the Philippine Sea generally receives positive surface heat flux during El Niño. The involvement of oceanic dynamics in generating the cold SST anomalies has been proposed, but the actual oceanic processes are not clear. The oceanic variability of this region associated with ENSO is investigated using data from the three dimensional, eddy-resolving Ocean General Circulation Model for the Earth Simulator (OFES). The 1997/98 El Niño event is chosen as an example. OFES result indicates that the dynamical process of the thermocline upwelling in this region involves both the local effect related to the current variability and non-local waves. The thermocline variation is essential for producing strong and large cooling off the equator in the Western Pacific while the contribution of vertical entrainment is mostly important.