Figure 4 Anomalies of (a) SST and (b) suface wind stress corresponding to the first mode at the phase lag 120°, obtained from linear regressions on the temporal CEOF fot the VAT with the phase lag.
Along with the eastern subtropical wind anomaiy, subsurface ocean temperature signals are formed in the eastern Pacific, then it propagates westward along 20｡? at the upper thermocline depth of the model (Fig. 6a). The westward propagating speed is slower than the free first baroclinic Rossby wave, which implies influence of the wind stress curl forcing. The wind stress curl is large around 170W but shows little propagation (not shown). The positive wind stress curl enforces the negative upper thermocline temperature anomaly in the west end of the location.
When the subtropical signal reaches the western Pacific, phase change of subsurface temperatur at the equator seems to onset (Fig. 6a-b, φ=30°). This phase change is accompanied by negative anomaly of heat transport into the equatorial western Pacfic warm pool (not shown) which triggers eastward migration of the equatorial subsurface temperature anomaly. With slight lags to the subsurface change, there appears change of signs in SST and zonal wind stress along the equator.This leads a opposite sign of SST anomaly as in Fig.4a. The timescale of this mode is associated with the travel time for subtropical signal to transvers the basin. The above spatial structure and temporal evolution is similar to what is known for the ENSO except for its timescale and latitudinal extent.
