Predictability of summer northwest Pacific climate in 11 coupled model hindcasts: Local and remote forcing

The skills of 11 coupled ocean-atmosphere general circulation models (CGCMs) are investigated in the prediction of seasonal rainfall and circulation anomalies over the northwest (NW) Pacific for the period 1980-2001, with a focus on the summer following the mature phase of El Nino (hereafter JJA(1)). It is shown that the first empirical orthogonal function (EOF) mode of sea level pressure is closely tied to the second EOF mode of rainfall variability over the NW Pacific during JJA(1), indicative of strong feedback between circulation and convection. Most coupled models and the associated multimodel ensemble well predict these EOF modes and their relationship with high fidelity. Coupled models are capable of predicting suppressed rainfall over the NW Pacific in JJA(1). A few models fail to predict the concurrent weak negative sea surface temperature (SST) anomalies on the southeastern flank of the anomalous anticyclone. This suggests that remote forcing via teleconnections is important for NW Pacific rainfall prediction in those models. In some models, local air-sea interactions seem also to play a role. Specifically, remote forcing by tropical Indian Ocean (TIO) SST variability is identified as influential on NW Pacific climate during JJA(1). TIO SST affects the atmosphere over the NW Pacific by two mechanisms, via the equatorial Kelvin wave and the intensification of the subtropical westerly jet. Overall, models are successful in predicting the antisymmetric patterns of precipitation and winds over TIO during spring, which are critical in sustaining the TIO warming through the subsequent summer.