Model consistency for the underlying mechanisms for the Inter-decadal Pacific Oscillation-tropical Atlantic connection

Modeling evidence suggests that the Inter-decadal Pacific Oscillation (IPO) can remotely affect the tropical Atlantic sea surface temperature (SST) variability. However, the root causes of the IPO-tropical Atlantic inter-basin teleconnections are not fully understood. Using idealized pacemaker experiments wherein the observed IPO-SST anomalies are specified, we show that a warm-phase IPO-SST anomaly drives a basin-wide SST warming over the tropical Atlantic. The trans-basin IPO-tropical Atlantic connection is established via the tropical tropospheric temperature mechanism and the atmospheric bridge teleconnections. An IPO positive-phase SST initiates the warming tropospheric temperature anomalies, leading to a more humid atmosphere and increasing longwave radiation downward into the tropical Atlantic. By comparison, the reduced Pacific Walker circulation and mid-latitude Rossby wave responses cause the trade winds to strengthen, acting to suppress the tropical Atlantic warming through the Bjerknes positive feedback mechanism. Thus, similar to previous studies, the tropical Atlantic widespread warming is ultimately traced back to the warming effects generated by the water vapor-longwave radiation-SST positive feedback, which, contrary to previous studies, overwhelms the cooling effects associated with the intensified trade winds. Our results highlight the model dependence on the details of mechanisms that connect the tropical Pacific and tropical Atlantic on the decadal timescales.