Climate responses and variability in the tropical Pacific associated with Atlantic warming in recent decades

Abstract

In this study, we investigated the impact of the Atlantic decadal modulation on the decadal and climate variability in the tropical Pacific, using the Atmospheric General Circulation Model (AGCM). During the recent decade from 2000 to 2010 when the Atlantic SST has sharply increased, observations have shown that the strong easterly and increased precipitation anomalies were confined over the western-central Pacific. It is different from the conventional Gill-type response in which the easterly due to heating in the Atlantic is expected to be extended to the Indian Ocean. We have found that a warm pool over the western Pacific plays an important role in confining the atmospheric response on the Atlantic SST forcing it to the Pacific basin. Simplified Aqua planet GCM experiments showed that the location of the anomalous easterly over the Pacific produced by the Atlantic SST forcing is confined depending on the location of the idealized warm pool. The reason for this is because the moisture feedback is strongest over the warm pool region, which leads to additional local anomalous convergence; therefore, the easterly produced by the Atlantic SST forcing is enhanced only over the east of the warm pool region. In addition, we examine the modulation of El Nino Southern Oscillation (ENSO) variability due to Atlantic SST forcing using hybrid coupled model, and show there is reduction of ENSO variability due to Atlantic warm SST. It is hypothesized that this weakening of ENSO variability is due to the enhanced (reduced) convection over the western (eastern) Pacific through the enhanced Walker Circulation, which leads ENSO-related wind stress anomaly to the west.