A Coupled Quadrupole Mode in the South Pacific

Abstract Although links between the atmospheric convergence zone and the local ocean dipole in the South Atlantic are well established, relationships between the South Pacific convergence zone (SPCZ) and the South Pacific quadrupole (SPQ) remain largely unexplored. Based on maximum covariance analysis applied to a 110-yr monthly coupled atmosphere–ocean reanalysis, we describe a coupled quadrupole mode (CQM) that connects the SPCZ and SPQ during austral summer December–February (DJF). The CQM is linked to the “enhanced SPCZ” mode in the atmosphere and the SPQ in the ocean, with the atmospheric signal leading the ocean signal by about 1 month. This coupled mode essentially represents the atmospheric and oceanic responses to a stationary Rossby wave train that propagates from low- to high latitudes before reflecting back toward lower latitudes around 150°E. Coupled atmosphere–ocean feedbacks help to maintain anomalous convective activity in the SPCZ and related circulation anomalies. The stationary waves that organize the CQM are often rooted in anomalous convection over the Maritime Continent and have close connections with the atmospheric wavenumber-4 mode in the midlatitude Southern Hemisphere. Significance Statement In this study, we investigate the relationships between coherent large-scale patterns in the South Pacific Ocean and the overlying atmosphere. These patterns, which we refer to as a coupled quadrupole for their four centers of action, impact both local communities and the global climate by shaping rainfall and temperature anomalies across the “four corners” of the South Pacific: east–west and north–south. We show that this coupled quadrupole arises as the joint atmospheric and oceanic response to a large-scale wave that arcs across the entire South Pacific basin more than 10 km above the surface and that feedbacks from the ocean to the atmosphere help it to last longer.