Mechanism of Interannual Cross-Equatorial Overturning Anomalies in the Pacific Ocean

Recent evidence shows that the variability of meridional overturning circulation (MOC) in the Indian and Pacific Oceans (PMOC) is characterized by a prominent deep cross-equatorial cell (CEC) spanning the tropics between 20S and 20N, but the mechanism responsible for this CEC is not understood. Using version 4.2 of the Estimating the Circulation and Climate of the Ocean (ECCO) state estimate, our investigation shows the mechanism responsible for CEC can be conceptualized by following mechanistic chain: 1) Anomalous winds produce equatorially antisymmetric anomalies of zonal mean sea surface temperature (SST) in the Pacific Ocean, 2) These temperature anomalies generate equatorially antisymmetric anomalies of sea surface height (SSH), 3) The SSH anomalies generate a cross-equatorial flow in the upper Pacific Ocean, and 4) This anomalous cross-equatorial flow in the upper layers drives compensating circulation in the deep Pacific.