Role of the meridional dipole of SSTA and associated cross-equatorial flow in the tropical eastern Pacific in terminating the 2014 El Niño development

In the boreal spring of 2014, the oceanic and atmospheric conditions were favorable for an El Niño's development. It was predicted that in 2014, a super El Niño or at least a regular El Niño with normal magnitude, would initiate. However, the growth rate of the sea surface temperature anomaly (SSTA) in the equatorial eastern Pacific suddenly declined in the boreal summer. The physical processes responsible for the termination of the 2014 El Niño were addressed in this study. We hypothesized that a meridional dipole of SSTA, characterized by a pronounced warm SSTA over the eastern North Pacific (ENP) and cold SSTA over the eastern South Pacific (ESP), played a crucial role in blocking the 2014 El Niño’s development. The observational analysis revealed that the meridional dipole of SSTA and the relevant anomalous cross-equatorial flow in the tropical eastern Pacific, induced anomalous westward (u^′OpenSPiltSPi 0) and upwelling (w^′CloseSPigtSPi 0) currents in the equatorial eastern Pacific, leading to negative anomalous zonal advection term (- u^′∂T¯ / ∂xOpenSPiltSPi 0) and anomalous upwelling advection term (- w^′∂T¯ / ∂zOpenSPiltSPi 0). Additionally, the anomalous cross-equatorial flow also induced northward meridional current anomalies that transported subtropical cold water to the equator. All the changes of the oceanic dynamic terms collectively caused negative SSTA tendency in the boreal summer, and thus killed off the budding 2014 El Niño. The idealized numerical experiments further confirmed that the 2014 El Niño’s development could be suppressed by the meridional dipole of SSTA, and both the ENP pole and ESP pole make a contribution.