Zonal Structure of Tropical Pacific Surface Salinity Anomalies Affects ENSO Intensity and Asymmetry

Previous studies have revealed the potential importance of salinity in El Nino-Southern Oscillation (ENSO) asymmetry, but the responsible mechanisms remain unclear. Here, we investigate how the zonal structure of surface salinity anomalies affects ENSO intensity and asymmetry by modifying freshwater flux in ocean general circulation model simulations. Results show that the amplitudes of El Nino and La Nina are both highly sensitive to zonal patterns of salinity anomalies, with the strongest sea surface temperature change occurring when maximum salinity anomalies are located near 170 degrees W. Furthermore, the effect of salinity anomalies in the central Pacific on El Nino warming is larger than those in the western Pacific on La Nina cooling. Thus, the asymmetric salinity anomalies strengthen the temperature asymmetry between El Nino and La Nina. Temperature budget analysis shows that vertical mixing and entrainment due to salinity-induced changes in stratification are a major response to different zonal patterns of freshwater flux forcing.