Zonal Structure of Tropical Pacific Surface Salinity Anomalies Affects the Eastern and Central Pacific El Ninos Differently

Maximum sea surface salinity (SSS) anomalies are found in the central Pacific during the eastern Pacific El Nino (EPEN) and located further westward during the central Pacific El Nino (CPEN), but whether these differences affect event strengths is unclear. By performing ocean general circulation model experiments via modifying freshwater flux anomalies, we find salinity effects on surface warming during both types are highly sensitive to zonal locations of SSS anomalies, with the strongest warming induced by the SSS anomalies near the international dateline. Further analysis reveals that vertical mixing and entrainment dominate this temperature sensitivity, with the strongest response to SSS anomalies occurring in the central Pacific. The central-Pacific SSS anomalies increase EPEN warming by 0.15 degrees C while the westward-located SSS anomalies make little contribution to CPEN warming. Therefore, the distinct zonal structures of SSS anomalies facilitate stronger EPEN than the CPEN, increasing their difference in intensity by about 10%. The El Nino-Southern Oscillation (ENSO) is the strongest year-to-year climate variability in the planet. The central Pacific El Nino (CPEN) have been recognized in recent decades, with weaker surface warming located more westward, in contrast to the traditional eastern Pacific El Nino (EPEN). Previous studies have underscored various air-sea processes in shaping these differences, however, the impact of salinity remains unknown. Here based on ocean model experiments, we found the salinity effect on El Nino warming is very sensitive to zonal locations of salinity anomalies. The salinity anomalies located in the central Pacific are more effective in modulating local ocean vertical stratification, weakening the colder subsurface water into the mixed layer and further enhancing the surface warming. Therefore, the central equatorial Pacific-located salinity anomalies during EPEN contributes to its stronger warming than those west-located salinity anomalies during CPEN, enhancing the sea surface temperature difference between the two events by about 10%. Our results provide new insight in understanding the ENSO diversity and also its low-frequency variability, which may be helpful for interpreting more complex model simulations and for and predicting ENSO variations. Salinity anomalies in the central Pacific induce the strongest surface warming during both types of El Nino, tapering off to the east and westThe distinct sea surface salinity zonal structures between the two El Ninos amplify their difference in sea surface temperature magnitude by about 10%Salinity effects on vertical mixing and entrainment account for the different eastern Pacific and central Pacific El Nino responses