Distinguished Effects of Interannual Salinity Variability on the Development of the Central-Pacific El Niñ Events

Abstract

El Niño events in the central equatorial Pacific (CP) are gaining increased attention, due to their increasing intensity within the global warming context. Various physical processes have been identified in the climate system that can be responsible for the modulation of El Niño, especially the effects of interannual salinity variability. In this work, a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset. It is demonstrated that during the developing phase of an El Niño event, a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML), decrease oceanic density in the upper ocean, and stabilize the upper layers. These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML, which further enhances the warm sea surface temperature (SST) anomalies associated with the El Niño event. However, the effects of interannually variable salinity are much more significant during the CP-El Niño than during the eastern Pacific (EP) El Niño, indicating that the salinity effect might be an important contributor to the development of CP-El Niño events.