Interannually varying salinity effects on ENSO in the tropical pacific: a diagnostic analysis from Argo

Abstract

In this paper, three-dimensional temperature and salinity fields from Argo profiles are used to diagnose the interannual variations of some related upper oceanic fields in the tropical Pacific, with a focus on interannually varying salinity effects on the El Nio-Southern Oscillation (ENSO) events. It is clearly demonstrated that the salinity field plays a significantly large role in modulating the density and mixed layer (ML) over the western-central tropical Pacific. In particular, the contribution of interannually varying salinity to the interannual variations in density, ML, and stratification is surprisingly larger than that of interannually varying temperature. Over the entire region west of the dateline, the salinity effects are not limited to the surface but are clearly seen below the ML as represented in density and stratification fields. Furthermore, the mechanism for how the anomalous salinity field is modulating the ENSO cycle is investigated and explained through the El Nio (2009-2010) and La Nia (2010-2011) cases. Evidently, salinity field is shown to exert a significant influence on interannual variability as it directly affects the vertical mixing and entrainment at the base of the ML, the processes important to sea surface temperature (SST) in the equatorial regions.