Salinity variability in the tropical Pacific during the Central-Pacific and Eastern-Pacific El Nino events

In this study, sea surface salinity (SSS) variability associated with two types of El Nino in the tropical Pacific is investigated using observational data and reanalysis products for the period from 1979 to 2017. The results show that the central (CP) and eastern (EP) Pacific El Nino events have distinct SSS signatures. During a CP El Nino event, negative SSS anomalies appear in the western equatorial Pacific, and positive SSS anomalies in the east. During an EP El Nino event, large negative SSS anomalies occur in the central equatorial Pacific and positive SSS anomalies in the west, with the core of negative SSS anomalies being shifted by about 25 degrees longitude eastward compared with a CP El Nino event. A composite analysis indicates that large differences in SSS anomalies between the two types of El Nino are confined to the fresh pool and Nino 3.4 regions. Surface freshwater flux and horizontal advection are two major factors modulating the SSS there, but their relative importance in the two regions is different. In the fresh pool region, the positive SSS anomalies during an EP El Nino are much larger than those during a CP El Nino event. Their differences are mainly caused by surface freshwater flux anomalies, and horizontal advection anomalies play a secondary role. In the Nino 3.4 region, SSS anomalies are positive during a CP El Nino but negative during an EP El Nino. These differences are mainly caused by horizontal advection anomalies rather than freshwater flux anomalies associated with El Nino.