Presented at the 2014 AGU Fall MeetingThe eastern tropical Pacific Ocean is characterized with low salinity (less than 33 psu) waters due to excess of precipitation over evaporation. Monitoring the salinity variation in this region is of primary importance to ENSO studies. The precipitation, evaporation, and the ocean current all contribute to complex surface salinity variability in the eastern tropical Pacific Ocean. This study attempts to address the atmospheric and oceanic causes of sub-monthly, monthly, seasonal variability in mixed-layer salinity from observational data sets. The data sets include measurements from the Aquarius sea surface salinity, SMOS sea surface salinity, Argo profiling float data, CMORPH precipitation, OAFlux evaporation and the ocean current measurements from OSCAR.