Presented at the 2014 Aquarius/SAC-D Science Team MeetingThis study investigates the sea surface salinity (SSS) variability in the equatorial Pacific using recently available Aquarius and Argo data. For the period of observation from August 2011 to present, Aquarius nicely resolves the SSS front and its zonal displacement along the equator. The on-going collection of Argo data shows high correlations between this SSS front and the existing indices of El Niño, suggesting its potential important role in ENSO evolution. Further analysis reveals that SSS variability in the southeastern tropical Pacific is crucial to identify the type of El Niño. The longitudinal location of the SSS front and the SSS variability in the southeastern tropical Pacific can be used as indices to characterize ENSO events and their types. The processes that possibly control these SSS indices are also discussed.