Date of Award


Document Type

Open Access Thesis


Earth and Ocean Sciences


College of Arts and Sciences

First Advisor

Subrahmanyam Bulusu


Conventionally, El Niño-Southern Oscillation (ENSO) is studied using sea surface temperature (SST) observations in the central and eastern equatorial Pacific Ocean. Recently, sea surface salinity (SSS) in the equatorial Pacific has been studied in relation to the phases of ENSO. Previously, SSS was observed in the equatorial Pacific using the Tropical Ocean Global Atmosphere (TOGA) / Tropical Atmosphere Ocean (TOA), the Argo float network, and Oceanic General Circulation Models (OGCM). The launch of NASA’s Aquarius Salinity Mission and ESA’s Soil Moisture Ocean Salinity (SMOS) opened a new era in which high resolution global near real-time SSS observations are readily available. These satellites have made the collection and analysis of SSS data easier and have improved our understanding of salinity variability during ENSO.

This study examines the accuracy and validity of the Aquarius and SMOS SSS datasets and compares them to the Argo float observations. This comparison shows that the three datasets are comparable, although there are some discrepancies. These differences are mainly focused in the regions of upwelling and high precipitation. The performance of these datasets is analyzed specifically during the 2014-15 ENSO event. Their observations are comparable during this event, but there are notable differences. These salinity discrepancies cannot be explained with evaporation and precipitation patterns (E-P).

Further examination of the 2014-15 ENSO event is conducted, and it is compared to the strong 1997-98 El Niño event and the similarly failed 2012-13 ENSO event. This study demonstrates that both E-P variability and anomalously eastward surface currents are required for the full development of El Niño conditions. It is also essential that anomalous fresh SSS migrate eastward of the International Date Line in order for a successful El Niño to occur. Observed SSS variability in the equatorial Pacific is clearly linked to the onset and death of El Niño conditions.

Finally, a new index called the Western Pacific Salinity Index (WPSI) is developed based on the SSS variability observed in the region defined from 5°N to 5°S and 160°E to 170°W. When calculated using Argo and SMOS SSS data, this index is capable of identifying warm, cool, and neutral phases of ENSO. However, the Aquarius dataset is less capable of observing the phases of ENSO. WPSI is highly correlated to other ENSO indices that are commonly used for monitoring and forecasting.

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