Date of Award

2016

Document Type

Open Access Dissertation

Department

Marine Science

Sub-Department

College of Arts and Sciences

First Advisor

Subrahmanyam Bulusu

Abstract

For several decades, researchers have explored Indian Ocean climate variability primarily using numerical models because of a lack of observations. Remote sensing technology has helped overcome this scarcity of observational data, but satellite-derived salinity has only been recently made available by the ESA’s Soil Moisture and Ocean Salinity (SMOS, operating since November 2009-present) and NASA’s Aquarius SAC-D (operated during June 2011-June 2015) satellites. Along with the Lagrangian in situ Argo floats array, these new datasets may be used to validate widely used numerical models, such as the HYbrid Coordinate Ocean Model (HYCOM), and also potentially observe new salinity phenomena that were previously not resolved by less capable observational systems.

In the northern Indian Ocean this study found Aquarius sea surface salinity (SSS) data useful for validating model simulations because of its higher horizontal resolution when compared with the Argo floats dataset. Analyses of the regional subsurface found that HYCOM produced spurious vertical profiles of salinity in the near surface environment due to over mixing and also overestimated meridional depth-integrated salt transports because of erroneous subsurface currents it manufactured.

The southwest tropical Indian Ocean (SWTIO) has been linked to year-to-year changes in the Asian monsoon and is strongly forced by regional climate scale variability in the form of both El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). This study found that strong remote forcing in the form of annual downwelling Rossby waves combined with local salinity stratification generates a seasonal barrier layer with maximum thickness in boreal fall (August-October). A new methodology for estimating barrier layer thickness (BLT) was also introduced that combines the satellitederived SSS with subsurface Argo data. Additionally, correlation between interannual variability in SWTIO BLT and MJO formation over the region was described. The discovery of annual MJO genesis within the SWTIO is important for future forecasting efforts that with this new information may be able to better predict interannual variability in the Asian and Australian monsoons as well as the phase of ENSO.

Finally, the Agulhas western boundary current has been shown to be an important driver of climate variability because of leakage of salt and heat from the southern Indian Ocean into the southern Atlantic Ocean that occurs at its point of retroflection. This leakage affects Atlantic Meridional Overturning Circulation (AMOC), but is not well quantified because of poor observational density in the southern hemisphere at high latitudes. This study demonstrated that both Aquarius and SMOS data have high accuracy in the region when compared with Argo and the higher spatio-temporal resolutions of both satellites make them advantageous for improving both the monitoring and prediction of future changes in AMOC, and thus global climate.

Rights

© 2016, Joseph Matthew D’Addezio

Download

Share

COinS