The Relative Influence of Surface Sea Salinity and Temperature on Surface Density Gradient in the Tropical Pacific Ocean

Horizontal gradients of surface density in the ocean are important to frontal genesis and instability (e.g., Tropical Instability Waves - TIWs) associated with ocean currents. They also have significant implications to air-sea interaction and biogeochemistry. Sea Surface Temperature (SST) and Salinity (SSS) both contribute to the horizontal density gradient. For the first time surface density can be globally inferred from remote sensing with unprecedented spatial and temporal scales. Since August 2011, NASA's Aquarius/SAC-D satellite mission and since January 2010, ESA's SMOS mission have provided global high resolution SSS datasets. In this study, we use various satellite measurements of SSS and SST to characterize the mean spatial structure and temporal variability of surface density gradients in the tropical Pacific Ocean from 2011 to present. In particular, we focus on the equatorial region where TIWs are present. We also investigate the relative contributions of SSS and SST on density and contrast them with the estimate from an objective analysis based on Argo float and other in-situ measurements. The study of multiple datasets of SSS and SST from satellite and in-situ observations allow us to estimate the uncertainties in estimating surface density gradients. This comparison furthermore highlights the regions where satellite measurements provide estimated surface gradients at finer scales than sparser in situ observations. The results have strong implications to the interpretation of the characteristics of TIWs as seen from satellite measurements of SSS and SST.