Signature of Mesoscale Eddies in Satellite Sea Surface Salinity Data

A persistent signature of transient mesoscale eddies in sea surface salinity (SSS) is revealed by analyzing the relationship between satellite SSS and sea surface height (SSH) variability. The SSS fields used in the study are Aquarius SSS optimum interpolation analysis recently developed at the University of Hawaii. The satellite altimetry data set is provided by Aviso and consists of weekly SSH anomaly data objectively analyzed on a regular 0.25-degree grid. The SSS signature of mesoscale eddies is reconstructed by collocating SSS and SSH anomaly maps along the trajectories of mesoscale eddies identified and tracked from the SSH anomaly data. The resulting composites reveal a clear signature of mesoscale eddies in satellite SSS with typical SSS anomalies of 0.05 psu. Overall, the spatial structure of eddy-induced SSS perturbations in the eddy-following reference frame can be characterized as a superposition of a dipole structure, arising from horizontal advection of the background SSS gradient by anomalous velocity field, and a monopole structure related to the eddy core. The relative contribution of the two processes depends on the eddy polarity, the magnitude and direction of the background SSS gradient, and the vertical salinity stratification in the near-surface layer. The observed relationships between SSS and SSH anomalies in different parts of the ocean are used to assess the role of mesoscale eddies in the ocean freshwater transport.