Detecting the surface salinity signature of Gulf Stream cold‐core rings in Aquarius synergistic products

Abstract

New sea surface salinity (SSS) observations derived from satellite remote sensing platforms provide a comprehensive view of salt exchanges across boundary currents such as the Gulf Stream. The high resolution (45 km spatial resolution and 3 day repeat subcycle) of the Soil Moisture and Ocean Salinity (SMOS) observations allows detection (and tracking) of meander and ring structures of the Gulf Stream from SSS maps. These structures are, however, not resolved by the relatively lower resolution (100 km and 7 day repeat subcycle) of Aquarius observations. A recently developed fusion technique, based on singularity analysis, is applied in this study to reconstruct these mesoscale (from 100 km and 3 days) features in Aquarius-derived products. New quarter-degree SSS maps are obtained by fusing Aquarius data with three different geophysical templates: sea surface height (SSH) from AVISO, SSS from SMOS, and sea surface temperature (SST) from AVHRR. The proposed method exploits the theoretical correspondence among the singularity exponents of different maps of ocean-surface remotely sensed scalar fields. The analysis results over the year 2012 show that merging Aquarius with SSH data provides a series of negative salinity anomalies that better collocate with the position of the cyclonic eddies identified from sea level anomaly maps. This result is consistent with the hypothesis that this SLA derived cyclonic eddies in this area are indeed CCRs shed off the GS.

Signature of mesoscale eddies in satellite sea surface salinity data

“…Resent state of the art satellite observations of SSS, by NASA's Aquarius/SAC‐D satellite [ Lagerloef et al ., ] and ESA's Soil Moisture and Ocean Salinity (SMOS) satellite [ Kerr et al ., ], present an opportunity to complement the existing satellite observations of SST, surface winds, air‐sea fluxes, and other variables, to observe the signature of mesoscale eddies. The potential of new satellite measurements to observe mesoscale features and eddies have been demonstrated in a few recent studies [ Reul et al ., ; Umbert et al ., ; Isern‐Fontanet et al ., ]. Yet extracting such information from medium‐resolution and noisy satellite data requires application of selective data analysis tools.…”

Retrieval of eddy dynamics from SMOS sea surface salinity measurements in the Algerian Basin (Mediterranean Sea)

“…Recent studies have demonstrated the potential of new satellite measurements of SSS to describe features not well captured by SST maps such as fresh‐core Gulf String rings [ Reul et al , ; Umbert et al , ]. However, eddies in the Algerian Basin are more difficult to detect by SMOS because they are attached to the coast or located at distances from coast were the contamination from land in the L band microwave is important [ Font et al , ].…”

“…SMOS SSS maps are well correlated with in situ measurements although the former has a smaller dynamical range. Despite this limitation, SMOS SSS maps capture the key dynamics of Algerian eddies allowing to retrieve velocities from SSS with the correct sign of vorticity.Recent studies have demonstrated the potential of new satellite measurements of SSS to describe features not well captured by SST maps such as fresh-core Gulf String rings [Reul et al, 2014;Umbert et al, 2015]. However, eddies in the Algerian Basin are more difficult to detect by SMOS because they are attached to the coast or located at distances from coast were the contamination from land in the L band microwave is important…”

Error Characterization of Sea Surface Salinity Products Using Triple Collocation Analysis

“…While there have been notable efforts to improve the quality of retrievals [5], [6], L-band radiometry is still in its infancy, and the quality of derived salinity products is expected to improve with time. Currently, higher-level processing efforts, i.e., various spatial and temporal averaging and data fusion techniques, have been implemented to better recover structured and meaningful geophysical information from remote sensing SSS retrievals [7], [8], [9].…”