Lagrangian Reconstruction to Extract Small‐Scale Salinity Variability From SMAP Observations

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Barceló-Llull, Bàrbara, Drushka, Kyla, Gaube, Peter
• Other Authors: National Aeronautics and Space Administration (US), European Commission
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2021
• Subjects: Lagrangian methods; Lagrangian reconstruction; Ocean salinity; Remote sensing; Submesoscale; Northwest Atlantic
• Online Access: http://hdl.handle.net/10261/230392; https://doi.org/10.1029/2020JC016477; https://doi.org/10.13039/501100000780; https://doi.org/10.13039/100000104

As the resolution of observations and models improves, emerging evidence indicates that ocean variability on 1–200‐km scales is of fundamental importance to ocean circulation, air‐sea interaction, and biogeochemistry. In many regions, salinity variability dominates over thermal effects in forming density fronts. Unfortunately, current satellite observations of sea surface salinity (SSS) only resolve scales ≥40 km (or larger, depending on the product). In this study, we investigate small‐scale variability (≲25 km) by reconstructing gridded SSS observations made by the Soil Moisture Active Passive (SMAP) satellite in the northwest Atlantic Ocean. Using altimetric geostrophic currents, we numerically advect SMAP SSS fields to produce a Lagrangian reconstruction that represents small scales. Reconstructed fields are compared to in‐situ salinity observations made by a ship‐board thermosalinograph, revealing a marked improvement in small‐scale salinity variability when compared to the original SMAP fields, particularly from the continental shelf to the Gulf Stream. In the Sargasso Sea, however, both SMAP and the reconstructed fields contain higher variability than is observed in situ. Enhanced small‐scale salinity variability is concentrated in two bands: a northern band aligned with the continental shelfbreak and a southern band aligned with the Gulf Stream mean position. Seasonal differences in the small‐scale variability appear to covary with the seasonal cycle of the large‐scale SSS gradients resulting from the freshening of the coastal waters during periods of elevated river outflow. This study has been developed in the framework of the (Sub)mesoscale Salinity Variability at Fronts project (NNX17AK04G) funded by the National Aeronautics and Space Administration (NASA). https://doi.org/10.20350/digitalCSIC/12830 (Barceló‐Llull et al., 2020). During the revision of the manuscript, Bàrbara Barceló‐Llull was working at IMEDEA (CSIC‐UIB, Spain) in the framework of the EuroSea project that has received funding from ...