Abstract
Observations of sea surface salinity (SSS) from NASA’s Soil Moisture Active-Passive (SMAP) and ESA’s Soil Moisture and Ocean Salinity (SMOS) satellite missions are used to characterize and quantify the contribution of mesoscale eddies to the ocean transport of salt. Given large errors in satellite retrievals and, consequently, SSS maps, we evaluate two products from the two missions and also use two different methods to assess the eddy transport of salt. Comparing the two missions, we find that the estimates of the eddy transport of salt agree very well, particularly in the tropics and subtropics. The transport is divergent in the subtropical gyres (eddies pump salt out of the gyres) and convergent in the tropics. The estimates from the two satellites start to differ regionally at higher latitudes, particularly in the Southern Ocean and along the Antarctic Circumpolar Current (ACC), resulting, presumably, from a considerable increase in the level of noise in satellite retrievals (because of poor sensitivity of the satellite radiometer to SSS in cold water), or they can be due to insufficient spatial resolution. Overall, our study demonstrates that the possibility of characterizing and quantifying the eddy transport of salt in the ocean surface mixed layer can rely on the use of satellite observations of SSS. Yet, new technologies are required to improve the resolution capabilities of future satellite missions in order to observe mesoscale and sub-mesoscale variability, improve the signal-to-noise ratio, and extend these capabilities to the polar oceans.
Highlights
Two satellite-derived sea surface salinity (SSS) datasets are used in this study, which are hereafter called Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active-Passive (SMAP) SSS for short
The maps are for the same week (9-day and 8-day running averages, to be more exact) and technically, have to “see” the same structure
As a result of the averaging over a large number of eddies in a given geographic area, composite eddies result in quite small standard errors (
Summary
Sea surface salinity (SSS) is an essential climate variable that reflects changes in the marine hydrological cycle and plays an important role in ocean dynamics [1]. Variations in SSS affect the density of sea water, influencing the stability of the upper-ocean stratification and mixing [2]. This is important at high latitudes, where salinity is a major factor controlling seawater density. Knowledge of the SSS distribution is necessary for understanding the hydrological cycle, ocean circulation, and for monitoring changes in the ocean component of the Earth’s climate system. A better understanding of the physical processes governing the distribution of SSS is required
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