Abstract
The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite has been providing data, including sea surface salinity (SSS) measurements, for more than five years. However, the operational ESA Level 2 SSS data are known to have significant spatially and temporally varying biases between measurements from ascending passes (SSSA) and measurements from descending passes (SSSD). This paper demonstrates how these biases are reduced through the use of SSS anomalies. Climatology products are constructed using SMOS Level 2 data to provide daily, one-degree by one-degree climatologies separately for ascending and descending passes using a moving window approach (in time and space). The daily, one-degree products can then be averaged to provide values of climatological SSS at different spatial and/or temporal resolutions. The averaged values of the SMOS climatology products are in good general agreement with data from the World Ocean Atlas 2013. However, there are significant differences at high latitudes, as well as in coastal and dynamic regions, as found by previous studies. Both the mean and standard deviation of the differences between data from ascending passes and data from descending passes for the anomalies are reduced compared with those obtained using the original salinity values. Geophysical signals are clearly visible in the anomaly products and an example is shown in the Southern Indian Ocean of westward-propagating signals that we conclude represent the surface expression of Rossby waves or large-scale non-linear eddies. The signals seen in salinity data agree (in speed) with those from sea surface temperature and sea surface height and are consistent with previous studies.
Highlights
Sea surface salinity (SSS) is an essential climate variable (GCOS, 2011) and critical to our understanding of ocean circulation and the global water cycle
This paper will demonstrate a methodology for reducing these variable biases in the open ocean through the use of SSS anomalies based on data only from Soil Moisture and Ocean Salinity (SMOS). These anomaly products are well-suited to observing oceanographic processes: as an example we show evidence of westward propagating signals in the South Indian Ocean (SIO), which represent the surface expression of Rossby waves or large-scale non-linear eddies
The average climatology products for climatologies separately for ascending (CLIMA) and CLIMD are shown in Fig. 1 alongside the equivalent results for World Ocean Atlas 2013 (WOA13)
Summary
Sea surface salinity (SSS) is an essential climate variable (GCOS, 2011) and critical to our understanding of ocean circulation and the global water cycle. There are still large areas of the global oceans with limited or no in situ measurements of SSS. The utility of SSS data from SMOS for scientific exploitation has been demonstrated for a variety of locations and uses, for example: the relationship of rainfall rate and SSS (Boutin et al, 2014; the relationship is problematic); monitoring of large, freshwater river plumes (Grodsky et al, 2012; Fournier, Chapron, Salisbury, Vandemark, & Reul, 2015); tropical salinity variability (Tzortzi, Josey, Srokosz, & Gommenginger, 2013); observation of tropical instability wave signals in the equatorial Pacific Ocean (Yin et al, 2014b); and the study of mesoscale features in the Gulf Stream (Reul et al, 2014)
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