Measurements from the Soil Moisture Ocean Salinity (SMOS) satellite acquired during 2012 in the western North Atlantic are used to reveal the evolution of the sea surface salinity (SSS) structure of the meandering Gulf Stream with an unprecedented space and time resolution. Combined with in situ surface and profile measurements, satellite-derived surface currents, sea surface height (SSH), surface temperature (SST), and chlorophyll (Chl) data, SMOS SSS observations are shown to coherently delineate meanders pinching off from the current to form well-identified salty- (warm-) and fresh- (cold-) core Gulf Stream rings. A covariance analysis at two locations along the separated Gulf stream path (south of Nova Scotia and in the Gulf Stream Extension) reveals a systematically higher correlation between SSS and sea level variability than between SST and SSH during the warmer half of the year. Within (75°W–40°W; 30°N–50°N), Chl concentration is also found to significantly depend on the SSS as SST increases above 20°C.
Abstract The Eastern Pacific Fresh Pool (EPFP) is a large region of low sea surface salinity (SSS) defined by values lower than 34 practical salinity scale within (5°S–30°N, 75°W–180°W). The fresh pool dynamically responds to strong regional and seasonally varying ocean‐atmosphere‐land interactions (including monsoon rain, trade and gap winds, and strong currents). Using more than 5 years of Soil Moisture and Ocean Salinity (SMOS) satellite sea surface salinity (SSS) and complementary satellite wind, rain, currents, and sea surface temperature data together with a historical ensemble of in situ products, the present study explores the seasonal and interannual dynamics of the fresh pool over the period 2004–2015. An important interannual variability of the maximal surface extension of the EPFP over the past decade is revealed with two extreme events (2012, 2015) occurring during the SMOS satellite period. These extremes are found to be related to the El Niño‐Southern Oscillation (ENSO) phases and associated anomalies of precipitation, surface currents, and trade wind in the central Pacific. In 2012 (La Niña), stronger trade winds coupled with a deficit of precipitation induced a minimum extension of the pool during the rainy season. Whereas, during the strong El Niño 2014–2015, the EPFP extension reached an unprecedented maximum value. A modification of the atmospheric freshwater fluxes and ocean surface currents during winter 2014 is found to have favored the onset of this abnormal fresh event.
Radar is being developed in many work fields essentially in coastal areas and mounted on satellites (ERS, Seasat). Only a few experiments have been made these last decades in order to study sea surface salinity from microwave radiation (Miller et al., 1998). It has become a real key in coastal area remote sensing. The tool we are working with is a P-band airborne synthetic aperture radar (SAR) called RAMSES made by the ONERA (Paillou et al., 2001). It is a multiband frequency radar which works for all four-polarizations. The active P-band challenge is that such an airborne radar has never been experimented before this day for the study of salinity. This is particularly surprising because of its rising sensibility with salinity gradient. The major aim is to discuss how we can discern bathymetry effects in the Gironde mouth from salinity response into the radar signal. Adding to the radar data, simulations of salinity fields (MARS 3D model from IFREMER) over the Atlantic platform were run for this date contributing to ensure what we suppose with the radar signal. Then we modeled the intensity of the radar (/spl sigma//sub 0/) found on a dielectric constant model (Klein & Swift, 1977) and on Bragg diffusion theory from sea surface. The model simulates a variability of less than 1 dB with the signal intensity for a 1% gradient considering a P-band radar and three time less for a L-band one. This range is ten times less than what is observed from the data. From a qualitative point of view, the intensity of the retrodiffusion globally increases along the saline gradient from low to high salinities. Moreover, the VV polarization is getting more dependent to salinity with higher incidence angles. The study of the saline plume with chlorophyll and suspended matter has permitted to make coincided the 10 to 20 dB drop in the signal with the turbidity limit and phytoplanktonic bloom.
<p>Since 2010, the Soil Moisture and Ocean Salinity (SMOS) satellite mission monitors the earth emission at L-Band, providing the longest time series of Sea Surface Salinity (SSS) from space over the global ocean. However, retrieving SSS at high latitudes with a reasonable accuracy remains challenging, in particular due to the low sensitivity of L-Band radiometric measurements to SSS in cold waters and to the contamination of SMOS measurements by the vicinity of continents and sea ice as well as the presence of Radio Frequency Interferences.&#160;In this paper, we assess the quality of weekly SSS fields derived from swath-ordered instantaneous SMOS SSS (so called Level 2) distributed by the European Space Agency. These products are filtered according to new criteria. We use&#160;the pseudo-dielectric constant retrieved from SMOS brightness temperatures to filter SSS pixels polluted by sea ice. We identify that the dielectric constant model and the sea surface temperature auxiliary parameter&#160;used as prior information in the SMOS SSS retrieval&#160;are significant sources of uncertainty. We develop a novel correction methodology accordingly.</p><p>SSS Standard deviation of differences (STDD) between weekly SMOS SSS and in-situ near surface salinity significantly decrease after applying the SSS correction, from 1.46 pss to 1.26 pss. The correlation between new SMOS SSS and in-situ near surface salinity reaches 0.94. SMOS estimates better capture SSS variability in the Arctic Ocean in comparison to TOPAZ reanalysis (STDD = 1.86&#160;pss), particularly in river plumes fresher by about 10&#160;pss than surrounding waters. Furthermore, comparisons with in-situ measurements ranging from 1 to 11 m depths identify huge vertical stratification in fresh regions. This emphasizes the need to consider in-situ salinity as close as possible to the sea surface when validating L-band radiometric SSS which are representative of the first top centimeter.</p>
Abstract Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.
Measurements from the Soil Moisture Ocean Salinity (SMOS) satellite acquired during 2012 in the western North Atlantic are used to reveal the evolution of the sea surface salinity (SSS) structure of the meandering Gulf Stream with an unprecedented space and time resolution. Combined with in situ surface and profile measurements, satellite-derived surface currents, sea surface height (SSH), surface temperature (SST), and chlorophyll (Chl) data, SMOS SSS observations are shown to coherently delineate meanders pinching off from the current to form well-identified salty- (warm-) and fresh- (cold-) core Gulf Stream rings. A covariance analysis at two locations along the separated Gulf stream path (south of Nova Scotia and in the Gulf Stream Extension) reveals a systematically higher correlation between SSS and sea level variability than between SST and SSH during the warmer half of the year. Within (75°W–40°W; 30°N–50°N), Chl concentration is also found to significantly depend on the SSS as SST increases above 20°C.
<p><span>An</span> impact of <span>the</span> upper <span>ocean response</span> to tropical cyclones (TC) is usually <span>considered</span> <span>as</span> a negative feedback mechanism between cooling of the mixed layer (ML) and intensity of a TC. <span>Influence of</span> TCs <span>on</span> the upper ocean is manifested as <span>anomalies</span> in sea surface temperature (SST) and sea surface salinity (SSS) <span>in wakes of hurricanes, that can vary significantly along tracks of TCs (Reul et al. 2021). Proper modelling of ML dynamics is still vital to explain surface cooling observed in satellite and in situ data. Although numerous models of the ML evolution have been developed (e.g., Zilitinkevich et al. 1979, Gillian et al. 2020, and works cited therein including many schemes incorporated in numerical models), there is still a controversy as to turbulent closure schemes and simplified approaches that could allow for a quick and high quality assessment of ML parameters.</span></p><p>The purpose of the <span>this work</span> is to apply a simplified model of the upper ocean response to TCs suggested by Kudryavtsev et al. 2019 with barotropic and baroclinic modes resolved. To describe ML dynamics, <span>results of Zilitinkevich and Esau (2003) are applied.</span> The cases studied are those of hurricanes passing over the Amazon-Orinoco river plume: Igor (Reul et al. 2014), Katia (Grodsky et al. 2012) and Irma (Balaguru et al. 2020).</p><p>Best track parameters of the TCs are obtained from the IBTrACKS archive. Multi-source GHRSST data on SST as well as SMOS and SMAP satellite data on SSS are used to compare the observed ocean responses to the simulated ones. ISAS20 in situ archive data are used to provide vertical profiles of temperature and salinity as an input to the model. Precipitation and evaporation data are obtained from TRMM measurements and ERA5 reanalysis, respectively. Subsets of IBTrACKS, GHRSST, ISAS20, TRMM and ERA5 data specific to domain of a TC&#8217;s wake were produced by the Centre de Recherche et d'Exploitation Satellitaire (CERSAT), at IFREMER, Plouzane (France) for ESA funded project MAXSS (Marine Atmosphere eXtreme Satellite Synergy). Model simulations are consistent with the observations and provide a deeper insight in the physics of relationship between SST and SSS anomalies in TC wakes. On the basis of analysis of the observations and model results, a semi-empirical expressions to predict SSS and SST anomalies using TC parameters (radius, wind speed and translation velocity) and prestorm stratification are suggested.</p><p>The work was supported by the Russian Science Foundation through the Project No. 21-47-00038, by Ministry of Science and Education of the Russian Federation under State Assignment No. 0555-2021-0004 at MHI RAS, and State Assi<span>gnment No. 0763-2020-0005 at RSHU (P.P. and V.K.). T</span><span>he ESA/MAXSS project support is also gratefully acknowledged (N.R. and B.C.).</span></p>
