A SSS trip from the surface to the thermocline…

Category : L2, Non classé, Ocean

By Christophe Maes

Retrievals of the Sea Surface Salinity from space-borne mission like SMOS or Aquarius SAC-D provide for the first time an essential variable in the determination of ocean mass. If the field will reveal a lot of new signal at the surface its influence on the ocean dynamics is even more important at depths where it participates to the stratification of the water column. Concomitant with temperature profiles, reliable in situ observations of salinity at depth are now available at the global ocean scales. Above the main pycnocline (50-250m in the Tropics), Maes and O’Kane (2014) have recently shown that the stabilizing effect due to salinity could be isolated from its thermal counterpart by separating its role in the computation of the buoyancy frequency. In addition, relationships between such salinity stratification at depths and the SSS are shown to be well defined and quasi-linear in the tropics (see figure), providing some indication that in the future, analyses that consider both satellite surface salinity measurements at the surface and vertical profiles at depth will result in a better determination of the role of the salinity stratification in climate prediction systems.

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Maes, C., and T. J. O’Kane (2014), Seasonal variations of the upper ocean salinity stratification in the Tropics, J. Geophys. Res. Oceans, 119, 1706–1722, doi:10.1002/2013JC009366.

SMOS and Hurricane tracking!

Category : CATDS, L2, Ocean

Nicolas Reul and his team have been busy finding ways to better track, monitor, tropical storms and hurricane (high wind speed) from SMOS data as depicted in several previous posts on this very blog.

Following this, in the framework of the ESA STSE- SMOS+STORM Evolution project a more exhaustive study was initiated as shown on their page.

Just to whet your appetite here is a lengthy but interesting animation showing the wind speed retrievals (click on the picture to get it started) over the Pacific ocean

2012_Pacirfic_Hurricane_Season_animationSMOS

Using SMOS to analyze the variability of the South Pacific Sea Surface Salinity maximum

Category : L3, Ocean

By Jacqueline BOUTIN

Understanding the variability of high-salinity surface waters, as shown in Fig. 1 for the south-eastern tropical Pacific, is important to improve our interpretation of climate and hydrological cycle changes at different time scales. SMOS CATDS-CEC LOCEAN SSS products have been used , in complement to Voluntary Observing Ships (VOS) thermo-salinograph data obtained from the French SSS Observation Service, to validate and understand the seasonal variability of the South Pacific Sea Surface Salinity maximum simulated by an ocean general circulation model with no direct SSS relaxation.

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Fig. 1. Mean 1990-2011 modelled mixed-layer salinity. The blue lines represent the Matisse Ship routes of 2010 and 2011.

All products reveal a consistent seasonal cycle of the displacement of the 36-isohaline barycenter (Fig. 2; about +/-400 km in longitude) in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity respectively associated with changes in precipitation and evaporation.

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Fig.2. Location of isohaline 36 (simulated) and of its barycentre (dots: model; stars: SMOS) for various months (colors).

The SSS from 8 VOS transects compare remarkably well with collocated SMOS SSS averaged over 100km, 18 days (std difference=0.2), as exemplified in Fig. 3 along a shipping track running from New Zealand to Panama ; the comparison with simulated SSS is slightly degraded due to a few degrees latitudinal shift of the simulated SSS maximum (std difference=0.26).

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Fig. 3. Example of comparison between SMOS (dots), VOS (straight line), and simulated (dashed line) SSS as a function of latitude.

Model results and in situ measurements further indicate a low frequency westward shift of the 36-isohaline barycenter (about 1400 km since 1992) that could not be linked to ENSO and may reflect the signature of decadal changes and/or global warming.

Details can be found in: Hasson, A., T. Delcroix, and J. Boutin (2013), Formation and variability of the South Pacific Sea Surface Salinity maximum in recent decades, J. Geophys. Res. Oceans, 118, doi:10.1002/jgrc.20367.

Smos Training course II

Category : Cal/Val, Data, L1, L2, L3

The second session of the SMOS training course at CESBIO is now over. We had 16 trainees from 10 different countries (from China to the US (E-W) and from Canada to Yemen (N-S)

In spite of the weather, all went well. We had also the good fortune to have the presence of our two mission managers (Susanne Mecklenburg and Carole Larigauderie) as well as a visit of Guillermo Buenadicha and his replacement at ESAC. We were also very lucky to have Ali Mahmoodi from Array (level 2 SM) for the training.

panoramique1_650panoramique2_650The SMOS training team covered all aspects of the mission from system to data use and applications. experts came from again many parts of the world (from Sweden to Spain and from Canada to India!

It was a very nice experience and it may be hoped that all participants (trainees and teachers) feel more « educated » after a dense week!