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!

Creation of the Satellite & In Situ Salinity Working Group: Understanding Stratification and Sub-Footprint Processes

Category : Cal/Val, Data, L2, Ocean, Satellite

Following the SMOS-AQUARIUS workshop, Jacqueline Boutin and Yi Chao have worked on defining the terms of reference for the SMOS AQUARIUS working group they co-chair, the:
‘Satellite & In Situ Salinity Working Group: Understanding Stratification and Sub-Footprint Processes’ (SISS in short).

With the help of Olga Hernandez, a mailing list and dedicated website have been established :
www.locean-ipsl.upmc.fr/SISS). The idea being that anyone can use the mailing list to exchange on SISS topics etc
You will find the charges or terms of reference on the web page!
So why wait: visit!

Large scale SSS contrasts detected by SMOS and in situ SSS analysis in the tropical Pacific and Indian Oceans

Category : CATDS, Cal/Val, L2, Ocean

Recent results from LOCEAN  team

Variability in the tropical Pacific and Indian Oceans between 2010 and 2011 is very large linked to the ending 2009-2010 El Nino, 2010 strong La Niña and 2011 weak La Niña events, and to negative Indian Ocean Dipole (IOD) in 2010 (see Figure below).

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figure1 Time series of SST anomalies in the four Niño regions from http://www.cpc.ncep.noaa.gov/data/indices/sstoi.indices in 2010-2011 and corresponding Indian Ocean Dipole (IOD) Index (SST difference between eastern and western equatorial Indian Ocean) from the Australian bureau of Meteorology.

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Large scale SSS variability is very consistently observed on SMOS SSS maps (1) compared with ISAS SSS maps (2) derived from in situ (ARGO floats and ship data) measurements, as seen on the film. SMOS anomalies are often more contrasted than ISAS anomalies due to fresher SMOS SSS in fresh regions associated with rain (Boutin et al., 2013). Signal is much noisier from January to May due to worse SMOS SSS quality during commissioning phase in January-May 2010, but nevertheless spatial structures of anomalies remain very consistent with ISAS maps.

(1) SMOS SSS maps are generated using ESA reprocessing version 5 as described in J. Boutin, N. Martin, G. Reverdin, X. Yin and F. Gaillard, Sea surface freshening inferred from
SMOS and ARGO salinity: Impact of rain, Ocean Sci., 9, 183-192, doi:10.5194/os-9-183-2013, 2013.