Upper ocean salinity stratification in the Tropics as derived from N 2 (the buoyancy frequency) Dr Christophe Maes Laboratoire de Physique des Océans - LPO Institut de Recherche pour le Développement – IRD - November OUTLINE General context and Motivations Data & Method N 2 stratification results Conclusion & Perspectives Maes, C., and T. J. O’Kane (2014), Seasonal variations of the upper ocean salinity stratification in the Tropics, J. Geophys. Res. Oceans, 119, doi: /2013JC

GENERAL CONTEXT Why care about the salinity stratification in the Tropics? -Influence directly the Sea Surface Salinity field as seen by satellite missions like SMOS and Aquarius (e.g., Asher et al. 2014), -Modify the momentum and heat budgets of the mixed layer, and consequently it affects the surface conditions and air-sea interactions (& climatic modes – see next), -Participate to the interannual salinity anomalies on isopycnal surfaces (like 25.5 kg/m3) with time scales of 2 to 3 years in the Southern Pacific (Kolodziejczyk and Gaillard 2012) or along the ocean storm track connecting the subtropical regions with the Tropics (O’Kane et al. 2014).

MOTIVATIONS How salinity stratification may change ENSO or mean state? With N 2 (T,S) With N 2 (T) Previously demonstrated that Barrier Layer effect has the potential to impact the onset of ENSO, and the heat build-up in pre-ENSO periods. It has also the potential to impact the mean state and the variability like ENSO From Maes and Belamari (SOLA, 2011) Mean state of the Mixed Layer Depth

MOTIVATIONS Impact on ENSO forecasts? (Scientific Reports published on 29 October 2014)

DATA & METHOD What product do we have to consider to determine the salinity stratification at the global scales?

DATA & METHOD What product do we have to consider to determine the salinity stratification at the global scales? SSS ( Qu et al )

DATA & METHOD - The model is the Australian Community Climate Earth System Simulator-Ocean (ACCESS-O) configuration of the GFDL MOM4p1 ocean-ice code Grid: tripolar Arctic north of 65°N with equatorial refinement to 1/3° between 10°S and 10°N and a Mercator (cosine dependent) implementation for the Southern Hemisphere, (¼° at 78°S to 1° at 30°S) 50 levels over m with a 10m in 0–200m to about 333m for the abyssal ocean - This study employ atmospheric fields from the CORE.v2 (Griffies et al. 2009) for global ocean–ice modelling - The model is integrated with a modified variant of the BODAS ensemble optimal interpolation (EnOI) data assimilation system to produce an ocean reanalysis for the period 1990–2007 (Oke et al. 2008) Data considered: eXpendable BathyThermograph (XBT), Conductivity-Temperature- Depth (CTD) and Argo and satellite SST Time window: 14-days Ocean reanalysis system considering in situ data

DATA & METHOD Ocean reanalysis system with in situ data Time evolution for background salinity innovations (difference between 1 month forecast and verifying analysis) through the upper 1000m along the Pacific averaged over 30S-30N degrees of latitude about the equator. Significant reduction in forecast errors occur post 2004 indicating sufficient Argo data to constrain the model.

DATA & METHOD We consider hereafter the Ocean Salinity Stratification (OSS) as: Methodology: The formalism of Ocean Salinity Stratification (OSS)

N2 STRATIFICATION RESULTS Atl. Indian

N2 STRATIFICATION RESULTS

March Sept. Jan Aug (34.4 and 35.2 for SSS)(34. and 35.5 for SSS)

N2 STRATIFICATION RESULTS

(de Boyer Montegut et al. 2007) Barrier layer m OSS from N 2 (S) cph How OSS compares to the formalism of the barrier layer? JULY

N2 STRATIFICATION RESULTS 5°N-5°S BAND WARM POOL (150°E-170°W) INDIAN SECTOR ATLANTIC SECTOR

N2 STRATIFICATION RESULTS 28°C24°C OSS seasonal cycle at the equator

N2 STRATIFICATION RESULTS 28°C24°C >5000 profiles > profiles OSS seasonal cycle at the equator

CONCLUSION AND PERSPECTIVES * The Ocean Salinity Stratification (stabilizing part of N 2 that is due to salinity only) is a natural variable of ocean dynamics, * In regions where the stratification of temperature and salinity differs between the base of the mixed layer and the top of the pycnocline, both the OSS and Barrier Layer (BLT) agree relatively well; however, unlike the BLT the OSS can be significant in regions where both T and S are mixed over the same depth The contribution of the OSS to N 2 could be as large as 40-50% of the contribution of the thermal stratification at the seasonal timescales, * The seasonal variability of the OSS is mainly dominated by the annual first harmonics, * Many regions of the Tropics exhibit a tight scatter relationship with SSS

Deploy, deploy… SMOS-Mission Oceanographic Data Exploitation SMOS-MODE SMOS-MODE supports the network of SMOS ocean-related R&D

SMOS-MODE (SMOS-Mission Oceanographic Data Exploitation) SMOS-MODE supports the network of SMOS ocean-related R&D Meetings Workshops Training school Short Term Scientific Missions Overall Aim: To coordinate pan-European teams to define common protocols to produce high-level salinity maps and related products, and broaden expertise in their use for operational applications. To bridge remote sensing and applications communities 21 countries represented. Co-chairs: Antonio Turiel, SMOS Barcelona Expert Centre (SMOS-BEC), Barcelona, Spain Nicolas Reul, IFREMER, Brest, France Last meeting during 2 nd SMOS Science Conference

ADDITIONAL MATERIAL

CONCLUSION AND PERSPECTIVES Time variations of the OSS (in cph) at the equator El Niño

N2 STRATIFICATION RESULTS Salinity sections

N2 STRATIFICATION RESULTS

30-yr mean (PERT) SSS SST MLD 30-yr mean (CTRL) (Maes and Belamari, SOLA 2011)