The French Sea Surface Salinity

(SSS) Observation Service Gaël Alory

gael.alory@legos.obs-mip.fr

+ Thierry Delcroix, Denis Diverrès, David Varillon, Philippe Téchiné,

Stéphane Jacquin, Sophie Cravatte, Rosemary Morrow, Yves Gouriou,

Gilles Reverdin...

• Why measuring Sea Surface Salinity?

• The French SSS network: how it works

• Data users and SSS-based research in the

Atlantic

The French Sea Surface Salinity

(SSS) Observation Service

Salinity & Water Cycle

• SSS: signature of global hydrological cycle at

ocean-atmosphere interface (75% of exchanges)

-200 -100 0 100 200

Water flux (1012 m3/yr)

evaporation

- precipitation

cm/yr

Sea Surface

Salinity

30.0 33.0 35.0 36.0 36.5 37.0 37.5 39.0 -200 -100 0 100 200

pss

Salinity & Ocean Circulation

• salinity triggers deep

convection in North

Atlantic through its

influence on density

thermohaline circulation (~1000 years) Salinity trends 1955-1998

Boyer et al., 2005

1500

latitude 80S 40S EQ 40N 80N

500

pro

fondeur

(m)

0

200

-

+

3000 Warm surface current

Cold deep current

Gulf Stream

• possible slowdown of

thermohaline circulation due to

global warming (ice melting)

Salinity & Climate Variability

• salt stratification can enhance ocean-atmosphere

coupling in the tropics (El Niño, cyclones...)

Barrier layer thickness

de Boyer Montegut et al., 2007; Mignot et al., 2007

Measuring Sea Surface Salinity

from Voluntary Observing Ships (VOS)

M/V Brazza, 1948-1964

M/V Tahitien, 1970 …

The early French (ORSTOM) contribution to VOS

Accuracy &

salty bias ~ 0.1

Towards an integrated network

(Deep Sea Research, 1996)

• 2002 : The French Sea Surface Salinity Observation Service (IRD, CNAP, CNES, CNRS, IFREMER, INSU, IPEV, OMP)

• 2010: integrated in the SOERE CTDO2

Accuracy

~ 0.02

Data distribution in time

• 12 VOS are presently equipped with TSG (38 since 1992)

• The network is submitted to commercial traffic

Ships transmitting in real time since 1998 Evolution of collected hourly data

Data distribution in space

Data freely available to the scientific community

Real time: www.coriolis.eu.org Delayed time + products: www.legos.obs-mip.fr/observations/sss

Main contribution

to the global

network of

underway data

World Ocean Atlas 1998-2009

1°x1° nobs Coriolis-GOSUD 2012

Coriolis-GOSUD 2012

Technical support from IRD (Brest, Nouméa)

• installation and maintenance of TSG instruments (Le Havre/ Nouméa)

• salinometer analysis of daily water samples for TSG correction

Data flux

time resolution QC transmission

delay

Real time Delayed time

1 hour

5 min

automatic

manual

1 day

1 year

SO-SSS

Real time data flux and QC

TSG trajectories from

17/10/12 to 31/10/12

• real time transmission with automatic alert in case of bad data

• monitoring tools through a restricted web site

• flagged, uncorrected hourly data

-5°C<SST<35°C 1<SSS<50

| SST – SSTReynolds | < 3°C

| SSS – SSSWOA | < 2

Automatic QC:

Good data if...

SSS

SST

LOCEAN Paris

Colocated Argo data

Delayed time data flux and QC

Individual « trip » files in .nc GOSUD format on SO-SSS website

IRD Brest/Nouméa Atlantic/Pacific

TSG QC level 1: attribution of QC flags

Analysis of daily water samples

LEGOS Toulouse

TSG QC niveau 2: Correction with samples/ARGO

Dedicated Matlab

tool: TSGQC

QC code applied by comparison with

SSS/SST climatology, ship speed,

problems identified onboard...

correction of drifts and

shifts (biofouling, shell

pieces...) by linear fit or

median filter of

external data - TSG

differences

Same processing now

applied to research ships

Data users

• Operational

oceanography

• Calibration/validation of

new satellite data

• Gridded Pacific and

Atlantic data products

(1°x1°x1 month) available

for research

accuracy: 0.1-0.2 pss (200 km, monthly)

SMOS (nov 2009) Aquarius (juin 2011)

1970-2009 update of

Reverdin et al., 2007

A few M2 studies with focus on SSS

• SSS and monsoon jump (Sadem 2010)

• Impact of rivers on SSS (Mama 2011)

• SSS and sea color (Ngo Ibiih Lapee 2012)

• Water cycle in GIEC climate models (Panassa 2012)

+ PhD C. Da-Allada (2013) :

Mixed layer salinity budget in Gulf of Guinea

SSS: seasonal cycle

SSS: seasonal variations due to rivers

2010

CDM

Obs

SSS: seasonal variations

SSS

Model

Influence of Congo river on interannual climate

• Congo river runoff can influence SSS and, through mixed

layer depth, SST and ocean-atmosphere interaction

Materia et al., 2012

Interannual anomalies of Congo runoff (Apr-May)

Composite anomaly (June) SSS SST

strong runoff

weak runoff

Long-term trends in SSS

• SSS reflects the expected enhancement of water cycle

• The Atlantic-Pacific SSS contrast is increasing

Terray et al., 2012

SSS trend (1970-2002) Precipitation-Evaporation trend

mean SSS

Network extension project in the Gulf of Guinea

• Preliminary steps for a new TSG line : Grimaldi West

Africa/Southern Express (4 ships, turn-around 45 days)

• Measurements in Congo/Niger plumes, cold tongue, upwellings...

Dakar

Conakry

Luanda

Pointe-Noire

Douala