The French Sea Surface Salinity (SSS) Observation Service Gaël Alory [email protected] + Thierry Delcroix, Denis Diverrès, David Varillon, Philippe Téchiné, Stéphane Jacquin, Sophie Cravatte, Rosemary Morrow, Yves Gouriou, Gilles Reverdin...
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The French Sea Surface Salinity
(SSS) Observation Service Gaël Alory
+ 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
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