Monitoring the Ocean State
from the Observations
Stéphanie Guinehut
Sandrine Mulet
Marie-Hélène Rio
Gilles Larnicol
Anne-Lise Dhomps
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Introduction
 Our approach :
– Consists of estimating 3D-thermohaline and current fields using ONLY observations
and statistical methods
– Represents a complementary approach to the one developed by forecasting
centers – based on model/assimilation techniques
– “Observation based” component of the Global MyOcean Monitoring and Forecasting
Center lead by Mercator Océan
 Previous studies have shown the capability of such approaches :
– In producing reliable ocean state estimates (Guinehut et al., 2004; Larnicol et al.,
2006)
– In analyzing the contribution and complementarities of the different observing
systems (in-situ vs. remote-sensing) (2nd GODAE OSE Workshop, 2009)
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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The principle
The observations
The method
Altimeter, SST, winds
Guinehut et al., 2004
Guinehut et al., 2006
Larnicol et al., 2006
Rio et al., 2011
Global 3D Ocean State
[T,S,U,V,H]
Weekly – 1993-2009
[0-1500m] 24 levels
[1/3°]
 MyOcean V1 RT/RAN
+ MDT
estimate
T/S profiles, surface drifters
The products
Intercomparison with independent data sets
and model simulations
Analysis of the ocean variability
Observing System Evaluation
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Global T/S  Armor3D - Method
1
vertical projection of satellite data (SLA, SST)
T(x,y,z,t) = (x,y,z,t).SLAsteric + (x,y,z,t).SST’ + Tclim (x,y,z,t)
S(x,y,z,t) = ’(x,y,z,t).SLAsteric
+ Sclim (x,y,z,t)
2
combination of synthetic and in-situ profiles
synthetic T(z),
S(z)
SLA, SST
multiple linear
regression
1
optimal
interpolation
2
in-situ T(z),
S(z)
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Armor3D T(z),
S(z)
Armor3D - 1993-2009 reanalysis
SSALTO-DUACS MSLA 1/3° weekly DT - 04/07/2007
NCEP Reynolds OI-SST 1/4° daily - 04/07/2007
Arivo climatology – July – T at 100 m
Synthetic T’ – at 100m
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Armor3D - 1993-2009 reanalysis
Synthetic T’ – at 100m
In-situ observations – Coriolis data center
Argo T’
Armor3D T’
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Armor3D - Hydrographic variability patterns
 Temperature variability over the 2004-2008 period (global zonal averaged) :
Synthetic
ARMOR3D
SCRIPPS
SODA 2.2.4
2004
2005
 2006
Very similar results for Synthetic/ARMOR3D/SCRIPPS
 No bias introduced by the method
 Very promising to study the variability of the 1993-2000 period
2007
which suffers from poor in-situ measurements coverage
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
2008
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Hydrographic variability patterns
 Temperature variability from 1993 to 2008 (global zonal averaged) :
1993
2001
1997
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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2005
2008
Armor3D - Hydrographic variability patterns
 Salinity variability over the 2004-2008 period (global zonal averaged) :
Synthetic
SCRIPPS
ARMOR3D
2004
2005
2006
2007
 Argo obs sys mandatory
2008
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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SODA 2.2.4
Global U/V/H  Surcouf3D - Method
Surcouf :
Field of absolute geostrophic surface currents
weekly - 1/3°
Armor3D :
3D T/S fields
weekly - 1/3° - [0-1500]m
g
u (z  z i )  u (z  0) 
ρf

z0 y' (z)dz
g
f

z0 x' (z)dz
v(z  z i )  v(z  0) 
zi
zi
Surcouf3D
3D geostrophic current fields
weekly (1993-2008)
1/3° - 24 levels from 0 to1500m
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - Comparison with model outputs
 Vertical section at 60°W, in 2006
Surcouf3D at 500m
*geost. current with level of no motion at 1500m
Armor3D*
Surcouf3D
GLORYS at 500m
GLORYS
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - Validation of 1000-m currents
 Global statistics over the Atlantic outside the equateur (10°S-10°N)
Comparison between 3 different methods (Surcouf3D, GLORYS, Armor3D) and in-situ
observations (ANDRO) at 1000 m over the 2006/2007 period (Taylor, 2001)
Meridional component
● SURCOUF3D (weekly, 1/3°)
▲GLORYS = Mercator-Ocean reanalysis
Standard deviation (cm/s)
(weekly, 1/4°)
Ferry et al., 2010
skill score
♦ Armor3D = geostrophic current with
level of no-motion at 1500m
(weekly, 1/3°)
● ANDRO = 1000-m currents from
drifting velocities from the Argo floats
(≈10days, ≈50/100km)
Ollitraut et al, 2010
Standard deviation (cm/s)
 Results
are very similar for the zonal component
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - Validation
 Comparison with GoodHope VM-ADCP observations from
14/02–17/03/2008
Meridional velocities (cm/s)
Zonal velocities (cm/s)
ADCP obs courtesy
of S. Speich
 Good correlation with
independent in-situ obs.
 Other time series to be
compared
14/02/08
17/03/2008
SURCOUF3D
ADCP
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - Validation
 Comparison with RAPID current-meters in the
Western boundary current off the Bahamas from
April 2004 to April 2005
Florida
Africa
26.5°North
76.5°West
SURCOUF3D
RAPID (current meters)
GLORYS
 Good correlation with
independent obs., and with
GLORYS
 Importance of in-situ T/S
profiles obs at depth for the
inversion of the current
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - AMOC variability at 25°N
 Comparison with Bryden et al, 2005 (section at 24.5° from Africa to 73°W and at 26.5°N off Bahamas)
Floride Strait Transport
from electrical cable
(Bryden et al,2005)
AMOC = Geost + Ekman + Florida
(Surcouf3D, Bryden et al., 2005)
Ekman Transport from wind stress ERAInterim
Geostrophic Transport from 75°W to
15°W and from the surface to 1000m
(Surcouf3D, Bryden et al., 2005)
Very consistent with Bryden et al, 2005
Hight inter-annual variability
Hard to distinguish a long-term trend
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Surcouf3D - AMOC variability at 26.5°N
 Comparison with RAPID and GLORYS from April 2004 to December 2007
(monthly means + 12-month filtered)
SURCOUF3D
RAPID
GLORYS
 Similar seasonal cycle
 Amplitude differences
~ 10%
 Higher variability in
Surcouf than in Glorys
that has to be further
analyzed
GODAE OceanView-GSOP-CLIVAR workshop - 13-17 June 2011
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Conclusions / Perspectives
Armor3D/Surcouf3D tools are very useful :
to perform intercomparison exercices
to study the interannual variability of the hydrographic patterns, the AMOC …
Intercomparison studies will be continued between Armor3D and Surcouf3D
and MyOcean global reanalysis
Further study the ocean state (T/S variability, MOC, Heat/Salt transport) in
key regions and for the 1993-2009 periods
Armor3D/Surcouf3D reanalysis are distributed as part of MyOcean
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…
…
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