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Discussion on the impact of physical data
assimilation
Assessment of global hindcast and real-time
biogeochemical systems designed at
Mercator Ocean:
PERRUCHE1 C., Y. DRILLET1, E. GUTKNECHT1, C., J. PAUL1,
E. GREINER2, M. GEHLEN3
1 Mercator Océan, France 2 CLS, France 3 LSCE, France
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Introduction
Copernicus Marine Service
Copernicus: EU program dedicated to Earth Observation and Monitoring
- Collect satellite and in situ Data
- Turn these data into information through services divided in 6 thematic
streams: atmosphere, land, marine and climate monitoring, emergency
management, security
Marine service coordinated by
Mercator Ocean
Mercator Ocean in charge of the
Global Analysis and Forecast
product in the catalogue
physical state
biogeochemical state
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
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Introduction
The PISCES model
Aumont et al. (2015)
- 24 prognostic variables, 5 limiting nutrients, 2
phytoplankton and zooplankton species, 3 detritus
compartments
- Redfieldian model (constant C/N/P ratio)
- variable C / Chl, C/Fe, C/Si ratios
- Carbon and oxygen cycles
- No feedback of chlorophyll concentration on
temperature profile
- Monod model (Monod, 1942): no diurnal cycle
- Balance between external inputs and losts in the
sediments after particule sinking
- External inputs: rivers (Fe, Si, and P), dust (Fe, Si
and P) and sedimentary iron (friction)
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Introduction
GLOBAL ¼°
REAL TIME
- NEMO3.2
- Spatial resolution: ¼°
- 50 vertical levels
- Initial conditions: WOA et GLODAP
- 2007 – real time
- Offline coupling
- Ocean forcing: operational analyses ¼°
daily (with physical data assimilation of
SST, SLA data and in situ T et S)
- Atmospheric forcing: operational analyses
ECMWF bulk CORE
- Anthropogenic Carbon (Masarie and Tans,
1995)
HINDCAST (1998 – 2014)
- NEMO3.5
- Spatial resolution: ¼°
- 75 vertical levels
- Initial conditions: WOA et GLODAP
- 1992 – 2014 (disseminated from 1998 on)
- Offline coupling
- Ocean forcing: free hindcast (1/4°) daily (no
assimilation)
- Atmospheric forcing: ERA-INTERIM bulk
CORE
- Anthropogenic Carbon (Masarie and Tans,
1995)
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Outputs:
Weekly means
each week: hindcast,
nowcast, forecast
Outputs:
Daily and monthly
means
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Good accordance in large scale structures
CHL
Air-Sea CO2
flux
(gC/m2/yr)
Globcolour DATA 2014
Takahashi clim
MODEL 2014
MODEL clim 1998 - 2014
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Seasonal cycle in North Atlantic
CHL
Globcolour
Daily
CHL Model
Daily
MLD Model
Daily
2002 2010 - Seasonal cycle correctly reproduced
- Secondary bloom in autumn during
the mixed layer deepening
(nutrient limitation)
- Main bloom in spring during the
mixed layer shallowing (light
limitation)
- In summer, the mixed layer is very
shallow, and there is low primary
production
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Seasonal cycle in North Atlantic
CHL
Globcolour
Daily
CHL Model
Daily
MLD Model
Daily
2002 2010 - Almost no chlorophyll in modelled
oligotrophic gyre (in data ~0.05 mg/m3)
- Beginning of the bloom too early (lag of
one month)
Mean chl
Median chl
Percentile
80 chl
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
2002
- The bloom is propagating too fast northward
- The bloom is not lasting enough in summer
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Data
Model
Seasonal cycle in North Atlantic
CHL
Globcolour
Daily
CHL Model
Daily
MLD Model
Daily
2002 2010
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
- Almost no chlorophyll in modelled
oligotroph gyres (in data ~0.05 mg/m3)
- Beginning of the bloom too early (lag of
one month)
- The bloom is propagating too fast northward
- The bloom is not lasting enough in summer
- Restratification: not a continuous process, successive
shallowing periods interrupted by periods of deepening:
phytoplankton react instantaneously
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Seasonal cycle in North Atlantic
CHL
Globcolour
Daily
CHL Model
Daily
MLD Model
Daily
2002 2010
- Strong interannual
variability of the
bloom timing
- Earlier bloom in
2010
- Stronger bloom in
2002
- Well reproduced by
the model
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Interannual variability of the bloom in North Atl.
North-South spatial variability of the seasonal
bloom triggering : well reproduced by the model
local process: due to the variability of the ML
deepening in winter
CHL
Globcolour
Monthly
CHL
Model
Monthly
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
GlobColour Model
Good representation of the two 1st modes of variability (spatial signature and time series)
Clear correlation with ENSO index (Thomas et al., 2012)
Mo
de
#1
Mo
de
#2
Interannual variability in the Pacific Ocean
EOF decomposition of chlorophyll (1998 – 2014)
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Anomaly Chl 40S-40N (detrended and deseasonalized)
ENSO index (MEI) x(-1)
Distribution of OMZs (Oxygen Minimum Zone)
MODEL clim 1998 - 2014 CLIM WOA 2013
O2 min
Thickness of
the hypoxic
layer
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
Coherency between model and climatology
Year 1995: Annual mean at the equator
ASSIM
WITH ASSIM
Stronger equatorial
upwelling in average
Subsurface upwelling
between 200 and 1000 m
depth
More variability in
equatorial vertical velocities
The assimilation system:
• Kalman filter with SEEK formulation
• 3D-Var bias correction in temperature and salinity for the slowly evolving large scales
Data assimilated: SST, SLA, In situ temperature and salinity
Both
with IAU
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Mean W
(m/day)
Impact of assimilation
Equatorial Upwelling
NO ASSIM
Std W
(m/day)
NO ASSIM ASSIM
DATA
Year 1995: Annual mean of chlorophyll concentration
Tropical band much larger with ASSIM
No warmpool anymore
Still a work in progress
Next system with a corrected MSSH
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Impact of assimilation
Equatorial Upwelling
Chl Globcolour 8days OSS2015 product (L4), superimposed modelled SSH with assimilation
Gulf Stream
Mid-august
2000
Agulhas current
Mid-september
2000
Good accordance
between the
modelled front of
SSH and the
chlorophyll
distribution: the front
acts as a natural
boundary from
which eddies are
detaching
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Impact of assimilation
Positioning of fine-scale structures
Modelled Chl (daily), superimposed modelled SSH with assimilation
NO ASSIM
January, 15th
ASSIM
January, 15th
Better positioning of
the front with
assimilation of
physical data
Boundary between
oligotrophic gyre and
subpolar gyre more
zonal
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Impact of assimilation
Positioning of fine-scale structures
Conclusion & Perspectives
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
• Adjustement of the equatorial upwelling to physical data assimilation: Still work-in-progress, need to disentangle the effect of each parameter assimilation (T, S, SSH)
• The assimilation clearly allows a better positioning of frontal and mesoscale structures
• September 2016: In Copernicus, new operational system forced by the GLOBAL 1/12° operational analysis (coarsening offline towards ¼°)
• Next simulation NEMO3.6: Start from the 20th century simulation realized in the ERACLIM2 project (cf talk of P. Laloyaux)
• Assimilation of ocean color data for 2017 (see poster J. Lamouroux)
22/07/2016 Name of the event, Place
The end !
GLOBAL ¼°: Next systems
• September 2016: In Copernicus, new operational system
forced by the GLOBAL 1/12° operational analysis
(coarsening offline towards ¼°)
• Next simulation NEMO3.6: Start from the 20th century
simulation realized in the ERACLIM2 project: see talk of
P. Laloyaux (NEMO3.6, 1°, 130 years of spin-up)
• Assimilation of ocean color data for 2017 (see poster J.
Lamouroux)
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
ANIMATION
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ANIMATION
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Impact of assimilation: better positionning of
fronts and mesoscale structures
Mo
de
#1
Mo
de
#2
Modèle GlobColour
Anomaly Chl 40S-40N x (-1)
SST anomaly
Good representation of the two 1st modes of variability (spatial signature and time series)
Good correlation with ENSO index (Thomas et al., 2012)
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Interannual variability
EOF decomposition of chlorophyll
Assessment HINDCAST
GLOBAL ¼°: Interannual simulation
NO ASSIM
April, 15th
ASSIM
April, 15th
Modeled Chl (daily), superimposed modeled SSH with assimilation
Better positionning
of the front with
assimilation of
physical data
12/07/2016 GODAE Joint MEAP-DA-TT, Santa Cruz
Impact of assimilation
Positionning of fine-scale structures
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