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Mercator Ocean

Components of systems

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The operational forecasting systems developed by Mercator Ocean are based on ocean models described by primitive equations. They assimilate in real-time ocean measurements from satellite and in situ observation systems. Currently only the physical models assimilate observations. Work is now being done on marine biogeochemistry which should make it possible to assimilate observations of water colour, among others, in the near future.

The three main system components are:

  • input data (atmospheric forcing and observations)
  • assimilation data
  • modelling
Input dataAssimilationModelling

Input data in Mercator Ocean systems

The operational Mercator Ocean systems receive input from many data sources for operational requirements (real-time data) but also for reanalysis (delayed time data). These data sources are also used to validate systems.

Real-time data

Atmospheric forcing

Data• The wind vector at 10m in m.s-1 (noted: Uair)
• Air temperature at 2m in °C (noted: Tair)
• Relative humidity in the air at 2m in % (noted: RH)
• Surface atmospheric pressure in Pa (noted: Ps)
• Incident solar flux in W.m-2(noted: radsolaire)
• Incident infrared flux in W.m-2 (noted: radir)
• Precipitation flux in mm.s-1 (noted: P)
Resolution• Real-time analysis and forecasting: 34, T1279 0.125°x0.125°
• ERAINTERIM reanalysis: 6h, T255, 80km
Data source• Atmospheric forecasting model
Data center• European Centre for Medium-Range Weather Forecasts (ECMWF)

Assimilated data

Satellite data

Sea Level Anomaly (SLA)

Resolution• Daily updating
• Along-track data
Use• Assimilation: along-track data are assimilated in all Mercator operational forecasting systems.
• Along-track data are also used for validation purposes.
Data source• AVISO
Data center• Ssalto/Duacs

Sea Surface Temperature (SST)

Resolution• Temporal: daily (AVHRR SST, RTG-SST and OSTIA)
• Spatial: 0,5° for RTG-SST (re-interpolated on model grids), 1° for AVHRR SST, 0.05° for SST OSTIA.
Use• AVHRR SST is assimilated in Mercator systems.
• All the SSTs are used for validation purposes.
Data source• Objective analyses from satellite and in situ data. The satellites are NOAA/AVHRR, but also ENVISAT, MSG, SSM/I (for sea ice), AQUA, TRMM. In situ data are: drifting buoys, ships, data available via the Global Transmission System (GTS or SMT).
Data center• RTG-SST (Real Time Global SST) by Thiebaut et al. 2003, produced by NOAA/NCEP, distributed by ECMWF.
• SST AVHRR Pathfinder produced and distributed by NOAA/NCEP.
• SST OSTIA produced by the UK Met Office OSI TAC CMEMS.

In situ data TAC CMEMS

In Situ Sea Surface Temperature

Resolution• Temporal: variable measurements, daily data file
• Spatial: variable
Use• Assimilated in Mercator systems
• Used for validation purposes
Data sourceThermosalinographs (TSG) and drifting buoys
Data centerCoriolis, in-situ TAC CMEMS

Temperature/Salinity Profiles

Resolution• Temporal: variable measurements, daily data file.
• Spatial: variable
Use• Argo TAO/Pirata moorings (regular measurements)
• CTD, XBT, Gliders, Thermosalinographs (TSG - one-off measurements)
Data source• Argo TAO/Pirata moorings (regular measurements)
• CTD, XBT, Gliders, Thermosalinographs (TSG - one-off measurements)
Data centerCoriolis, in-situ TAC CMEMS

Surface Currents

Resolution• Temporal: measurements every 10 hours, weekly file containing data from the previous 10 days
• Spatial: variable
Use• The surface currents are deduced from the trajectories of drifting buoys. These data are used to validate the data source.
Data source• Drifting buoys
Data center• Coriolis, in-situ TAC CMEMS

Data that remain contact over time

Climatology

Levitus

Data• T(0-1500m), S(0-1500m) + monthly-mean statistics
• T(0-5500m), S(0-5500m) + seasonal-mean statistics
• T(0-5500m), S(0-5500m) + annual-mean statistics
Time period coveredCentury (1900-2000)
Spatial resolution1°x1°
Geographic coverageGlobal
Data CentreNOAA/NODC

Medatlas

Data• T(0-4000m), S(0-4000m) + monthly-mean statistics
• T(0-4000m), S(0-4000m) + seasonal-mean statistics
• T(0-4000m), S(0-4000m) + annual-mean statistics
Time period coveredCentury (1900-2000)
Spatial resolution0.2°x0.2°
Geographic coverageMediterranean
Data CentreEuropean MEDAR/MEDATLAS II project, distributed by SISMER

Bathymetry

ETOPO
Used in:
ORCA1 (PSY2G3R3)
ORCA12-T321
PSY4
ORCA25_LIM-T323
GLORYS2V3
PSY3
PSY2
BIOMER

Spatial resolution1 or 2 minutes angle following the session.
Geographic coverage+90° to -89°58' in latitude et -180W° to +179°58' in longitude.
Data centreNOAA/NGDC

GEBCO
Used in:
ORCA12-T321
PSY4
ORCA25_LIM-T323
GLORYS2V3
PSY3
NEATL36 (IBI36)
NEATL12 (IBIRYSV1R1)
BIOMER

Spatial resolution1 minute angle
Geographical coverageGlobal
Data sourceNOAA/NGDC: General Bathymetric Chart of the Oceans (GEBCO) one minute grid

base10
Used in NEATL36 (IBI36) et NEATL12 (IBIRYSV1R1)

Geographical coverageGlobal
Data sourceNOAA/NGDC : General Bathymetric Chart of the Oceans (GEBCO) one minute grid

 

Illustration credit: ECMWF (extract of a heat flow map)

Illustration credit: Tara Expédition

Illustration credit: NOAA/NODC

Data assimilation in Mercator Ocean systems

Since its creation, the Mercator operational oceanography system has adopted a strategy for incremental improvement of assimilation systems. The initial version of the Mercator Assimilation System (SAM), named SAM1, consisted of an optimal interpolation scheme and was built using SOFA, a reduced-order optimal interpolation software package which had proved its worth for assimilating altimetry data. SAM1 was then improved so that it could assimilate satellite observations (altimetery and surface temperature measurements) and in situ measurements (XBT, profilers). SAM1 then became a multivariate/multidata version used for operational applications which remained in activity until 2007. The SAM2 assimilation system is the second generation of the Mercator Assimilation System. This tool was built around a SEEK (Singular Evolutive Extended Kalman filter) analysis kernel. Compared to the previous version, its main characteristic is its improved modelling of the first-run error by representation of a 3D multivariate error subspace. This made it possible to overcome some known limitations of the SAM1 tool such as its unsuitability for shallow zones and tropical oceans as well as the difficulty of controlling the surface layer efficiently. The formulation of the SEEK/LETKF analysis kernel is a significant innovation due to its extremely efficient processing of large volumes of observation measurements. The first release of this tool also included two major parameterizations: a local approach for the analysis (already used in SAM1) and a variance adaptation scheme which improved the coherence of the error statistics entering the filter. The system in its initial SAM2V1 version was gradually deployed as of 2007 for all of the Mercator operational and reanalysis systems. It then underwent a significant upgrade in 2010-2011 and is henceforth the main structure of the current version.

Moreover, and in order to better constrain the large-scale component solutions, a complementary module was developed to correct large-scale (spatial and temporal) systematic thermohaline bias. It consists of a 3D-Var analysis (available with the SAM tool) of temperature and saline innovations from the last few cycles.

Ocean modelling at Mercator Océan

Mercator Océan develops and uses a range of ocean circulation models based on the NEMO community code   (http://www.nemo-ocean.eu/). This code and some configurations are maintained by the European NEMO consortium. The consortium groups together several national and European bodies including Mercator Océan.

These pages give a description of all the configurations implemented at Mercator Océan.

Résolution spatiale1°1/4°1/12°1/36°
Conf. globalesORCA1
utilisée pour GLO1G4R1

ORCA025_LIM
utilisée pour PSY3V3R3 et les réanalyses GLORYS2

BIOMER
utilisée pour BIOMER


ORCA12
utilisée pour PSY4V3R1
Conf. régionalesNEATL12
utilisée pour MEDRYS

NEATL 36
utilisée pour IBI36

These configurations are developed and maintained by the team of scientists. They may be made available for collaboration with academic research projects. Please send any requests to the users’ office (products@mercator-ocean.fr).

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