GECCO3

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Access

UNRESTRICTED:

View GECCO3 data at LAS: Interpolated fields on a regular 1x1° grid
Get GECCO3 data via FTP: all files of both versions with wget-script
Access GECCO3 data via OPeNDAP: Interpolated fields on a regular 1x1° grid | Fields on the native model grid

RESTRICTED: This link to the data set is only available for a restricted user group. The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account. Please contact ICDC if you would like to access this data from outside the network.

Data access via file system: /data/icdc/ocean_syntheses/GECCO3

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Description

The GECCO3 ocean synthesis is the German contribution of the Estimating the Circulation and Climate of the Ocean project (ECCO, see references) and is the new version of the GECCO2 synthesis already available at ICDC. The synthesis also uses the adjoint method to adjust the initial temperature and salinity in 1948 together with the air temperature, humidity, precipitation, shortwave radiation, and zonal and meridional wind every 10 days to bring the model into consistency with the data, which derive from the EN4.2.1 data base AVISO along track SLA, DTU10 mean sea surface minus GOCO5s geoid to yield the mean dynamic topography, HadISST SST, and the WOA18 climatology. The global model is based on the MITgcm model, has 40 levels, and uses the horizontal and vertical grid of the ocean component of MPI-ESM in the MR/HR configuration, which is with nominally 0.4° resolution eddy-permitting. The bathymetry is also adopted from this configuration. The background atmospheric state is taken from the 6 hourly NCEP/NCAR Reanalysis 1.

GECCO3 and GECCO3S6m

The GECCO3 synthesis covers the period 1948-2018 and, unlike GECCO2, is optimized over only one assimilation window. The state after 41 iterations is available. There are two versions of the synthesis, which differ in the time constant of the relaxation of the surface salinity. The product with the extension 41 uses a relaxation time of 60 days, whereas for the extension 41S6m a time of 180 days was used. Globally and averaged over all data types, there is a slight advantage for the stronger relaxation. However, an evaluation with ESA-CCI surface salinity data for the years 2011-2018 showed a somewhat more realistic variability with less relaxation. In other variables that were examined, mainly differences between the two products on multi-decade time scales were found. The difference between the products gives an impression of the robustness of the estimate, but it must be taken into account that only one aspect was changed. Overall, the GECCO3S6m version can be recommended.

Model: MITgcm
Resolution: 0.4°, 40 z-levels, partial cells
Data assimilated: EN4.2.1 T/S (XBT corrected)+ AVISO along track SLA , GOCO5s MDT, HadISST SST, WOA18 climatology
Assimilation method: 4D-VAR (adjoint) method
Forcing and relaxation used: NCEP RA1 atm. Fields, Bulk formulae, Large and Yeager, 2009

Last update of data set at ICDC:

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Parameters

Parameters of the GECCO3 data set. Velocities are oriented along gridlines, which are only south of the equator exactly zonal and meridional. Interpolated Fields are rotated and follow gridlines as well as zonal and meridional directions at the same time.
Name	Unit	filename
water temperature	deg C	temp*
sea surface height	m	zeta*
salinity	g/kg	salt*
net shortwave flux	W/m^2	qsw*
totel heat flux	W/m^2	qnet*
fresh water flux	kg/s/m^2	emp*
meridional wind stress	N/m^2	fv*
zonal wind stress	N/m^2	fu*
u velocity	m/s	u*
v velocity	m/s	v*
w velocity	m/s	w*
bottom pressure	Pa	bp*
effective sea ice thickness	m	heff*
sea ice area	%	area*
meridional ice velocity	m/s	vice*
zonal ice velocity	m/s	uice*
GM X Streamfunction	m^2/s	gmpsix
GM Y Streamfunction	m^2/s	gmpsiy
Diffusivity	m^2/s	diff
Viscosity	m^2/s	visc
HBL Mixing Layer	m	hbl
Heat Flux (including relaxation)	W/m²	tflux
Salt Flux (including relaxation)	kg/s	sflux
Snow Height	m	hsnow

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Coverage, spatial and temporal resolution

Period and temporal resolution:

1948-2018
monthly
SSH (daily upon request)

Coverage and spatial resolution:

Global
Spatial resolution: 1°x1° (interpolated product)
Dimension: 360x180x40
Altitudes: 40 depth levels

Format:

NetCDF4

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Data quality

Variational methods fit the trajectory best during the middle section of the assimilation period. During the first few years spin-up effects are noticeable such that the variability during this period should be considered with care. Changes in the densities and type of assimilated data leave signatures in the product, in particular noticeable in year 1992 and at the beginning of the 2000s during the advent of altimeter and Argo data.

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Contact

Armoin Köhl
CEN / University of Hamburg
E-Mail: armin.koehl (at) uni-hamburg.de

Remon Sadikni
ICDC / CEN / University of Hamburg
E-Mail: remon.sadikni"AT"uni-hamburg.de

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References

Literature:

Köhl, A. (2020), Evaluating the GECCO3 1948-2018 Ocean Synthesis - a configuration for initializing the MPI-ESM climate model, Q. J. R. Met. Soc., doi: 10.1002/qj.3790. https://doi.org/10.1002/qj.3790

Websites:

ECCO, www.ecco-group.org
ESA-CCI surface salinity data, http://cci.esa.int/salinity

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Data citation, License, and Acknowledgments

Please contact Armin Köhl: armin.koehl (at) uni-hamburg.de for citation information.

and with the following acknowledgments:

Thanks to ICDC, CEN, University of Hamburg for data support.

License

The data was published under the Creative Commons Attribution 4.0 International License (CC-BY-4.0).

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