ECMWF Ocean Reanalysis System 4 (ORAS4)

Area: Global

Period: 1958-2017

Data available: YES

Disclamer: The climate quality of the ORAS4 data produced in real time (from January 2010 onwards) can be affected by incidents associated to the real-time operations
Model: NEMO V3.0
Resolution: (ORCA1_Z42): Horizontal 1°x1° with equatorial refinement (0.3). 42 vertical levels, about 10m-15m level thickness in upper 200m.
Data assimilated: Temperature and Salinity profiles from the EN3 v2a XBT bias corrected database (1958-2009), including XBT, CTD, Argo, Mooring, and from realtime GTS thereafter. Along track altimeter sea level anomalies and global trends from AVISO. SST and sea-ice are from the ERA-40 archive prior to November 1981, from the NCEP OI v2 weekly product (1981 until December 2009) and , and from OSTIA analysis from January 2010 onwards.The SST and sea-ice information is used to constrain the upper level ocean temperature via a newtonian relaxation scheme.
Assimilation method: NEMOVAR in its 3D-var FGAT mode. The assimilation window is 10 days. A bias correction scheme is used to correct the model/forcing errors.
Forcing and relaxation used: Daily surface fluxes of heat, momentum and fresh water are used. Prior to 1989, the surface fluxes are from the ERA-40 atmospheric reanalysis. From the period 1989-2009, the surface fluxes are from ERA-Interim reanalysis. From 2010 onwards, when ORAS4 started operational running, daily surface fluxes were derived from the operational ECMWF atmospheric analysis.
Download Data: OPeNDAP at ICDC, FTP at ICDC, View in LAS at ICDC
Contact: Magdalena Balmaseda, Magdalena.Balmaseda (at) ecmwf.int
References: Balmaseda M.A,. K. Mogensen, A. Weaver, 2013: Evaluation of the ECMWF Ocean Reanalysis ORAS4. Q. J. R. Meteorol. Soc. DOI:10.1002/qj.2063
Mogensen, K., M. Alonso Balmaseda, A. Weaver, 2012: The NEMOVAR ocean data assimilation system as implemented in the ECMWF ocean analysis for System4. ECMWF Thechnical Memorandum 668. 59 pages.
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