DESCRIPTION:{excerpted from Balmeseda et al. (2013)

Version 4: ORAS4 has been produced by combining, every 10 days, the output of an ocean model forced by atmospheric reanalysis fluxes and quality controlled ocean observations. These consist of temperature and salinity (T/S) profiles from the Hadley Centre's EN3 data collection [Ingleby and Huddleston, 2007], which include eXpendable BathyThermographs (XBTs, T only, with depth corrections from Table 1 of Wijffels et al., [2009]), Conductivity-Temperature-Depth sensors (CTDs, T/S), TAO/TRITON/PIRATA/RAMA moorings (T/S), Argo profilers (T/S), and Autonomous Pinniped Bathythermograph (APBs or elephant seals, T/S). Altimeter-derived along track sea level anomalies from AVISO are also assimilated. Gridded maps of SST from NOAA are used to adjust the heat fluxes via strong relaxation, and altimeter global mean sea- levels are used to constrain the global average of the fresh-water flux.

The ocean model horizontal resolution is approximately 1o, refined meridionally down to 1/3o at the equator. There are 42 vertical levels with separations varying smoothly from 10 m at the surface to 300 m at the bottom, with partial cell topography. A model bias correction [BMW13] is used to reduce potential spurious variability resulting from changes in the observing system. The bias correction first guess - a seasonal cycle of 3- dimensional model error- is estimated from the data-rich Argo period, and applied to ORAS4 from the beginning of the record. This is updated as the analysis progresses via an adaptive scheme (see BMW13 for details; see also Fig S03 of auxiliary material). The 5 ensemble members of ORAS4 sample plausible uncertainties in the wind forcing, observation coverage, and the deep ocean.

The uncertainty is probably underestimated in ORAS4, since the uncertainty in observations and their quality control [Lyman et al., 2010] is not sampled. Quality improvements in ORAS4 relative to earlier ocean reanalyses stem from the use of improved atmospheric surface fluxes, improved data assimilation, and more comprehensive quality- control of the observation data set, with important corrections to the ocean observations. The methods section S01 in auxiliary material provides more specific information on the model, surface forcing, observation datasets, bias correction and ensemble generation. A detailed description and evaluation of ORAS4 is given in BMW13, as well as a discussion of the sensitivity of the reanalysis to several aspects not included in the ensemble generation.

HISTORY:

These files were provided by Magdalena Balmaseda and incorporated into the Data Catalog by John Fasullo on Oct. 9, 2013.

AVAILABILITY:

The data are available for non-commercial use and can be downloaded directly here for the total column OHC and here for the 0-700m OHC.

FORMAT: ASCII

GRID: Timeseries

TIMES: Analyzed Monthly Means

DATES: January 1958 - December 2009

LEVELS: Data are provided for the total column and 0-700 m

REFERENCES

Balmaseda, M. A., K. Mogensen, and A. T. Weaver (2013a), Evaluation of the ECMWF Ocean Reanalysis ORAS4. Q. J. R. Meteorol. Soc. DOI:10.1002/qj.2063.

Balmaseda, M. A., Trenberth, K. E., & Kallen, E. (2013b). Distinctive climate signals in reanalysis of global ocean heat content. Geophysical Research Letters.

Ingleby, B., and M. Huddleston (2007), Quality control of ocean temperature and salinity profiles - historical and real-time data. J. Mar. Sys., 65, 158–175.

Lyman J. M., et al. (2010). Robust warming of the global upper ocean, Nature, 465, 334-337.

Wijffels, S., et al. (2009), Changing expendable bathythermograph fall rates and their impact on estimates
of thermosteric sea level rise. J. Climate, 21, 5657-5672.

Back to the CAS Data Catalog

Back to the CAS Home Page


Dennis Shea: shea@ucar.edu