What is in MARS? - Data types and format

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Data types


Operational forecast data.

We receive data for up to 2 days ago (i.e. not forecast forward in time).


The 4D-Var analysis uses the model dynamics and physics to create, over a time window, (currently 12 hours), a sequence of model states that fits as closely as possible with the available observations and background.

The 4D-Var system handles all observational data similarly, including radiances from satellites. It compares the actual observations with what would be expected, given the model fields. For satellite radiances the variational scheme modifies the model fields of temperature, wind, moisture and ozone in such a way that the simulated observations are brought closer to the observed values.



- reanalyses from 12/1978 to 02/1994

- spectral T106 resolution with 31 vertical hybrid levels


- reanalyses from mid-1957 to 2001

- T159 spectral resolution with 60 vertical levels


- reanalyses from 01/1979 up to 3 months ago

- T255 spectral resolution with 60 vertical levels

- corrected for different models so should be consistent

- useful for long term analyses

ERA-CLIM is the new set of reanalysis that will span the entire 20th century (from 1899). Not yet released.

See http://www.era-clim.eu/

The Re-analysis data are publicly available via http://data-portal.ecmwf.int

One does not need to be an authorized user but only register.

The public ERA-40 data are not the high-resolution data, and the public ERA-Interim data are not including all fields.


The MARS archive also includes observation data.


The forecast/analysis/re-analysis data are in GRidded BInary (GRIB) format. Two different versions are used:

 - GRIB1
 - GRIB2 was implemented on 18 May 2011.

Information on the GRIB2 migration can be found here http://www.ecmwf.int/products/changes/grib2_migration/index.html

The observations are in BUFR format.