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As MARS and the dissemination system are different applications, they don't necessarily return by default identical fields for any given request. However, with the help of some MARS keywords it should be possible. In any case you should include STYLE=DISSEMINATION to instruct MARS to perform postprocessing post-processing in a way as close to the dissemination system as possible. With the keyword accuracy the number of bits per value to be used in the generated GRIB coded fields can be specified to match that used in the dissemination, see Table 4.2 in the Dissemination Manual.
How can I handle and manipulate the data retrieved from MARS?
Retrieved data can of course be manipulated in any way outside MARS, e.g. using Fortran programs. Python scripts etc. To users with less programming experience some tools available at ECMWF might be of particular interest:
The GRIB offers handy tools to examine the content and to manipulate GRIB files on the command line.
With ECMWF's interactive meteorological application METV you can access (both directly from MARS and from file), manipulate and visualise GRIB data. In particular its macro language, which can also be used in batch mode, provides a convenient and powerful tool to manipulate and visualise data. Metview's grib examiner, which can be started on ecgate as
metview -e grib [filename]
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offers a GUI to some functionality of GRIB API's examination tools.
CDO is a collection of Climate Data Operators, including, e.g. vertical interpolation, which can by applied to meteorological fields in various formats, including GRIB. This tool box is installed at ECMWF but has been developed and is maintained by MPI, Hamburg. Please direct all queries to them. For more details refer to the CDO home page.
Various tools are available to convert GRIB to netCDF.
Metview also provides an examiner for BUFR data, which can be started on ecgate as
metview -e bufr [filename]
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