Users are referred to
Meteorological Bulletin M3.2 for information on the meteorological
characteristics of products, the forecast model documentation
contained in Meteorological Bulletin M1.6 and analysis
documentation contained in Meteorological Bulletin M1.5.
Products on
latitude-longitude grids are interpolated from the spectral or
(quasi regular - reduced) Gaussian grid associated with the ECMWF
forecast model. Interpolation is made to a 0.125 degree
latitude-longitude grid and resulting products are generated by
selecting required points. Regular Gaussian grids are also
available. Where appropriate, the interpolation to a
latitude-longitude grid uses a land/sea mask so that an
interpolated land point is assigned a value calculated using only
neighbouring land grid points, and an interpolated sea point is
assigned a value using only neighbouring sea grid points. For
precipitation fields, the interpolation assigns a zero value if the
value at the nearest grid point is zero; also any value within one
per cent of the global minimum for the field is taken to be equal
to zero.
Products on polar
stereographic grids are interpolated from the 0.125 degree
latitude-longitude interpolated fields; thus they are subject to a
double interpolation error.
Rotated
latitude-longitude grid point products are generated using FULLPOS
post-processing package (ARPEGE/IFS, IFS Documentation,
Meteorological Bulletin M1.6/7). This package generates rotated
latitude-longitude grid by rotating quasi-regular (reduced)
Gaussian grid using 12 point horizontal interpolation scheme.
Upper-air fields (except parameter Q which is a Gaussian grid
field) are first converted from spherical harmonics to
quasi-regular (reduced) Gaussian grid before passing as input to
the FULLPOS. Any rotation angle or resolution can be requested.
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