MARS/Dissemination

Specifies the output target grid which can be either a Gaussian or a Latitude/Longitude grid.

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• grid = F160  - full (or regular) Gaussian grid with 160 latitude lines between the pole and equator
• grid = N320  - ECMWF original reduced Gaussian grid with 320 latitude lines between the pole and equator, see Reduced Gaussian Grids for grid numbers used at ECMWF
• grid = O640 - ECMWF octahedral (reduced) Gaussian grid with 640 latitude lines between the pole and equator

Not all grid names and grid number combinations are supported. Currently, the Gaussian grid names and numbers supported for MARS retrievals are:

MARS requests specifying an unsupported grid will fail. For example, a retrieval request with grid=O123 will return an error.  If the letter denoting the type of Gaussian grid is omitted, e.g. grid=320, a full (or regular) Gaussian grid with 320 grid lines is returned.

For other keywords controlling the interpolation see the diagram below.

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Examples

Dissemination

Specifies the output grid which can be either a Gaussian or a Latitude/Longitude grid.

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grid=<value>

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.Dissemination  lat/lon grids allowed are describe for each data set in the Catalogue pages