Gaussian grid descriptions

Descriptions of the Gaussian grids introduced for the horizontal resolution upgrade at IFS cy42r1 and used for HRES and ENS are available:

• HRES:  N1280 Gaussian grid
• ENS Leg A (days 1 to 10): N640 Gaussian grid
• ENS Leg B (days 10 to 15 and monthly extension to day 46): N320 Gaussian grid

The descriptions provide the latitude values and the number of longitude points at each latitude for both the standard and octahedral reduced Gaussian grids.

The number of points at each latitude is encoded as the PL array in the Grid description section of the GRIB header of a grid point field.  This is accessible with grib_api using the pl key.

 At  As of grib_api 1.14.0, a new computed key isOctahedral is introduced which allows users to query the grid type. For the cubic an octahedral grid, isOctahedral=1; otherwise, isOctahedral=0.