Gaussian grid descriptions

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

• HRES:  Gaussian grid number 1280
• ENS Days 1 to 15: Gaussian grid number 640
• ENS Extended (Days 16 to 46): Gaussian grid number 320

The descriptions provide the latitude values and the number of longitude points at each latitude for both the original 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 as the pl key.

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

From grib_api 1.14.4 onwards, the computed key grid_name gridName can be used to query the grid name.  For an octahedral with 1280 latitudes between pole and equator grid_namegridName=O1280; for an original reduced Gaussian grid with 640 atitudes latitudes between pole and equator, grid_namegridName=N640 while the corresponding regular Gaussian grid has grid_namegridName=F640.