Basic definitions

Each TIGGE partner provides their ensemble data on the grid of their choice, although regular grids are favoured. Partners are encouraged to provide also their deterministic forecast (as additional control) projected on the same horizontal grid and resolution as the ensemble members.

Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree. If this accuracy is not sufficient to describe your grid (latitude/longitude of first and last points, as well as grid increments) without loss of information, you can use a GRIB2 feature that provides a way to describe any regular grid.

Explanation of i/j coordinates and how they are used to describe the encoded fields in GRIB 2 (and ecCodes):

Example of the required GRIB 2 encoding of the gridded data (i.e. scanningMode should be equal to 0)

Scanning mode 0

  • iScansPositively (west to east)
    • i points are consecutive
  • jScansNegatively (north to south)

TIGGE common resolution

It was agreed with TIGGE panel that since 1 October 2026 providers would start using the same common grid for their contribution as soon as possible after that date. 

Comment from Sarah-Jane Lock, WMO PDEF member

Under the TIGGE project, there has been an expectation that the data that Centres archive is ‘close to’ the resolution of their operational forecasts. However over time, models have been upgraded to finer resolutions, but the resolution of the archived data has not always kept pace. With different models archiving data on different grids, it is difficult to draw meaningful conclusions from comparisons of verification against in-situ observations. These difficulties have become more apparent as increasingly fine detail is captured in (some of) the model data. Moving to data on a common grid would significantly enhance efforts to understand the differences in model performance and thus, feed into model developments. 

We believe that most of the TIGGE contributors would be able to provide data on these grids; and that the resolutions would enable useful insight into differences between the forecast systems.

The agreed common resolution is as follows:

  • 0.5/0.5 deg for upper-air fields
  • 0.25/0.25 deg for surface fields

As a part of the migration to the common resolution, the providers should use the grid_ccsds compression instead of the previous grid_simple.

Sample GRIB 2 metadata

Examples of eccodes grib_dump outputs with the common resolution

(related code tables for section 3: https://codes.ecmwf.int/grib/format/grib2/ctables/3/3/)

sfc parameters

...
======================   SECTION_3 ( length=72, padding=0 )    ======================
1-4       section3Length = 72 
5         numberOfSection = 3 
6         sourceOfGridDefinition = 0 [Specified in Code table 3.1 (grib2/tables/4/3.0.table) ]
7-10      numberOfDataPoints = 1038240
11        numberOfOctectsForNumberOfPoints = 0
12        interpretationOfNumberOfPoints = 0 [There is no appended list (grib2/tables/4/3.11.table) ]
13-14     gridDefinitionTemplateNumber = 0 [Latitude/longitude (Also called equidistant cylindrical, or Plate Carree)  (grib2/tables/4/3.1.table) ]
15        shapeOfTheEarth = 6 [Earth assumed spherical with radius of 6,371,229.0 m (grib2/tables/4/3.2.table) ]

16        scaleFactorOfRadiusOfSphericalEarth = MISSING
17-20     scaledValueOfRadiusOfSphericalEarth = MISSING
21        scaleFactorOfEarthMajorAxis = MISSING 
22-25     scaledValueOfEarthMajorAxis = MISSING
26        scaleFactorOfEarthMinorAxis = MISSING
27-30     scaledValueOfEarthMinorAxis = MISSING
31-34     Ni = 1440
35-38     Nj = 721
39-42     basicAngleOfTheInitialProductionDomain = 0
43-46     subdivisionsOfBasicAngle = MISSING
47-50     latitudeOfFirstGridPoint = 90000000
51-54     longitudeOfFirstGridPoint = 0
55        resolutionAndComponentFlags = 48 [00110000 (grib2/tables/4/3.3.table) ]
56-59     latitudeOfLastGridPoint = -90000000
60-63     longitudeOfLastGridPoint = 359750000
64-67     iDirectionIncrement = 250000
68-71     jDirectionIncrement = 250000
72        scanningMode = 0 [00000000 (grib2/tables/4/3.4.table) ]

vertical level parameters

...
======================   SECTION_3 ( length=72, padding=0 )    ======================
1-4       section3Length = 72
5         numberOfSection = 3
6         sourceOfGridDefinition = 0 [Specified in Code table 3.1 (grib2/tables/4/3.0.table) ]
7-10      numberOfDataPoints = 259920
11        numberOfOctectsForNumberOfPoints = 0
12        interpretationOfNumberOfPoints = 0 [There is no appended list (grib2/tables/4/3.11.table) ]
13-14     gridDefinitionTemplateNumber = 0 [Latitude/longitude (Also called equidistant cylindrical, or Plate Carree)  (grib2/tables/4/3.1.table) ]
15        shapeOfTheEarth = 6 [Earth assumed spherical with radius of 6,371,229.0 m (grib2/tables/4/3.2.table) ]

16        scaleFactorOfRadiusOfSphericalEarth = MISSING
17-20     scaledValueOfRadiusOfSphericalEarth = MISSING
21        scaleFactorOfEarthMajorAxis = MISSING
22-25     scaledValueOfEarthMajorAxis = MISSING
26        scaleFactorOfEarthMinorAxis = MISSING
27-30     scaledValueOfEarthMinorAxis = MISSING
31-34     Ni = 720
35-38     Nj = 361
39-42     basicAngleOfTheInitialProductionDomain = 0
43-46     subdivisionsOfBasicAngle = MISSING
47-50     latitudeOfFirstGridPoint = 90000000
51-54     longitudeOfFirstGridPoint = 0
55        resolutionAndComponentFlags = 48 [00110000 (grib2/tables/4/3.3.table) ]
56-59     latitudeOfLastGridPoint = -90000000
60-63     longitudeOfLastGridPoint = 359500000
64-67     iDirectionIncrement = 500000
68-71     jDirectionIncrement = 500000
72        scanningMode = 0 [00000000 (grib2/tables/4/3.4.table) ]