1. GRIB2 and its implementation in INT2LM and the COSMO-Model
Ulrich Schättler
Source Code Administrator
COSMO-Model and (still) INT2LM

2. Contents Structure of GRIB2 Usage of grib_api Local Use Areas
New: General Vertical Coordinate
WG 6 Meeting / Sibiu

3. GRIB2 ? - WMO - Code for forecast products
GRIdded Binary : Edition 0 (1985/88), Edition 1 (1990ff)
General Regularly-distibuted Information in Binary form: Edition 2 (2001)
self explaining, compressed / packed
GRIB message contains metadata (explaining the product, grid,…) plus data
Edition 2 is more flexible through a template/table structure,
ammendments by adding templates/tables.
Version 2: 2003
Version 3: 2005
Version 4: 2007
Version 5: 2008
Version 6: 2009
etc.
Changes include
coding of new elements/parameter
new product definition templates
new packing/compressing formats
new horizontal grid(s), e.g. ICON
new vertical coordinate type
 Dörte Liermann
WG 6 Meeting / Sibiu

4. Comparing GRIB1 – GRIB2 GRIB 1 vs. 2: Different Structure GRIB 1
SECTION 0 Indicator (GRIB)
SECTION 1 Product definition
SECTION 2 Grid Description
SECTION 3 Bitmap
SECTION 4 Binary Data
SECTION 5 End (7777)
GRIB 2
SECTION 0 Indicator(GRIB,…)
SECTION 1 Identification
SECTION 2 Local Use
SECTION 3 Grid Definition
SECTION 4 Product Definition
SECTION 5 Data Representation
SECTION 6 Bitmap
SECTION 7 Binary Data
SECTION 8 End (7777)
In GRIB 2 several variables are defined with more precision (e.g. angles are in micro-degrees, more vertical coordinates possible)
see:
In GRIB 2 the description of the data (parameter, time, statistics,…) is more complex and is template/table based
 Dörte Liermann
WG 6 Meeting / Sibiu

5. Element coding of model fields in GRIB2
GRIB1: Element coding by ee (element) and tab (table)
Example: temperature is ee=11 in tab=2 (WMO)
GRIB2: Element coding by a triplet
Discipline
Category
Parameter
Example: temperature is (0,0,0)
Through setting of shortName, these three parameters are set (and for some products also some other keys; see shortName.def in definitions.edzw)
 Dörte Liermann
WG 6 Meeting / Sibiu

6. GRIB_API (Application Programmers Interface)
ECMWF source code for de-/encoding of GRIB1 AND GRIB2
no internal knowledge of GRIB structure needed
each element of a grib message has an alphanumeric name (key) that can be used to access the information linked to it (value)
key – value approach: shortName=T
typeOfLevel = hybridLayer
topLevel = 37
bottomLevel = 38
How to find keys: grib_keys –F file.grib lists all keys of a file
flexible – local definitions for each centre possible
i.e. local definition tables shortName.def for edzw (GRIB1 and GRIB2),
local definition of GME icosahedral grid for GRIB1
But: needs more coordination within COSMO
 Dörte Liermann
WG 6 Meeting / Sibiu 6

7. Product Identifying Keys
significanceOfReferenceTime (GRIB2-WMO Tab. 1.2)
productionStatusOfProcessedData (GRIB2-WMO Tab. 1.3)
typeOfProcessedData (GRIB2-WMO Tab. 1.4)
generatingProcessIdentifier (local definition in GRIB1/2)
backgroundGeneratingProcessIdentifier (local definition in GRIB2)
typeOfGeneratingProcess (GRIB2-WMO Tab. 4.3)
localDefinitionNumber (local section = 254, 253, 252; 250 for COSMO)
localNumberOfExperiment (GRIB2)
localInformationNumber (GRIB2) / localElementNumber (GRIB1)
localDecodeDate:s
WG 6 Meeting / Sibiu

8. Product Identifying Keys (II)
Values
significanceOfReferenceTime
0 analysis
1 start of forecast
2 verifying time of forecast
3 observation time
productionStatusOf ProcessedData
(possible local use)
0 operational – Routine
1 operational test – Parallelsuite
2 research – Experiments
3 re-analysis products
typeOfProcessedData
1 forecast
2 analysis and forecast
3 control forecast
4 perturbed forecast
5 control and perturbed forecast
WG 6 Meeting / Sibiu

9. Product Identifying Keys (III)
Values
typeOfGeneratingProcess
(local use)
0 analysis
1 initialization
2 forecast
195 interpolated analysis / forecast
backgroundGeneratingProcessIdentifier
0 main run
1 pre-assimilation
2 assimilation
3 test
generatingProcessIdentifier
Represents data base identifier
WG 6 Meeting / Sibiu

10. Local Use Section (localDefinitionNumber=254)
localDefinitionNumber Identifier for content (historical: 254)
localHostIdentifier
localCreationDateYear/Month/Day/Hour/Minute/Second
localValidityDateYear/Month/Day/Hour/Minute/Second
localNumberOfExperiment Number of Experiment
localInformationNumber
Identifier for host system/ computer
Also need a local use section for COSMO (localDefinitionNumber = 250)
WG 6 Meeting / Sibiu

11. Implementation of Local Use
SELECT CASE (ncenter)
CASE (78) ! DWD …
CASE DEFAULT
END SELECT
We soon need to know about your local use of special keys!
We want to document local use on the Web Page!
WG 6 Meeting / Sibiu

12. General Vertical Coordinate
typeOfLevel = 150

13. Why a new vertical coordinate?
As a non-hydrostatic model, COSMO needs a special vertical grid: fixed in space and time
Also post-processing programs have to be aware of this grid (or the HHL)
But the algorithm to compute it, is rather complex (not just ak + bk * ps)
Therefore a proposition was made to WMO, to introduce a new typeOfLevel=150
To process atmospheric data using that typeOfLevel, another 3D field is necessary: the HHL fields
If a product has typeOfLevel=150, then there are 6 additional meta data in the Product Definition Section, which replace the vertical coordinate parameters
numberOfVGridUsed to identify a special vertical coordinate
nlev number of levels of the HHL file
uuidOfVGrid: unique universal identifier
to ensure correct identification of HHL
WG 6 Meeting / Sibiu

14. Current Situation
INT2LM and the COSMO-Model both compute the HHL fields and the reference atmosphere p0.
The necessary vertical coordinate parameters (for HHL) and the reference atmosphere parameters are given to
INT2LM by Namelist variables
COSMO-Model by GRIB1 meta data: but this always was a non-standard GRIB usage!
The new generalized vertical coordinate does not know meta data for vertical coordinate parameters and for the reference atmosphere.
How to compute HHL and p0 when using GRIB2?
Or what can we do?
WG 6 Meeting / Sibiu

15. What can be done?
HHL can be transferred from INT2LM to COSMO or within the assimilation cycle from COSMO to COSMO by an extra file.
Do we then still need to transfer the vertical coordinate parameters vcoordk and vcflat?
YES! For computations in the nudging and some diagnostices (meanvalues, convective indices). Try to discuss this with the code experts.
Can we also transfer p0? Or the full pressure?
For full pressure the problem is the GRIB packing. But we could use more bits for the packing (pressure deviation is a more homogeneous field with less precision loss in the packing)
Other question: Has anybody ever changed the Namelist variables in INT2LM (p0sl, t0sl, dt0lp, delta_t, h_scal) to compute another p0?
WG 6 Meeting / Sibiu

16. Current implemented Method for HHL
INT2LM can compute HHL and write an extra file COSMO_HHL_xxx.g2 (if lnewVGrid = .TRUE.) or read it from such a file (is done in IEEE 64-bit)
(Note: for COSMO  COSMO such a HHL file has also to be read for the coarse grid)
INT2LM computes the atmospheric variables based on this HHL
The COSMO-model has to read the same COSMO_HHL_xxx.g2 file to get the same HHL field as the INT2LM (checking the UUID should ensure using the correct HHL field)
INT2LM and the COSMO-Model define several sets of vertical coordinate parameter defaults (for COSMO-EU, COSMO-DE, COSMO-I7, COSMO-7, etc.). Every set has a special ID
HHL stores the ID of the default set used in the localInformationNumber in HHL
WG 6 Meeting / Sibiu

17. Current implemented Method for p0
INT2LM and the COSMO-Model both compute p0 (as before).
To get the correct reference atmosphere parameters, both programs store several sets of default parameters. Every set has a special ID
pp stores the ID of the used set in the local information number
INT2LM and the COSMO-Model now use the new module vgrid_refatm_defaults.f90
WG 6 Meeting / Sibiu

18. Problems and Drawbacks of this Approach
Have to deal with another file in our suites
Have to hard-code all possible COSMO configurations in the source code
WG 6 Meeting / Sibiu

19. What can be done about HHL
Can we transfer HHL through the laf-file? Perhaps in higher precision? But this imposes problems to archiving!
Do we need full precision?
Check , whether usage of vcoordk, vcflat is really necessary or can be avoided
WG 6 Meeting / Sibiu

20. What can be done about p0
Can we transfer full pressure (or p0) through the laf-file? Perhaps in higher precision? Again this imposes problems to archiving!
Which precision is really needed?
Check , whether usage of reference atmosphere parameters can be „fixed“
WG 6 Meeting / Sibiu

21. Migration to GRIB2: Timetable
The plans already pronounced by DWD have been revised last week
A prerequisite for GRIB2 at DWD is the stable operation of the new database software SKY (old software is not able to process GRIB2 meta data). And this is not the case at the moment.
New date for operational use of SKY („only the SKY is the limit“): November
If this date can be kept, then we could switch to GRIB2 in January If not, GRIB2 will not come before May / June Because in February / March we are migrating to the new CRAY computer system.
Message for COSMO and other partners:
Be prepared to read GME data in GRIB2 with INT2LM
WG 6 Meeting / Sibiu

22. Thank you very much for your attention 12.04.2017 WG 6 Meeting / Sibiu
COSMO General Meeting 2012 22