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

Contents Structure of GRIB2 Usage of grib_api Local Use Areas New: General Vertical Coordinate 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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: www.cosmo-model.org/content/model/documentation/grib/grib2keys.htm In GRIB 2 the description of the data (parameter, time, statistics,…) is more complex and is template/table based  Dörte Liermann 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu 6

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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) 12.04.2017 WG 6 Meeting / Sibiu

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! 12.04.2017 WG 6 Meeting / Sibiu

General Vertical Coordinate typeOfLevel = 150

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 12.04.2017 WG 6 Meeting / Sibiu

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? 12.04.2017 WG 6 Meeting / Sibiu

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? 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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 12.04.2017 WG 6 Meeting / Sibiu

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“ 12.04.2017 WG 6 Meeting / Sibiu

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 2014. If not, GRIB2 will not come before May / June 2014. 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 12.04.2017 WG 6 Meeting / Sibiu

Thank you very much for your attention 12.04.2017 WG 6 Meeting / Sibiu 10.09.2012 COSMO General Meeting 2012 22