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

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Deutscher Wetterdienst Contents Structure of GRIB2 Usage of grib_api Local Use Areas New: General Vertical Coordinate WG 6 Meeting / Sibiu2

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Deutscher Wetterdienst 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 WG 6 Meeting / Sibiu3 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

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Deutscher Wetterdienst WG 6 Meeting / Sibiu4 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

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Deutscher Wetterdienst 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) WG 6 Meeting / Sibiu5 Dörte Liermann

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Deutscher Wetterdienst GRIB_API ( A pplication P rogrammers I nterface) 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 WG 6 Meeting / Sibiu6 6 Dörte Liermann

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Deutscher Wetterdienst 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 / Sibiu7

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Deutscher Wetterdienst Product Identifying Keys (II) KeyValues significanceOfReferenceTime0 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 typeOfProcessedData0 analysis 1 forecast 2 analysis and forecast 3 control forecast 4 perturbed forecast 5 control and perturbed forecast WG 6 Meeting / Sibiu8

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Deutscher Wetterdienst Product Identifying Keys (III) KeyValues typeOfGeneratingProcess (local use) 0 analysis 1 initialization 2 forecast 195 interpolated analysis / forecast backgroundGeneratingProcessIdentifier (local use) 0 main run 1 pre-assimilation 2 assimilation 3 test generatingProcessIdentifier (local use) Represents data base identifier WG 6 Meeting / Sibiu9

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Deutscher Wetterdienst Local Use Section (localDefinitionNumber=254) localDefinitionNumberIdentifier 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 / Sibiu10

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Deutscher Wetterdienst 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 / Sibiu11

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Deutscher Wetterdienst General Vertical Coordinate typeOfLevel = 150

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Deutscher Wetterdienst 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 a k + b k * p s ) 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 numberOfVGridUsedto identify a special vertical coordinate nlevnumber of levels of the HHL file uuidOfVGrid:unique universal identifier to ensure correct identification of HHL WG 6 Meeting / Sibiu13

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Deutscher Wetterdienst Current Situation INT2LM and the COSMO-Model both compute the HHL fields and the reference atmosphere p 0. 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 p 0 when using GRIB2? Or what can we do? WG 6 Meeting / Sibiu14

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Deutscher Wetterdienst 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 vcoord k 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 p 0 ? 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 p 0 ? WG 6 Meeting / Sibiu15

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Deutscher Wetterdienst 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 / Sibiu16

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Deutscher Wetterdienst Current implemented Method for p 0 INT2LM and the COSMO-Model both compute p 0 (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.f WG 6 Meeting / Sibiu17

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Deutscher Wetterdienst 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 / Sibiu18

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Deutscher Wetterdienst 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 vcoord k, vcflat is really necessary or can be avoided WG 6 Meeting / Sibiu19

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Deutscher Wetterdienst What can be done about p 0 Can we transfer full pressure (or p 0 ) 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 / Sibiu20

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Deutscher Wetterdienst 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 / Sibiu21

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Deutscher Wetterdienst WG 6 Meeting / Sibiu COSMO General Meeting Thank you very much for your attention

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