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  1. GRIB2 usage at NCEP Dr. V. KRISHNA KUMAR & BOI VUONG NOAA/NWS/NCEP/Central Operations NCEP WWB GRIB2 Seminar 20 December 2010 Room 209, WWB Camp Springs, MD

  2. Overview • GRIB1 and GRIB2 Sections • GRIB2 Documentation • Format differences between GRIB1 and GRIB2 • GRIB2 in NCEP Operations – Encoding & Decoding routines, NCEP Utilities (cnvgrib, degrib2, overdateg2, overmodelg2, copygb2……..) • NCEP Transition to GRIB2 and NWS FTP Servers that provide GRIB2 data • GRIB2 – Section 7 Data Section • GRIB2 – Packing Options • How to diagnose a Degrib2 output from NCEP GRIB2 tables? • How to write GRIB2 data directly? – A specific example • NCO GRIB2 Templates software

  3. Overview • Parallel GRIB2 in NCEP Post • GRIB2 Options in POST • Parallel generating and writing GRIB2 messages • Parallel GRIB2 results • GRIB2 Encoding routines • GRIB2 Decoding routines • Declaration of Derived type “gribfield” • How to use routine “getgb2”? • How to use routine “putgb2”? • GRIB2 read and write examples • Summary and Conclusions

  4. GRIB1 Sections 0 – Indicator Section - ‘GRIB’ (octet 1-4 = 32bits), length of message (octet 5-7=24bits), edition number -1 (octet 8=8bits) - 1 octet = 1byte = 8bits - octets are numbered 1, 2, 3, etc., Bit positions within octets are from bit 1 to bit 8. - bit 1 = most significant bit & bit 8 = least significant) 1 – Product Definition Section (PDS) - Length of PDS, parameter table version number, ID of center, generating process ID, grid identification (Table B), Ref time, parameter and units, level, valid time … 2 – Grid Definition Section (GDS) – optional - Length of sec., sec. no, defn of grid surf and geometry of data values within the surface 3 – Bit-Map Section (BMS) – optional - Length of sec., sec. no, indication of presence or absence of data at each of the grid points, as applicable example sst 4 – Binary Data Section (BDS) - Length of sec., sec. no, data values 5 – End Section = ‘7777’

  5. GRIB2 Sections • 0 – Indicator Section - ‘GRIB’, length, version, discipline – (16 octets long) • Section 1 – Identification - Ref time, orig center, table versions, …(length of the section is expressed as the first four octets (32 bits) -the section number in the fifth octet and octets beyond 21 are reserved for future use) • 2 – Local Use Section – optional================== • 3 – Grid Definition Section======= | • 4 – Product Definition Section====| | - parameter, level, valid time | | | • 5 – Data Representation Section|| | - packing algorithm used, info needed to unpack | | | • 6 – Bit Map Section| | | • 7 – Data Section================== -packed data • 8 – End Section = ‘7777’

  6. GRIB2 – Documentation • NCEP GRIB2 Documentation (internet - www) • http://www.nco.ncep.noaa.gov/pmb/docs/grib2/ • http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc.shtm • NCEP GRIB2 Resources (Detailed Documentation) (intranet – www2) http://www2.nco.ncep.noaa.gov/sib/grib2/ • GRIB2 specification from WMO contains template definitions and table entries: http://www.wmo.ch/web/www/DPS/grib-2.html • Local Tables: http://www.nco.ncep.noaa.gov/pmb/docs/grib2 • NCEP source files and utilities on the web for decoding and encoding data in GRIB2 format • http://www.nco.ncep.noaa.gov/pmb/codes/GRIB2/

  7. GRIB1 & GRIB2 Major Differences • One GRIB2 message can contain multiple fields. - Sequences of GRIB sections 2 to 7, sections 3 to 7 or sections 4 to 7 may be repeated within a single GRIB message. - Once a section is repeated all the following sections must appear in order. - A section remains in effect until redefined. - Could be used for vector fields such as u & v components, or ensemble members - IEEE single precision floating point representation used instead of standard IBM representation. The representation occupies four octets. • GDS, PDS, DRS, and DS are all template driven. Octet assignments within a section are based on the Template specified. • Parameters are defined by three values: Discipline (specified in Section 0) Category (PDS) Parameter number (PDS).

  8. GRIB1 and GRIB2 Major differences contd. • Table versions, originating center, initial reference time and grid ID removed from GRIB1 PDS. Most are now in Identification Section. • All longitudes MUST be in degrees East and be between 0 and 360 degrees. No negatives. No degrees West. No change in latitude definitions –900 to 900. • GDS and BMS no longer optional. They must be included. Only Section 2 (Local Use) is optional. • Latitudes, Longitudes are in units of micro-degrees (10 –6 degrees). Includes distance between grid points for Lat/Lon grids (GRIB1 was milli-degrees) • All other grid point increments are in millimeters (GRIB1 was in meters) • Floating point values are now stored in IEEE format (GRIB1 was IBM 360/195 format HDS)

  9. GRIB2 in NCEP operations Encoding Routines GRIB2 message can contain gridded fields for many parameters on a number of different grids. Start a new GRIB2 message with a call to: (1) call GRIBCREATE – encodes sections 0 and 1 at the beginning of message. (2) call ADDLOCAL – adds a Local Use Section (Section 2) optional (3) call ADDGRID – encodes a grid definition into Section 3. Defines the geometry of the data values in the fields that follow it. ADDGRID can be called again to change the grid definition describing subsequent data fields. (4) call ADDFIELD – adds each data field which adds Sections 4, 5, 6, and 7 to the message. (5) call GRIBEND – adds the final section 8 to the message which updates the length of the message. GRIBEND is required for each GRIB2 message. Boi will demonstrate these routines with examples in the latter half of this seminar

  10. GRIB2 in NCEP operations contd. Decoding Routines call GB_INFO – finds out how many Local Use sections and data fields are contained in a given GRIB2 message. Also returns the number of octets of the largest Local Use section in the message. Ensures the dimensionality of the input array of GETLOCAL call GETLOCAL – returns the requested occurrence of Section 2 from a given GRIB2 message. call GF_GETFLD – gets all information pertaining to the nth data field in the message – returns all the unpacked values for each Section and Template in a f90 “type gribfield” with options to unpack the Bit-map (if applicable) and the data values or just return the field description information. call GF_FREE(gfld) – frees up memory held by gfld as many elements in derived type gribfield are dynamically allocated when decoded. Example: use grib_mod type(gribfield) ::gfld … … call gf_getfld(cgrib,lengrib,1,.true.,.false.,gfld,ierr) print*,’Num of grid points =‘,gfld%ngrdpts print*,’First data value=‘,gfld%fld(1) call gf_free(gfld) How to extract GRIB2 fields from a GRIB2 file? GETGB2 – extracts a specified field from a file containing many GRIB2 messages. Boi will demonstrate these with examples in the latter half of this seminar.

  11. GRIB2 in NCEP operations contd. Create GRIB2 Message call PUTGB2 – if a variable of derived type of “gribfield” already exists, this subroutine can be used to pack it up and write it to a file – Boi will demonstrate this NCEP GRIB2 Utilities /grb2index grib2file grib2indexfile - creates a GRIB2 index file /cnvgrib –h (packing options: 1 => 2, 2=>1, 2=>2) -converts all fields in a file between GRIB1 and GRIB2 /degrib2 grib2file -dumps the meta-data for each GRIB2 field in grib2file - basically prints contents of each element in derived type gribfield /wgrib2 grib2file Grads for GRIB2 sh convert_grib2_to_grads.sh #!/bin/sh set -xa # file_list=`ls grib2.t00z.wafs_grbf06.45 gfs.t00z.wafs_grb45f06.grib2` for list in $file_list do # /usrx/local/grads/bin/g2ctl -verf $list > ${list}.ctl /usrx/local/grads/bin/g2ctl $list > ${list}.ctl /usrx/local/grads/bin/2.0.a3/xgribmap -i ${list}.ctl done exit

  12. GRIB2 in NCEP Operations $ /nwprod/util/exec/cnvgrib -h Usage: cnvgrib [-h] {-g12|-g21|-g22} [-m] [{-p0|-p2|-p31|-p32|-p40|-p41|-p40000|-p40010}] ingribfileoutgribfile cnvgrib: version cnvgrib-1.1.1 Must use one of the following options: -g12 converts GRIB1 to GRIB2 -g21 converts GRIB2 to GRIB1 -g22 converts GRIB2 to GRIB2 (used to change packing option) Optional packing options: (for use with -g12 and -g22 only) -p0 simple packing -p2 complex packing -p31 complex pack with 1st order diffs -p32 complex pack with 2nd order diffs -p40 JPEG2000 encoding -p41 PNG encoding Other Optional options: -m Use missing values instead of bitmap (valid with -p2, -p31 or -p32 options only)

  13. GRIB2 in NCEP Operations /nwprod/util/sorc/overmodelg2.fd $ more sample.script # THIS SCRIPT READS A FORECAST FILE (UNIT 11), REPLACES MODEL INDENTIFIER IN # PRODUCT TEMPLATE 4.x FROM A ID FILE UNIT 51. # STANDARD INPUT IS A ID (2-DIGIT INTEGER), FOR EXAMPLE: 96 (GFS Model) set -x export XLFRTEOPTS="unit_vars=yes" # Allow overriding default names. export XLFUNIT_11=gfs.t00z.pgrb2f12.2p5deg export XLFUNIT_51=gfs.t00z.pgrb2f12.2p5deg.new overmodelg2 << EOF 98 EOF /nwprod/util/sorc/overdateg2.fd # THIS SCRIPT READS A FORECAST FILE (UNIT 11), MODIFIES REFERENCE TIME YEAR MONTH # DATE AND HOUR IN SECTION 1 AND IN PRODUCT TEMPLATE 4.x TO REPLACE INTERNAL # REFERENCE TIME FROM A DATE IN FILE UNIT 51. # STANDARD INPUT IS A YYYYMMDDHH (10-DIGIT INTEGER), FOR EXAMPLE 2010090112 set -x export XLFRTEOPTS="unit_vars=yes" # Allow overriding default names. export XLFUNIT_11=gribfile export XLFUNIT_31=gribfile_indx export XLFUNIT_51=gribfile.new overdateg2 << EOF 2010090112 EOF

  14. GRIB2 in NCEP Operations /nwprod/util/sorc/copygb2.fd NAME copygb2 - copies GRIB2 files SYNOPSIS copygb2 [-g "kgdtn [kgdt]"] [-i "ip [ipopts]"] [-k "kpdtn kpdt"] [-v "uparms"] [-X] [-B mapgrib [-b mapindex] [-A "<> mapthreshold"] [-K "mapkpds"]] [-M "mask"|mergegrib [-m mergeindex]] [-a] then either: grib2in index2in grib2out or: -x grib2in grib2out DESCRIPTION The command copygb2 copies all or part of one GRIB2 file to another GRIB2 file, interpolating if necessary. Unless otherwise directed (-x option), the GRIB2 index file is also used to speed the reading. The fields are interpolated to an output grid if specified (-g option). The interpolation type defaults to bilinear but may be specified directly (-i option). The copying may be limited to specific fields (-k option). It may also be limited to a specified subgrid of the output grid or to a subrange of the input fields (-B and -b, -A, and -K options). Fields can be identified as scalars or vectors (-v option), which are interpolated differently. The invalid data in the output field can be filled with mask values or merged with a merge field (-M and -m options). The output GRIB2 message can also be appended to a file (-a option). If grib2out is specified as '-', then the output GRIB file is written to standard output.

  15. GRIB2 in NCEP Operations # # Script to convert a RTMA 2p5 grib2 file to a 5p0 grib2 file # # Author: V. Krishna Kumar October 5, 2010 NCO/Systems Integration Branch # set -x # # clean the output file prior to running this script # # I created a single field grib2 file from the original production grib2 file using # wgrib2 -d 1 in_grb2file -grib out_grb2file # rm rtma5p0.t12z.2dvaranl_ndfd.1field.grb2 # # HGT - Conversion from 2p5 to 5 # Input file : rtma2p5.t12z.2dvaranl_ndfd.1field.grb2 # Output file : rtma5p0.t12z.2dvaranl_ndfd.1field.grb2 # # 2p5 Grid template 3.30 : 6 0 0 0 0 0 0 2145 1377 20191999 238445999 8 25000000 265000000 2539703 2539703 0 64 25000000 25000000 -90000000 0 # 5p0 Grid template 3.30 : 6 0 0 0 0 0 0 1073 689 20191999 238445999 8 25000000 265000000 5079406 5079406 0 64 25000000 25000000 -90000000 0 export grid_new="30 6 0 0 0 0 0 0 1073 689 20191999 238445999 8 25000000 265000000 5079406 5079406 0 64 25000000 25000000 -90000000 0 0" export grib_in=rtma2p5.t12z.2dvaranl_ndfd.1field.grb2 # # Create a grib2 index file of the input grib file # /nwprod/util/exec/grb2index $grib_in ${grib_in}_ix export grib_index=${grib_in}_ix /nwprod/util/exec/copygb2 -g "${grid_new}" -i0 ${grib_in} ${grib_index} rtma5p0.t12z.2dvaranl_ndfd.1field.grb2 echo "Max Min value from the original 2p5 grid " /nwprod/util/exec/wgrib2 -grid -max -min rtma2p5.t12z.2dvaranl_ndfd.1field.grb2 echo "Max Min value from the converted 5p0 grid " /nwprod/util/exec/wgrib2 -grid -max -min rtma5p0.t12z.2dvaranl_ndfd.1field.grb2 echo " Max Min from the current operational 5 degree grid " /nwprod/util/exec/wgrib2 -grid -max -min rtma.t12z.2dvaranl_ndfd.1field.grb2 exit

  16. GRIB MESSAGE  1  starts at 1  SECTION 0:  0 2 60463  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  Contains  0  Local Sections  and  1  data fields.FIELD  1  SECTION 0:  0 2  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  SECTION 3:  0 65160 0 0 0  GRID TEMPLATE 3. 0 :  6 0 0 0 0 0 0 360 181 0 0 90000000 0 48 -90000000 359000000 1000000 1000000 0  NO Optional List Defining Number of Data Points.  PRODUCT TEMPLATE 4. 0 :  3 5 2 0 96 0 0 1 36 100 0 100000 255 0 0  TEXT: HGT      1000 mb valid at  36 hr after 2010110906:00:00  NO Optional Vertical Coordinate List.  Num. of Data Points =  65160     NO BIT-MAP  DRS TEMPLATE 5. 3 :  -979087360 0 1 11 0 1 0 0 0 5124 0 4 1 1 32 5 1 2 Data Values:MIN=        -525.79998779 AVE=          70.36888123 MAX=         313.10000610 GRIB MESSAGE  2  starts at 60464  SECTION 0:  0 2 59574  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  Contains  0  Local Sections  and  1  data fields.FIELD  1  SECTION 0:  0 2  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  SECTION 3:  0 65160 0 0 0  GRID TEMPLATE 3. 0 :  6 0 0 0 0 0 0 360 181 0 0 90000000 0 48 -90000000 359000000 1000000 1000000 0  NO Optional List Defining Number of Data Points.  PRODUCT TEMPLATE 4. 0 :  3 5 2 0 96 0 0 1 36 100 0 97500 255 0 0  TEXT: HGT      975 mb valid at  36 hr after 2010110906:00:00  NO Optional Vertical Coordinate List.  Num. of Data Points =  65160     NO BIT-MAP  DRS TEMPLATE 5. 3 :  -984977408 0 1 11 0 1 0 0 0 5130 0 4 1 1 32 5 1 2 Data Values:MIN=        -323.89999390 AVE=         278.48535156 MAX=         514.00000000

  17. GRIB MESSAGE  149  starts at 7050617  SECTION 0:  0 2 93572  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  Contains  0  Local Sections  and  2  data fields.FIELD  1  SECTION 0:  0 2  SECTION 1:  7 0 2 1 1 2010 11 9 6 0 0 0 1  SECTION 3:  0 65160 0 0 0  GRID TEMPLATE 3. 0 :  6 0 0 0 0 0 0 360 181 0 0 90000000 0 48 -90000000 359000000 1000000 1000000 0  NO Optional List Defining Number of Data Points.  PRODUCT TEMPLATE 4. 0 :  2 2 2 0 96 0 0 1 36 100 0 100000 255 0 0TEXT: U GRD    1000 mb valid at  36 hr after 2010110906:00:00  NO Optional Vertical Coordinate List.  Num. of Data Points =  65160     NO BIT-MAP  DRS TEMPLATE 5. 3 :  -1014333440 0 1 9 0 1 0 0 0 4835 0 4 1 1 32 5 1 2 Data Values:MIN=         -27.70000076 AVE=            .24823742 MAX=          27.20000076 FIELD  2  SECTION 3:  0 65160 0 0 0  GRID TEMPLATE 3. 0 :  6 0 0 0 0 0 0 360 181 0 0 90000000 0 48 -90000000 359000000 1000000 1000000 0  NO Optional List Defining Number of Data Points.  PRODUCT TEMPLATE 4. 0 :  2 3 2 0 96 0 0 1 36 100 0 100000 255 0 0TEXT: V GRD    1000 mb valid at  36 hr after 2010110906:00:00  NO Optional Vertical Coordinate List.  Num. of Data Points =  65160     NO BIT-MAP  DRS TEMPLATE 5. 3 :  -1015873536 0 1 9 0 1 0 0 0 4934 0 4 1 1 16 5 1 2 Data Values:MIN=         -24.30000114 AVE=            .03596115 MAX=          30.39999962 GRIB MESSAGE  150  starts at 7144189

  18. GRIB2 in NCEP Operations Currently about 90-95 % of the GRIB2 products are generated using CNVGRIB from GRIB1 files. Users are encouraged to generate GRIB2 files directly for all new operational products. Source codes in NCEP operations that generate GRIB2 products directly: /nwprod/sorc $ ls -d *grb2* *grib2* *rtma*post*fd cdas_ex_grib2.cd mdl_grb2mdlp.fd mdl_ra2grib2.fd sstoiqd_grib2sst.fd gfdl_mkgrib2n.fd mdl_grb2tomdlp.fd multiwavegrib2.fd wavesteepgrb2.fd akrtma_post.fd hirtma_rtmapost.fd rtma2p5_post.fd gurtma_post.fd prrtma_rtmapost.fd rtma_post.fd See Manuel Pondeca’s – rtma_post.fd (well written code) cnv_to_grib2.f for GRIB2 creation /nwprod/util/sorc $ ls -d *grib2* *grb2* degrib2.fd grb2index.fd tocgrib2.fd wgrib2.cd TRANSITION TO GRIB2 ON NCEP AND NWS FTP SERVERS http://www.nco.ncep.noaa.gov/pmb/docs/GRIB1_to_GRIB2.shtml Current GRIB2 data sets available on the TOC ftp servers.  Access ftp tgftp.nws.noaa.gov through anonymous FTP and go to: For NAM: /SL.us008001/ST.opnt/MT.nam_CY.CC/RD.YYYYMMDD/PT.grid_DF.gr2/ For GFS: /SL.us008001/ST.opnt/MT.nam_CY.CC/RD.YYYYMMDD/PT.grid_DF.gr2/ where CC is the cycle (00,06,12,18) and YYYYMMDD is the date.

  19. GRIB2 Section 7 – Data Section • Data coded with the minimum number of bits necessary to provide the accuracy. • Simple scaling – data multiplied by an appropriate power of 10 before forming the non-negative differences, and then using the binary scaling to select the precision of the transmitted value. • Data coded in the form of non-negative scaled differences from a reference value of the whole field plus, if applicable, a local reference value. (reference value is normally the minimum value of the data set which is represented).

  20. GRIB2 Section 7 – Data Section contd. • Complex packing for grid-point values – split the whole set of scaled data values into groups on which local references (local minima) are removed – pre-processing may be needed on the scaled data. • Complex packing for spectral data. • The original data value Y can be recovered with the formula • Y*10D=R+(X1+X2)*2E • where E=Binary scale factor, D=Decimal scale factor, R=Reference value of the whole field, X1=0, X2=Scaled (encoded) value.

  21. GRIB2 – Packing Methods • GRIB2_com – Group packing – DR Template 5.2 • GRIB2_1od – Group packing –with 1st order differencing Template 5.3 • GRIB2_2od – Group packing – with 2nd order differencing Template 5.3 • Image compression algorithms within the GRIB2 standard. • Both treat grid point data as a grey scale image (single component) • JPEG_2000 (Part-1 standard) (ISO/IEC 15444-1) • http://www.jpeg.org/JPEG2000.html • PNG (Portable Network Graphics image compression format) • http://www.libpng.org/pub/png/.

  22. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example SECTION 0: 0 2 201721 SECTION 1: 9 170 2 1 1 2007 10 23 23 0 0 0 1 Contains 0 Local Sections and 1 data fields. FIELD 1 SECTION 0: 0 2 SECTION 1: 9 170 2 1 1 2007 10 23 23 0 0 0 1 SECTION 3: 0 987601 0 0 20 GRID TEMPLATE 3. 20 : 0 0 0 0 0 0 0 1121 881 23097000 240964000 8 60000000 255000000 4762000 4762000 0 64 NO Optional List Defining Number of Data Points. PRODUCT TEMPLATE 4. 8 : 1 8 2 0 190 0 0 1 0 1 0 0 255 0 0 2007 10 24 0 0 0 1 0 1 2 1 1 255 0 FIELD: A PCP Surface valid 0 hr before 2007102323:00:00 to 2007102400:00:00 NO Optional Vertical Coordinate List. Num. of Data Points = 987601 with BIT-MAP 0 DRS TEMPLATE 5. 2 : 0 -3 0 7 0 1 0 0 0 12587 0 3 1 1 49 10 Data Values: MIN= .00000000 AVE= .14565143 MAX= 19.25000000 Total Number of Fields Found = 1 $ GRIB MESSAGE 1 starts at 1 SECTION 0: 0 2 1111248 SECTION 1: 9 170 2 1 1 2007 10 23 23 0 0 0 1 Contains 0 Local Sections and 1 data fields. ----------------------------------------------------------- FIELD 1 SECTION 0: 0 2 0 = GRIB2-Table0.0 Discipline Section 0, Octet7 => Meteorological Products 2 = GRIB2 - Section 0 Indicator Section Octet8 => Edition Number ------------------------------------------------------------ SECTION 1: 9 170 2 1 1 2007 10 23 23 0 0 0 1 9 = ON388-Table0 Grib2 (National/International Orig Ctr) - Section1 , Octets6-7 => US NWS - Other (WMC) 170 = ON388-TableC Grib2 (National Subcenters) - Section 1, Octets8-9 => Locally defined by originating center

  23. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example 2 = GRIB2-Table1.0 Section1, Octet10 => Future Operational Version Numbers (2-254) 1 = GRIB2-Table1.1 GRIB Local Tables Version Number Section 1, Octet 11 => Number of local table version used 1 = GRIB2-Table1.2 Significance of reference time Section 1, Octet12 => Start of Forecast 2007 10 23 23 0 0 => year,month,day hour minutes second 0 = GRIB2-Table1.3 Production Status of Data Section1, Octet20 => Operational products 1 = GRIB2-Table1.4 Type of data Section 1, Octet 21 => Forecast Products ---------------------------------------------------------------------- SECTION 3: 0 987601 0 0 20 ********************************* From GRADS Analysis of the file GRIB2400 (GRIB1) Gridded data that are mapped onto a particular map projection are called ‘pre-projected’. An example of pre- projected data is the output from a weather forecast model that is mapped onto a north polar stereographic grid. Number of data points = 987601 => dtype grib 255 pdef 1121 881 nps 401.03817080455 1601.18158182199 -105.000000 4.762 PDEF isize jsize NPS ipole jpole lonref gridinc PDEF isize jsize SPS ipole jpole lonref gridinc Example: PDEF 1121 881 nps 401.03817080455 1601.18158182199 -105.000000 4.762 Args: isize The size of the native grid in the x direction jsize The size of the native grid in the y direction ipole the i coordinate of the pole referenced from the lower left corner, assumed to be at (1,1) jpole the j coordinate of the pole referenced from the lower left corner, assumed to be at (1,1) lonref reference longitude gridinc distance between gripoints in km. Value should be negative for Southern Hemisph ere data. Notes: Polar stereographic projections (N and S) are defined as at NCEP. Wind rotation has also been added so that vector data will be properly displayed. ***********************

  24. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example 0 = GRIB2-Table3.0 Source of Grid Definition Section3, Octet 6 => Specified in Table 3.1 (Grid Definition template number) 987601 = GRIB2-Section3 Grid Definition Section Octet7-10 Number of data points 0 = GRIB2-Section3 Grid Definition Section Octet 11 => Number of octets for optional list of numbers defining number of points (See note 2 below) 0 = GRIB2-Section3 Grid Definition Section Octet 12 => Interpolation of list of numbers defining number of points (See Table 3.11 Interpretation of list of numbers defining number of points) Section 3, Octet 12 => There is no appended list 20 = GRIB2-Section3 Grid Defintion Section Octets13-14 Grid definition template number(=N) (See Table3.1 -GRIB2-Table3.1 Grid Definition Template Number Section3,Octets13-14) => Polar Stereographic Projection (North or South) (See Template 3.20) GRID TEMPLATE 3. 20 : 0 0 0 0 0 0 0 1121 881 23097000 240964000 8 60000000 255000000 4762000 4762000 0 64 GRIB2 - GRID Template 3.20 Polar stereographic projection has 18 values from octets 15-65 0 = GRID Template 3.20 Octet15 - Shape of the Earth (see Table3.2) => Earth assumed spherical with radius = 6,367,470.0 m 0 = GRID Template 3.20 Octet16 => Scale factor of radius of spherical Earth 0 = GRID Template 3.20 Octet17-20 => Scaled value of radius of spherical Earth 0 = GRID Template 3.20 Octet21 => Scale factor of major axis of oblate spheroid Earth 0 = GRID Template 3.20 Octet22-25 => Scaled value of major axis of oblate spheroid Earth 0 = GRID Template 3.20 Octet26 => Scale factor of minor axis of oblate spheroid Earth 0 = GRID Template 3.20 Octet27-30 => Scaled value of minor axis of oblate spheroid Earth 1121 = GRID Template 3.20 Octet31-34 => Nx - number of points along the x-axis 881 = GRID Template 3.20 Octet35-38 => Ny - number of points along the y-axis 23097000 = GRID Template 3.20 Octet39-42 => La1 -latitude of first grid point in millidegrees (10**(-6)) 240964000 = GRID Template 3.20 Octet43-46 => Lo1 - longitude of first grid point in millidegrees (10**(-6)) 8 = GRID Template 3.20 Octet 47 => Resolution and component flags (see Flag Table 3.3 and Note 1) Note1-The resolution flags (bits3-4 Flag table3.3) are not applicable 60000000 = GRID Template 3.20 Octet48-51 => LaD - latitude where Dx and Dy are specified (in millidegrees)

  25. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example 255000000 = GRID Template 3.20 Octet52-55 => LoV – orientation of the grid (see Note2) Note2-LoV is the longitude value of the meridian which is Parallel to the y-axis (or columns of the grid) along which latitude increases as the y-coordinate increases (the orientation longitude may or may not appear on a particular grid) 4762000 = GRID Template 3.20 Octet56-59 => Dx direction grid length (see Note2) 4762000 = GRID Template 3.20 Octet60-63 => Dy - y- direction grid length (see Note3) Note3-Grid length is in units of 10**(-3) m at the latitude specified by LaD. 0 = GRID Template 3.20 Octet64 => Projection centre flag (see Flag Table 3.5) (see Note4) Note4-Bit2 of the projection flag is not applicable to the polar stereographic projection. 64 = GRID Template 3.20 Octet65 => Scanning mode (see Flag Table 3.4) ---------------------------------------------------------------------- NO Optional List Defining Number of Data Points. PRODUCT TEMPLATE 4. 8 : 1 8 2 0 190 0 0 1 0 1 0 0 255 0 0 2007 10 24 0 0 0 1 0 1 2 1 1 255 0 29 values from GRIB2 - GRID Template 4.8 Product definition template - average, accumulation and/or extreme values or other statistically-processed values at a horizontal level or in a horizontal layer in a continuous or non-continuous time interval. 1 = GRIB2 - GRID Template 4.8 Octet10 - Parameter category (see Code Table 4.1) Parameter Category by product discipline section 4, octet 10 => Moisture (see Table 4.2-0-1) 8 = GRIB2 - GRID Template 4.8 Octet11 – Parameter number (see Code Table 4.2) => Total Precipitation (see Table 4.2-0-1) kg m**(-2) APCP 2 = GRIB2 - GRID Template 4.8 Octet12 - Type of generating process (see Code Table 4.3) => Forecast 0 = GRIB2 - GRID Template 4.8 Octet13 - Background generating process identifier (defined by originating center) 190 = GRIB2 - GRID Template 4.8 Octet14 - Analysis or forecast generating process identified (see Code ON388 Table A) => National Convective Weather Diagnostic generated by NCEP/AWC

  26. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example 0 = GRIB2 - GRID Template 4.8 Octet15-16 - Hours after reference time data cutoff (see Note 1) Note1 - Hours greater than 65534 will be coded as 65534 0 = GRIB2 - GRID Template 4.8 Octet17 - Minutes after reference time data cutoff (see Note1) 1 = GRIB2 - GRID Template 4.8 Octet18 - Indicator of unit of time range (see Code Table4.4) => Hour 0 = GRIB2 - GRID Template 4.8 Octet19-22 - Forecast time in units defined by octet 18 (see Note2) Note2-The reference time in section 1 and the forecast time together define the beginning of the overall time interval. 1 = GRIB2 - GRID Template 4.8 Octet23 - Type of first fixed surface (see Code Table4.5) => Ground or water surface 0 = GRIB2 - GRID Template 4.8 Octet24 - Scale factor of first fixed surface 0 = GRIB2 - GRID Template 4.8 Octet25-28 - Scaled value of first fixed surface 255 = GRIB2 - GRID Template 4.8 Octet29 - Type of second fixed surface (see Code Table 4.5) => Missing 0 = GRIB2 - GRID Template 4.8 Octet30 - Scale factor of second fixed surface 0 = GRIB2 - GRID Template 4.8 Octet31-34 - Scaled value of second fixed surfaces 2007 10 24 0 0 0 = GRIB2 -GRID Template 4.8 Octet35-36(year) 37(month) 38(day) 39(hour) 40(minute) 41(second) 1 = GRIB2 - GRID Template 4.8 Octet42 - n - number of time ranges specifications describing the time intervals used to calculate the statistically-processed field 0 = GRIB2 - GRID Template 4.8 Octet43-46 Total number of data values missing in statistical process 47-58 specification of the outermost (or only) time range over which statistical processing is done. 1 = GRIB2 - GRID Template 4.8 Octet47 - Statistical process used to calculate the processed field from the field at each time increment during the time range (see Code Table 4.10) => Accumulation 2 = GRIB2 - GRID Template 4.8 Octet48 - Type of time increment between successive fields used in the statistical processing (see Code Table 4.11) => Successive times processed have same start time of forecast, forecast time is incremented. 1 = GRIB2 - GRID Template 4.8 Octet49 - Indicator of unit of time for time range over which statistical processing is done (see Code Table 4.4) => Hour

  27. How to diagnose a degrib2 output from NCEP GRIB2 tables? Example 1 = GRIB2 - GRID Template 4.8 Octet50-53 - Length of time range over which statistical processing is done, in units defined by the previous octet => same value as for Octet49 255 = GRIB2 - GRID Template 4.8 Octet54 - Indicator of unit of time for the increment between the successive fields used (see Code Table 4.4) => Missing 0 = GRIB2 - GRID Template 4.8 Octet55-58 - Time increment between successive fields, in units defined by the previous octet (see Notes 3 and 4) 59-nn These octets are included only if n>1, where nn=46+12 x n Note3-An increment of zero means that the statistical processing is the result of continuous (or near continuous) process, not the processing of a number of discrete samples. ...... Note4-The reference and forecast times are successively set to their initial plus or minus the increment, as defined by the type of time increment (one of octets 48,60,72...). ........ ---------------------------------------------------------------------- TEXT: A PCP Surface valid 0 hr after 2007102323:00:00 to 2007102400:00:00 NO Optional Vertical Coordinate List. Num. of Data Points = 987601 with BIT-MAP 0 DRS TEMPLATE 5. 0 : 0 -3 0 8 0 GRIB2-GRID TEMPLATE 5.0 (Grid point data - simple packing) has 5 values GRIB2 - Section 5 Data Representation Section 987601 = Octet6-9 - Number of data points where one or more values are specified in Section 7 when a bit map is present, total number of data points when a bit map is absent => total number of data points with bit map = 0 DRS TEMPLATE 5. 0 = GRIB2 - Section 5 Octet10-11 – Data representation template number (See Table 5.0) => 0 is Grid Point Data - Simple Packing (see Template 5.0) 0 = GRIB2 - Grid Template 5.0 Octet12-15 – reference value (R) (IEEE 32-bit floating-point value) -3 = GRIB2 - Grid Template 5.0 Octet16-17 - Binary scale factor (E) 0 = GRIB2 - Grid Template 5.0 Octet18-19 - Decimal scale factor (D) 8 = GRIB2 - Grid Template 5.0 Octet20 - Number of bits used for each packed value for simple packing, or for each group reference value for complex packing or spatial differencing 0 = GRIB2 - Grid Template 5.0 Octet21 - Type of original field values (see Code Table 5.1) => Floating Point ----------------------------------------------------- Data Values: MIN= .00000000 AVE= .14565143 MAX= 19.25000000 total number of fields found = 1

  28. How to write GRIB2 directly? An example to convert APCP data into GRIB2 The degrib2 diagnostic was generated from APCP GRIB2 output and the source code is in: $ hostname c2n6.ncep.noaa.gov $ pwd /nco/save/sib/wx12kk/degrib2_analysis/sorc Input binary data file: XMRG2417 run script: sh runGRIB2.sh output: GRIB2417_grib2 Usage: HEtoGrib2_exec <input XMRG DIR> <XMRG file name> <output GRIB DIR> <output GRIB2 file name> For full details, see the source code: HEtoGrib2.f90 call write_nesdis_grib2(gnesdis,nx,ny,nflds,& varname,typeproc,isign, & rtime(1),rtime(2),rtime(3),rtime(4),rtime(5),rtime(6), & ityped,g2Path, accumHour, modelId, subCenter)

  29. NCO GRIB2Templates The template source code is in /nwprod/util/sorc/g2tmpl.fd Makefile grib2_all_tables_module.f params_grib2_tbl_new gdtsec3.f incmod process_4dot2.c gdtsec3.template libg2tmpl.a params_grib2_tbl_new ! !Table History Log: !2010-01-21 V. Krishna Kumar/NCO/SIB ! !GRIB2 parameter table for all disciplines and categories !The fields in order are grib2_discipline grib2_category !grib2_parameter_number grib2_table_information (0 for the parameter !from the WMO table and 1 for the parameter from teh NCEP local table) !grib2_NCEP_mnemonic (locally defined at NCEP). WMO parameters have values !ranging from 0 to 191 and NCEP local table parameters have values from 192 !to 254 and the parameter value 255 is a missing or undefined. !Comment cards with the !will not be read by the program ! ! ! GRIB2 - TABLE 4.2-0-0 PARAMETERS FOR DISCIPLINE 0 CATEGORY 0 ! 0 0 0 0 TMP 0 0 1 0 VTMP 0 0 2 0 POT 0 0 3 0 EPOT 0 0 4 0 TMAX 0 0 5 0 TMIN 0 0 6 0 DPT 0 0 7 0 DEPR

  30. NCO Grib2 Templates … grib2_all_tables_module.f contains subroutine get_g2_subcenters(key,value,ierr) subroutine get_g2_sigreftime(key,value,ierr) subroutine get_g2_prodstatus(key,value,ierr) subroutine get_g2_typeofdata(key,value,ierr) subroutine get_g2_typeofgenproc(key,value,ierr) subroutine get_g2_versionno(key,value,ierr) subroutine get_g2_loctabversno(key,value,ierr) …. subroutine get_g2_fixedsurfacetypes type sigreftime character(len=20) :: sigrefkey integer :: sigrefval end type sigreftime ! Declare a variable of type discipline type(sigreftime),dimension(MAXREFTIME) :: table1_2 data table1_2(1) /sigreftime('anal',0)/ data table1_2(2) /sigreftime('fcst',1)/ data table1_2(3) /sigreftime('vfcst',2)/ data table1_2(4) /sigreftime('obstime',3)/ data table1_2(5) /sigreftime('missing',255)/ ! ! !

  31. NCO Grib2 Templates integer(4) listsec0(2) ! Length of section 0 octets 7 & 8 integer(4) listsec1(13) ! Length of section 1 from octets 6-21 integer(4) ipdstmpl0(15) ! Length of Section 4 PDS Template 4.0 subroutine g2sec0(idisc,listsec0) subroutine g2sec1(origin_key,subcen_key,vers_key,lvers_key, sigreftime_key,refyear_val, refmon_val,refday_val,refhour_val, refmin_val,refsec_val,prodstatus_key,typeofdata_key,listsec1) subroutine g2sec4_temp0(icatg,iparm,typ_gen_proc_key, & gen_proc_or_mod_key,hrs_obs_cutoff,min_obs_cutoff, & unit_of_time_key,fcst_time,lvl_type1,scale_fac1, & scaled_val1,lvl_type2,scale_fac2,scaled_val2, & ipdstmpl0) Subroutine g2sec4_temp8(icatg,iparm,typ_gen_proc_key,gen_proc_or_mod_key, & hrs_obs_cutoff,min_obs_cutoff,unit_of_time_key, & fcst_time,lvl_type1,scale_fac1,scaled_val1,lvl_type2, & scale_fac2,scaled_val2,year_intvl, & mon_intvl,day_intvl,hour_intvl,min_intvl,sec_intvl, & num_time_range,stat_miss_val,type_of_stat_proc, & type_of_time_inc,stat_unit_time_key, & leng_time_range_stat,stat_unit_time_key_succ, & time_inc_betwn_succ_fld,ipdstmpl8)

  32. NCO Grib2 Templates subroutine g2sec5_temp0(dec_scale_fac,type_of_field,ifield5) subroutine g2sec5_temp40(dec_scale_fac,bin_scale_fac,tlnumbits, & type_of_field, type_of_compression,ifield5,len,fld) Makefile SHELL=/bin/sh LIB = ./libg2tmpl.a -------------Library Name INCMOD = ./incmod/g2tmpl FC = ncepxlf90 CC = ncepxlc FFLAGS = -qnosave -O3 -q free=f90 -I$(INCMOD) AR = ar ARFLAGS = -rv -X64 $(LIB): $(LIB)(process_4dot2.o) $(LIB)(grib2_all_tables_module.o) $(LIB)(gdtsec3.o) $(LIB)(process_4dot2.o): process_4dot2.c $(CC) -O3 -c $< $(AR) $(ARFLAGS) $@ $*.o rm -f $*.o

  33. NCO Grib2 Templates gdtsec3.template (Fix file of all NCEP Grids) # # PREDEFINED GRIB2 GRID DEFINITION TEMPLATE # # The format of the file scanned by routine getgridnum is as follows. # Each line contains one Grid ID entry containing eight fields, each separated # by a space " ". The fields are: # 1) - The first character is a space # 2) - predefined grid ID number # 3) - Grid Definition Template number # 4) - Number of entries in the Grid Definition Template # 5) - Contains information read from the appropriate GRIB Grid # 6) - A list of values for each entry in the Grid Definition Template. # 7) - The number of entries in array ideflist i.e., number of rows # (or columns) for which optional grid points are defined. eg. WAFS grid # 8) - Optional integer array containing the number of grid points contained # in each row (or columns). # # Comments can be included in the file by specifying the symbol "#" as the first # character on the line. # # 1 10 19 0 1679 0 0 10 6 0 0 0 0 0 0 73 23 -48090000 0 48 22500000 48090000 0 64 0 513669000 5 13669000 0 0 gdtsec3.f (Fortran code that reads the fix grid files)

  34. Changes are made into NCEP POST to add an option to generate GRIB2 output files directly 1. Using XML post control files 2. Apply NCO’s grib2 templates and g2 lib to generate grib2 message 3. parallel generate grib2 messages and parallel write out the messages The changes are backward compatible, nothing need to be changed to run NCEP POST for grib1 output Details are on Cirrus: /climate/noscrub/wx20wa/grib2 See Jun’s power point on SIB WWW2 GRIB2 Resources page Courtesy of Jun Wang Parallel GRIB2 In NCEP POST Jun Wang

  35. Add grib2 option in post • Grib2 option is passed into post from scripts • All post fields are computed and saved in a data array, field information related to the post control file is save in fld_info • Gribit2 is called to parallel generate grib2 messages and to parallel write out grib2 message Courtesy Jun Wang

  36. Parallel generating and writing grib2 message • Each processor holds partial domain of data for all the output data fields in post computation; the data is then redistributed to all processors through mpi_alltoallv so that each processor holds whole domain data, but only with certain number of data fields. • All processors generate grib2 messages simultaneously • All processors exchange the information of their total grib2 message length • All processors will write out simultaneously through mpi_write_all Courtesy Jun Wang

  37. Courtesy Jun Wang Parallel generating and writing grib2 message PE1 PE1 PE1 gengrb2msg MPI IO MPI_ALLTOALLV Grb2 file PE2 PE2 PE2 gengrb2msg MPI IO MPI_ALLTOALLV PE3 PE3 PE3 MPI IO gengrb2msg Grib2 messages for certain fields Partial domain data with all the output fields Whole domain data with certain number of output fields

  38. Grib2_module.f Contains subroutines to parallel generate grib2 messages using grib2 templates and to parallel write out grib2 file Public num_pset,nrecout type(paramset_t),save :: pset, subroutine grib_info_init(first_grbtbl) subroutine grib_info_finalize subroutine gribit2(post_fname) Private: subroutine gengrb2msg(idisc,icatg, iparm,nprm,nlvl,ntrange,tinvstat,datafld1,cgrib,lengrib) subroutine getgds(ldfgrd,len3,ifield3len,igds,ifield3) use gridspec_mod, only: DXVAL,DYVAL,CENLAT,CENLON,LATSTART, LONSTART, & LATLAST, LONLAST,MAPTYPE,STANDLON,latstartv,cenlatv,lonstartv, cenlonv, TRUELAT1, TRUELAT2 Courtesy Jun Wang

  39. Parallel GRIB2 Results from Jun Wang GFS master files from NEMS GFS (1152*576, 664 fields) B grid 8KM output from NEMS NMMB (954*835, 1098 fields)

  40. GRIB2 Encoding Routines To write a new GRIB2 message, the following routines are called: gribcreate, addlocal, addgrid, addfield and gribend. Gribcreate (gribcreate.f) This routine must be called first to initialize a new grib2 message. It uses to encode and pack section 0 and section 1. call gribcreate (cgrib,lcgrib,listsec0,listsec1,ierr) Section 0: Indicator Section This section uses to serve as the beginning of GRIB2 message. The length of this section is 16 bytes Octet 1-4 : Identifier ‘GRIB’ 5-6: Reserved 7: Discipline 8: GRIB edition number 2 9-16 Total length of GRIB message Example: Section 0 : 0 2 37048 Section 1: Identification The content of section are: originating center, sub-center, GRIB master table version, local table version, start of forecast, reference time, production status and type of processed data in this GRIB message (i.e., analysis, forecast, ...) Example: Section 1: 7 0 2 1 1 2010 12 17 12 0 0 0 1

  41. GRIB2 Encoding Routines Addlocal (addlocal.f) optional is used to add a Local Use Section 2 to GRIB2 message call addlocal (cgrib,lcgrib,csec2,lcsec2,ierr) Addgrid (addgrid.f) is used to add a Grid Definition Section (grid geometry of the data values in the field) to a GRIB2 message. call addgrid (cgrib, lcgrib, igds, igdstmpl, igdstmplen, ideflist, idefnum, ierr) For example: Section 3: 0 41760 0 0 0 Where octet (6 to 12) numbers are: 0 Lat-Lon grid 41760 number of data points 0 regular grid 0 regular grid 0 grid definition template 3.0 For example: 3.0 is Lat/Lon grid, 3.10 is Mercator grid See grid definition template 3.0 for details in NCEP GRIB2 documentation. Example: GRID TEMPLATE 3.0: 6 0 0 0 0 0 0 288 145 0 0 90000000 0 48 -90000000 385750000 1250000 1250000 0

  42. GRIB2 Encoding Routines • Addfield (addfield.f) This routine uses to add and packs up: Production Definition Section (section 4), Data Representation Section (section 5), Bit-Map section (section 6) and Data Section (section 7) to a GRIB2 message. call addfield (cgrib, lcgrib, ipdsnum, ipdstmpl, ipdstmplen, coordlist, numcoord, idrsnum, idrstmpl, idrstmplen, fld, ngrdpts, ibmap, bmap, ierr) For example: - Product Definition Section (section 4): 34 4 0 0 Where: 34 is length of section 4 4 number of section (4) 0 No values present (number of coordinate after template) 0 Product template number 0 (analysis or forecast at a point in time) See product template 4.0 for details in NCEP GRIB2 documentation. For example: PRODUCT TEMPLATE 4.0: 3 5 2 0 96 0 0 1 6 100 0 10000 255 0 0 FIELD: HGT 100 mb valid at 6 hr after 2010121700:00:00 NOTE: Parameter HGT defines by Discipline 0 (find in Section 0), category 3 and parameter 5

  43. GRIB2 Encoding Routines -Data Representation Section (section 5) DRS TEMPLATE 5. 40 : 1156161536 0 1 9 0 0 255 Where: 1156161536 Reference value of IEE (degrib2 will provide this value) – users will need to give only 0 Binary scale factor binary scale or decimal scale and number of bits (precision) 1 Decimal scale factor 9 Number of bits required to hold the resulting scaled and referenced data values. 0 Floating point (see table 5.1) 0 Lossless (see table 5.40) 255 Target compression ratio -Bit-Map Section (section 6) 1-4 Length of the section in octets (nn) Number of the section 6 Bit-map indicator see table 6.0 i.e., 0 bit-map applied to this product, 1-253 a bit-map predetermined by generating center and 255 No bit-map 7-nn Bit-map -Data Section (section 7) Where: 1-4 Length of the section in octet (nn) Number of the section 7 6-nn Data in format described by template 7.x where x is the data representation template number given in octets 10-11 of section 5

  44. GRIB2 Encoding Routines Gribend (gribend.f) This routine finalizes a GRIB2 message after all grids and fields have been added. It adds the End Section (“7777”) to the end of the GRIB2 message and calculates the length of GRIB2 message and stores it in the section 0 in (octet 9 – 16) call gribend (cgrib, lcgrib, lengrib, ierr)

  45. GRIB2 Decoding Routines To Read a GRIB2 message with call routines are following: Gb_info (gb_info.f) Is used to search through a GRIB2 message to find out how many local use sections and data fields found in the a given GRIB2 message call gb_info (cgrib, lcgrib, listsec0, listsec1, numfields, numlocal, maxlocal, ierr) Gf_getfld (gf_getfld.f) Is used to get all information of grid definition (section 3), product template (section 4), Bit-map (if applicable), and the unpack data values for a given data field. All information returned is store in a derive type variable “gfld” call gf_getfld (cgrib, lcgrib, ifldnum, unpack, expand, gfld, ierr) gfld is a type of gribfield which is defined in module grib_mod (see grib_mod.f for declaration of derive type gribfield) Users of this routine have to include the line below in your code. Example: use grib_mod parameter (maxsize=200000) integer :: listsec0(3), listsec1(13) type (gribfield) :: gfld . . . See the example of program degrib2.f that how to call routines gb_info.f and gf_getfld.f to get the information and data values in the GRIB2 message.

  46. Declaration of Derived type gribfield • type gribfield          integer :: version,discipline          integer,pointer,dimension(:) :: idsect          integer :: idsectlen          character(len=1),pointer,dimension(:) :: local          integer :: locallen          integer :: ifldnum          integer :: griddef,ngrdpts          integer :: numoct_opt,interp_opt,num_opt          integer,pointer,dimension(:) :: list_opt          integer :: igdtnum,igdtlen          integer,pointer,dimension(:) :: igdtmpl          integer :: ipdtnum,ipdtlen          integer,pointer,dimension(:) :: ipdtmpl          integer :: num_coord          real,pointer,dimension(:) :: coord_list          integer :: ndpts,idrtnum,idrtlen          integer,pointer,dimension(:) :: idrtmpl          logical :: unpacked          logical :: expanded          integer :: ibmap          logical*1,pointer,dimension(:) :: bmap          real,pointer,dimension(:) :: fld      end type gribfield • If variable “gfld” is declared of type gribfield. For example: Type (gribfield) :: gfld The variable “gfld” would have the following components: gfld%version = GRIB edition number ( currently 2 )

  47. Declaration of Derived Type Gribfield gfld%discipline = Message Discipline ( see Code Table 0.0) gfld%idsect() = Contains the entries in the Identification section 1 gfld%idrtmpl() = Contains the data values for the specified Data Representation Template gfld%idsectlen = Number of elements in gfld%idsect().   gfld%local() = Pointer to character array containing contents                     of Local Section 2, if included gfld%locallen = length of array gfld%local() … etc … See routine (gribmod.f) in documentation block for more components of variable “gfld” is declared of type gribfield

  48. How to use routine getgb2? • Getgb2 (getgb2.f) Is used to search for selected fields and unpack from a GRIB2 message Call getgb2 (lugb,lugi,j,jdisc, jids, jpdtn, jpdt, jgdtn,jgdt, unpack, k, gfld, iret) Where: J INTEGER NUMBER OF FIELDS TO SKIP ( J=0 search from beginning) JDISC    GRIB2 DISCIPLINE NUMBER OF REQUESTED FIELD                  ( IF = -1, ACCEPT ANY DISCIPLINE)   JIDS    INTEGER ARRAY OF VALUES IN THE IDENTIFICATION SECTION                 (=-9999 FOR WILDCARD)  JPDTN    INTEGER PRODUCT DEFINITION TEMPLATE NUMBER (N)                  ( IF = -1, DON'T BOTHER MATCHING PDT - ACCEPT ANY )  JPDT     INTEGER ARRAY OF VALUES DEFINING THE PRODUCT DEFINITION                  TEMPLATE 4.N OF THE FIELD FOR WHICH TO SEARCH                  (=-9999 FOR WILDCARD)  JGDTN  INTEGER GRID DEFINITION TEMPLATE NUMBER (M)                  ( IF = -1, DON'T BOTHER MATCHING GDT - ACCEPT ANY )  JGDT   INTEGER ARRAY OF VALUES DEFINING THE GRID DEFINITION                  TEMPLATE 3.M OF THE FIELD FOR WHICH TO SEARCH                  (=-9999 FOR WILDCARD)

  49. How to Use Getgb2? An example of using getgb2 to search for field (Temperature at 100 mb) by product definition template. Initialize all variables to default -9999 or -1 for wildcard J = 0 Search from the beginning of GRIB2 file DJDSC=-1 Discipline number JIDS=-9999 Identification Section JGDTN=-1 Grid Definition Template Number JGDT=-9999 Grid Definition Template JPDTN=-1 Product Definition Template Number JPDT=-9999 Product Definition Template Search selected field by product definition template number and the values of product definition template 4.n of the field JPDTN = 0 Production template 4.0 for Temperature at 100mb JPDT(1:15)=(/ 0,0,2,0,96,0,0,1,6,100,0,10000,255,0,0 /)

  50. How to use Getgb2? How do we get this information for field Temperature at 100mb from GRIB2 message ? We can use utility degrib2 to display the content of GRIB2 message degrib2 grib2file GRIB MESSAGE 2 starts at 49405 SECTION 0: 0 2 17175 SECTION 1: 7 0 2 1 1 2010 12 13 0 0 0 0 1 Contains 0 Local Sections and 1 data fields. FIELD 1 SECTION 0: 0 2 SECTION 1: 7 0 2 1 1 2010 12 13 0 0 0 0 1 SECTION 3: 0 41760 0 0 0 GRID TEMPLATE 3. 0 : 6 0 0 0 0 0 0 288 145 0 0 90000000 0 48 -90000000 358750000 1250000 1250000 0 NO Optional List Defining Number of Data Points. PRODUCT TEMPLATE 4. 0 : 0 0 2 0 96 0 0 1 6 100 0 10000 255 0 0 FIELD: TMP 100 mb valid 6 hr after 2010121300:00:00 NO Optional Vertical Coordinate List. Num. of Data Points = 41760 NO BIT-MAP DRS TEMPLATE 5. 40 : 1156022272 0 1 9 0 0 255 Data Values: MIN= 185.19999695 AVE= 207.57528687 MAX= 232.00000000