GRIB Catalogue Autumn 2006

Met Office FitzRoy Road Exeter EX1 3PB United Kingdom

Version 2.1

EXETER NUMERICAL WEATHER PREDICTION

GRIB PRODUCTS GUIDE

Autumn 2006

For more information, please contact: Jim Galvin Tel: +44(0)1392 886997 National Meteorological Service Customer Manager Fax: +44(0)1392 885681 Met Office E-mail: [email protected] Road Internet: http://www.metoffice.gov.ukExeter EX1 3PB UNITED KINGDOM

mailto:[email protected]

http://www.metoffice.com/

Exeter numerical weather prediction GRIB products guide – autumn 2006

This report supersedes The use of gridded binary code in producing products from Exeter

(FM92-IX GRIB – Edition 1), 2004 and

Exeter numerical weather prediction GRIB products manual, autumn 2004 Please note that GRID products are no longer available from the Met Office Amendments made to tabulated contents and new data types added to guide produced 31 March 2006

31 October 2006

Version 2.1 2


Contents Page

1. Introduction to GRIB 5

2. Data packing method 6

3. Indicator section (Section 0) 6

4. Product definition section (Section 1) 6

5. Grid description section (Section 2) 10

6. Bitmap section (Section 3 – optional) 10

7. Binary data section (Section 4) 11

8. End section (Section 5) 11

9. Availability of GRIB products and further guidance on GRIB coding 11

10. GRIB bulletins available from the Met Office 11

11. WMO Resolution 40 12

12. Code forms 12

13. Requests for products 12

14. Availability 13

15. Format of bulletins 13

16. Reference 13

Catalogue of Met Office GRIB products 14

Annex 1: GRIB code 27

Annex 2: ICAO thinned grid 29

Annex 3: Procedure or model used to generate the data field: Exeter definitions of code mm 31 Annex 4: Scale factor E used in ICAO ‘Thinned GRIB’ bulletins issued by the Met Office 32 Appendix A: Tables of GRIB parameters 33 Appendix B: Example of a GRIB bulletin 37 List of abbreviations used in this guide 39

Version 2.1 3


Version 2.1 4


EXETER NUMERICAL WEATHER PREDICTION GRIB PRODUCTS GUIDE 1. Introduction to GRIB

1.1 GRIB (GRIdded Binary) code is a general-purpose bit-orientated code developed by the World Meteorological Organization (WMO) as a highly efficient data exchange format, used for the transmission of large volumes of gridded data over high-speed telecommunication lines. The data are packed into GRIB code, making the bulletins more compact, so decreasing the transmission time between computers. Each bulletin contains a grid-point field of a single parameter at a single level as a continuous bit stream made up of a sequence of octets (1 octet = 8 bits) within a communications envelope. The octets of a GRIB message are grouped into sections. Each section will always contain an even number of octets, so that there may be zero filling at the end of a section. The Exeter GRIB bulletin consists of between four and six sections, as follows:

Indicator section (Section 0)*

Product definition section (Section 1)

Grid description section – optional (Section 2)

Bitmap section – optional (Section 3)

Binary data section (Section 4)

End section (Section 5)

1.2 Octets are numbered consecutively from the start of each section; bits within an octet are also numbered from left (the most significant bit) to right (the least significant bit). Thus an octet with bit 8 set to the value 1 would have the integer value 1; with bit 7 set to the value 1 it would have an integer value of 2; with bit 6 set to the value 1 it would have an integer value of 4 etc.

1.3

1.4

1.5

In this document, all hexadecimal numbers are enclosed in parentheses, followed by the word hex.; decimal numbers are printed as they are; and a single string of characters is represented inside single quotes. Character representation in GRIB is in 7-bit ASCII code (CCITT-ITA No. 5).

The numbering of tables in this text is as follows. Tables given within the main text contain code definitions that are defined by the Met Office and which may be unique to the Met Office. Appendix A contains tables described for GRIB in the WMO Manual on codes (WMO 2001), which is the final authority on GRIB coding.

Met Office GRIB bulletins appear in GRIB Edition 1 (FM92-XI).

*GRIB data exchanged over the WMO Global Telecommunication System (GTS) are encapsulated in a telecommunications envelope. The content of this envelope depends on the communications protocol used. After the end section, an ASCII string: ‘carriage return, carriage return, line feed, end of transmission’ (0D0D0A03)hex. is added.

Version 2.1 5


2. Data packing method

Data are coded as binary integers using the minimum number of bits required for accuracy: values are given relative to an encoded reference value and are scaled by an appropriate power. The representation of a single value is such that:-

Y * 10D = R + (X * 2E) where

Y = real value D = decimal scale factor R = reference value (32 bits) X = packed value E = scale factor (sign bit, followed by a 15-bit integer)

The value of D is always set to 0 in Met Office GRIB bulletins, so that Y = R + (X * 2E). However, please note that the Met Office is able to decode GRIB bulletins that use D, rather than E, to pack data. In Met Office GRIB bulletins, the reference value R is always the minimum value of the data that are being represented in the code. R is a four-octet single-precision floating-point number, the first bit indicating the sign (s), the next seven bits, the biased exponent (A) and the remaining 24 bits, the mantissa (B). The characteristic is converted to a power of 16 by subtraction of 64 from its 7-bit representation. The value of R is calculated using the following formula:-

R = (-1)S * 2-24 * B * 16(A−64)

3. Indicator section (Section 0)

Octet No.

1 – 4 ‘GRIB’ (coded in CCITT-ITA No. 5)

5 – 7 Total length of GRIB message in octets

8 GRIB edition number (1 for this implementation)

4. Product definition section (Section 1)

Octet No. 1 – 3 Length of section (in the Met Office, 28 octets)

4 Version number of parameter table (3 for international exchange)

5 Identification centre: Exeter is (4A)hex. (i.e. 74)

6 Model identification (Table 1)

7 Grid identification (Table 2)

8 Indicator for presence of grid description section and bitmap section (Table 3)

9 Indicator of parameter and units (Table A1, p. 29 and Table 4)

10 Indicator of type of level (Table A2, p. 30)

11 – 12 Level parameter (Table A2, p. 30)

13 Year of century: 3 for 2003 )

14 Month of year )

15 Day of month ) Reference time of data

16 Hour of day )

17 Minute of hour )

18 Indicator of forecast time unit (Table A3)

Version 2.1 6


19 Time range (number of forecast time units)

20 Reserved (set to zero)

21 Time range indicator for accumulated or averaged variables (Table A4)

22 – 23 Number included in calculation when octet 21 refers to a statistical process, such as average or accumulation, otherwise set to zeros (Table A4)


25 Century of reference time of data (for 21st century, code 21)


27 – 28 Units decimal scale factor (D = 0 in Met Office GRIB bulletins)

Table 1. Generating model (octet 6 of the product definition section)

Designator Designator

dec. hex.

Model

dec. hex.

Model

12 0C Bespoke (limited-area) storm-surge analysis

87 57 Bespoke (mesoscale) area storm-surge forecast

13 0D Bespoke (limited-area) atmospheric analysis

43 2B Bespoke (mesoscale) area atmospheric forecast

15 0F Global atmospheric analysis 45 2D Global atmospheric forecast

17 11 Bespoke (limited-area) shelf-seas analysis

86 56 Bespoke (mesoscale) area shelf-seas forecast

18 12 European wave hindcast 88 58 European wave forecast

19 13 Global wave hindcast 89 59 Global wave forecast

21 15 Balkans mesoscale-model analysis 51 33 Balkans mesoscale-model forecast

22 16 Middle East mesoscale-model analysis

52 34 Middle East mesoscale-model forecast

23 17 Stratospheric model analysis 53 35 Stratospheric model forecast

24 18 South-west Asia mesoscale-model analysis

54 36 South-west Asia mesoscale-model forecast

25 19 Global ocean-atmosphere analysis (FOAM)

27 1B Global sea-surface-temperature analysis

85

55

Global multi-layer ocean-

atmosphere forecast (FOAM)

30 1E UK waters wave-model analysis 60 3C UK waters wave-model forecast

Version 2.1 7


Table 2. Grid area and location

Octet 7 of the product definition

section

Resolution (lat./lon.)

Area covered Grid columns

Grid rows

Grid points

14 2.5o x 2.5o 50oW – 70oE, 0o – 90oN

37 49 1813

15 2.5o x 2.5o 70oE – 170oW, 0o – 90oN

37 49 1813

16 2.5o x 2.5o 170oW – 50oW, 0o – 90oN

37 49 1813

17 2.5o x 2.5o 50oW – 70oE, 90oS – 0o

37 49 1813

18 2.5o x 2.5o 70oE – 170oW, 90oS – 0o

37 49 1813

19 2.5o x 2.5o 170oW – 50oW, 90oS – 0o

37 49 1813

37 1.25o x 1.25o

30oW – 60oE,

0o – 90oN 73 73 3447

‘thinned’ 38 1.25o x 1.25o 60oE – 150oE,

0o – 90oN 73 73 3447

‘thinned’ 39 1.25o x 1.25o 150oE – 120oW,

0o – 90oN 73 73 3447

‘thinned’ 40 1.25o x 1.25o 120oW – 30oW,

0o – 90oN 73 73 3447

‘thinned’ 41 1.25o x 1.25o 30oW – 60oE,

90oS – 0o73 73 3447

‘thinned’ 42 1.25o x 1.25o 60oE – 150oE,

90oS – 0o73 73 3447

‘thinned’ 43 1.25o x 1.25o 150oE – 120oW,

90oS – 0o73 73 3447

‘thinned’ 44 1.25o x 1.25o 120oW – 30oW,

90oS – 0o73 73 3447

‘thinned’ 255

‘missing’ 1.25o x 1.25o 70oW – 35oE,

32.5oN – 75oN 35 85 2975

255 ‘missing’

2.5o x 2.5o 30oW – 60oE, 60oS – 60oN

37 49 1813

255 ‘missing’

0.25o x 0.25o 11.5ºE − 13ºW, 48ºN − 63ºN

61 99 6039

255 ‘missing’

0.25o x 0.25o 27°E − 3°E 33.5°N − 48.5°N

61 99 6039

255 ‘missing’

0.25o x 0.25o 54.5°E − 39.5°E 17.5°N − 41.5°N

61 99 6039

255 ‘missing’

0.25o x 0.4o 13ºE − 14ºW 40ºN − 67ºN

68 109 ~4560 (sea-surface points

only)

Notes on Table 2

1) The grid points are laid out in a linear array, such that the longitude index is the most rapidly varying. The first point in the message is at the westernmost meridian and the southern circle of latitude.

2) Data for the pole points are given as a polar row. Wind components at the pole are given by the formulae: U = −speed * sin(dd)

V = −speed * cos(dd)

Version 2.1 8


where dd is the direction, as reported according to the specification of wind direction at the poles (WMO No. 306 Manual on codes, Vol. I, Part A, Code Table 878). At the North Pole, the observer faces into the wind and reports the value of the west longitude meridian along which the wind is coming; at the South Pole, the observer does likewise, but reports the east longitude meridian value.

3) Most of the “thinned” GRIB products are owned by the ICAO and the permission of the national civil aviation meteorological authority must be obtained for their receipt and use.

Table 3. Octet 8 of the product definition section

Grid description section Bitmap section Coded value No No 0 No Yes 64 Yes No 128 Yes Yes 192

Table 4. Parameter number (octet 9 of product definition section) defined by the Met Office

Code figure Field parameter Unit Code figure Field parameter Unit 128 Wet-bulb potential

temperature K 153 Convective cloud base Pa

129 Potential vorticity on θ surface

Km2kg-1s-1 154 Convective cloud top Pa

130 Fog fraction at 1.5 m Pa s-1 155 Duct height m 131 Snow probability % 156 Duct intensity (max.

wavelength) m

132 Surface moisture flux per time slice

kg m-2 157 Sea-surface temperature

K

133 Wind mixing energy Wm-2 158 Evaporation from sea kg m-2s-1

134 Net solar radiation flux (top or bottom)

Wm-2 159 Sea-ice cover (amount) -

135 Net infra-red radiation flux (top or bottom)

Wm-2 160 -20oC isotherm pressure

Pa

136 u-component of surface wind stress

Nm-2 161 -20oC isotherm ICAO height

ft. x 1000

137 v-component of surface wind stress

Nm-2 162 Freezing-level isotherm ICAO height

ft. x 1000

138 Fog fraction at 1.5 m (for use on DPDS)

% 163 Contrail lower limit ft. x 1000

139 (Not used) - 164 Contrail upper limit ft. x 1000 140 Accumulated convective

precipitation kg m-2 165 Freezing-level pressure Pa

141-142 (Not used) - 166 -20oC isotherm true height

m

143 Dynamic rainfall rate kg m-2s-1 167 D factors - 144 Convective rainfall rate kg m-2s-1 168 Mean icing potential % 145 Convective local rainfall

rate kg m-2s-1 169 Max. icing potential %

146 Dynamic snowfall rate kg m-2s-1 170 Mean in-cloud turbulence potential

% 100 km-1

147 Convective snowfall rate kg m-2s-1 171 Max. in-cloud turbulence potential

% 100 km-1

148 Orography m 173 Max. clear-air turbulence potential

% 100 km-1

149-152 (Not used) - 174 Cumulonimbus horizontal extent

Version 2.1 9


Code figure Field parameter Unit Code figure Field parameter Unit 175 Pressure at CB base Pa 225 Sea-water density kg m-3

176 Pressure at CB top Pa 226 Small-sediment density kg m-3

177 Pressure at embedded CB base

Pa 227 Large-sediment density kg m-3

178 Pressure at embedded CB top

Pa 228 Wave peak period s

179 ICAO height at CB base ft. x 1000 229 Surge height m 180 ICAO height at CB top ft. x 1000 230 Surge current speed ms-1

181 ICAO height at embedded CB base

ft. x 1000 231 Surge current direction o true

182 ICAO height at embedded CB top

ft. x 1000 232 Tide water level m

183-186 (Reserved) - 233 Tide current speed ms-1

187-222 (Not used) - 234 Tide current direction o true 223 Canopy water near

surface kg m-2

(mm) 235-255 (Not used) -

224 Total elevation of tide and surge

m

5. Grid description section (Section 2)

Octet No.

1 – 3 Length in octets of the grid description section

4 Number of vertical co-ordinates

5 Location (octet) of vertical co-ordinate parameters (coded as 255 – missing, if none)

6 Type of grid (Table A5)

7− 32 Grid definition

For latitude/longitude grid:

7 – 8 number of columns

9 – 10 number of rows

11 – 13 latitude of first grid point

14 – 16 longitude of first grid point

17 resolution and component flag

18 – 20 latitude of last grid point

21 – 23 longitude of last grid point

24 – 25 i direction increment

26 – 27 j direction increment

28 scanning mode indicator

29 – 32 reserved (set to zero)

33 – 52 If present, extension to define rotated grids, space-view, Lambert conformal or Mercator grids, as given in WMO No. 306: Manual on codes, Vol. I.2, Part B (WMO 2001)

33 − 178 If present, extension used to define the WAFC thinned grid (shown in Annex 2)

Version 2.1 10


6. Bitmap section (Section 3 – optional)

Octet No.

1 – 3 Length of bit-map section in octets (even number)

4 Number of vertical co-ordinates

5 – 6 If 0, a bitmap follows; if 1, a predetermined bitmap is referenced.

7 – nnn The bitmap (zero filled to an even number of octets)

7. Binary data section (Section 4)

The binary data section contains both the scaling information needed to reconstruct the original data and the packed data. The data are zero filled to an even number of octets.

Octet No.

1 – 3 Length of binary data section in octets (even number)

4 First 4 bits set to zero, last 4 bits give number of unused bits at the end of the section (0 to 7)

5 – 6 Scale factor (E – determined according to the level of accuracy required in the bulletin and the value of R). A negative value is indicated by setting the first bit to 1.

7 – 10 Reference value (R – minimum value)

11 Number of bits into which each element of the data is packed

12 – nnn Packed binary data (values of parameter being transmitted)

8. End section (Section 5)

Octet No.

1 – 4 ‘7777’ indicates end of message (CCITT-ITA No. 5)

9. Availability of GRIB products and further guidance on GRIB coding

9.1 Most GRIB products are available for immediate transmission. However, there is a very small number of products not produced on a regular basis; arranging regular production of these will take up to 3 weeks.

9.2 A guide to GRIB coding for Met Office staff (only) in FORTRAN 77 can be found at http://www01/metdb/ documentation/other/gribreadme_stash.htm.

10. GRIB bulletins available from the Met Office

Details of the Met Office’s Numerical Weather Prediction (NWP) GRIB products, available from Exeter*, appear in the tables on pages 12-21. (Readers should be aware of the World Meteorological Organization’s policy and practice for the exchange of meteorological and related data and products, as given in WMO Resolution 40. This resolution is published in Exchange of meteorological data: guidelines on relationships in commercial meteorological activities – WMO policy and practice (WMO No. 837).

Version 2.1 11

http://www01/metdb/documentation/other/gribreadme_stash.htm


11. WMO Resolution 40

11.1 Exeter GRIB products are classified as follows:

GRIB products (T1 = H or Y)

(a) (i) ICAO Thinned GRIB products [A1 = (I−P), A2 = (B−G), viz.: H*(I−P)(B−G)** EGRR] are not covered by WMO Resolution 40. ICAO owns these bulletins and the permission of the national civil aviation meteorological authority must be obtained for their receipt and use. [Annex 2 is a description of Thinned GRIB products.]

(ii) All other GRIB products in this range are produced for commercial distribution and use.

(b) Global atmospheric NWP products [A1 = (S−X,Z), viz.: H*(S−X,Z)*** EGRR] and Regional atmospheric NWP products [A1 = R, viz.: Y*R*** EGRR]

(i) The following are classified as “essential”:

Mean sea-level pressure products for T+0, T+24, T+48, T+72, T+96 and T+120; 10-m (surface) wind products for T+0, T+24 and T+48; 850-hPa and 700-hPa height, relative humidity, temperature and wind products for T+0, T+24 and T+48; 500-hPa height products for T+0, T+24, T+48, T+72, T+96 and T+120; 500-hPa relative humidity, temperature and wind components for T+0, T+24, T+48.

(ii) All other GRIB products in this range are classified as “additional”.

(c) Ocean model products

(i) Products A1 = (S−X), viz.: H*(S−X)*88 EGRR are distributed on the same basis as “essential” atmospheric model products.

(ii) All other ocean-model GRIB products are produced for commercial distribution and use.

11.2 Conditions placed on additional data and products originating from the Met Office are in accordance with WMO Resolution 40.

12. Code forms

The Met Office uses a number of different code forms for the transmission of data. One of the most widely used is the World Meteorological Organization’s FM 92-XI Ext. GRIB code format. GRIB (gridded-binary) data is coded in binary form for transmission. This allows the transmission of large volumes of data over high-speed telecommunication lines. Full details of the code are given in Annex 1.

13. Requests for products

All requests for products should be addressed to:

Jamie Palmer Tel: +44(0)1392 886286 Customer Service and Performance Fax: +44(0)1392 885681 Met Office E-mail: [email protected] Road Exeter EX1 3PB United Kingdom

* Note that the indicator for Exeter remains EGRR following Met Office relocation from Bracknell.

Version 2.1 12

mailto:[email protected]


14. Availability

a. Most GRIB products are available for immediate transmission. However, there is a very small number of products that are not produced on a regular basis; arranging regular production of these will take up to 3 weeks. The “available about” times show when the last bulletin in the set is produced; delivery times need to be added to the quoted time (see table on p. 24).

b. Note that not all products are available for every level: for instance, surface data are not available for mean sea level and many products are only available for the surface.

15. Format of Bulletins

The basic unit of meteorological data and products issued by the Met Office is a Meteorological Bulletin. Full details of the format of a meteorological bulletin, also the structure that is added as part of the telecommunications transmission, can be found in Manual on the Global Telecommunication System (WMO No. 386), Volume I: Global Aspects, Part II: Operational Procedures for the Global Telecommunication System.

16. Reference

World Meteorological Organization (2001) Manual on codes, Vol. I.2, Part B: Binary codes (WMO No. 306). WMO, Geneva (amended to November 2003)

Version 2.1 13


Catalogue of Met Office GRIB products

GRIB code (FM 92-XI Ext.)

Page

T2 Parameter decode table 14

A1 Grid-area and grid-length decode table 18

A2 Analysis and forecast-time decode table 19

GRIB bulletin availability (atmosphere models) 20-22

GRIB bulletin availability (ocean models) 23

Forecast and analysis availability (atmosphere and ocean models) 24-25

GRIB bulletin size 26

Time of availability of Met Office GRIB bulletins 26

Annex 1. GRIB code 27

Annex 2. ICAO ‘thinned’ grid 29 Annex 3. Procedure or model used to generate the data field: Exeter definitions

of code mm 31

Annex 4. Scale factor E used in ICAO ‘Thinned GRIB’ bulletins issued by the Met Office 32

Note: this catalogue lists only those GRIB bulletins available for routine distribution by the Met

Office.

Version 2.1 14


T2 Parameter decode

Units Bulletin headers

B Pressure at cumulonimbus base Pa HB(I-P)(B-G)01

B Pressure at cumulonimbus top Pa HB(I-P)(B-G)02

B Pressure at embedded CB base Pa HB(I-P)(B-G)03

B Pressure at embedded CB top Pa HB(I-P)(B-G)04

B ICAO height at cumulonimbus base 103 ft. HB(I-P)(B-G)05

B ICAO height at cumulonimbus top 103 ft. HB(I-P)(B-G)06

B ICAO height at embedded CB base 103 ft. HB(I-P)(B-G)07

B ICAO height at embedded CB top 103 ft. HB(I-P)(B-G)08

B Cumulonimbus horizontal extent HB(I-P)(B-G)09

C Mean CAT potential % 100 km-1 HC(I-P)(B-G)(15,20,25,30,40)

C Maximum CAT potential % 100 km-1 HC(I-P)(B-G)(16,21,26,31,41)‡

E Total accumulated precipitation mm HE(A,B)(A,C,E,G,I,K)98, HEC(A-E,G,I-O)98, HE(I-P)(A-K)98, HE(S-X)(A-K,M,O,Q)98, YEA(A-G)98

G Total convective precipitation mm HG(A,B)(A,C,E,G,I,K)98, HGC(A-E,G,I-O)98, HG(I-P)(A-K)98, HG(S-X)(A-K,M,O,Q)98, YGA(A-G)98

H Height m HH(A-C)(A-G,I,K,M,O)(20,25,30,40,50,70), HH(A-C)(A-G,I,K,M,O)(85,99),

HH(I-P)(A,H-K)(07,10), HH(I-P)(A,H-K)(15,20,25,30,40,50,70,85,92)

HH(I-P)(A,H-K)(95-97,99), HH(I-P)(B-G) (07,10), HH(I-P)(B-G)(15,20,25,30,40,50,60,70,85,92),

HH(I-P)(B-G)(95-97,99), HH(I-P)(M,O,Q)50, HH(S-X)(A-I)(05,10,15,20,25,30,40,50,70,85,99)

I Mean icing potential % HI(I-P)(B-G)(70,60,50,40,30)

I Maximum icing potential % HI(I-P)(B-G)(71,61,51,41,31)†

J Fog fraction at 1.5 m YJR(B-I)98 only

J Significant wave height m YJN(A-O)88, HJ(S-X)(A-K,M,O)88

K Wind mixing J YKR(B-I)98 only

K Swell period s YKN(A,C,E,G,I,K,M,O)88, HK(S-X)(A-K,M,O)88

L Sensible heat flux Wm-2 Bulletins YLR(B-I)98 only

L Swell height m Bulletins YL(N,P)(A,C,E,G,I,K,M,O)88, HL(S-X)*88

Version 2.1 15



M Mean in-cloud turbulence potential % HM(I-P)(B-G)(30,40,50,60,70)

M Maximum in-cloud turbulence % HM(I-P)(B-G)(31,41,51,61,71)

M Latent heat flux Wm-2 YMR(B-I)98

M Wind-sea height m YMN(A,C,E,G,I,K,M,O,Q)88, HM(S-X)(A-K,M,O)88

N Net solar radiation Wm-2 YNR(B-I)98 only

N Swell direction o true YN(N,P)(A,C,E,G,I,K,M,O,Q)88, HN(S-X)(A,K,M,O)88

O Vertical velocity ms-1 HO(I-P)(A-K)(30,40,50,70,85,92,95)

P Pressure (at mean sea level) Pa HP(A-D,I-P,S-X)(A-K,M,O,Q)89

P Pressure (level of a defined Pa HP(A-D,I-P,S-X)(A-K)(96,97) parameter)

Q Net infra-red radiation Wm-2 YQR(B-I)98 only

Q Wind-sea direction o true YQN(A,C,E,G,I,K,M,O,Q)88, HQ(S-X)(A-K,M,O)88

R Relative humidity % HR(A,B)(A-G,I,K)(50,70,85,95,99), HRC(A-E,G,I-O)(50,70,85,95), HR(I-P)(B-H)(50,60,70,85,92,95,99), HR(I-P)(I-K)(50,70,85,92,95,99), HR(S-X)(A-K,M,O,Q)(50,70,85,95,98,99), YRR(A-M)(50,60,70,85,92,95,99)

T Temperature K HT(A-C)(A-G,I-O)(05,07,10,15,20,25,30,40), HT(A-C)(A-G,I-O)(50,70,85,95,98,99), HTD(A-I)(70,85,95,99),

HT(I-P)(A-K)(07,10,15,20,25,30,40), HT(I-P)(A-K)(50,70,85,95,97-99), HT(I-P)(B-H)60, HT(S-X)(A,I)(03,05,10,15,20,25,30,40,50,70,85,95), HT(S-X)(A,I)(97-99), HT(S-X)(B-H,J,K)(05,10,15), HT(S-X)(M,O,Q)(05,10,15) HT(S-X)(B-H,J,K)(20,25,30,40,50,70,85,95), HT(S-X)(M,O,Q)(20,25,30,40,50,70,85,95), HT(S-X)(B-H,J,K,M,O,Q)(97-99), HTZ(F,H)98, YTST(50,90,92,95), YTR(A-M)(10,15,20), YTR(A-M)(25,30,40,50,60,70,85,92,95,98,99)

U Eastward wind component ms-1 HUA(A-G,I,K,M,O)(20,25,30,40,50,70,85,96), HUA(A-G,I,K,M,O)(97-99), HUB(I,K)98,

HUB(A-G)(20,25,30,40,50,70,85,96,98,99), HUC(A-E,G,I-O)(05,07,10,15,20,25,30,40,50), HUC(A-E,G,I-O)(50,70,85,95,98,99), HUD(A-I)(70,85,95,99), HU(I-P)(A,I-K)(07,10,15,20,25,30,40,50,70,85),

HU(I-P)(A,I-K)(92,95,96,98,99),

Version 2.1 16



HU(I-P)(B-H)(07,10,15,20,25,30,40,50,60,70), HU(I-P)(B-H)(85,92,95,96,98,99),

HU(S-X)(A,E,I)(03,05,10,15,20,25,30,40,50,70), HU(S-X)(A,E,I)(85,92,95,96,98,99),

HU(S-X)(B-H,J,K,M,O,Q)(05,10,15,20,25,30,40), HU(S-X)(B-H,J,K,M,O)(50,70,85,92,95,96,98,99), YUR(A-M)(10,15,20,25,30,40,50,60,70), YUR(A-M)(85,92,95,98,99)

V Northward wind component ms-1 HVA(A-G,I,K,M,O)(20,25,30,40,50,70,85,96), HVA(A-G,I,K,M,O)(97-99), HVB(I,K)98,

HVB(A-G)(20,25,30,40,50,70,85,96,98,99), HVC(A-E,G,I-O)(05,07,10,15,20,25,30,40,50,70), HVC(A-E,G,I-O)(85,95,98,99),

HVD(A-I)(70,85,95,99), HV(I-P)(A,I-K)(07,10,15,20,25,30,40,50,70,85), HV(I-P)(A,I-K)(92,95,96,98,99),

HV(I-P)(B-H)(07,10,15,20,25,30,40,50,60,70), HV(I-P)(B-H)(85,92,95,96,98,99), HV(S-X)(A,E,I)(03,05,10,15,20,25,30,40,50,70), HV(S-X)(A,E,I)(85,92,95,96,98,99),

HV(S-X)(B-H,J,K,M,O,Q)(05,10,15,20,25,30,40), HV(S-X)(B-H,J,K,M,O)(50,70,85,92,95,96,98,99), YVR(A-M)(10,15,20,25,30,40,50,60,70), YVR(A-M)(85,92,95,98,99)

Y Wind-sea period s HY(S-X)(A-K,M,O)88,YYN(A,C,E,G,I,M,O,Q)88 * Note: some bulletins listed may not be available, especially issues from the 0600 and 1800 UTC model runs.

‡ Standard pressure levels indicated in these bulletins are at 150, 200, 250, 300 and 400 hPa.

† Standard pressure levels indicated in these bulletins are at 300, 400, 500, 600 and 700 hPa.

Version 2.1 17


A1 Grid-area and grid-length decode

Atmosphere models Ocean models

I 0o – 90o N, 30o W – 60o E 1.25o x 1.25o

J 0o – 90o N, 60o E – 150o E 1.25o x 1.25oN

66.25o N – 31.25o N,

31.75o W – 41.25o E 1.25o x 1.25o

K 0o – 90o N, 150o E – 120o W 1.25o x 1.25o S 0o – 90o N, 50o W – 70o E 2.5o x 2.5o

L 0o – 90o N, 120o W – 30o W 1.25o x 1.25o T 0o – 90o N, 70o E – 170o E 2.5o x 2.5o

M 90o S – 0o, 30o W – 60o E 1.25o x 1.25o U 0o – 90o N, 170o E – 70o W 2.5o x 2.5o

N 90o S – 0o, 60o E – 150o E 1.25o x 1.25o V 90o S – 0o, 50o W – 70o E 2.5o x 2.5o

O 90o S – 0o, 150o E – 120o W 1.25o x 1.25o W 90o S – 0o, 70o E – 170o W 2.5o x 2.5o

P 90o S – 0o, 120o W – 30o W 1.25o x 1.25o X 90o S – 0o, 170o W – 50o W 2.5o x 2.5o

R 32.5o – 75o N, 70o W – 35o E 1.25o x 1.25o

S 0o – 90o N, 50o W – 70o E 2.5o x 2.5o

T 0o – 90o N, 70o E – 170o W 2.5o x 2.5o

U 0o – 90o N, 170o W – 50o W 2.5o x 2.5o

V 90o S – 0o, 50o W – 70o E 2.5o x 2.5o

W 90o S – 0o, 50o E – 170o W 2.5o x 2.5o

X 90o S – 0o, 170o W – 50o W 2.5o x 2.5o

Z* 60o S – 60o N, 30o W – 60o E 2.5o x 2.5o

* Only bulletins for surface temperature available: HTZ(F,H)98

Version 2.1 18


Version 2.1 19

A2 Analysis and forecast-time decode

Global atmospheric model GRIB (2.5o x 2.5o resolution) H*(S-Z)***

A T + 0 (analysis) F T + 30 K T + 72 B T + 6 G T + 36 M T + 96 C T + 12 H T + 42 O T + 120 D T + 18 I T + 48 Q T + 144 E T + 24 J T + 60

Regional GRIB (1.25o x 1.25o resolution) Y*R***

A T + 0 (analysis) F T + 15 J T + 27 B T + 3 G T + 18 K T + 30 C T + 6 H T + 21 L T + 33 D T + 9 I T + 24 M T + 36 E T + 12

Global ocean model GRIB (2.5o x 2.5o resolution) H*(S-X)*88

A T + 0 (analysis) F T + 30 J T + 60 B T + 6 G T + 36 K T + 72 C T + 12 H T + 42 M T + 96 D T + 18 I T + 48 O T + 120 E T + 24

North-west European shelf-seas model GRIB (1.25o x 1.25o resolution) Y*N*88

A T + 0 (analysis) F T + 15 K T + 30 B T + 3 G T + 18 L T + 33 C T + 6 H T + 21 M T + 36 D T + 9 I T + 24 O T + 42 E T + 12 J T + 27 Q T + 48

Global atmospheric model “Thinned” GRIB for civil aviation (1.25o x 1.25o resolution) H*(I-P)***

A T + 0 (analysis) E T + 24 I T + 48 B T + 6 F T + 30 J T + 60 C T + 12 G T + 36 K T + 72 D T + 18 H T + 42

Not all parameters are available. Those bulletins regularly produced are listed in the T2 parameter decode on pp. 14-15 and the tables below.


H GRIB products available from RSMC, Exeter

Global model (UM5) – atmosphere

T2 ii = 99 ii = 98 ii = 97 ii = 96 ii = 95 ii = 89 ii = 85 ii = 70 ii = 60 ii = 50 ii = 40 ii = 30 ii = 25 ii = 20 ii = 15 ii = 10 ii = 05

E No Yes No No No No No No No No No No No No No No No

G No Yes No No No No No No No No No No No No No No No

H Yes No No No Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

P No No Yes Yes No Yes No No No No No No No No No No No

R Yes No No No Yes No Yes Yes Yes Yes No No No No No No No

T Yes Yes Yes No Yes No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes

U Yes Yes No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

V Yes Yes No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

Notes: ii = 98: Air properties at the earth’s surface Bulletins HH(S-X)(A-K)03 are also available at limited times.

Ii = 96, 97: Air properties at the tropopause and maximum wind level, respectively

ii = 89: Any parameter reduced to sea level

Bulletin size varies, dependent on element and packing; see table on p. 24

ii = 95, 85, 70,… : 950 hPa, 850 hPa, 700 hPa etc. mm = 15 (T + 0) or 45, see Annex 3

Not all elements are available at all times (see pp. 14-15).

Version 2.1 20


Y GRIB products available from RSMC, Exeter

Global model (UM5) for a limited-area – atmosphere

T2 ii = 99 ii = 98 ii = 95 ii = 92 ii = 89 ii = 85 ii = 70 ii = 60 ii = 50 ii = 40 ii = 30 ii = 25 ii = 20 ii = 15 ii = 10

E No Yes No No No No No No No No No No No No No

H Yes No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

J No Yes No No No No No No No No No No No No No

K No Yes No No No No No No No No No No No No No

L No Yes No No No No No No No No No No No No No

M No Yes No No No No No No No No No No No No No

N No Yes No No No No No No No No No No No No No

P No No No No Yes No No No No No No No No No No

Q No Yes No No No No No No No No No No No No No

R Yes No Yes Yes No Yes Yes Yes Yes No No No No No No

T Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

U Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

V Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes

Notes: ii = 98 : Air properties for the Earth’s surface (e.g. 10-m wind)

ii = 89 : Any parameter reduced to sea level

Bulletin size varies, dependent on element and packing; see table on p. 24

ii = 95, 92, 85, … : 950 hPa, 925 hPa, 850 hPa etc. mm = 15 (T + 0) or 45, see Annex 3

Not all elements are available at all times (see pp. 14-15).

Version 2.1 21


H GRIB products available from RSMC, Exeter

Global model (UM5) – atmosphere

ICAO Thinned GRIB for civil aviation

Please note that Thinned GRIB bulletins for T+6 to T+36 are owned by ICAO and the permission of the national civil aviation meteorological authority must be obtained for their receipt and use.

T2 ii = 99 ii = 98 ii = 97 ii = 96 ii = 95 ii = 92 ii = 89 ii = 85 ii = 70 ii = 60 ii = 50 ii = 40 ii = 30 ii = 25 ii = 20 ii = 15 ii = 10 ii = 07 ii = 01 to 09 B* No No No No No No No No No No No No No No No No No No YesC* No No No No No No No No No No No Yes Yes Yes Yes Yes No No NoE No Yes No No No No No No No No No No No No No No No No NoG No Yes No No No No No No No No No No No No No No No No NoH Yes No Yes Yes Yes Yes No Yes Yes Yes† Yes Yes Yes Yes Yes Yes Yes Yes NoI* No No No No No No No No Yes Yes Yes Yes Yes No No No No No No

M* No No No No No No No No Yes Yes Yes Yes Yes No No No No No NoO No No No No No No No Yes Yes No Yes Yes Yes Yes No No No No NoP No No Yes‡ Yes‡ No No Yes‡ No No No No No No No No No No No NoR Yes No No No Yes Yes No Yes Yes Yes† Yes No No No No No No No NoT Yes Yes Yes No Yes Yes No Yes Yes Yes† Yes Yes Yes Yes Yes Yes Yes Yes NoU Yes Yes No Yes Yes Yes No Yes Yes Yes† Yes Yes Yes Yes Yes Yes Yes Yes NoV Yes Yes No Yes Yes Yes No Yes Yes Yes† Yes Yes Yes Yes Yes Yes Yes Yes No

Notes: Not all elements are available at all times (see pp. 14-15). † A limited range of products is available for T + 6 to T + 36 for these levels or parameters.

ii = 98 : Air properties at the earth’s surface ‡ Bulletins H**A89, H**A96, H**A97 are available only from 0000 and 1200 UTC.

ii = 97 : Data valid for the tropopause mm = 15 (T + 0) or 45, see Annex 3

ii = 96 : Maximum wind speed or wind-pressure-level data

ii = 89 : Any parameter reduced to sea level

* These products are initially designated as "evaluation" use only and are expected to be available as GRIB bulletins later this year. They are not yet approved as operational.

ii = 95, 92, 85,… : 950 hPa, 925 hPa, 850 hPa etc. Bulletin size varies, dependent on element and packing; see table on p. 24. ii = 01 to 09 (T2 = B) : Cumulonimbus base and top levels

Version 2.1 22


H/Y GRIB products available from RSMC, Exeter

Ocean models (UM5) – for T1 = Y, A1 = N; for T1 = H, A1 = S-X

ii = 88 (ocean surface)

T2 J K L M N Q Y

T1 = H Yes Yes Yes Yes Yes Yes Yes

T1 = Y Yes Yes Yes Yes Yes Yes Yes

Notes: See p. 24 for available validity times for these bulletins.

† Bulletins H***88 and Y**88 are available only from 0000 and 1200 UTC. mm = 18/19 (T + 0) or 88/89, see Annex 3

Version 2.1 23


Forecast and analysis availability - atmosphere: most elements

Model type A2 T + 0 T + 3 T + 6 T + 9 T + 12 T + 15 T + 18 T + 21 T + 24 T + 30 T + 36 T + 42 T + 48

H Yes No Yes No Yes No Yes No Yes Yes Yes Yes YesAtmosphere

Y Yes Yes Yes Yes Yes Yes Yes Yes Yes No No No No

Thinned GRIB H Yes No Yes No Yes No Yes No Yes No Yes No No

Forecast and analysis availability - atmosphere: some elements‡

Model type A2 T + 27 T + 30 T + 33 T + 36 T + 39 T + 42 T + 48 T + 60 T + 72 T + 96 T + 120 T + 144

H No - No - No - - Yes Yes Yes Yes YesAtmosphere

Y Yes Yes Yes Yes Yes Yes Yes No No No No No

Thinned GRIB H No No No - No Yes Yes Yes Yes No No No

Notes: T + 0 : Analysis or initialised analysis

T + 3, T + 6 ...: Number of hours from initialisation time (T)

‡ Only a limited number of bulletins is available at these times (details can be supplied on request).

mm = 15 (T + 0) or 45, see Annex 3 Bulletin size is dependent on element and packing; see table on p. 24.

Version 2.1 24


Forecast and analysis availability – ocean model: all elements

Model type A2 T + 0 T + 6 T + 12 T + 18 T + 24 T + 30 T + 36 T + 42 T + 48 T + 60 T + 72 T + 96 T + 120

H Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes YesOcean

Y Yes Yes Yes Yes Yes Yes Yes No No No No No No

Forecast and analysis availability – ocean model: some elements

Model type A2 T + 3 T + 9 T + 15 T + 21 T + 27 T + 33 T + 42 T + 48

Ocean Y Yes Yes Yes Yes Yes Yes Yes Yes

Notes: T + 0 : Analysis or initialised analysis mm = 18 (T + 0) or 88, see Annex 3

T + 3, T + 6 ...: Number of hours from initialisation time (T)

Bulletin size is dependent on element and packing (see table on p. 24).

Version 2.1 25


26

GRIB bulletin size

Header Size Header Size

H*(S-Z)(A-Q)** 1.5 – 4 kbytes, average 2.2 kbytes H*(S-X)(A-O)88 1 – 1.5 kbytes, average 1.2 kbytes

Y*R(A-M)** 1.2 – 5 kbytes, average 3.1 kbytes Y*N(A-Q)88 0.7 – 1 kbyte, average 0.9 kbytes

H*(I-P)(A-K)** 3 – 6 kbytes, average 4.4 kbytes

Time of availability of Met Office GRIB bulletins

Header Time available Header Time available

H*(S-Z)(A-Q)** 0500 UTC, 1700 UTC H*(S-X)(A-O)88 0400 UTC, 1600 UTC

Y*R(A-M)** 0330 UTC, 1530 UTC Y*N(A-Q)88 0430 UTC, 1630 UTC

H*(I-P)(A-K)** 0500 UTC, 0900 UTC, 1700 UTC, 2100 UTC

Version 2.1

Exeter numerical weather prediction GRIB products guide – spring 2006

Version 2.0 27

Annex 1

GRIB Code

Coding data using GRIB code The Met Office uses a number of different code forms for the transmission of data. One of the most widely used is the World Meteorological Organization’s FM 92-XI Ext. GRIB code format1. GRIB is, as the name suggests, a binary code. This annex gives an overview of how GRIB is coded.

GRIB - FM 92-XI Ext. GRIB (gridded-binary) code is a World Meteorological Organization (WMO) standard code. It is used for the transfer of processed data in the form of grid point values. The data are coded in binary form for transmission. This allows the transmission of large volumes of data over high-speed telecommunication lines.

A GRIB record is made up of a number of sections. These are as follows: - Section 0 Indicator section Section 1 Product definition section Section 2 Grid description section (optional) Section 3 Bitmap section (optional) Section 4 Binary data section Section 5 7777

Section 0

This gives the start of the message, which is always the letters GRIB. This allows quick identification of the record as a GRIB record. It is followed by the total length of the record and the GRIB edition number (1).

Section 1

This section describes the product being transmitted in detail. Apart from the data itself, this is probably the most important section. As with all sections, the first part is the length. It allows identification of any additional information being coded at the end of the general section and is followed by the version number of the parameter table being used. However, to increase the flexibility of the code it is possible for an NWP centre to create its own parameter table. To identify the area that the data covers, WMO have defined a number of standard grid areas. If one of these is used, all that is required is the catalogue number of that grid. However, if a different grid is used, the grid description section is required, as explained below. The rest of the section is used to describe the data being transmitted, what the parameter is, its level, the forecast period and the data time.

Section 2

This section describes the grid area that the data covers. This need only be used if a WMO grid does not exist for the area being used. GRIB code can handle a number of grid types, including latitude/longitude, polar stereographic, rotated grids and spherical harmonic coefficients.

1 See WMO-No. 306 Manual on Codes, Volume I.1 Part A - Alphanumeric Codes and Volume I.2 Part B - Binary Codes, Part C - Common Features to Binary and Alphanumeric Codes.


Version 2.0 28

Section 3

This section is used to describe a bitmap used for missing data. One example of using such a bitmap is for wave data where there will be no data for land points. This reduces the number of data points being coded. The bitmap is coded as contiguous bits set to 0 and 1 with a bit to data point correspondence. An example of a bitmap to bitmap out missing data for wave data for Britain is shown in Figure 1.

Section 4

This section contains the data in a coded form, as well as the information required to reconstruct it. The most common method of packing the data is described below:-

a) The data are scanned to find the minimum value. This value is the reference value and is subtracted from all the values to give a field of values that are positive and have a zero base.

b) The number of bits in which the data is packed and the scale factor are now required. These are found in one of two ways:-

(i) The scale factor is set and the number of bits required is calculated. The advantage of this method is that the precision of all areas used can be the same, if so required.

(ii) The number of bits is set and the scale factor calculated. This method has the advantage that the length of the bulletin will always be the same.

c) Having obtained these values the data are packed using the following formula:-

Y = R + ( X * 2E ) where Y = real value R = reference value X = packed value E = scale factor The resulting field is truncated to be integer. To make up this section, the scale factor, reference value and number of bits containing each packed value are coded, followed by the field of integer values.

Section 5

This is the final section and contains the indicator group 7777 to mark the end of the message.

Example of a GRIB bulletin decoded into octet pairs in hexadecimal:-

4752 4942 0008 4C01 0000 1C01 4A2D FF80 0B64 0352 5E0C 120C 0001 0C00 0000 0000 1400 0000 0000 2000 FF00 0031 0025 0000 0004 BAF0 8001 5F90 0111 7009 C409 C440 0000 0000 0008 040B 8003 42EC 8274 09D5 EAB5 3AAD 5E7B 3198 CF66 B2D9 8CD6 6F37 A3D1 68F3 FA6D 3E7F 49A6 D56C 367B 0DBE C767 B1D9 6D76 9A2D 3EBB 4FA3 D3EA B45A 5D16 934F AAD4 E874 7A6D 1687 359A CC67 B359 8CF6 833B 9DD1 68F4 DA8D 66BB 4DA7 DB6E F7FC 4E16 FB7B BAE0 6E38 1B6D 96CF 4BA4 D369 F49A 6D16 9B4D AAD7 EAB4 99ED ... and so on ...

NNNN

Figure 1. Example of a GRIB bulletin. The data are for an 850-hPa temperature forecast chart (T+12 hours) for 18 December 1994.


Version 2.0 29

Annex 2

ICAO Thinned Grid

The ‘Thinned’ Grid The ‘thinned’ grid is broken into 8 octants of the globe, to reduce the bulletins to an acceptable size. This is constrained by WMO to be less than 15,000 octets (8-bit groups), but in practice the size of an octant bulletin will vary between 5,000 and 7,000 octets. Rather than starting the octants at multiples of 90 degrees longitude (e.g. prime meridian, 90°W) the starting point is at 30°W (330°E). This will permit some recipients of the "thinned" grid to use only a single octant, because the borders of the octants are now along less critical longitudes; and Europe, for example, is contained within the “I” area.

90oN

37 38 39 40

I J K L 0o

41 42 43 44

90oS M N O P

330oE 60oE 150oE 240oE 330oE

Figure 2. The borders of the WAFS

In Figure 2, the boxes indicate the location of the octants of the globe; the numbers are the corresponding grid identification numbers (Product Definition Section Octet 7 of the GRIB code), and the letters are the Area identification codes (A1) used in the Abbreviated Header.

The left and right meridional columns of each octant/grid are shared with the neighbours, as is the equator. The basic grid point separation is 1.25 x 1.25 degrees on a latitude/longitude array, but the grid is "thinned" by reducing the number of points in each row northward (or southward) from the equator. In GRIB terms, this is referred to as a "quasi-regular" grid. The latitudinal increment is always 1.25 degrees; this results in 73 rows where the pole is included as a "row", not a single grid-point. The longitudinal spacing at the equator is also 1.25 degrees; thus there will be 73 grid points at the equator in each octant. The number of points on each latitudinal row, other than the equator, is given (using FORTRAN notation) by:

NPOINTS = IFIX (2.0 + ( 90.0 / 1.25 ) * COS (LATITUDE))

Thus at the pole there will be two grid points, one each at the meridians that delineate the edges of the octant. The formula was worked out so that there is approximately equal geographic separation between the grid points uniformly across the globe.


Version 2.0 30

Because of variations in precision and round-off error in different computers, the value of NPOINTS may vary by 1 at "critical" latitudes when calculated on various hardware platforms. Here is a table of the exact values of NPOINTS as a function of latitude as used in the internationally exchanged grids. Of course, these numbers will be found in the Grid Description Section of each GRIB bulletin.

Row No. in Row No. in Row No. in N.

Hem. S.

Hem.

Lat.

No. of

Pts. N.

Hem. S.

Hem.

Lat.

No. of

Pts. N.

Hem.S.

Hem.

Lat.

No. of

Pts. 1 73 0.00 73 26 48 31.25 63 50 24 61.25 36 2 72 1.25 73 27 47 32.50 62 51 23 62.50 35 3 71 2.50 73 28 46 33.75 61 52 22 63.75 33 4 70 3.75 73 29 45 35.00 60 53 21 65.00 32 5 69 5.00 73 30 44 36.25 60 54 20 66.25 30 6 68 6.25 73 31 43 37.50 59 55 19 67.50 29 7 67 7.50 73 32 42 38.75 58 56 18 68.75 28 8 66 8.75 73 33 41 40.00 57 57 17 70.00 26 9 65 10.00 72 34 40 41.25 56 58 16 71.25 25

10 64 11.25 72 35 39 42.50 55 59 15 72.50 23 11 63 12.50 72 36 38 43.75 54 60 14 73.75 22 12 62 13.75 71 37 37 45.00 52 61 13 75.00 20 13 61 15.00 71 38 36 46.25 51 62 12 76.25 19 14 60 16.25 71 39 35 47.50 50 63 11 77.50 17 15 59 17.50 70 40 34 48.75 49 64 10 78.75 16 16 58 18.75 70 41 33 50.00 48 65 9 80.00 14 17 57 20.00 69 42 32 51.25 47 66 8 81.25 12 18 56 21.25 69 43 31 52.50 45 67 7 82.50 11 19 55 22.50 68 44 30 53.75 44 68 6 83.75 9 20 54 23.75 67 45 29 55.00 43 69 5 85.00 8 21 53 25.00 67 46 28 56.25 42 70 4 86.25 6 22 52 26.25 66 47 27 57.50 40 71 3 87.50 5 23 51 27.50 65 48 26 58.75 39 72 2 88.75 3 24 50 28.75 65 49 25 60.00 38 73 1 90.00 2 25 49 30.00 64

When all this is put together the result is that there are 3447 points of data actually transmitted in any individual GRIB bulletin containing one octant of the globe.


Version 2.0 31

Annex 3

Procedure or model used to generate the data field: Exeter definitions of code mm

GRIB code indicators

Met Office, Exeter defines the code numbers for mm as follows. mm 13 Objective analysis using variational data assimilation — bespoke area 14 Objective analysis using variational data assimilation – North Atlantic–European area 15 Objective analysis using variational data assimilation — global area 18 Wave hindcast — bespoke area 19 Wave hindcast — global area 43 Multilayer numerical forecast using new dynamics — bespoke area 44 Multilayer numerical forecast using new dynamics – North Atlantic–European area 45 Multilayer numerical forecast using new dynamics — global area 88 Wave-forecasting numerical model — bespoke area 89 Wave-forecasting numerical model — global area 115 Field-modified field from a multilayer numerical forecast using new dynamics

As model changes are implemented, codes 13, 18, 43 and 88 will be used for forecasts produced from new high-resolution versions of the Met Office Unified Model. All products available from the global versions of the Unified Model will use the codes 15, 19, 45 and 89.

As changes are made to Met Office ocean models, the following codes and definitions are expected also to be introduced.

mm

12 Objective storm-surge analysis — mesoscale model 16 Objective ocean–atmosphere analysis — global model 17 Shelf-seas analysis — mesoscale model

85 Ocean-atmosphere multilayer coupled model — global area 86 Shelf-seas forecast model — bespoke area 87 Storm-surge forecast model — bespoke area

The timing of changes, as they occur, will appear on the Met Office web site.

As field-modified GRIB data become available, it is expected that a further series of GRIB-code indicators will be defined.


Version 2.0 32

Annex 4

Scale factor E used in ICAO ‘Thinned GRIB’ bulletins issued by the Met Office

Field parameter Scale factor (E) Field parameter Scale factor (E)

Total accumulated precipitation (E)

-3 Total convective Precipitation (G)

-3

Geopotential height (H) 0 Vertical velocity (O) -10 Pressure (P) +3 Relative humidity (R) 0 Temperature (T) -3 Wind components (U, V) -3


Version 2.0 33

Appendix A: Tables of GRIB parameters defined by the World Meteorological Organization

Table A1. Parameter number (octet 9 of product definition section) defined by WMO

Code figure Field parameter Unit Code figure Field parameter Unit 001 Pressure Pa 039 (not used) - 002 Mean sea-level pressure Pa 040 Vertical velocity* ms-1

003 Pressure tendency Pa s-1 041 Absolute vorticity* s-1

004 Potential vorticity* Km2kg-1s-1 042 Absolute divergence* s-1

005 ICAO ISA reference height*

m 043 Relative vorticity* s-1

006 Geopotential* m2s-2 044 Relative divergence* s-1

007 Geopotential height gpm 045 Vertical u-component shear(1)*

s-1

008 Geometric height* m 046 Vertical v-component shear(1)*

s-1

009 Standard deviation of height*

m 047 Direction of current o true

010 Total ozone* Dobsons 048 Speed of current* ms-1

011 Temperature K 049 u component of current(1)

ms-1

012 Virtual temperature* K 050 v component of current(1)

ms-1

013 Potential temperature K 051 Specific humidity* kg kg-1

014 Equivalent potential temperature*

K 052 Relative humidity %

015 Maximum temperature K 053 Humidity mixing ratio* kg kg-1

016 Minimum temperature K 054 Precipitable water* kg m-3

017 Dew-point temperature* K 055 Vapour pressure* Pa 018 Dew-point depression* K 056 Saturation deficit* Pa 019 Lapse rate* K m-1 057 Evaporation* kg m-2

020 Visibility* m 058 Cloud ice* kg kg-1

021-023 Radar spectra* - 059 Precipitation rate kg m-2s-1

024 Parcel lifted index (to 500 hPa)*

K 060 Thunderstorm probability*

%

025 Temperature anomaly* K 061 Total accumulated precipitation

kg m-2

(mm) 026 Pressure anomaly* Pa 062 Total large-scale

precipitation kg m-2

(mm) 027 Geopotential height

anomaly* gpm 063 Total convective

precipitation kg m-2

(mm) 028-030 Wave spectra* - 064 Water-equivalent

snowfall rate† kg m-2s-1

(mm s-1) 031 Wind direction* o true 065 Water-equivalent

accumulated snow† kg m-2

(mm) 032 Wind speed ms-1 066 Snow depth m 033 u component of wind(1) ms-1 067 Mixed-layer depth* m 034 v component of wind(1) ms-1 068 Transient thermocline

depth* m

035 Stream function* m2s-1 069 Main thermocline depth*

m

036 Velocity potential* m2s-1 070 Main thermocline anomaly*

m

037 Montgomery stream function*

m2s-1 071 Total cloud cover %

038 (Not used) - 072 Convective cloud cover %


Version 2.0 34

Code figure Field parameter Unit Code figure Field parameter Unit 073 Low-cloud cover* % 101 Wind-wave direction ° true 074 Medium-cloud cover* % 102 Wind-wave height m 075 High-cloud cover* % 103 Wind-wave period s 076 Cloud water* kg kg-1 104 Swell-wave direction ° true 077 Best lifted index * K 105 Swell-wave height m 078 Convective snow* kg m-2 106 Swell-wave period s 079 Large-scale snow* kg m-2 107 Primary wave

direction* ° true

080 Water temperature K 108 Primary wave period* s 081 Surface cover

proportion (land/sea) (2)- 109 Secondary wave

direction* ° true

082 Deviation of sea level from mean

m 110 Secondary wave period*

s

083 Surface roughness* m 111 Net solar radiation (bottom) (3)

Wm-2

084 Albedo* - 112 Net IR flux (bottom) (3) Wm-2

085 Soil temperature K 113 Net short-wave radiation (top) (3)

Wm-2

086 Soil moisture content* kg m-2 114 Net long-wave radiation (top) (3)

Wm-2

087 Vegetation cover* % 115 Long-wave radiation(3) Wm-2

088 Salinity* % 116 Short-wave radiation(3) Wm-2

089 Density* kg m-3 117 Global radiation flux(3) Wm-2

090 Water runoff kg m-2 118 Brightness temperature*

K

091 Ice cover proportion(2)* - 119 Radiance (with respect to wave number)*

Wm-1sr-1

092 Ice thickness* m 120 Radiance (with respect to wave length)*

Wm-3sr-1

093 Direction of ice drift* ° true 121 Net latent heat flux* Wm-2

094 Speed of ice drift* ms-1 122 Net sensible heat flux* Wm-2

095 u component of ice drift(1)*

ms-1 123 Boundary-layer dissipation*

Nm-2

096 v component of ice drift(1)*

ms-1 124 u component of momentum flux(1)*

Nm-2

097 Ice growth rate* ms-1 125 v component of momentum flux(1)*

Nm-2

098 Ice divergence* s-1 126 Wind mixing energy J 099 Snow melt* % 127 Image data - 100 Significant height of

wind waves and swell m 255 Missing value -

(From WMO No. 306 Manual on codes, Vol. I.2, Part B, Code Table 2)

*These field parameters are not routinely available in Met Office GRIB bulletins. † Included in rainfall.

Notes on Table A1

1) The u and v components of vector quantities are defined by Octet 17 of the grid description section. However, if the grid description section is not included in a message, any wind components are assumed to be resolved relative to the grid specified in the Product Definition Section with u and v defined as positive in the direction of increasing x and y (or i and j) co-ordinates respectively.

2) Parameters 081 and 091 show the units as “fraction”, thus allowing for a range of coverage.

3) By convention, downward net fluxes of radiation or other quantities are assigned negative values; upward net fluxes of radiation or other quantities are assigned positive values.


Version 2.0 35

Table A2. Octets 10, 11 and 12 of the product definition section.

Octet 10 Octet 11 Octet 12

Value Meaning

01 02 03 04 05 06 07 08 09

Earth’s surface Cloud-base level Cloud-top level

Level of 0oC isotherm Lifted condensation level

Maximum wind Tropopause

Nominal top of atmosphere Sea bottom

0

0

20 Isothermal level Temperature (x10-2 K)

100 Isobaric level Pressure in hPa

101 Layer between two isobaric levels

Pressure of top (kPa) Pressure of bottom (kPa)

102 Mean sea level 0 0

103 Specified altitude Altitude in m

104 Layer between two specified altitudes

Altitude of top (hm) Altitude of bottom (hm)

105 Specified height-level above ground

Height (m)

106 Layer between two specified heights above ground

Height of top (hm) Height of bottom (hm)

109 Hybrid level Level number 0

110 Layer between two hybrid levels Level number at top Level number at bottom

111 Depth below ground Depth (cm)

112 Layer between two depths below ground

Depth of upper surface (cm)

Depth of lower surface (cm)

113 Isentropic (θ) level Potential temperature (K)

114 Layer between two isentropic levels

(475 K - θ) level of top (475 K - θ) level of bottom

115 Level at specified pressure difference from ground to level

Pressure difference (hPa)

116 Layer between two levels at specified pressure difference

from ground to level

Pressure difference from ground to top level

(hPa)

Pressure difference from ground to bottom level

(hPa) 117 Potential vorticity (pv) surface pv value (x 10-6K m2kg-1)

119 Eta (η) level η value in 1/10000 120 Layer between two specified eta

(η) levels η value at top of layer in

1/100 η value at bottom of

layer in 1/100 121 Layer between two isobaric

surfaces (high precision) 1100 hPa – pressure of

top of layer 1100 hPa – pressure of

bottom of layer 125 Specified height level above

ground (high precision) Height (cm)

141 Layer between two isobaric surfaces (mixed precision)

Pressure of top 1100 hPa – pressure of bottom

160 Depth below sea level Depth (m)

200 Entire atmosphere (considered as a single layer)

0 0

201 Entire ocean (considered as a single layer)

0 0



Version 2.0 36

Table A3. Indicator of forecast time unit (octet 18 of the product definition section)

Value Time unit Value Time unit Value Time unit 0 Minute 4 Year 10 3 hours 1 Hour 5 Decade 11 6 hours 2 Day 6 Normal (30 years) 12 12 hours 3 Month 7 Century 254 Second


Table A4. Indicator of forecast time unit (octet 21 of the product definition section)

Value Meaning 0 Forecast product valid for time indicated by octets 13-20, or uninitialized analysis 1 Initialized analysis 2 Product valid between the times indicated by octets 13-20 3 Average of values between times indicated by octets 13-20 4 Accumulation between times indicated by octets 13-20 5 Difference between values at times indicated by octets 13-20 6 Average between values at times indicated by octets 13-18 – (octet 19 + octet 20) 7 Average between values at times indicated by octets 13-18 – (octet 19)+(octet 20)

(From WMO No. 306 Manual on codes, Vol. I.2, Part B, Code Table 5, amended November 2003)

Table A5. Grid type (octet 6 of grid description section)

Code figure Grid type Code figure Grid type 0 Latitude/longitude 3 Lambert conformal projection 1 Mercator projection* 4 Gaussian latitude/longitude* 2 Gnomonic projection* 5 Polar stereographic projection


*These projections are not routinely used in Met Office GRIB.

Note on Table A5

Other projections are listed in the WMO Manual on codes, Vol. I.2, Table 6.

Table A6. Flag table (Octet 4 of the binary data section)

Bit Value Meaning Bit Value Meaning 0 Grid-point data 0 Original data were floating-

point values 1

1 Spherical harmonic coefficients

3

1 Original data were integer values

0 Simple packing 0 No additional flags at octet 14 2 1 Second-order

(“complex”) packing

4 1 (Not used)


Notes on Table A6:

1) Bit 3 is set to 1 to indicate that the original data were integers; when this is the case, any non-zero reference values should be rounded to an integer value prior to placing in the GRIB binary data section.

2) Additional variations are included in WMO No 306 Manual on codes, Vol. I.2. Part B.


Version 2.0 37

Appendix B: example of a GRIB bulletin

In this example, the encoded message is for a 6-hour forecast of temperature at 250 hPa for 50°W-70°E, 0°-90°N from a data time of 0000 UTC on 29 August 2003. The format is as used for transmissions on the Global Telecommunication System. WMO header

Octet No. Hex. form Description 1 48 ‘H’ (GRIB information) 2 54 ‘T’ (temperature) 3 53 ‘S’ (grid identification: 50°W-70°E, 0°-90°N) 4 43 ‘B’ (6-hour time difference between the reference

time and the validity time, i.e. T+6) 5-6 3235 ‘25’ (level of data = 250 hPa) 7 20 Blank

8-11 45475252 ‘EGRR’ (originating centre) 12 20 Blank

13-14 3239 ‘29’ (day of month) 15-18 30303030 ‘0000’ (hour and minute of reference time) 19-21 0D0D0A Two carriage returns and a line feed

Indicator section

Octet No. Hex. form Description 1-4 47524942 ‘GRIB’ 5-7 000738 Length of message in octets 8 01 GRIB edition number

Product definition section

Octet No. Hex. form Description 1-3 00001C 28 (length of section in octets) 4 03 3 (parameter table version number – international exchange) 5 4A Identification of centre = 74 (Exeter) 6 2D 45 (global atmosphere forecast) 7 0E 14 (grid description section identifier) 8 80 128 (flag indicating grid description section included) 9 0B 11 (parameter = temperature)

10 64 100 (isobaric level type) 11-12 00FA 250 (250-hPa pressure level)

13 03 3 (year of century) 14 08 8 (month of year) 15 1D 29 (day of month)

16-17 0000 0000 (reference time of data) 18 01 Forecast time unit = hours 19 06 Forecast range (T+6)

20-24 0000000000 Reserved 25 15 21 (century number)

26-27 0000 Reserved 28 00 Decimal scale factor D = 0


Version 2.0 38

Grid description section

Octet No. Hex. form Description 1-3 000020 32 (number of octets in section) 4 00 0 (number of vertical co-ordinates) 5 FF 255 (co-ordinates missing) 6 00 Latitude/longitude grid

7-8 0031 49 (number of columns) 9-10 0025 37 (number of rows)

11-13 000000 000000 (latitude of first grid point = 0.000o) 14-16 04BAF0 310000 (longitude of first grid point = 310.000oE)

17 80 Resolution and component flag 18-20 015F90 090000 (latitude of last grid point = 90.000oN) 21-23 068FB0 430000 (longitude of last grid point = 430.000oE) 24-25 09C4 2500 (i direction increment = 2.500o) 26-27 09C4 2500 (j direction increment = 2.500o)

28 40 Scanning mode 29-32 00000000 Set to zero

Bitmap section

Not included Binary data section Octet No. Hex. form Description

1-3 0006F0 1776 (number of octets in binary data section) 4 00 0 (number of unused bits at end of section)

5-6 8003 Scale factor (E = −3) 7-10 42CE5FFF Reference value (R = 206.357) 11 08 8 (number of bits into which data are packed)

12-1776 XX … Packed binary data End section Octet No. Hex. form Description

1-4 37373737 ‘7777’ The end section is followed by the communications trailer (0D0D0A03) hex. The transmitted message looks like this: 4854 5343 3235 2045 4752 5220 3239 3030 3030 0D0D 0A

4752 4942 0007 3801 0000 1C03 4A2D 0E80 0B64 00FA 0308 1D00 0001 0600 0000 0000 1500 0000 0000 2000 FF00 0031 0025 0000 0004 BAF0 8001 5F90 068F B009 C409 C440 0000 0000 0006 F000 8003 42CE 5FFF 08XX XXXX … 3737 3737 0D0D 0A03

Example of a bitmap section

Octet No. Hex. form Description 1-3 000232 564 (number of octets in bitmap section) 4 04 4 (number of unused bits at end of section)

5-6 0000 0 (bitmap follows) 7-564 dddd … Bitmap code


Version 2.0 39

List of abbreviations used in this guide

ASCII American Standard Code for Information Interchange

CCITT-ITA International Telegraph and Telephone Consultative Committee – International telegraph alphabet (of the International Telecommunication Union)

GRIB Gridded binary code

GTS Global Telecommunication System

ICAO International Civil Aviation Organization

ISA International Standard Atmosphere

WMO World Meteorological Organization

GRIB Catalogue Autumn 2006

Documents

Transcript of GRIB Catalogue Autumn 2006