Solution to grib_dump and grib_keys practical
1. To view the keys available for GRIB1 and GRIB2 have a look at GRIB API or http://old.ecmwf.int/publications/manuals/grib_api/
2. To use grib_dump to inspect the contents of file1.grib1:
% grib_dump file1.grib1
By using grib_dump on its own and with the various options, (-O, -a, etc), you should find:
• the message is encoded using GRIB edition 1 (editionNumber=1);
• it contains the 2 metre temperature field (shortName=2t, marsParam=167.128);
• the dataDate= 20110225, the dataTime=12 and the forecast step=12;
• the data is on a reduced Gaussian grid (typeOfGrid=reduced_gg) with N=128 (Nj=256);
Alternatively, with grib_dump inspect some templates in the “GRIB_SAMPLES_PATH” directory.
3. For the file file2.grib2
% grib_dump file1.grib2
By using grib_dump on its own and with various options, (-O, -a etc), you should find:
• the message is encoded using GRIB edition 2 - grib_edition=2;
• it contains the temperature field on a specified hight of 2 m above ground (shortName=2t, paramId = 167, discipline = 0, parameterCategory = 0, parameterNumber = 0, typeOfFirstFixedSurface = 103);
• the dataDate=20110225, the dataTime=12 and the forecast step=12;
• the data is on a reduced Gaussian grid (typeOfGrid=reduced_gg) with N=128 (Nj=256);
4. To quickly find the maximum, minimum and average values of the field, look for the computed keys max, min, and average.
For both files you should find:
• maximum = 314.204
• minimum = 222.44
• average = 285.261
Solution to grib_ls practical
1. To list the GRIB messages in msl.grib1 | Code Block |
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ecgb11{/scratch/us/usc/Carsten/grib_tools/grib_ls}:47 --> grib_ls msl.grib1
msl.grib1
edition centre typeOfLevel level dataDate stepRange dataType shortName packingType gridType
1 ecmf surface 0 20110225 0 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 6 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 12 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 18 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 24 cf msl grid_simple regular_gg
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e |
ecgb11{/scratch/us/usc/Carsten/grib_tools/grib_ls}:47 --> grib_ls msl.grib1
% grib_ls msl.grib1 msl.grib1 edition centre typeOfLevel level dataDate stepRange dataType shortName packingType gridType gridType 1 ecmf surface 0 20110225 0 cf msl grid_simple regular_gg 1 ecmf surface 0 20110225 6 cf msl grid_simple regular_gg 1 ecmf surface 0 20110225 12 cf msl grid_simple regular_gg 1 ecmf surface 0 20110225 18 cf msl grid_simple regular_gg 1 ecmf surface 0 20110225 24 cf msl grid_simple regular_gg 5 of 5 grib messages in msl.grib1 5 of 5 total grib messages in 1 files
The file contains mean sea-level pressure (shortName=msl) from the ECMWF EPS control forecast (dataType=cf) for 6-hourly steps from 0 to 24 hours for dataDate=20110225. The messages are encoded in GRIB edition 1.
2. To list the GRIB messages in msl.grib2
% grib_ls msl.grib2
msl.grib2
edition centre date dataType gridType stepRange typeOfLevel level shortName packingType
2 ecmf 20110225 cf regular_gg 0 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 6 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 12 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 18 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 24 meanSea 0 msl grid_simple
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The file also contains mean sea-level pressure (shortName=msl) from the ECMWF EPS control forecast (dataType=cf) for 6-hourly steps from 0 to 24 hours for dataDate=20110225. In this file the messages are encoded in GRIB edition 2.
The lists show the default keys printed by grib_ls for GRIB 1 and GRIB 2.
3. To print the mars keys, use grib_ls -m:
% grib_ls -m msl.grib1
msl.grib1
domain levtype date time step param class type stream expver
g sfc 20110225 0000 0 151.128 od cf enfo 0001
g sfc 20110225 0000 6 151.128 od cf enfo 0001
g sfc 20110225 0000 12 151.128 od cf enfo 0001
g sfc 20110225 0000 18 151.128 od cf enfo 0001
g sfc 20110225 0000 24 151.128 od cf enfo 0001
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% grib_ls -m msl.grib1
msl.grib2
domain date time expver class type stream step levtype levelist param
g 20110225 0000 0001 od cf enfo 0 sfc 0 151
g 20110225 0000 0001 od cf enfo 6 sfc 0 151
g 20110225 0000 0001 od cf enfo 12 sfc 0 151
g 20110225 0000 0001 od cf enfo 18 sfc 0 151
g 20110225 0000 0001 od cf enfo 24 sfc 0 151
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4. Output can be printed in descending step order using grib_ls with the -B option. Note it is necessary to use “step:l” here as step has a default type of ‘string’.
% grib_ls -B "step:l desc" msl.grib1
edition centre typeOfLevel level dataDate stepRange dataType shortName packingType gridType
1 ecmf surface 0 20110225 24 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 18 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 12 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 6 cf msl grid_simple regular_gg
1 ecmf surface 0 20110225 0 cf msl grid_simple regular_gg
% grib_ls -B "step:l desc" msl.grib2
edition centre date dataType gridType stepRange typeOfLevel level shortName packingType
2 ecmf 20110225 cf regular_gg 24 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 18 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 12 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 6 meanSea 0 msl grid_simple
2 ecmf 20110225 cf regular_gg 0 meanSea 0 msl grid_simple
5. To specify a set of keys to print, use the -p option:
% grib_ls -p centre,dataDate,stepRange,typeOfLevel,shortName msl.grib1
msl.grib1
centre dataDate stepRange typeOfLevel shortName
ecmf 20110225 0 surface msl
ecmf 20110225 6 surface msl
ecmf 20110225 12 surface msl
ecmf 20110225 18 surface msl
ecmf 20110225 24 surface msl
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Using the "key:l" for centre and levelType prints these keys as their integer values rather than strings:
% grib_ls -p centre:l,dataDate,stepRange,levelType:l,shortName,paramId msl.grib1
msl.grib1
centre dataDate stepRange levelType shortName paramId
98 20110225 0 1 msl 151
98 20110225 6 1 msl 151
98 20110225 12 1 msl 151
98 20110225 18 1 msl 151
98 20110225 24 1 msl 151
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Similarly for msl.grib2:
% grib_ls -p centre:l,dataDate,stepRange,levelType:l,shortName,paramId msl.grib2
msl.grib2
centre dataDate stepRange levelType shortName paramId
98 20110225 0 101 msl 151
98 20110225 6 101 msl 151
98 20110225 12 101 msl 151
98 20110225 18 101 msl 151
98 20110225 24 101 msl 151
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Solution to grib_ls -l practical
1. To list the nearest points to ECMWF (Lat 51.42 N, Lon 0.95 W) use
% grib_ls -l 51.42,-0.95 msl.grib1
…
5 of 5 total grib messages in 1 files
Input Point: latitude=51.42 longitude=-0.95
Grid Point chosen #3 index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
Other grid Points
- 1 - index=17599 latitude=50.72 longitude=359.10 distance=77.54 (Km)
- 2 - index=17598 latitude=50.72 longitude=358.20 distance=97.59 (Km)
- 3 - index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
- 4 - index=17198 latitude=51.62 longitude=358.20 distance=62.87 (Km)
Note we specify the longitude of 0.95 W with -0.95 !
The nearest grid point is at latitude=51.62 longitude=359.10 (=0.9 W) and is 22.57 km from ECMWF.
2. To output only the forecast step and MSLP value at the nearest grid point use:
% grib_ls -l 51.42,-0.95,1 -p stepRange msl.grib1
msl.grib1
stepRange value
0 102527
6 102365
12 102456
18 102289
24 101862
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Input Point: latitude=51.42 longitude=-0.95
Grid Point chosen #3 index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
Other grid Points
- 1 - index=17599 latitude=50.72 longitude=359.10 distance=77.54 (Km)
- 2 - index=17598 latitude=50.72 longitude=358.20 distance=97.59 (Km)
- 3 - index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
- 4 - index=17198 latitude=51.62 longitude=358.20 distance=62.87 (Km)
Note it is necessary to specify MODE=1 in order to print the value of the nearest grid point only.
To output the values at the four grid points nearest to ECMWF, use MODE=4 which is the default:
% grib_ls -l 51.42,-0.95 -p stepRange msl.grib1
msl.grib1
stepRange value1 value2 value3 value4
0 102674 102663 102527 102501
6 102532 102516 102365 102333
12 102633 102585 102456 102426
18 102444 102390 102289 102259
24 102057 101959 101862 101760
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Input Point: latitude=51.42 longitude=-0.95
Grid Point chosen #3 index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
Other grid Points
- 1 - index=17599 latitude=50.72 longitude=359.10 distance=77.54 (Km)
- 2 - index=17598 latitude=50.72 longitude=358.20 distance=97.59 (Km)
- 3 - index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
- 4 - index=17198 latitude=51.62 longitude=358.20 distance=62.87 (Km)
3. To specify the land-sea mask, use:
% grib_ls -l 51.42,-0.95,1,lsm.grib1 -p stepRange msl.grib1
msl.grib1
stepRange value
0 102527
6 102365
12 102456
18 102289
24 101862
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Input Point: latitude=51.42 longitude=-0.95
Grid Point chosen #3 index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km)
Mask values:
- 1 - index=17599 latitude=50.72 longitude=359.10 distance=77.54 (Km) value=0.00
- 2 - index=17598 latitude=50.72 longitude=358.20 distance=97.59 (Km) value=1.00
- 3 - index=17199 latitude=51.62 longitude=359.10 distance=22.57 (Km) value=1.00
- 4 - index=17198 latitude=51.62 longitude=358.20 distance=62.87 (Km) value=1.00
Here the mask value at the end of the line showing the four nearest grid points indicates which are land points: Land points have mask ≥ 0.5; sea points have mask<0.5. |