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Solution to

1. Experiment with using the different grib_dump

practical1. 

options
(-O,  -a and –t).  Inspect the GRIB message in the files file1.grib1 and file1.grib2 and identify:

  • the GRIB edition used to encode the messages

  • the (MARS)parameter ID, date, time, forecast step and the grid geometry

  • What are the maximum, minimum and average values of the fields?


Expand
titleSolution...

To view the keys available for GRIB1 and GRIB2 have a look at the parameter database at http://apps.ecmwf.int/codes/grib/

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


  • the message is encoded using GRIB edition 1 (editionNumber=1);
•    it
  • it contains the 2 metre temperature field (shortName=2t, marsParam=167.128, paramId=167);
•    the
  • the dataDate=
20110225
  • 20190201, the dataTime=
12
  • 00 and the forecast step=12;
•    the
  • the data is on
a
  • an octahedral reduced Gaussian grid (typeOfGrid=reduced_gg) with N=
128
  • 640 (Nj=
256);
Alternatively, with grib_dump inspect some templates in the “GRIB_SAMPLES_PATH” directory.
 
3.  For
  • 1280) and gridName=0640.

Similarly 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


  • the message is encoded using GRIB edition 2 -
grib_edition
  • editionNumber=2;
•    it
  • it contains the temperature field on a specified height of 2 m above ground (shortName=2t, paramId = 167, discipline = 0, parameterCategory = 0, parameterNumber = 0, typeOfFirstFixedSurface = 103);
•    the
  • the dataDate=
20110225
  • 20190201, the dataTime=
12
  • 00 and the forecast step=12;
•    the
  • the data is on
a
  • an octahedral reduced Gaussian grid (typeOfGrid=reduced_gg) with N=
128
  • 640 (Nj=
256);
4.
  • 1280) and gridName=0640.


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


2. Use grib_ls to print the centre, dataDate, stepRange, levelType, shortName and paramId for msl.grib1 and msl.grib2 and order by ascending stepRange.

  • Experiment with both –P and –p options and ‘key:i’, 


  • ‘key:s’

  • Which keys does

Solution to

  • grib_ls

practical
1. 

  • show by default for the two files ?

  • What fields do they contain


Expand
titleSolution...

To list the GRIB messages in msl.grib1, use:

%  grib_ls msl.grib1
edition      centre       typeOfLevel  level        dataDate     stepRange    dataType     shortName    packingType  gridType
1            ecmf         surface      0           

20110225    

20190201     0            cf           msl          grid_simple  regular_gg
1            ecmf         surface      0           

20110225    

20190201     6            cf           msl          grid_simple  regular_gg
1            ecmf         surface      0           

20110225    

20190201     12           cf           msl          grid_simple  regular_gg
1            ecmf         surface      0           

20110225    

20190201     18           cf           msl          grid_simple  regular_gg
1            ecmf         surface      0           

20110225    

20190201     24           cf           msl          grid_simple  regular_gg
5 of 5 grib messages in msl.grib1

The file contains mean sea-level pressure (shortName=msl) from the ECMWF

EPS

ENS control forecast (dataType=cf) for 6-hourly steps from 0 to 24 hours for dataDate=

20110225

20190201.  The messages are encoded in GRIB edition 1.

2. 


To list the GRIB messages in msl.grib2

%  grib_ls msl.grib2
edition      centre       date         dataType     gridType     stepRange    typeOfLevel  level        shortName    packingType
2            ecmf        

20110225    

20190201     cf           regular_gg   0            meanSea      0            msl          grid_simple
2            ecmf        

20110225    

20190201     cf           regular_gg   6            meanSea      0            msl          grid_simple
2            ecmf        

20110225    

20190201     cf           regular_gg   12           meanSea      0            msl          grid_simple
2            ecmf        

20110225    

20190201     cf           regular_gg   18           meanSea      0            msl          grid_simple
2            ecmf        

20110225    

20190201     cf           regular_gg   24           meanSea      0            msl          grid_simple
5 of 5 grib messages in msl.grib2


The file also contains mean sea-level pressure (shortName=msl) from the ECMWF

EPS

ENS control forecast (dataType=cf) for 6-hourly steps from 0 to 24 hours for dataDate=

20110225

20190201.  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     _leg_number 
g         sfc       20110225     0000     0         151.128      od        cf       enfo      0001       1          
g         sfc       20110225     0000     6         151.128      od        cf       enfo      0001       1          
g         sfc       20110225     0000     12        151.128      od        cf       enfo      0001       1          
g         sfc       20110225     0000     18        151.128      od        cf       enfo      0001       1          
g         sfc       20110225     0000     24        151.128      od        cf       enfo      0001       1           

5 of 5 messages in msl.grib1
5 of 5 total messages in 1 files% grib_ls -m msl.grib2
msl.grib2
domain    date         time      expver    class        type      stream    _leg_number  step      levtype      param       
g         20110225     0000      0001      od           cf        enfo      1            0         sfc          151        
g         20110225     0000      0001      od           cf        enfo      1            6         sfc          151        
g         20110225     0000      0001      od           cf        enfo      1            12        sfc          151        
g         20110225     0000      0001      od           cf        enfo      1            18        sfc          151        
g         20110225     0000      0001      od           cf        enfo      1            24        sfc          151         5 of 5 messages in msl.grib2
5 of 5 total messages in 1 files4.  Output can be printed in descending step order using grib_ls with the -B option.  Note it is necessary to use “step:i” here as step has a default type of ‘string’.
   % grib_ls -B "step:i 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:i 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
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
5 of 5 grib messages in msl.grib1

The same keys are listed but the order in which they appear differs between GRIB edition 1 and GRIB edition 2.

Using the "key:i" for centre and levelType prints these keys as their integer values rather than strings:

 

% grib_ls -p centre:i,dataDate,stepRange,levelType:i,shortName,paramId msl.grib1
centre       dataDate     stepRange    levelType   shortName    paramId
98          

20110225    

20190201     0            1            msl          151
98          

20110225    

20190201     6            1            msl          151
98          

20110225    

20190201     12           1            msl          151
98          

20110225    

20190201     18           1            msl          151
98          

20110225    

20190201     24           1            msl          151
5 of 5 grib messages in msl.grib1

Similarly for msl.grib2:

 


% grib_ls -p centre:i,dataDate,stepRange,levelType:i,shortName,paramId msl.grib2
centre       dataDate     stepRange    levelType  shortName    paramId
98          

20110225    

20190201     0            101          msl          151
98          

20110225    

20190201     6            101          msl          151
98          

20110225    

20190201     12           101          msl          151
98          

20110225    

20190201     18           101          msl          151
98          

20110225    

20190201     24           101          msl          151
5 of 5 grib messages in msl.grib2


 
Solution to grib_ls -l  practical
1. 


3. Find the value of the MSLP at the grid point nearest to ECMWF (Lat 51.42°N, Lon 0.95° W) at each forecast step

  • What is the lat-lon value of the grid point nearest to ECMWF ?

  • How far is the chosen grid point from ECMWF ?

  • Use the file lsm.grib1 to provide a land-sea mask - are all four nearest grid points land points (mask ≥ 0.5) ?


Expand
titleSolution...

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
   stepRange    value
   0           102527
   6           102365
   12          102456
   18          102289
   24          101862
   5 of 5 grib messages in msl.grib1

   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
   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
   5 of 5 grib messages in msl.grib1

   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
stepRange    value
0           102527
6           102365
12          102456
18          102289
24          101862
5 of 5 grib messages in msl.grib1

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.