Reading ECMWF data with NCL, GrADS or Ferret

Last modified on May 13, 2022 11:21

Problem

You downloaded data from the ECMWF data server or another ECMWF repository in NetCDF format.

Then you are trying to read the data with the NCAR Command Language (NCL) , GrADS or Ferret, but get an error message, for example for NCL:

ncl 0> f = addfile("ECMWF-data.nc","r")
ncl 1> print (getfilevarnames (f))

(0)     longitude

(1)     latitude

(2)     time

(3)     p83.162

(4)     p86.162

ncl 3> x = f->p83.162

fatal:syntax error: line 3 before or near .162

x = f->p83.162

-------------^

ncl 4> x = f->"p83.162"

fatal:syntax error: line 4 before or near >

x = f->

------^

Cause

NCL, GrADS and Ferret do not support dots in variable names.

Solution for NCL

Enclose the variable name in double quotes and Dollar signs:

ncl 0> f = addfile("ECMWF-data.nc","r")

ncl 1> print (getfilevarnames (f))     
(0)     longitude
(1)     latitude
(2)     time
(3)     p83.162
(4)     p86.162
 q

ncl 2> x = f->$"p83.162"$

ncl 3> print (x)

Variable: x

Type: short

Total Size: 7172160 bytes

            3586080 values

Number of Dimensions: 3

Dimensions and sizes:   [time | 31] x [latitude | 241] x [longitude | 480]

Coordinates:

            time: [1024872..1025592]

            latitude: [90..-90]

            longitude: [ 0..359.25]

Number Of Attributes: 6

  scale_factor :        0.6170104064936749

  add_offset :  -3072.290927078247

  _FillValue :  -32767

  missing_value :       -32767

  units :       W m**-2

  long_name :   Vertical integral of divergence of thermal energy flux

Workaround

Rename the variable so the name contains only allowed character:

Rename with CDO: https://code.mpimet.mpg.de/boards/2/topics/4057
Rename with NCO: http://research.jisao.washington.edu/data_sets/nco/#example

_{This document has been produced in the context of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S).}

_{The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of CAMS and C3S on behalf of the European Union (Delegation Agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.}

_{The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.}

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