CDO

Hi Sam,

you have to add some attributes to the coordinate variables and the data variable, first.

ncatted -O -a coordinates,emissions,c,c,"Latitude Longitude" \
           -a standard_name,Latitude,c,c,"latitude" \
           -a standard_name,Longitude,c,c,"longitude" \
              cropped_example.nc tmp.nc

cdo remapnn,grid_180 tmp.nc example.nc

But did you see that your data is always 0.0?

cdo infon cropped_example.nc 
    -1 :       Date     Time   Level Gridsize    Miss :     Minimum        Mean     Maximum : Parameter name
     1 :-0001-12-31 01:00:00       0       11       0 :      79.875      81.125      82.375 : Latitude      
     2 :-0001-12-31 01:00:00       0       26       0 :     -173.62     -170.50     -167.38 : Longitude     
     3 :-0001-12-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     4 : 0000-01-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     5 : 0000-02-29 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     6 : 0000-03-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     7 : 0000-04-30 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     8 : 0000-05-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
     9 : 0000-06-30 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
    10 : 0000-07-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
    11 : 0000-08-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
    12 : 0000-09-30 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
    13 : 0000-10-31 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
    14 : 0000-11-30 01:00:00       0      286       0 :      0.0000      0.0000      0.0000 : emissions     
cdo infon: Processed 3469 values from 3 variables over 12 timesteps ( 0.00s 21MB )

-Karin

Hi Karin,

Thank you very much! but I do not know why the 'time' variable changed to

Time = 1, 2, 2.93548387096774, 4, 4.96774193548387, 6, 6.96774193548387, 8, 
    9, 9.96774193548387, 11, 11.9677419354839 ;

rather than 1,2,3,...12

Cheers
Sam

The time coordinate variable Time is not set properly:

cdo showtimestamp cropped_example.nc 
 -0001-12-31T01:00:00  0000-01-31T01:00:00  0000-02-29T01:00:00  0000-03-31T01:00:00  0000-04-30T01:00:00  0000-05-31T01:00:00  0000-06-30T01:00:00  0000-07-31T01:00:00  0000-08-31T01:00:00  0000-09-30T01:00:00  0000-10-31T01:00:00  0000-11-30T01:00:00
cdo showtimestamp: Processed 3 variables over 12 timesteps ( 0.00s 20MB )

The reference time is

Time:units = "months since Jan 01, 1997" 

but should be

Time:units = "months since 1997-1-1 01:00:00" 

To get the right time values you have to use the settaxis operator:

cdo -L -settaxis,1997-01-01,01:00:00,1mon -remapnn,grid_180 tmp.nc example.nc

Now, the time is ok:

cdo showtimestamp example.nc
  1997-01-01T01:00:00  1997-02-01T01:00:00  1997-03-01T01:00:00  1997-04-01T01:00:00  1997-05-01T01:00:00  1997-06-01T01:00:00  1997-07-01T01:00:00  1997-08-01T01:00:00  1997-09-01T01:00:00  1997-10-01T01:00:00  1997-11-01T01:00:00  1997-12-01T01:00:00
cdo showtimestamp: Processed 1 variable over 12 timesteps ( 0.00s 20MB )

and

ncdump -v Time example.nc
netcdf example {
dimensions:
    Time = UNLIMITED ; // (12 currently)
    lon = 96 ;
    lat = 72 ;
variables:
    double Time(Time) ;
        Time:standard_name = "time" ;
        Time:units = "months since 1997-1-1 01:00:00" ;
        Time:calendar = "standard" ;
        Time:axis = "T" ;
    float lon(lon) ;
        lon:standard_name = "longitude" ;
        lon:long_name = "longitude" ;
        lon:units = "degrees_east" ;
        lon:axis = "X" ;
    float lat(lat) ;
        lat:standard_name = "latitude" ;
        lat:long_name = "latitude" ;
        lat:units = "degrees_north" ;
        lat:axis = "Y" ;
    double emissions(Time, lat, lon) ;

// global attributes:
        :CDI = "Climate Data Interface version 1.9.2 (http://mpimet.mpg.de/cdi)" ;
        :Conventions = "CF-1.6" ;
        :history = "Mon Aug 20 15:53:24 2018: cdo -L -settaxis,1997-01-01,01:00:00,1mon -remapnn,grid_180 tmp.nc example.nc\nMon Aug 20 15:53:24 2018: ncatted -O -a coordinates,emissions,c,c,Latitude Longitude -a standard_name,Latitude,c,c,latitude -a standard_name,Longitude,c,c,longitude cropped_example.nc tmp.nc\nMon Aug 20 11:01:24 2018: ncks -d lat,30,40 -d lon,25,50 emis_1997.nc -O cropped_example.nc\nCreated by Sam 20/08/18" ;
        :description = "Emissions (gc/m2/month) in each grid cell" ;
        :NCO = "4.6.7" ;
        :CDO = "Climate Data Operators version 1.9.2 (http://mpimet.mpg.de/cdo)" ;
data:

 Time = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ;
}

-Karin

Hi Karin,

Thank you very much. You solved my problem perfectly.
Sam