Copying from GrADS

Thu Dec 3 12:21:01 EST 2009

Hyacinth,

Are you able to open the file?  What output do you get from GrADS when 
you try to open the ctl file?  One thing is to check "zdef" in the ctl 
file (should be a space between zdef and 5, and change "linear" to 
"levels"):

zdef5 linear 0.995 0.8458 0.2582 0.2101, 0.1682 

Using the information at 
http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.derived.sigma.html

        Temporal Coverage:

    * Daily and Monthly Values for 1948/01 - present.
    * Long term monthly means, derived from data for years 1968 - 1996.

        Spatial Coverage:

    * T62 Gaussian grid with 192x94 points
    * 88.542N-88.542S, 0E-358.125E

*Temporal coverage:*

    * 1/1/1958 - 11/2001 monthly means (not in CDAS update)
    * Daily psi and chi: Jan 1 1948 to "present".
    * Long-Term term monthly mean files are averaged over 1968-1996

....check the "tdef" record very carefully (should be 732 time levels, 
and is the initial time correct?) and is "options yrev" needed?

...are the longitude values uniform (if not, get these and also add them 
to the ctl file)?

On a more general note, since the data are in netCDF format, have you 
tried using "sdfopen" for the netCDF file in GrADS?

Hope this helps,
Chuck

Hyacinth Cyprain Nnamchi wrote:
> Thanks Chuck. You are right, I was later able to figure out how to do that with ncdump.
>
> However, the problem remains as I am not able to read the data.The data 'am using is the NCEP Reanalysis derived from: http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.derived.sigma.html. This is the ctl file I am trying to use (I have also included details on the original data below):
>
> title monthly mean values of v. potential from 1950 to 2006
> undef -9.96921e+36 
> options yrev
> xdef 192 linear 0 1.875 
> ydef 94	levels  -88.542  -86.6531  -84.7532  -82.8508  -80.9473 -79.0435 -77.1394 -75.2351 -73.3307 -71.4262 -69.5217 -67.6171 -65.7125 -63.8079 -61.9033 -59.9986 -58.0939  -56.1893 -54.2846 -52.3799 -50.4752  -48.5705  -46.6658 -44.7611     -42.8564 -40.9517 -39.047 -37.1422 -35.2375 -33.3328 -31.4281  -29.5234 -27.6186
> 	-25.7139 -23.8092 -21.9044 -19.9997 -18.095 -16.1902  -14.2855 -12.3808 -10.47604 -8.57131 -6.66657 -4.76184 -2.8571 -0.952368 0.952368 2.8571 4.76184 6.66657 8.57131 10.47604 12.3808 14.2855 16.1902 18.095 19.9997 21.9044 23.8092 25.7139  27.6186	29.5234 31.4281 33.3328 35.2375 37.1422 39.047  40.9517 42.8564
> 	44.7611 46.6658 48.5705 50.4752 52.3799 54.2846 56.1893 58.0939	59.9986 61.9033 63.8079 65.7125 67.6171 69.5217 71.4262 73.3307	75.2351 77.1394 79.0435 80.9473 82.8508 84.7532 86.6531 88.542
> zdef5 linear 0.995 0.8458 0.2582 0.2101, 0.1682 
> tdef 684 linear 01JAN1950 1mo
> vars 1
> chi 5 -999 monthly mean values of v. potential from 1950 to 2006
> endvars
>
>
>
> ********original data**********
> netcdf chi.mon.mean {
> dimensions:
> 	lon = 192 ;
> 	lat = 94 ;
> 	level = 5 ;
> 	time = UNLIMITED ; // (732 currently)
> variables:
> 	float lat(lat) ;
> 		lat:units = "degrees_north" ;
> 		lat:actual_range = 88.542f, -88.542f ;
> 		lat:long_name = "Latitude" ;
> 	float lon(lon) ;
> 		lon:units = "degrees_east" ;
> 		lon:long_name = "Longitude" ;
> 		lon:actual_range = 0.f, 358.125f ;
> 	float level(level) ;
> 		level:units = "sigma_level" ;
> 		level:long_name = "Sigma" ;
> 		level:positive = "down" ;
> 		level:actual_range = 0.995f, 0.1682f ;
> 	double time(time) ;
> 		time:units = "hours since 1-1-1 00:00:0.0" ;
> 		time:long_name = "Time" ;
> 		time:actual_range = 17067072., 17601072. ;
> 		time:delta_t = "0000-01-00 00:00:00" ;
> 		time:avg_period = "0000-01-00 00:00:00" ;
> 		time:prev_avg_period = "0000-00-01 00:00:00" ;
> 	float chi(time, level, lat, lon) ;
> 		chi:long_name = "Monthly Mean of Velocity Potential" ;
> 		chi:valid_range = -9.96921e+36f, 9.96921e+36f ;
> 		chi:actual_range = -3.1595e+07f, 3.0159e+07f ;
> 		chi:units = "m*m/s" ;
> 		chi:add_offset = 0.f ;
> 		chi:scale_factor = 1.f ;
> 		chi:missing_value = -9.96921e+36f ;
> 		chi:precision = 3s ;
> 		chi:least_significant_digit = 3s ;
> 		chi:var_desc = "Velocity Potential" ;
> 		chi:dataset = "CDC Derived NCEP Reanalysis Products" ;
> 		chi:level_desc = "Multiple Level" ;
> 		chi:statistic = "Mean" ;
> 		chi:parent_stat = "Mean" ;
>
> // global attributes:
> 		:title = "NCEP reanalysis" ;
> 		:history = "created 2002/08/30 by Hoop" ;
> 		:description = "Data is from NCEP initialized reanalysis\n",
>     "(daily means).  It consists of T42  variables." ;
> 		:Conventions = "COARDS" ;
>   

-- 

Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.

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 Charles Seman                                Charles.Seman at noaa.gov
 U.S. Department of Commerce / NOAA / OAR
 Geophysical Fluid Dynamics Laboratory         voice: (609) 452-6547
 201 Forrestal Road                              fax: (609) 987-5063
 Princeton, NJ  08540-6649            http://www.gfdl.noaa.gov/~cjs/
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