[gradsusr] Reading CMIP5 GCM data with GrADS

[Jennifer Adams]

There are two problems: 
1. The variable tasmax does not vary in Z, only (time,lat,lon), so you should change your variable declaration to:
 “tasmax 0  t,y,x  Daily maximum near-surface air temperature [K]”

2. The time axis is a 360_day calendar, and you have ‘OPTIONS 365_day_calendar’. Unfortunately, GrADS doesn’t support 360-day calendars. I am surprised they are still being used in CMIP5. You can open the file and look at the data, but will have to ignore the time metadata and rely strictly on T index values to move through your file. 
—Jennifer


On Jul 30, 2015, at 6:42 AM, itesh dash <itesh at rimes.int> wrote:

> Dear All,
> 
> I am trying to read the CMIP5 HADGEM-AO GCM (nc file) data sets using grads. I have prepared a descriptor file. However, it seems the file is not read correctly, and I receive wrong temperature values.
> 
> The GCM attributes are:
> 
> netcdf tasmax_day_HadGEM2-AO_rcp45_r1i1p1_20060101-21001230 {
> dimensions:
> 	time = UNLIMITED ; // (34200 currently)
> 	lat = 145 ;
> 	lon = 192 ;
> 	bnds = 2 ;
> variables:
> 	double time(time) ;
> 		time:bounds = "time_bnds" ;
> 		time:units = "days since 2006-01-01" ;
> 		time:calendar = "360_day" ;
> 		time:axis = "T" ;
> 		time:long_name = "time" ;
> 		time:standard_name = "time" ;
> 	double time_bnds(time, bnds) ;
> 	double lat(lat) ;
> 		lat:bounds = "lat_bnds" ;
> 		lat:units = "degrees_north" ;
> 		lat:axis = "Y" ;
> 		lat:long_name = "latitude" ;
> 		lat:standard_name = "latitude" ;
> 	double lat_bnds(lat, bnds) ;
> 	double lon(lon) ;
> 		lon:bounds = "lon_bnds" ;
> 		lon:units = "degrees_east" ;
> 		lon:axis = "X" ;
> 		lon:long_name = "longitude" ;
> 		lon:standard_name = "longitude" ;
> 	double lon_bnds(lon, bnds) ;
> 	double height ;
> 		height:units = "m" ;
> 		height:axis = "Z" ;
> 		height:positive = "up" ;
> 		height:long_name = "height" ;
> 		height:standard_name = "height" ;
> 	float tasmax(time, lat, lon) ;
> 		tasmax:standard_name = "air_temperature" ;
> 		tasmax:long_name = "Daily Maximum Near-Surface Air Temperature" ;
> 		tasmax:comment = "daily-maximum near-surface (usually, 2 meter) air temperature." ;
> 		tasmax:units = "K" ;
> 		tasmax:original_name = "TASMAX" ;
> 		tasmax:cell_methods = "time: maximum (interval: 1.000000 days)" ;
> 		tasmax:cell_measures = "area: areacella" ;
> 		tasmax:history = "2012-10-29T09:05:42Z altered by CMOR: Treated scalar dimension: \'height\'. 2012-10-29T09:05:42Z altered by CMOR: replaced missing value flag (-1.07374e+09) with standard missing value (1e+20)." ;
> 		tasmax:coordinates = "height" ;
> 		tasmax:missing_value = 1.e+20f ;
> 		tasmax:_FillValue = 1.e+20f ;
> 		tasmax:associated_files = "baseURL: http://cmip-pcmdi.llnl.gov/CMIP5/dataLocation gridspecFile: gridspec_fx_HadGEM2-AO_rcp45_r0i0p0.nc areacella: areacella_fx_HadGEM2-AO_rcp45_r0i0p0.nc" ;
> 
> // global attributes:
> 		:institution = "NIMR (National Institute of Meteorological Research, Seoul, South Korea)" ;
> 		:institute_id = "NIMR-KMA" ;
> 		:experiment_id = "rcp45" ;
> 		:source = "HadGEM2-AO r6.6.3 (2010): atmosphere:  HadGAM (HadGAM2, N96L38); atm: HadGOM (HadGOM2, 1x1L40, increased res at Equator); sea ice: part of HadGOM2; land: MOSES-2" ;
> 
> 
> The descriptor (.ctl) file :
> 
> DSET ^tasmax_day_HadGEM2-AO_rcp45_r1i1p1_20060101-21001230.nc
> TITLE Air Temperature
> DTYPE netcdf
> OPTIONS 365_day_calender
> UNDEF 1.e+20f
> xdef 192 linear 0 1.875
> ydef 145 linear -90 1.25
> zdef 1 levels 1013.0
> tdef 34200 linear 00Z1Jan2006 1dy
> VARS 1
> tasmax 1 t,z,y,x Air Temperature [K]
> ENDVARS
> 
> 
> 
> Kindly, help in understanding where we are doing wrong.
> 
> Much appreciate your help in this. 
> 
> 
> Regards,
> Itesh Dash
> RIMES
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--
Jennifer M. Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
111 Research Hall, Mail Stop 2B3
George Mason University
4400 University Drive
Fairfax, VA 22030 





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