[gradsusr] Help on displaying NetCDF data with Grads.

Anil Kumar Sharma aanil649 at gmail.com
Tue Jan 28 02:15:53 EST 2014


Hi Jennifer and GrADS Users,



I have NetCDF file (RTOFS
Global<http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20140127/rtofs_glo_2ds_n024_daily_prog.nc>)
downloaded from NOMADS
server<http://nomads.ncep.noaa.gov/pub/data/nccf/com/rtofs/prod/rtofs.20140127/rtofs_glo_2ds_n024_daily_prog.nc>.
Ncdump of the file is


netcdf
D\:/OceanCurrentData/2014/01/22/20140122_rtofs_glo_2ds_n024_daily_prog {
dimensions:
        MT = UNLIMITED ; // (1 currently)
        Y = 3298 ;
        X = 4500 ;
        Layer = 1 ;
variables:
        double MT(MT) ;
                MT:long_name = "time" ;
                MT:units = "days since 1900-12-31 00:00:00" ;
                MT:calendar = "standard" ;
                MT:axis = "T" ;
        double Date(MT) ;
                Date:long_name = "date" ;
                Date:units = "day as %Y%m%d.%f" ;
                Date:C_format = "%13.4f" ;
                Date:FORTRAN_format = "(f13.4)" ;
        int Layer(Layer) ;
                Layer:units = "layer" ;
                Layer:positive = "down" ;
                Layer:axis = "Z" ;
        int Y(Y) ;
                Y:point_spacing = "even" ;
                Y:axis = "Y" ;
        int X(X) ;
                X:point_spacing = "even" ;
                X:axis = "X" ;
        float Latitude(Y, X) ;
                Latitude:standard_name = "latitude" ;
                Latitude:units = "degrees_north" ;
        float Longitude(Y, X) ;
                Longitude:standard_name = "longitude" ;
                Longitude:units = "degrees_east" ;
                Longitude:modulo = "360 degrees" ;
        float u_velocity(MT, Layer, Y, X) ;
                u_velocity:coordinates = "Longitude Latitude Date" ;
                u_velocity:standard_name = "eastward_sea_water_velocity" ;
                u_velocity:units = "m/s" ;
                u_velocity:_FillValue = 1.267651e+030f ;
                u_velocity:valid_range = -2.09935f, 2.310735f ;
                u_velocity:long_name = " u-veloc. [90.9H]" ;
        float v_velocity(MT, Layer, Y, X) ;
                v_velocity:coordinates = "Longitude Latitude Date" ;
                v_velocity:standard_name = "northward_sea_water_velocity" ;
                v_velocity:units = "m/s" ;
                v_velocity:_FillValue = 1.267651e+030f ;
                v_velocity:valid_range = -2.275719f, 2.274807f ;
                v_velocity:long_name = " v-veloc. [90.9H]" ;
        float sst(MT, Y, X) ;
                sst:coordinates = "Longitude Latitude Date" ;
                sst:standard_name = "sea_surface_temperature" ;
                sst:units = "degC" ;
                sst:_FillValue = 1.267651e+030f ;
                sst:valid_range = -6.057281f, 32.59346f ;
                sst:long_name = " sea surf. temp.   [90.9H]" ;
        float sss(MT, Y, X) ;
                sss:coordinates = "Longitude Latitude Date" ;
                sss:standard_name = "sea_surface_salinity" ;
                sss:units = "psu" ;
                sss:_FillValue = 1.267651e+030f ;
                sss:valid_range = 1.749605f, 40.75261f ;
                sss:long_name = "sea surf. salnity  [90.9H]" ;
        float layer_density(MT, Layer, Y, X) ;
                layer_density:coordinates = "Longitude Latitude Date" ;
                layer_density:standard_name = "sea_water_potential_density"
;
                layer_density:units = "sigma" ;
                layer_density:_FillValue = 1.267651e+030f ;
                layer_density:valid_range = 0.f, 0.f ;
                layer_density:long_name = " density [90.9H]" ;

// global attributes:
                :Conventions = "CF-1.0" ;
                :title = "HYCOM ATLb2.00" ;
                :institution = "National Centers for Environmental
Prediction" ;
                :source = "HYCOM archive file" ;
                :experiment = "90.9" ;
                :history = "archv2ncdf2d" ;
}

The dataset has 32 hybrid layers and a horizontal grid size of (4500 x
3298) . The grid has an Arctic bi-polar patch north of 47°N and a Mercator
projection south of 47°N through 78.6°S. More details can be found at
link<http://polar.ncep.noaa.gov/global/about/?>.


The CTL file Am using is to display variable values :



dset ^20140122_rtofs_glo_2ds_n024_daily_prog.nc

title HYCOM ATLb2.00

undef 1.26765e+30

dtype netcdf

XDEF 4320 LINEAR 74.16 0.08333

YDEF 2160 LINEAR -90.   0.08333

zdef 1 linear 1 1

tdef 1 linear 00Z31DEC1900 1mn

options template

PDEF 4500 3298 bilin sequential binary-big
D:\OceanCurrentData\PDEF\pdef_ncep_global


vars 8

Date=>date  0  t  date

Latitude=>latitude  0  y,x  latitude

Longitude=>longitude  0  y,x  longitude

u_velocity=>u_velocity  1  t,z,y,x   u-veloc. [90.9H]

v_velocity=>v_velocity  1  t,z,y,x   v-veloc. [90.9H]

sst=>sst  0  t,y,x   sea surf. temp.   [90.9H]

sss=>sss  0  t,y,x  sea surf. salnity  [90.9H]

layer_density=>layer_density  1  t,z,y,x   density [90.9H]

endvars

The file used for interpolation pdef_ncep_global can be downloaded from
http://nomad3.ncep.noaa.gov/pub/rtofs_global/20140122/



When Am displaying current variables u_velocity and v_velocity in GrADS
with following commands

ga->open
C:/OceanCurrentData/2014/01/22/20140122_rtofs_glo_2ds_n024_daily_prog.ctl

ga-> set lon -180 180

ga-> set lat -90 90
ga-> d skip(u_velocity*1.95,50,50);v_velocity*1.95

The output produced with above commands is attached herewith. The output
shown to grads windows is only for lon 74.16 to 179.95 approx. Understand
that Longitude starts is set 74.16 in XDEF entry in CTL file (as NetCDF
file contains rectilinear data from 74.16 onward and data is packed 1/12 th
the degree)


XDEF 4320 LINEAR 74.16 0.08333




is defining Start point of LON.



My Question is : How can I make command d
skip(u_velocity*1.95,50,50);v_velocity*1.95 working so that plot is on
entire globe ??? not for just LON 74.16 to 179.65. (Understand that NetCDF
file has linear data from 74.16 to 434, but How can I make these
Cartesian coordinate
equivalent to geographical coordinates ????)



Center of Plot is necessarily to be at POINT (0,0) as plot need to be
overlaid on google map.



*Any help or guidance would be greatly appreciated.*

*Thanks & Regards*

*Anil Kumar – **Sr. Software Developer*

*OceanManager Inc. *| www.oceanmanager.com

Tel: +1 (801)-758-7101, (801)-758-7207

Fax: +1 (801)-758-7101

*OceanManager- Marine Software*
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