How to create regular lat/lon NC file from a "line NC file"

Hi, I have a netcdf file with the following structure:

dimensions:
nobs = UNLIMITED ; // (23562010 currently)
variables:
double Observation_Type(nobs) ;
double Latitude(nobs) ;
double Longitude(nobs) ;
double Pressure(nobs) ;
double Analysis_Use_Flag(nobs) ;
double u_Obs_Minus_Forecast_unadjusted(nobs) ;
double u_Obs_Minus_Forecast_unadjusted(nobs) ;

I need to create a LAT/LOn regular netcdf file where lat and lon are the coordinates of the fields observation_type, pressure, Analysis_use, u_Obs_Minus_Forecast_unadjusted, v_Obs_Minus_Forecast_unadjusted.

Basically, I'll choose a delta lat and delta lon and each values of the variables that falls within each lat/lon bin would be averaged to get one variable value per lat/lon cell.

I will also need to add a time coordinate/time stamp. Each of the input nc files have in its name the corresponding time (ex, name_20100115_00z.nc). How can I add this info as a coordinate or time stamp inside the files, since I will have several times inside each output nc file?

Any suggestions in how can I do this with NCO, or CDO?

Thanks!

Replies (2)

RE: How to create regular lat/lon NC file from a "line NC file" - Added by Karin Meier-Fleischer over 7 years ago

Hi David,

in my opinion there is no way to remap the station data to a regular grid using cdo (hopefully I'm not wrong). But you can use NCL to read the data and regrid it with ESMF to a regular latlon grid. Here is the example how to read and regrid the Pressure variable from a file called data.nc and write it to a new file called data_regridded.nc.

load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl" 

begin
  f =  addfile("data.nc","r")                       ;-- open file for reading

  Pressure =  f->Pressure                           ;-- read variable
  lat1d    =  f->Latitude                           ;-- read latitudes
  lon1d    =  f->Longitude                          ;-- read longitudes

;-- ESMF settings
  Opt                 =  True                       ;-- regridding options
  Opt@ForceOverwrite  =  True                       ;-- overwrite existing temporary files
  Opt@SrcGridLat      =  lat1d                      ;-- latitude of source grid
  Opt@SrcGridLon      =  lon1d                      ;-- longitude of source grid
  Opt@DstGridType     = "0.5deg"                    ;-- 0.5 x 0.5 degrees destination grid
  Opt@DstLLCorner     = (/-90.0d,   0.0d /)         ;-- destination lower left grid corner
  Opt@DstURCorner     = (/ 90.0d, 360.0d /)         ;-- destination upper right grid corner

  Pressure_regrid = ESMF_regrid(Pressure,Opt)
  printVarSummary(pw_regrid)                        ;-- print variable information to stdout

;-- write regridded data to new netcdf file
  system("rm -rf data_regridded.nc")                ;-- first, delete if exists
  ofile = addfile("data_regridded.nc","c")          ;-- open file for creation
  ofile->Pressure  = Pressure_regrid                ;-- write variable Pressure to file
end

Let us assume the NCL script is named station2regular.ncl then run the NCL script

ncl station2regular.ncl

To add the date as a time variable to the file you can use the cdo operator settaxis

cdo -settaxis,2010-01-15,00:00:00,1day data_regridded.nc data_regridded_plus_date.nc

Hope this helps

-Karin

RE: How to create regular lat/lon NC file from a "line NC file" - Added by david moreno over 7 years ago

Thanks so much Karin, I'll give it a try!!

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