Re: CCSM conversion of Geoptential Height

You do not indicate what the
"problem with conversion of geopotential heights"
actually is.

*Extrapolation is always dangerous.*
  EG: over the Himalaya the function uses the sfc T
  and assumes a constant lapse rate. The (say) 1000hPa
  hgt is based on the assumed lapse rate and the
  hydrostatic equation. Sometimes this yields non realistic values.

See Example 3 at
http://www.ncl.ucar.edu/Applications/grid_fill.shtml

This does not use geopotential heights but I might suggest
using vinh2p or vinth2p_ecmwf *without* extrapolation.
Then use poisson_grid_fill to file out the levels.

Good luck

Vijayaraghavan Srivatsan wrote:
> Hi all,
>
>
>
> I am using the vert_1.ncl to convert CCSM data (for WRF) from hybrid to
> pressure.
>
>
>
> Although, T, U, V and Humidity were successful, there is a problem with
> conversion of geopotential heights, despite using surface geopotential
> and surface pressure.
>
>
>
> I use vinth2p_ecmwf, since I need values upto 1000mb .( ie extrapolation).
>
>
>
> My code is below
>
>
>
> Any help in conversion please..
>
>
>
> Thanks a lot
>
>
>
> Sri
>
>
>
> ---------------------------
>
>
>
> ;*************************************************
>
> ; NCL tutorial script: vert_1.ncl
>
> ;************************************************
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>
> ;************************************************
>
> begin
>
>
>
> Ntime = 1
>
>
>
> ;************************************************
>
> ; file handling
>
> ;************************************************
>
>
>
> fn1 =
> "b30.042e.cam2.h3.Z3.60E-150E_50S-50N.2000-01-01_cat_2000-12-31.nc" ;
> define filename
>
> in1 = addfile(fn1,"r") ; open netcdf file
>
>
>
> Z3 = in1->Z3 ; select variable to ave
>
>
>
> P0mb =1000.
>
> hyam = in1->hyam ; get a coefficiants
>
> hybm = in1->hybm ; get b coefficiants
>
>
>
> fn2 =
> "b30.042e.cam2.h3.PS.60E-150E_50S-50N.2000-01-01_cat_2009-12-31.nc" ;
> define filename
>
> in2 = addfile(fn2,"r") ; open netcdf file
>
>
>
> PS = in2->PS
>
>
>
> fn3 =
> "b30.042e.cam2.h3.PHIS.60E-150E_50S-50N.2000-01-01_cat_2009-12-31.nc" ;
> define filename
>
> in3 = addfile(fn3,"r") ; open netcdf file
>
>
>
> PHIS = in3->PHIS
>
>
>
> fn4 =
> "b30.042e.cam2.h3.TS.60E-150E_50S-50N.2000-01-01_cat_2009-12-31.nc" ;
> define filename
>
> in4 = addfile(fn4,"r") ; open netcdf file
>
>
>
> TS = in4->TS
>
>
>
>
>
> ;************************************************
>
> ; define other arguments required by vinth2p
>
> ;************************************************
>
> ; type of interpolation: 1 = linear, 2 = log, 3 = loglog
>
> interp = 2
>
>
>
> ; is extrapolation desired if data is outside the range of PS
>
> extrap = True
>
>
>
> ; create an array of desired pressure levels:
>
> pnew =
> (/1000,950,900,850,800,750,700,650,600,550,500,450,400,350,300,250,200,150,100/)
>
>
>
> ;************************************************
>
> ; calculate T on pressure levels
>
> ;************************************************
>
> ; note, the 7th argument is not used, and so is set to 1.
>
> ;************************************************
>
> ; VARonP =
> vinth2p(Z3(0:Ntime,:,:,:),hyam,hybm,pnew,PS(0:Ntime,:,:),interp,P0mb,1,extrap)
>
>
>
> VARonP =
> vinth2p_ecmwf(Z3(0:Ntime,:,:,:),hyam,hybm,pnew,PS(0:Ntime,:,:),interp,P0mb,1,extrap,-1,TS(0:Ntime,:,:),PHIS(0:Ntime,:,:))
>
>
>
> ;output in nc file
>
> system("/bin/rm -f ./Z3_pressure.nc") ; remove any pre-existing file
>
> ncdf = addfile("./Z3_pressure.nc" ,"c") ; open output netCDF file
>
> filedimdef(ncdf,"time",-1,True)
>
>
>
> VARonP!0 = "time" ; assign named dimensions
>
> VARonP!1 = "lev"
>
> VARonP!2 = "lat"
>
> VARonP!3 = "lon"
>
>
>
> VARonP&time = in1&time(0:Ntime)
>
> VARonP&lev = pnew
>
> VARonP&lat = in1&lat
>
> VARonP&lon = in1&lon
>
>
>
> VARonP@long_name = "Geopotential Height on plevel" ; assign name
>
> VARonP@units = "m"
>
>
>
> ncdf->Z3_pres = VARonP
>
>
>
> print("finish convert Z3 to pressure level")
>
> print("output .nc: ./Z3_pressure.nc")
>
>
>
>
>
> end
>
>
>
>
>
>
> ------------------------------------------------------------------------
>
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Received on Tue Feb 2 07:25:30 2010