about vertmean
Added by Jen Sun about 8 years ago
Hello
I am trying to use this command, "cdo vertmean", to calculate vertical integration weighted by pressure level depth.
but something frustrated is that I always get this response :
"cdo vertmean (Warning): Layer bounds not available, using constant vertical weights for variable th!"
I know what happened because my ncfile is without any bnds in vertical lev, so I write a bnds and append on this nc file, and the ncudmp is as followed :
netcdf test {
dimensions:
x = 1 ;
y = 1 ;
lev = 45 ;
Time = UNLIMITED ; // (1 currently)
bnds = 2 ;
variables:
double lev(lev) ;
lev:long_name = "generic" ;
lev:units = "level" ;
lev:axis = "Z" ;
double Time(Time) ;
Time:standard_name = "time" ;
Time:long_name = "Time" ;
Time:units = "minutes since 1900-1-1 00:00:00" ;
Time:calendar = "standard" ;
Time:axis = "T" ;
float th(Time, lev, y, x) ;
th:standard_name = "potential_temperature" ;
th:long_name = "potential temperature" ;
th:units = "K" ;
th:_FillValue = 9.96921e+36f ;
th:missing_value = 9.96921e+36f ;
float lev_bnds(lev, bnds) ;
// global attributes:
:CDI = "Climate Data Interface version 1.7.1 (http://mpimet.mpg.de/cdi)" ;
:Conventions = "CF-1.4" ;
:history = "Wed Mar 23 12:35:02 2016: ncks -A -v lev_bnds test_mat.nc test.nc\n",
"Wed Mar 23 12:35:02 2016: ncks -A -v lev F_info/A21/plev.nc test.nc\n",
"Wed Mar 23 12:35:02 2016: cdo selindexbox,50,50,1,1 -seltimestep,240 F_MODEL/A21/th3d.nc test.nc" ;
:institution = "Colorado State University" ;
:model_tag = "CSU VVM" ;
:references = "http://kiwi.atmos.colostate.edu/pubs/joon-hee-tech_report.pdf" ;
:contact = "jung@atmos.colostate.edu" ;
:VVM_casename = "GATE_PHASE_III " ;
:CDO = "Climate Data Operators version 1.7.1 (http://mpimet.mpg.de/cdo)" ;
:NCO = "4.3.7" ;
}
the result is the same.
what do I lose ?
thanks a lot
Replies (3)
RE: about vertmean - Added by Uwe Schulzweida about 8 years ago
The following attribute is missing:
lev:bounds = "lev_bnds" ;
You can add it with the NCO tool ncatted:
ncatted -a bounds,lev,c,c,"lev_bnds" file.nc
RE: about vertmean - Added by Josué Bock over 6 years ago
Hello,
When creating a level bounds variable, which values do you set for the level bounds? Just +/- 0.5 for each level?
If so, is it the correct way to weight the level thicknesses? I mean: two sets of hybrid coefficients are generally provided, either for the layer centre, or for the layer boundaries. But a centered value is not the average of the boundaries values, but stem from a separate calculation (according to https://rda.ucar.edu/datasets/ds627.0/docs/Eta_coordinate/, the average results in a systematic pressure overestimation).
So I wonder if the creation of a level bounds variable as the level number +/- 0.5 would lead to the same bias?
Thanks