[gradsusr] Atmosphere_hybrid_sigma_pressure_coordinate

[Jeff Duda]

Have you actually tried just plotting the data with an arbitrary set of
vertical levels? The values you specify for ZDEF in your control file do
not have to exactly match the vertical levels of your data. What really
matters is how many vertical levels there are.

Now, if you want to start performing calculations such as the spatial
average of Q at a specific level like 850 mb, that's a bit more tricky, but
as long as you know the structure of the vertical levels, you should be
able to calculate it.

Jeff Duda

On Thu, May 26, 2016 at 12:12 PM, Corey Gabriel <cjgabriel7 at gmail.com>
wrote:

> Dear gradsusr community,
>
> I am attempting to create a zonal mean plot of a variable (Q), which has
> 26 levels.
>
> The vertical coordinates are "hybrid sigma pressure."  I have created a
> data descriptor file and entered the vertical coordinates in the following
> manner: ZDEF 26 levels L1 L2 ... L26.
>
> I have reviewed the GrADS documentation, and it seems that several
> examples suggest that the vertical coordinates should be in pure pressure
> coordinates and that GrADS may not read these hybrid coordinates.
>
> The relevant ncdump infomration is provided below.  Just below the
> dimensions, you can see that the formula from which the sigma coordinates
> are calculated from actual pressure and surface pressure are provided.
>
> Has anyone attempted to plot hybrid sigma pressure coordinates in GrADS
> before?  If so, would someone be able to provide an explanation of how to
> convert the vertical coordinate into something GrADS will read?
>
> Thanks so much!
> Corey
>
> ncdump -c q.corey30.001.cam.2020-01-2089-12.nc
>
> netcdf q.corey30.001.cam.2020-01-2089-12 {
>
> dimensions:
>
> lev = 26 ;
>
> time = UNLIMITED ; // (840 currently)
>
> lat = 192 ;
>
> lon = 288 ;
>
> nbnd = 2 ;
>
> variables:
>
> double lev(lev) ;
>
> lev:long_name = "hybrid level at midpoints (1000*(A+B))" ;
>
> lev:units = "level" ;
>
> lev:positive = "down" ;
>
> lev:standard_name = "atmosphere_hybrid_sigma_pressure_coordinate" ;
>
> lev:formula_terms = "a: hyam b: hybm p0: P0 ps: PS" ;
>
> double time(time) ;
>
> time:long_name = "time" ;
>
> time:units = "days since 2004-01-01 00:00:00" ;
>
> time:calendar = "noleap" ;
>
> time:bounds = "time_bnds" ;
>
> double lat(lat) ;
>
> lat:long_name = "latitude" ;
>
> lat:units = "degrees_north" ;
>
> double lon(lon) ;
>
> lon:long_name = "longitude" ;
>
> lon:units = "degrees_east" ;
>
> double time_bnds(time, nbnd) ;
>
> time_bnds:long_name = "time interval endpoints" ;
>
> float Q(time, lev, lat, lon) ;
>
> Q:mdims = 1 ;
>
> Q:units = "kg/kg" ;
>
> Q:long_name = "Specific humidity" ;
>
> Q:cell_methods = "time: mean" ;
>
>
> // global attributes:
>
> :Conventions = "CF-1.0" ;
>
> :source = "CAM" ;
>
> :case = "corey30" ;
>
> :title = "UNSET" ;
>
> :logname = "cgabriel" ;
>
> :host = "ys0861" ;
>
> :Version = "$Name$" ;
>
> :revision_Id = "$Id$" ;
>
> :initial_file =
> "/glade/p/acd/tilmes/inputdata/init/ccmi/b.e11.TSREFC2.f19.f19.ccmi23.1deg_26L.001"
> ;
>
> :topography_file = "/glade/p/cesmdata/cseg/inputdata/atm/cam/topo/
> USGS-gtopo30_0.9x1.25_remap_c051027.nc"
>
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>


-- 
Jeff Duda
Graduate research assistant
University of Oklahoma School of Meteorology
Center for Analysis and Prediction of Storms
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