[ferret_users] vertical formula embedded in netcdf file

[Albert Hermann - NOAA Affiliate <albert.j.hermann@xxxxxxxx>]

Hi group,

I am reading in a file created from one of the CMIP6 models. It appears to have a coordinate transformation embedded as metadata, which one might think would yield different z-levels for the 4D variable (vo) at each horizontal location. However, when I read the file into ferret v7.5, I get vo appearing on a single z-axis (which ferret labels as  "lev"), ranging from 1 to 7250. That axis has the same values as the "zlev" variable in the original file. Now, "zlev" is in fact used in the depth formula, but it is *not* the only term - other terms in the equation suggest that z-levels should vary by location and time (see the formula listed in the ncdump below). Is ferret in fact regridding to a uniform z-axis based on zlev, or is it erroneously assuming all is uniform?

Output from "show data", "show grid" and "ncdump" are appended below

Thanks for any insights or redirection to relevant text in the manual.

-Al Hermann

---------------------------------------------------

        NOAA/PMEL TMAP
        PyFerret v7.5 (optimized)
        Linux 4.15.0-1071-azure - 03/31/20
         7-May-20 14:19

yes? use vo_Omon_MIROC-ES2L_ssp585_r1i1p1f2_gn_201501-210012.nc
yes? sh dat
     currently SET data sets:
    1> /gscratch/bumblereem/wcheng/beast/cmip6/miroc-es2l/vo_Omon_MIROC-ES2L_ssp585_r1i1p1f2_gn_201501-210012.nc  (default)
 name     title                             I         J         K         L
 SIGMA    vertical coordinate formula ter  ...   & ;         sigma:long_name = "vertical coordinate formula term: sigma(k)" ;
        float eta(time, y, x) ;
                eta:long_name = "Sea Surface Height formula term: thetao" ;
                eta:units = "m" ;
                eta:original_units = "cm" ;
                eta:history = "2019-07-16T13:40:11Z altered by CMOR: Converted units from \'cm\' to \'m\'." ;
        float depth(y, x) ;
                depth:long_name = "Sea Floor Depth: formula term: thetao" ;
                depth:units = "m" ;
        double depth_c ;
                depth_c:long_name = "vertical coordinate formula term: depth_c" ;
        int nsigma ;
                nsigma:long_name = "vertical coordinate formula term: nsigma" ;
        double zlev(lev) ;
                zlev:long_name = "vertical coordinate formula term: zlev(k)" ;
        double sigma_bnds(lev, bnds) ;
                sigma_bnds:long_name = "vertical coordinate formula term: sigma(k+1/2)" ;
        double zlev_bnds(lev, bnds) ;
                zlev_bnds:long_name = "vertical coordinate formula term: zlev(k+1/2)" ;
        double y(y) ;
                y:bounds = "y_bnds" ;
          0;           :history = "2019-07-16T13:40:11Z ; CMOR rewrote data to be consistent with CMIP6, CF-1.7 CMIP-6.2 and CF standards." ;
                :initialization_index = 1 ;
                :institution = "JAMSTEC (Japan Agency for Marine-Earth Science and Technology, Kanagawa 236-0001, Japan), AORI (Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba 277-8564, Japan), NIES (National Institute for Environmental Studies, Ibaraki 305-8506, Japan), and R-CCS (RIKEN Center for Computational Science, Hyogo 650-0047, Japan)" ;
                :institution_id = "MIROC" ;
                :mip_era = "CMIP6" ;
                :nominal_resolution = "100 km" ;
                :parent_activity_id = "CMIP" ;
                :parent_experiment_id = "historical" ;
                :parent_mip_era = "CMIP6" ;
                :parent_source_id = "MIROC-ES2L" ;
                :parent_time_units = "days since 1850-1-1" ;
                :parent_variant_label = "r1i1p1f2" ;
                :physics_index = 1 ;
                :product = "model-output" ;
                :realization_index = 1 ;
                :realm = "ocean" ;
                :source = "MIROC-ES2L (2018): \n"