CDO

I have some model output (CESM LE) supplied on a hybrid sigma-pressure vertical structure. I combined Z3 (geopotential height) with surface pressure, as required to do the interpolation.

However, running the command cdo ml2pl,500 -selname,Z3 slice.nc result.nc results in the following error:

cdo(2) selname: Process started

cdo ml2pl (Abort): surface_air_pressure not found!
terminate called without an active exception
Aborted (core dumped)

An ncdump -h suggests this is present with the correct name, both containing geopotential height and surface pressure:

float Z3(time, lev, lat, lon) ;
        Z3:long_name = "Geopotential Height (above sea level)" ;
        Z3:units = "m" ;
        Z3:mdims = 1 ;
        Z3:cell_methods = "time: mean" ;

float surface_air_pressure(time, lat, lon) ;
        surface_air_pressure:standard_name = "surface_air_pressure" ;
        surface_air_pressure:long_name = "Surface pressure" ;
        surface_air_pressure:units = "Pa" ;
        surface_air_pressure:cell_methods = "time: mean" ;

I supplied a timeslice (netcdf) to support the query. Thanks in advance!