[CF-metadata] Specifying a wavelength for a standard_name

[Jonathan Gregory]

Dear Pepe

You should add a size-one coordinate variable or a scalar coordinate variable
of radiation_wavelength.

     float kd490(wavelength);
        kd490:standard_name = 
  "volume_attenuation_coefficient_of_downwelling_radiative_flux_in_sea_water"; 
        kd490:long_name = "Mean Diffuse Attenuation Coefficient at 490nm" ;
        kd490:units = "m-1" ;
     float wavelength(wavelength);
        wavelength:units="m";
        wavelength:standard_name="radiation_wavelength";

or

     float kd490;
        kd490:standard_name = 
  "volume_attenuation_coefficient_of_downwelling_radiative_flux_in_sea_water"; 
        kd490:long_name = "Mean Diffuse Attenuation Coefficient at 490nm" ;
        kd490:units = "m-1" ;
        kd490:coordinates="wavelength";
     float wavelength;
        wavelength:units="m";
        wavelength:standard_name="radiation_wavelength";

Best wishes

Jonathan