Absorption Output

Absorption coefficients can be calculated using the Spectroscopy object (described in the previous API section) by running:

# Calculate the absorption coefficients [m-1] and return them in an xarray Dataset.
absorption = spectroscopy.compute_absorption(output_format="all")

# Optional: convert dataset to netcdf.
absorption.to_netcdf("<name of output file>")

The output is returned as an xarray Dataset. The absorption coefficients are calculated in units of inverse meters, so that optical depths can be calculated by the user by integrationg them over any desired path. The exact format of the output data depends on the value of the output_format argument. When set to "all" (which is currently the default), the dataset will return the spectra split up by molecule and mechansim (lines, continuum, cross_section). If a mechanism does not apply to a specific molecule, then values are set to zero accordingly. An example viewed in netCDF format (i.e., like by running ncdump on the dataset) would look like this:

netcdf absorption {
dimensions:
        wavenumber = 49990 ;
        mechanism = 3 ;
        z = 1 ;
variables:
        double wavenumber(wavenumber) ;
                wavenumber:_FillValue = NaN ;
                wavenumber:units = "cm-1" ;
        string mechanism(mechanism) ;
        double H2O_absorption(z, mechanism, wavenumber) ;
                H2O_absorption:_FillValue = NaN ;
                H2O_absorption:units = "m-1" ;
        double CO2_absorption(z, mechanism, wavenumber) ;
                CO2_absorption:_FillValue = NaN ;
                CO2_absorption:units = "m-1" ;
        double O3_absorption(z, mechanism, wavenumber) ;
                O3_absorption:_FillValue = NaN ;
                O3_absorption:units = "m-1" ;
        double N2O_absorption(z, mechanism, wavenumber) ;
                N2O_absorption:_FillValue = NaN ;
                N2O_absorption:units = "m-1" ;
        double CO_absorption(z, mechanism, wavenumber) ;
                CO_absorption:_FillValue = NaN ;
                CO_absorption:units = "m-1" ;
        double CH4_absorption(z, mechanism, wavenumber) ;
                CH4_absorption:_FillValue = NaN ;
                CH4_absorption:units = "m-1" ;
        double O2_absorption(z, mechanism, wavenumber) ;
                O2_absorption:_FillValue = NaN ;
                O2_absorption:units = "m-1" ;
        double N2_absorption(z, mechanism, wavenumber) ;
                N2_absorption:_FillValue = NaN ;
                N2_absorption:units = "m-1" ;
data:
        mechanism = "lines", "continuum", "cross_section" ;
}

If the output_format argument is instead set to "gas", the spectra for the different mechanims will be summed for each molecule, yielding output that looks like this (in netCDF format):

netcdf absorption {
dimensions:
        wavenumber = 49990 ;
        z = 1 ;
variables:
        double wavenumber(wavenumber) ;
                wavenumber:_FillValue = NaN ;
                wavenumber:units = "cm-1" ;
        double H2O_absorption(z, wavenumber) ;
                H2O_absorption:_FillValue = NaN ;
                H2O_absorption:units = "m-1" ;
        double CO2_absorption(z, wavenumber) ;
                CO2_absorption:_FillValue = NaN ;
                CO2_absorption:units = "m-1" ;
        double O3_absorption(z, wavenumber) ;
                O3_absorption:_FillValue = NaN ;
                O3_absorption:units = "m-1" ;
        double N2O_absorption(z, wavenumber) ;
                N2O_absorption:_FillValue = NaN ;
                N2O_absorption:units = "m-1" ;
        double CO_absorption(z, wavenumber) ;
                CO_absorption:_FillValue = NaN ;
                CO_absorption:units = "m-1" ;
        double CH4_absorption(z, wavenumber) ;
                CH4_absorption:_FillValue = NaN ;
                CH4_absorption:units = "m-1" ;
        double O2_absorption(z, wavenumber) ;
                O2_absorption:_FillValue = NaN ;
                O2_absorption:units = "m-1" ;
        double N2_absorption(z, wavenumber) ;
                N2_absorption:_FillValue = NaN ;
                N2_absorption:units = "m-1" ;
}

Lastly, if the output_format argument is set to any other value, only the total absorption spectra (summed over all molecules) will be returned. In netCDF format, the resulting dataset will appear like this:

netcdf absorption {
  dimensions:
        wavenumber = 49990 ;
        z = 1 ;
  variables:
      double wavenumber(wavenumber) ;
              wavenumber:_FillValue = NaN ;
              wavenumber:units = "cm-1" ;
      double absorption(z, wavenumber) ;
              absorption:_FillValue = NaN ;
              absorption:units = "m-1" ;
}

We hope that formatted in this way will ease interaction between this package and other pangeo tools.