Building Tables Of Aerosol Optical Properties

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This page describes the main steps required to build new aerosol optical property tables for the Generic PCM.

Find a database

You first need to find the necessary indices for your aerosols of choice. The HITRAN database is an excellent place to start: https://hitran.org/aerosols/

You will end up with a table with the real and imaginary parts of the optical constants according to wavelength. If they are not there, you will have to dig into the literature. There are also several “Handbooks of Optical Constants”.

Run the Mie code

Once you have the optical indices for your aerosol, you will need to use the 'optpropgen' Mie code (developed by Jean-Baptiste Madeleine and Franck Montmessin).

The code is available on the SVN here: https://svn.lmd.jussieu.fr/Planeto/trunk/LMDZ.GENERIC/utilities/aerosols_utilities/


Several advices taken from the original user manual (by Laura Kerber):

  • Once you have the optical indices for your aerosol, divide the values into two separate files, one for the visible wavelengths and one for the infrared wavelengths.
  • In the Mie code, nsize is the number of bins used to integrate Qext, omega, and g over the particle radius. Usually 1E4 is a good number. You can try to increase this number to see if it changes the results, and if it does, keep increasing it until you reach constant and consistent results.
  • rmin and rmax are the minimum and maximum particle radii (in meter) used for the integration. In this case, 1.E-10 and 1E-4 usually work because the reference radius is often around 1.E-6 (this may change depending on your aerosol).
  • nreff is the number of bins of particle radii. We usually take it around 30 to 50.
  • Nsun is the number of wavelengths in the input file optind_*.dat. So you will run the Mie code twice, once to create the properties for the visible spectrum, once to make the properties for the infrared part of the spectrum.”
  • Save these as different files with names like “optprop_aerosolnamevis_n20.dat”, where n## indicates how many radii you used in the Mie code (only to help you remember).
  • Put these files in your datagcm/aerosol_properties/ directory.
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