The command line
   aerosol_refrac_file file_name
specifies the file containing the wavelength-dependent refractive index of the aerosol. Three columns are expected: wavelength [nm] and the real and imaginary parts of the refractive index. Together with aerosol_sizedist_file this forms the input to Mie calculations of the aerosol optical properties. Please note that only the single-scattering albedo, the scattering phase function, and the wavelength-dependence of the extinction coefficient are affected by the Mie calculation while the absolute value of the extinction coefficient is taken from other sources; generally, the extinction coefficient at the first internal wavelength is taken from whatever is available (either default Shettle (1989) or user-defined); the extinction at all other wavelengths is scaled according to the Mie calculation. For this reason, the absolute numbers are not relevant - only the shape of the size distribution matters. In detail: If the aerosol properties are defined using the refractive index and the size distribution, the wavelength dependence of the optical properties is determined by Mie theory. At present there are at least three ways to define the absolute value of the optical thickness: (1) visibility defines the profile at the first internal wavelength; for a monochromatic calculation and in correlated-k mode, the first internal wavelength equals the first wavelength output by uvspec; for spectral calculations, the first wavelength might be a little bit smaller than the first wavelength output by uvspec; (2) aerosol_tau_file defines the optical thickness profile at the first internal wavelength; or (3) absolute optical thickness and wavelength-dependence are defined by aerosol_angstrom. It is recommended to avoid this option and rather to calculate the aerosol optical properties externally e.g. with mie and to pass them to uvspec with aerosol_files.





Arve Kylling 2010-03-10