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 shettle89 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.