libRadtran aerosol profiles (Figure 3)
This Figure shows the four volcanic aerosol profiles
provided by Shettle (1989), as incorporated in libRadtran.
In addition to the stratospheric aerosol we included also
some tropospheric background aerosol (the libRadtran
default aerosol: spring/summer, rural, visibility 50km,
according to Shettle (1989)).
If the user modifies the integrated optical thickness of
the aerosol, using e.g. aerosol_set_tau, aerosol_set_tau550, or aerosol_angstrom
only the tropospheric profile is affected. The following image shows the
libRadtran aerosol profile for "high" volcanic conditions and different
values of the user-defined optical thickness:
We decided to modify only the tropospheric part because otherwise the specification
of a large optical thickness by the user can result in highly unrealistic peaks in the
stratosphere if simply the whole profile is scaled, while the user most probably
intended to describe a situation with haze in the boundary layer. As long as the
user-defined optical thickness is large enough, only the tropospheric part is
affected, but below a certain threshold (in this case between 0.1 and 0.2) the
stratospheric fraction needs to be reduced as well. The change in the profile
is as consistent as possible with the data of Shettle (1989).
Back to the overview page.