libRadtran aerosol profiles (Figure 3)

libRadtran aerosol profiles

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: libRadtran aerosol profiles

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).

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