Fixed dust opacity when using 1d without seasonal cycle

[jnaar]

Currently (29/06/2023) when using the 1D model with a dust scenario (variable "iaervar" set to a MY in callphys.def) the reference dust opacity still evolves with time. Instead, we would want it to be fixed to the prescribed Ls and location in .def files.

Some clarification: what is mentioned above is for the case where one also sets "seasonal=.false." And then indeed the dust opacity should remain fixed to its initial value (given by the dust scenario & time of year of initial condition). With "seasonal=.true." the opacity should be allowed to evolve with time.