Automatic Qext for lifted dust

[abierjon]

In initracer.F, the injection coefficient for dust :
"alpha_lift(igcm_dust_mass)" (or "alpha_lift(igcm_stormdust_mass)" when rocket dust storms are activated) is theoretically dependent on the dust extinction coefficient Qext at the visible wavelength of 0.67µm.

This Qext should depend on the value of the lifted dust effective size, "reff_lift". In practice though, it is currently hardcoded with the value of 2.4, corresponding to reff_lift=3µm.

Since sensitivity studies are to be done on the lifted dust size, and since the dust optical properties we use in the GCM may change one day, a more automatic assignment of value for Qext, depending on the reff_lift value, should be implemented.

This could be done by changing aeroptproperties.F into a module and restructuring it a bit in order to be able to get the properties for only one reff value (by calling only a subroutine of the aeroptproperties.F module, while the main routine of aeroptproperties would still deal with the sizes of the whole column)

[abierjon]

With a nueff=0.5 as used in the GCM :

Qext(reff1µm) = 2.85
Qext(reff2µm) = 2.6
Qext(reff2.5µm) = 2.5
Qext(reff3µm) = 2.46 (2.42 with no nueff)