Exploring dust lifting over CO2/H2O caps

[abierjon]

Currently in the GCM (r2796), it is not possible to lift dust in meshes that have CO2 ice at the surface - cf this line in vdifc_mod.F :

if(co2ice(ig).lt.1) then ! pas de soulevement si glace CO2

It raises 2 questions :

1) why can't dust be lifted over CO2 caps, but can be lifted over H2O caps?
2) how good does the GCM represent polar cap edges storms, which play a big part in the Martian dust lifting? indeed, while a whole mesh contains surface ice in the GCM, in reality only a fraction of it may be covered by ice near the cap edges, allowing for dust lifting in the rest of the mesh. What impact does it have to allow dust lifting over CO2/H2O caps? Would these polar cap edges storms, triggered by katabatic winds from the cap, require their own parametrization?