Schema of the subgrid-scale slope parameterization. Each coarse mesh of the global Pluto Volatile Transport Model/Pluto Planetary Climate Model (left) is decomposed into north-south facing subgrid slopes (defined by characteristic slopes μ_i; right) or flat terrain. Each of these subgrid surfaces is associated with its cover fraction δ_i, which represents the percentage of the mesh grid occupied by a given slope μ_i within the observed local topography (middle). These subgrid terrains have their own microclimate (insolation, surface, subsurface temperatures, condensation/sublimation of frosts, etc.), and the interactions between the atmosphere and surface are made through averaged values over the mesh. The bluish surfaces on the right show slopes that are colder than the flat surfaces (and warmer for reddish surfaces).