Model1 and model2 both have to define a grid to facilitate the exchange of their fields with OASIS3. Fortunately for any user, these fields can be arbitrary, as long as each coarse grid point governs in this case 7 fine grid points. This may harmlessly shake up the metadata from the output of model2, dscale_cosmo.nc, a little, so do not trust its coordinates. There are variables ‘dx’ and ‘dy’ declared in either dummy model, which bank on this freedom. Do not change dx or dy!