Profiles of the \(\delta\)^2H in water vapour were constructed using the in-situ observations made at Darwin and water vapour profiles from the climate forecast system version 2 (CFSv2) dataset. Profiles are capped at the tropopause, which is assumed as the first reversal of the temperature gradient with height (ie dT/dz>0). The 2 rayleigh models described above and 2 mixing models were applied to construct the profiles. These are just simple single-column models without complex cloud micro-physics.
For the rayleigh models, any reduction in water vapour with height was assumed to follow either an open or closed rayleigh model. Rewetting with height, is assumed to just move back along the rayleigh model (which contradicts the open rayleigh model assumption - condensation is immediately removed from the system). For the closed rayleigh model, below 263K, an open rayleigh model is assumed along the lines of ice condensation (reverse sublimation - deposition), and ice deposition fractionation factors are applied.
Two mixing models are applied, both have the wet end member equivalent to the surface \(\delta^2\)H and the CFSv2 mixing ratio. The two mixing models are separated by the mixing ratio and \(\delta\)^2H of dry air mass mixing with the surface. The first uses the minimum mixing ratio and \(\delta^2\)H at the top of the troposphere determined suing the open rayleigh model, the second uses the closed rayleigh model minima.