Evaluating climate model performance in the tropics with retrievals of water isotopic composition from Aura TES

Abstract

We evaluate the NASA Goddard Institute for Space Studies ModelE2 general circulation model over the tropics against water isotope (HDO/H<inf>2</inf>O) retrievals from the Aura Tropospheric Emission Spectrometer. Observed isotopic distributions are distinct from other observable quantities and can therefore act as an independent constraint. We perform a small ensemble of simulations with physics perturbations to the cumulus and planetary boundary layer schemes. We examine the degree to which model-data agreement could be used to constrain a select group of internal processes in the model, namely, condensate evaporation, entrainment strength, and updraft mass flux. All are difficult to parameterize but exert strong influence over model performance. We find that the water isotope composition is more sensitive to physics changes than precipitation, temperature, or relative humidity in the lower and upper tropical tropospheres. Among the processes considered, this is most closely, and fairly exclusively, related to midtropospheric entrainment strength. Our study indicates that water isotope observations could provide useful constraints on model parameterizations.