Atmospheric moisture transports from ocean to land and global energy flows in reanalyses

The NCAR CCSM4 model, along with most reanalysis models, the exception being MERRA, has too intense water cycling (P and E) over the ocean although ocean to land transports are very close to observed. Precipitation from reanalyses that assimilate moisture from satellite observations exhibits large changes identified with the changes in the observing system, as new and improved temperature and water vapor channels are assimilated and, while P improves after about 2002, E-P does not.

Discrepancies among hydrological cycle components arise from analysis increments that can add or subtract moisture. The large-scale moisture budget divergences are more stable in time and similar across reanalyses than model-based estimates of E-P. Results are consistent with the view that recycling of moisture is too large in most models and the lifetime of moisture is too short. For the energy cycle, most reanalyses have spurious imbalances ~10 W m⁻² within the atmosphere, and ~5-10 W m⁻² in net fluxes into the surface and to space.

Major improvements are needed in model treatment and assimilation of moisture, and surface fluxes from reanalyses should only be used with great caution.