Balancing the atmospheric hydrologic budget

The atmospheric hydrologic budget in an idealized general circulation model is difficult to balance, especially if samples are too infrequent, mainly because of an inaccurately determined moisture flux divergence. Although the climatology can be reasonably derived by considering longer time averages, the aliased anomalous moisture divergences due to insufficient sampling are intrinsic and cannot be removed; the effect is noticeable and detrimental out to seasonal timescales. Increased temporal resolution or even continuous accumulations are really required. Lack of temporal resolution also affects forecast skill as well as the perceived importance of the precipitable water tendency. Current atmospheric hydrologic analyses of moisture fluxes and even satellite precipitation observations may have similar sampling problems. We recommend that modern analyses should provide more frequently sampled or even continuously accumulated hydrologic quantities, just as precipitation is currently provided.