The Annual Cycle of the Tropical Ocean Water Balance as seen by the GEWEX Integrated Product

Abstract This paper examines water budget residuals using two GEWEX observational products – SeaFlux for evaporation and Global Precipitation Climatology Project (GPCP) for precipitation, while relying on ERA5 for water vapor divergence. Using six oceanic basins, each measuring 30°x30°, the water budgets are analyzed and residuals of 23-year monthly averages are documented. Evaporation is relatively constant across all basins, amounting to roughly 4 mm day −1 . Precipitation and water vapor divergence are more variable, with precipitation ranging up to 7 mm day −1 over the eastern Indian and western Pacific basins, while their respective water vapor convergence goes up to roughly 3 mm day −1 . Compared to absolute values, the residuals are generally smaller than 0.4 mm day −1 (10%) but go up to 1.5 mm day −1 during certain times, particularly in the eastern Indian Ocean. By focusing on the temporal evolution of the water budget residual, this study was able to assign physical sources of errors to some of the products. The errors, however, have different origins, with the wind speed biases being chiefly responsible for Indian Ocean water imbalances, while humidity was the major discrepancy in the eastern Pacific. Errors related to precipitation biases are more speculative, but generally related to observed convective organization in the western Pacific, while potential problems with ERA parameterizations of convection correlated best with residuals in the central Pacific. Both evaporation and precipitation seem to be responsible for water imbalances in the Atlantic, although both are small.