The Changing Nature of Convection over Earth’s Tropical Oceans from a Water Budget Perspective

Abstract The water budget components of an atmospheric column are precipitation, evaporation, and horizontal water vapor divergence. This study finds that when precipitation from the Global Precipitation Climatology Project (GPCP), evaporation from the SeaFlux product, and water vapor divergence from ERA5 are employed, the degree of budget closure depends strongly on the location and time period. Variations in this error are not random, and this study seeks to better understand these biases as the climate system evolves. Errors are particularly significant over ocean regions in and near the west Pacific warm pool, where there are multiyear budget residuals of roughly 10% of the magnitude of precipitation. Biases in other tropical ocean basins are more seasonal and smaller in magnitude. Time-varying budget errors are strongly linked to variations in convective organization that vary with the large-scale environment; errors correlating with deep organized rain show coefficients of 0.62 and 0.56 in the west Pacific and central Pacific, respectively. Errors are linked to a lesser extent with cloud microphysical structures in the East Indian. Both factors affect rainfall retrievals through well-known precipitation bias mechanisms (beam-filling, convective/stratiform effects). Characteristics of the large-scale environment that produce changes in convective organization and precipitable ice water content are explored.