Assessment of various global freshwater flux products for the global ice-free oceans

Abstract

In this study, we compare sea surface freshwater flux products over the global ocean for the period of 1988–2005, taking into consideration the average field, global water budget, and interannual variability and trends. The analysis considers satellite-based products (Japanese Ocean Flux Datasets with Use of Remote Sensing Observations [J-OFURO2], Hamburg Ocean–atmosphere Parameters from Satellite Data 3 [HOAPS3], Remote Sensing Systems [RSS], Global Precipitation Climatology Project [GPCP2], and Climate Prediction Center Merged Analysis of Precipitation [CMAP]); reanalysis (Japanese 25-year reanalysis [JRA25], National Centers for Environmental Prediction [NCEP]/National Center for Atmospheric Research reanalysis [NRA1], NCEP/Department of Energy reanalysis [NRA2], Climate Forecast System Reanalysis [CFSR]); and a hybrid product (Objectively Analyzed Air–Sea fluxes [OAFlux]). Recommendations are made for the developers of future freshwater flux products; these recommendations also aim to guide users to select products most suitable for their applications.For the global average field, evaporation and precipitation products of reanalysis are larger than satellite products in the tropical and subtropical regions. The large evaporation data values obtained by reanalysis are attributed to the low air specific humidity values and the differences between the bulk algorithms for the tropical and subtropical regions. Moreover, for the global water budget and the inter-annual variability and trends, the reanalysis precipitation product is largely dependent on its evaporation product. If we use reanalysis precipitation and satellite evaporation data, we obtain a negative value for the global ocean water budget. This study demonstrates the difficulty of using different evaporation and precipitation products to analyze the global hydrologic cycle.