Quantification of Global Sea Surface Water Exchange in the TRMM-era and the Importance of A-Train Observation of Light Rainfall

Remote sensing instruments onboard present-day satellite platforms have measured various components of the Earth's hydrological cycle. Retrieval and analysis products are now available for studies of the global hydrological cycle. We used TRMM Multisatellite Precipitation Analysis (TMPA; 3B42-V6) and estimates of surface evaporation fluxes (E) from the Goddard Satellite-based Surface Turbulent Fluxes (GSSTF) to assess the climatological balance of surface water exchange over the ocean. Our results using satellite observations suggest that the quasi-globally and climatologically averaged surface water exchange (P-E) over the ocean does not close and is much more negative than what is obtained from the reanalysis data product. The inconsistency in P-E between the observed and reanalysis data mainly occurs over the subtropical ocean where stratocumulus clouds are abundant. Using coincident observation of precipitation data from CloudSat, AMSR-E, and AMSU, and also by analyzing TRMM precipitation data, we assess the contribution of light rainfall by present-day precipitation measuring sensors to the surface water exchange. In addition, water vapor measurements from AIRS will be used to analyze the atmospheric moisture processes associated with this light rainfall. Our analysis of light rainfall fraction and volume not only assesses the importance of capturing light rainfalls to close the global surface water exchange, but also provides a means for climate model evaluations on their behaviors of generating these light rain events. Correct quantification of light rain generation is essential in assessing the changes in hydrological and energy cycles in a warming climate.