The atmospheric water cycle is one of the most important components of the global water cycle. Large amounts of water vapor that are evaporated from the ocean are transported to the continents through the atmosphere. The transported water vapor is converted into precipitation that provides vital water for living things on Earth. Precipitation and evaporation over the oceans change the sea surface salinity and help to drive the ocean thermohaline circulation. Changes in the phase of water in the atmosphere involve latent heat exchanges. Latent heat released by condensation is one of the major energy sources driving the general circulation of the atmosphere. Knowledge of the atmospheric water cycle is therefore essential in order to manage water resources and to understand the Earth's weather and climate.
 The atmospheric water cycle has been investigated in many regions. The Global Energy and Water Cycle Experiment (GEWEX) initiated by the World Climate Research Program is well known for its scientific studies of the water cycle. The GEWEX aims at observing, understanding, and modeling the hydrological cycle and energy fluxes in order to predict global and regional climate change. Under the missions of the GEWEX, projects including the Regional Hydroclimate Projects (RHPs) (formerly the Continental Scale Experiment) were initiated. The focus of the GEWEX was to solve the problems of closing the balance of water and energy. In addition, several water cycle studies were performed at the atmospheric branch in order to quantify the regional water balance, including the Mackenzie GEWEX Studies [e.g., Stewart et al., 1998 ; Rouse et al., 2003], the Baltic Sea Experiment [e.g., Raschke et al., 2001 ; Ruprecht and Kahl, 2003], the Climate Prediction Program for the Americas [e.g., Roads et al., 2003], and the Murray-Darling Basin [e.g., Draper and Mills, 2008].
 One of the major complications of the atmospheric water balance study is the selection of appropriate data sets. The atmospheric water balance equation includes water cycle components such as evaporation, precipitation, water flux convergence, and water tendency. The equation itself is not complicated, but accurate estimation of each of the water cycle components is difficult. Water cycle components have been acquired from direct measurements, numerical weather prediction (NWP) model-derived products, remotely sensed observations, and residual methods using the atmospheric water balance equation. Direct measurements provide relatively reliable data but have limited observation coverage. Earlier water cycle studies were usually performed using radiosonde data [Rasmusson, 1967, 1968]. Despite its limited spatial and temporal coverage, radiosonde data is still used over the regions with dense radiosonde networks [Kanamaru and Salvucci, 2003; Zangvil et al., 2004]. NWP-derived analysis and reanalysis data have been actively employed for the study of the water budget [e.g., Roads et al., 2003; Ruprecht and Kahl, 2003; Turato et al., 2004; Draper and Mills, 2008], because of their ability to minimize known errors and high spatiotemporal resolutions. NWP products, however, are highly dependent on model physics and parameterization. With advancement in satellite instruments and retrieval algorithms, more satellite observation data have become available [e.g., Bakan et al., 2000]. Satellite observations, which have better coverage than in situ observations particularly over the oceans, have been widely used for a complementary purpose or for comparison with other observations. Many satellite-based or merged data sets for water cycle components have been produced using such satellite observations.
 In this study, the atmospheric water balance is examined over oceans using various satellite-based and merged data sets. Reanalysis data sets are also used for comparison with satellite-based data sets for the atmospheric water balances over oceanic regions.