In this paper, we present a description of the atmospheric branch of the hydrologic cycle (AHC) in the Goddard Laboratory for Atmospheres interactive forecast retrieval analysis (IFRA) system. Global hydrologic parameters are estimated using a mix of satellite-retrieved geophysical parameters and general circulation model gridded wind fields. The global distribution of components of the AHC and their related fields such as the total precipitable water, rainfall estimate, latent heat flux/evaporation over the ocean, moisture transport, and associated seasonal and low-frequency variability (timescale ≥10 days) are studied. Results show that the seasonal variations of these variables are consistent with climatological observations. Positive surface hydrologic forcing (E-P>0) is found over extended regions in the subtropics and in the oceanic upwelling regions, while negative surface hydrologic forcing (E-P<0) is concentrated in small regions of heavy precipitation over warm water. Moisture is transported from the regions of positive E-P (evaporation-precipitation) toward regions of negative E-P. The moisture recycling timescale is much larger in the former compared with the latter. On the large scale, rainfall and moisture convergence are highly correlated. Also presented is an analysis of the IFRA tropical rainfall variability. Principal modes of tropical rainfall variation can be identified with the well-known intraseasonal or 30- to 60-day oscillations. Regional characteristics of these oscillations and relationship with other components of the atmospheric hydrologic cycle are investigated. The analysis reveals clearly a premoistening of the tropical atmosphere approximately 10 days prior to enhanced convection over the western Pacific followed by drying out of equatorial central and eastern Pacific. Results show that much of the variability of rainfall in the maritime continent associated with the 30- to 60-day oscillation can be connected with the zonal transport of moisture from the Indian Ocean and the eastern Pacific associated with Walker-type circulation anomalies. The water budget of the tropical western Pacific is strongly influenced by rainfall variability associated with these intraseasonal oscillations. |