It has been reported that precipitation characteristics differ between the eastern Pacific (EPAC) and the western Pacific (WPAC) by previous studies. First, we compare characteristics of precipitation systems over the EPAC ITCZ with those over the WPAC warm pool in the boreal autumn, in terms of “precipitation features” observed with the Tropical Rainfall Measuring Mission (TRMM) satellite, and the differences are examined in relation to the large-scale environment. As a result, there is more rain from congestus and organized systems with moderate heights over a very shallow convergence field of the EPAC, compared to the WPAC warm pool, where rain from tall small systems and very tall organized systems is dominant. Second, we explore characteristics of westward-propagating synoptic-scale disturbances over the EPAC ITCZ and the role played by the disturbances in determining the properties of precipitation systems. It is shown that synoptic-scale disturbances, which have a coupled structure, with both a vortex at its center near ITCZ and a Mixed Rossby-Gravity- (MRG-) wave-type disturbance, frequently exist over the EPAC. These disturbances are associated with both deep convection and congestus. It is also shown that moderately deep convection is allowed in association with deep convergence of the synoptic-scale disturbances over the EPAC ITCZ, where convergence tends to otherwise be shallow.

While the above analyses of the environment are based on reanalysis data and observed data, one should have a healthy skepticism about reanalysis data over tropical oceans where observational data assimilated into the model are scarce. If different reanalyses differ substantially among one another, this is important information to have. Finally, we introduce some results of intercomparison of reanalyses (MERRA, JRA25-JCDAS, and ERA-Interim) over the EPAC ITCZ. We examine environmental properties composited with respect to TRMM-observed precipitation properties, in terms of structures of meridional circulations and synoptic-scale disturbances. Some distinct differences in the large-scale and synoptic-scale environment are found depending upon whether convection is mostly deep or mostly shallow. At the same time, however, reanalyses have significant differences among themselves.