Differences in satellite estimates of precipitation over the tropical East Pacific

Over the tropical east Pacific a significant portion of the total precipitation is produced by warm rain systems containing little or no ice layer. Although rainfall from these shallow systems is not as intense as rainfall produced from deep convective systems, the lower cloud tops associated with these warm systems cannot be distinguished from nonprecipitating clouds using satellite infrared-based precipitation estimation techniques alone. As a result, substantial differences between infrared and passive microwave estimates of precipitation exist over the east Pacific Intertropical Convergence Zone (ITCZ). The lack of in-situ observations in this region combined with significant seasonal and interannual variability in the type of precipiting systems makes this a difficult problem to investigate. Using a combination of GOES and GMS-5 IR channel data matched up with coincident SSM/I overpasses, differences in the types of precipitation systems between the east Pacific ITCZ and warm pool region have been investigated. The results show a substantially higher percentage of warm rain systems over the east Pacific during normal or La Nina years, while more deep convective events are present during the strong 1997/98 El Nino.