Long‐term characterization of the Pacific ITCZ using TRMM, GPCP, and ERA‐Interim

An objective, automated Intertropical Convergence Zone (ITCZ) identification and characterization algorithm is developed and applied to European Centre for Medium‐Range Weather Forecasts Reanalysis Interim (ERA‐Interim) variables, and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Global Precipitation Climatology Project (GPCP) rain rates (RRs) to create 15 and 36 year climatologies, respectively, in the tropical Pacific ocean. Characteristics derived from the algorithm include ITCZ latitude, northern and southern ITCZ convection boundaries and extent, and precipitation intensity. The climatological location of the ITCZ was found near 8°N, consistent with previous studies, with a preferred southern boundary location of 4°N. The northern ITCZ boundary did not exhibit a preferred boundary with locations between 7° and 15°N having similar frequencies of occurrence. The northern and southern extents of the ITCZ were symmetric in the central Pacific and asymmetric in the east Pacific. Long‐term trends in the ITCZ width and precipitation intensity showed significant narrowing and intensifying. Separation of characteristics by season and location (i.e., central and eastern Pacific) revealed negative trends in ITCZ width in both domains, with trends in the east Pacific weaker than those in the central Pacific. Trends in precipitation intensity near the center of the ITCZ indicate a strong intensification, with slightly stronger trends in the central Pacific than in the east Pacific. These findings show that while the location of the ITCZ has not changed significantly over the past three decades, the ITCZ has narrowed and convection has intensified. Key Points Pacific ITCZ has narrowed over the past 36 years ITCZ precipitation has intensified, especially near the center ITCZ width less variable after 1998