Objective Identification and Characterisation of Pacific ITCZs using ERA5, GPCP and TRMM

Abstract Despite the intense research on the tropical climate and its features, primarily the Intertropical Convergence Zone (ITCZ), fewer studies investigated the state of the ITCZ through an objective and automated algorithm, particularly the double ITCZ. The study combines the European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5) variables, Global Precipitation ClimatologyProject (GPCP), and TRMM (TMPA 3B42 Daily) datasets to objectively and automatically identify the zonally elongated convergence regions (i.e. ITCZs) in the Pacific and provide 42 years climatologies. The algorithm utilises layer- and time-averaged winds in the lower troposphere (pressure levels between 1000 and 850 hPa) to obtain characteristics of ITCZs that include centre latitude, boundaries, widths, and additionally precipitation intensities using GPCP and TRMM datasets. The Northern Hemisphere (NH) ITCZs are found near 8° N, while the Southern Hemisphere (SH) ITCZs are near5° S. On the one hand, these results suggest that the NH ITCZs reach their northernmost centre latitude and the highest centre precipitation intensity in September and their southernmost in March; the full width peaks in August. On the other hand, the SH ITCZs start near the equator and migrate to reach the southernmost latitude in May. During their seasonal migration, the widths fluctuate with decreasing intensities. Generally, as found by previous studies, the NH ITCZs shift equatorward, narrow and intensify. The SH ITZCs shift poleward, narrow, and intensify under global warming.