Response of the global ITCZ to ENSO and how the ITCZ determined from maximum precipitation compares with the surface tropical wind convergence

Abstract

Shifts in the position of the intertropical convergence zone (ITCZ) may lead to amplification of climate extremes such as droughts and flooding. Its spatio-temporal variations respond to well-established oscillation processes like the El Niño Southern Oscillation (ENSO). This research establishes the global and regional response of the ITCZ position to ENSO. It also explores the alignment between the ITCZ as determined from two methods: the surface tropical wind convergence, and maximum precipitation. The ERA5 reanalysis data, 1990–2020, are used in this study. Each longitude is scanned for latitude of maximum precipitation, during each El Niño/La Niña/Neutral year, within the 20°N/S latitude range to identify the ITCZ position. An overlay of surface tropical wind convergence and the ITCZ position is employed for comparison of the two methods. The study concludes that the position established by the maximum precipitation aligns with the surface tropical wind convergence over the global oceanic areas. On seasonal average, the La Niña ITCZ position is consistently southward of its El Niño position over Africa and Central Pacific Ocean. Furthermore, the extreme cases of El Niño/La Niña leads to further north/south shifting of the ITCZ position from its normal El Niño/La Niña positions. The continental and Atlantic Ocean ITCZ is more persistent and shows a minimal fluctuation, in comparison to Oceanic ITCZ, during the El Niño/La Niña. Cross-wavelet analysis was explored as an African case study and it shows common high-power features between the Oceanic Niño Index (ONI) and ITCZ signals over a four-year periodicity, mirroring the ENSO periodicity albeit with slowly varying time lag across the years. The cross-correlation of the two signals is strongest in Austral summer (DJF), corresponding to the peak of ENSO. This study contributes to the understanding of the overall description of the global and regional (with Australia and South America as new additions) ITCZ along with its response to the ENSO phases using the latest ERA reanalysis data. The global/regional spatio-temporal ITCZ shifts open an opportunity for improved interpretation of seasonal forecasts of hydroclimatic events, especially under climate change conditions that reflect a possibility of an increase in the frequency of ENSO events in the future.