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

Abstract

The position of the intertropical convergence zone (ITCZ) may lead to drying/flooding in some parts of the world. Its spatial and temporal variation responds to well-established oscillation processes like the El-Niño-Southern Oscillation (ENSO). This research establishes the response of the ITCZ position to the ENSO phases and how its position, determined from maximum precipitation, relates to the convergence of surface tropical winds. The ERA5 reanalysis data, 1990 – 2020, is used in this study. Each longitude is scanned for latitude of maximum precipitation, during each El-Niño/La-Niña/Neutral years, within the 20°N/S latitude range to identify the ITCZ position. The study concludes that the position established by the maximum precipitation aligns with the surface tropical winds convergence over the global oceanic areas. On seasonal average, the La-Niña related ITCZ position is consistently southward of its El-Niño position over Africa and Central Pacific Ocean. The study uncovered that 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 during the El-Niño/La-Niña. Over Africa, cross-wavelet analysis shows common high-power features in 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). The global and temporal ITCZ shifts open an opportunity for improved interpretation of seasonal forecasts of hydroclimatic events, especially under climate change conditions