Multi-Cyclic Persistence and Trend Structure of Atlantic and Pacific Climate Teleconnection Indices (AMO, ENSO/ONI, NAO), 1994-2022: Implications for Rainfall Variability in Nigeria

Abstract

Rainfall variability across Nigeria is influenced by large-scale Atlantic and Pacific climate teleconnections, including the Atlantic Multidecadal Oscillation (AMO), El Niño-Southern Oscillation (ENSO), and North Atlantic Oscillation (NAO). Although rainfall–teleconnection relationships are well documented in West Africa, the statistical persistence and multi-cyclic structure of these climate drivers remain less commonly characterised within a unified framework. This study examines monthly AMO and NAO indices and the three-month overlapping-season ONI from January 1994 to December 2022 (n = 348), obtained from the NOAA Physical Sciences Laboratory and Climate Prediction Center. Mann-Kendall testing with Sen's slope, Hurst exponent analysis, detrended fluctuation analysis, and continuous Morlet wavelet transformation were applied. AMO exhibited a significant increasing trend (Z = 6.642, p < 0.001) and strong long-memory persistence (H = 0.749). ONI showed no significant trend (Z = 0.047, p = 0.963), confirming its predominantly oscillatory behaviour, while wavelet analysis identified a dominant ~3.3-year periodicity associated with major El Niño episodes. NAO also showed no significant trend (Z = 0.747, p = 0.455) but exhibited weaker persistence (H = 0.622). Cross-correlation indicated a moderate negative annual association between AMO and NAO (r = −0.412). These findings provide a quantitative characterisation of the persistence, trends, and periodic structures of major climate drivers relevant to Nigerian rainfall variability and provide a foundation for future station-level rainfall–teleconnection modelling