The Saharan Oscillation Index (1950–2024): Phase Structure, Regime Shifts, and Global Teleconnections

The Saharan Oscillation Index (SaOI) quantifies the pressure gradient between the Azores High and the Niamey Saharan low, capturing atmospheric variability that influences climate across the Euro-Atlantic-African sector. Despite its relevance to regional hydroclimate, dust transport, and air quality, the temporal structure of SaOI phases and their teleconnections with global climate modes remain poorly characterized. Here, we analyze 75 years (1950–2024) of SaOI variability using phase classification and seasonal lag-correlation analysis with fourteen large-scale climate indicators (LSCIs). We identify three distinct epochs: balanced phase distribution (1950–1965), sustained variability (1965–1990), and a pronounced shift toward positive-neutral dominance post-1990, with markedly reduced negative phase frequency after 2010. The SaOI exhibits moderate but statistically significant correlations with the North Atlantic Oscillation Index (NAOI; r = 0.42), Arctic Oscillation Index (AOI; r = 0.42), and Oceanic Niño Index (ONI; r = -0.44), with seasonal correlations revealing lagged teleconnections extending from late winter through summer. Positive phases are characterized by intensified pressure gradients that strengthen trade winds, suppress precipitation, and enhance dust mobilization, while negative phases promote moisture advection and convective activity. The apparent regime shift post-1990 raises critical questions about potential non-stationarity driven by anthropogenic forcing or natural multidecadal variability. These findings establish the SaOI as a key diagnostic tool linking regional Saharan dynamics to global climate variability, with applications for early warning systems addressing drought, air pollution, and heat-related risks across northwestern Africa and the Mediterranean.