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<p>This study investigates the synergistic effects of the Southern Annular Mode (SAM) and Atlantic Sea Surface Temperatures (SSTs) on the West African Summer Monsoon (WASM). It examines the atmospheric and oceanic teleconnections influencing seasonal rainfall variability across the region. Specifically, the analysis explores how interactions between the boreal winter SAM, extratropical Atlantic SSTs, and tropical Atlantic SSTs shape WASM dynamics, focusing on global SAM-SST-WASM associations. For the period 1983–2017, significant positive correlations between equatorial Atlantic SSTs and WASM are identified, which are the strongest during winter and persist into summer. The persistence of the Atlantic SST anomalies demonstrates that winter SST conditions influence atmospheric circulations into the subsequent monsoon season. This linkage further reveals that equatorial Atlantic SST anomalies display a sustained seasonal impact on WASM through atmospheric and oceanic feedback mechanisms. Moreover, the findings highlight that SAM-associated SST signals and Rossby Wave Source (RWS) in the Southern Hemisphere prompt upper-atmospheric wave train dynamics. A meridional wave pattern linked to extreme low phases of SAM propagates equatorward at 200&#xa0;hPa over the southern Atlantic, descending toward West Africa. This descent induces lower-level divergence over the Eastern Equatorial Atlantic, disrupting moisture convergence, weakening monsoonal wind circulation, and ultimately reducing rainfall across the West African region. Partial correlation assessments reveal that both SAM and Atlantic SSTs are key and nearly equal contributors to WASM variability, highlighting their combined influence on the predictability of summer monsoon rainfall in West Africa.</p>

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Potential role of Southern Annular Mode and Atlantic Ocean on West African summer monsoon rainfall

  • 期刊论文

  • 发表日期：

    2025年3月28日

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  • Amita Prabhu,
  • Siddhant Arya

摘要

This study investigates the synergistic effects of the Southern Annular Mode (SAM) and Atlantic Sea Surface Temperatures (SSTs) on the West African Summer Monsoon (WASM). It examines the atmospheric and oceanic teleconnections influencing seasonal rainfall variability across the region. Specifically, the analysis explores how interactions between the boreal winter SAM, extratropical Atlantic SSTs, and tropical Atlantic SSTs shape WASM dynamics, focusing on global SAM-SST-WASM associations. For the period 1983–2017, significant positive correlations between equatorial Atlantic SSTs and WASM are identified, which are the strongest during winter and persist into summer. The persistence of the Atlantic SST anomalies demonstrates that winter SST conditions influence atmospheric circulations into the subsequent monsoon season. This linkage further reveals that equatorial Atlantic SST anomalies display a sustained seasonal impact on WASM through atmospheric and oceanic feedback mechanisms. Moreover, the findings highlight that SAM-associated SST signals and Rossby Wave Source (RWS) in the Southern Hemisphere prompt upper-atmospheric wave train dynamics. A meridional wave pattern linked to extreme low phases of SAM propagates equatorward at 200 hPa over the southern Atlantic, descending toward West Africa. This descent induces lower-level divergence over the Eastern Equatorial Atlantic, disrupting moisture convergence, weakening monsoonal wind circulation, and ultimately reducing rainfall across the West African region. Partial correlation assessments reveal that both SAM and Atlantic SSTs are key and nearly equal contributors to WASM variability, highlighting their combined influence on the predictability of summer monsoon rainfall in West Africa.