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<p>The Quasi-Biennial Oscillation (QBO), a dominant stratospheric mode characterized by alternating easterly and westerly zonal winds, significantly influences tropical climate. Despite numerous studies on QBO in the tropical region, its association with rainfall over West Africa (WA) is rarely quantified. This study investigates the QBO’s impact on WA rainfall and atmospheric dynamics using Empirical Orthogonal Function (EOF) and composite analyses of reanalysis data (1960–2022). Results show that the westerly QBO phase (QBOW) enhances rainfall across the region, particularly in Southern West Africa (SWA), while the easterly phase (QBOE) is associated with suppressed precipitation. Dynamically, QBOW modulates the West African Westerly Jet (WAWJ) and the Intertropical Convergence Zone (ITCZ), intensifies low-level moisture advection from the Atlantic, and promotes upward motion through enhanced thermodynamic instability and upper-level divergence. These processes are accompanied by a colder tropical tropopause and increased cloud cover. In contrast, QBOE weakens these mechanisms. A partial least squares regression framework indicates that QBO signals alongside key climate drivers such as El Niño-Southern Oscillation(ENSO), Atlantic 3 Index (ATL3), and relative humidity significantly enhance rainfall prediction skill over SWA. The full model explains over 85% of the observed variance, with QBO indices at multiple pressure levels providing both short- and long-lag predictive signals. These findings provide a comprehensive understanding of stratosphere–troposphere interactions driven by the QBO and highlight the importance of incorporating QBO phases into seasonal rainfall prediction models for WA.</p>

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Dynamic response of West African rainfall to the quasi-biennial oscillation

  • 期刊论文

  • 发表日期：

    2025年9月30日

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  • Reuben Acheampong Asamoah,
  • Gizaw Mengistu Tsidu,
  • Gemechu Fanta Garuma,
  • Leonard Kofitse Amekudzi

摘要

The Quasi-Biennial Oscillation (QBO), a dominant stratospheric mode characterized by alternating easterly and westerly zonal winds, significantly influences tropical climate. Despite numerous studies on QBO in the tropical region, its association with rainfall over West Africa (WA) is rarely quantified. This study investigates the QBO’s impact on WA rainfall and atmospheric dynamics using Empirical Orthogonal Function (EOF) and composite analyses of reanalysis data (1960–2022). Results show that the westerly QBO phase (QBOW) enhances rainfall across the region, particularly in Southern West Africa (SWA), while the easterly phase (QBOE) is associated with suppressed precipitation. Dynamically, QBOW modulates the West African Westerly Jet (WAWJ) and the Intertropical Convergence Zone (ITCZ), intensifies low-level moisture advection from the Atlantic, and promotes upward motion through enhanced thermodynamic instability and upper-level divergence. These processes are accompanied by a colder tropical tropopause and increased cloud cover. In contrast, QBOE weakens these mechanisms. A partial least squares regression framework indicates that QBO signals alongside key climate drivers such as El Niño-Southern Oscillation(ENSO), Atlantic 3 Index (ATL3), and relative humidity significantly enhance rainfall prediction skill over SWA. The full model explains over 85% of the observed variance, with QBO indices at multiple pressure levels providing both short- and long-lag predictive signals. These findings provide a comprehensive understanding of stratosphere–troposphere interactions driven by the QBO and highlight the importance of incorporating QBO phases into seasonal rainfall prediction models for WA.