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<p>Previous studies have shown that the Madden–Julian Oscillation (MJO) influences March-May rainfall over East Africa; however, the extent of this impact and its modulation by the Quasi-Biennial Oscillation (QBO) are still not well quantified. Using rainfall data from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and atmospheric reanalysis data from the National Centres for Environmental Prediction (NCEP), for the period 1981–2023, this study employs composite and correlation analyses to investigate the individual MJO and combined MJO–QBO effects on precipitation variability during the March–May season over East Africa.</p><p>The findings show that during MJO phases 2–3, when convection intensifies over the central and eastern Indian Ocean, rainfall over East Africa on average increases by about 20% compared to the climatological mean. Conversely, during phases 5–6, as convection shifts toward the western Pacific Ocean, rainfall is substantially suppressed by about 19%. This pattern highlights distinct wet and dry periods linked to the MJO. The influence of the MJO on precipitation is significantly modulated by the phase of the QBO. The results found that during the easterly QBO (EQBO) phase, the precipitation increases by approximately 1.4% in phases 2–3, while it decreases by about 2.88% under the westerly QBO (WQBO) phase. Further, notably, in phases 5–6, the enhancement is substantially greater up to 17% during EQBO compared to WQBO, resulting in a more pronounced impact on regional rainfall variability. The results also showed a contrasting temperature pattern between 70 and 30-hPa, with warmer conditions during WQBO and cooler conditions during EQBO. Furthermore, stronger tropospheric vertical velocity is observed during EQBO compared to WQBO. This study highlights the critical role of the coupled MJO and QBO interaction in modulating East Africa’s long rains, demonstrating how intraseasonal and stratospheric dynamics jointly shape regional precipitation variability and may contribute to improve understanding of rainfall predictability in the region.</p>

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The joint influence of the Madden Julian Oscillation and Quasi Biennial Oscillation on the long rains over East Africa

  • 期刊论文

  • 发表日期：

    2026年3月20日

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  • Tewelde Berihu,
  • Wen Chen,
  • Lin Wang

摘要

Previous studies have shown that the Madden–Julian Oscillation (MJO) influences March-May rainfall over East Africa; however, the extent of this impact and its modulation by the Quasi-Biennial Oscillation (QBO) are still not well quantified. Using rainfall data from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and atmospheric reanalysis data from the National Centres for Environmental Prediction (NCEP), for the period 1981–2023, this study employs composite and correlation analyses to investigate the individual MJO and combined MJO–QBO effects on precipitation variability during the March–May season over East Africa.

The findings show that during MJO phases 2–3, when convection intensifies over the central and eastern Indian Ocean, rainfall over East Africa on average increases by about 20% compared to the climatological mean. Conversely, during phases 5–6, as convection shifts toward the western Pacific Ocean, rainfall is substantially suppressed by about 19%. This pattern highlights distinct wet and dry periods linked to the MJO. The influence of the MJO on precipitation is significantly modulated by the phase of the QBO. The results found that during the easterly QBO (EQBO) phase, the precipitation increases by approximately 1.4% in phases 2–3, while it decreases by about 2.88% under the westerly QBO (WQBO) phase. Further, notably, in phases 5–6, the enhancement is substantially greater up to 17% during EQBO compared to WQBO, resulting in a more pronounced impact on regional rainfall variability. The results also showed a contrasting temperature pattern between 70 and 30-hPa, with warmer conditions during WQBO and cooler conditions during EQBO. Furthermore, stronger tropospheric vertical velocity is observed during EQBO compared to WQBO. This study highlights the critical role of the coupled MJO and QBO interaction in modulating East Africa’s long rains, demonstrating how intraseasonal and stratospheric dynamics jointly shape regional precipitation variability and may contribute to improve understanding of rainfall predictability in the region.