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<p>The Quasi-Biennial Oscillation (QBO) influences the static stability and wind shear over the equatorial upper-tropospheric regions and lower-stratospheric regions, and hence the convections of underlying areas. This study evaluates the concurrent relationship between QBO phases and the Indian Summer Monsoon (ISM). QBO is identified by the Empirical Orthogonal Function analysis of equatorial zonal wind bounded by 10°S-10°N over 100 − 10&#xa0;hPa. Since the QBO affects the tropical troposphere, it is hypothesised that QBO can influence ISM through upper-level wind circulation, particularly the tropical easterly jet (TEJ). The easterly phase of QBO (EQBO) is associated with strong easterlies (westerlies) at 200&#xa0;hPa (850&#xa0;hPa), enhancing vertical zonal wind shear, strengthening the TEJ, and increasing upper-level divergence and lower-level convection—favourable conditions for a strong ISM. On the contrary, the westerly phase of QBO (WQBO) exhibits opposite features, signifying weak monsoon conditions. Temperature and static stability anomalies further support these findings. The QBO effect extends to the monsoon intraseasonal variability as well. The active spells are more persistent and spatially extended during EQBO, while break spells are shorter and weaker. Contrarily, the breaks are of higher amplitude and long-lived during WQBO. The robustness of these relationships is confirmed by ENSO-neutral cases, highlighting the independent role of QBO in modulating the subseasonal to seasonal variability of ISM. These findings emphasize the potential of incorporating QBO signals into monsoon prediction frameworks, aiding in the differentiation of QBO and ENSO-driven influences.</p>

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Role of Quasi-Biennial Oscillation in modulating subseasonal to seasonal variability of Indian Summer Monsoon

  • 期刊论文

  • 发表日期：

    2025年6月6日

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  • Shubham Waje,
  • Susmitha Joseph,
  • MKR Phani,
  • AK Sahai,
  • Avijit Dey,
  • Raju Mandal

摘要

The Quasi-Biennial Oscillation (QBO) influences the static stability and wind shear over the equatorial upper-tropospheric regions and lower-stratospheric regions, and hence the convections of underlying areas. This study evaluates the concurrent relationship between QBO phases and the Indian Summer Monsoon (ISM). QBO is identified by the Empirical Orthogonal Function analysis of equatorial zonal wind bounded by 10°S-10°N over 100 − 10 hPa. Since the QBO affects the tropical troposphere, it is hypothesised that QBO can influence ISM through upper-level wind circulation, particularly the tropical easterly jet (TEJ). The easterly phase of QBO (EQBO) is associated with strong easterlies (westerlies) at 200 hPa (850 hPa), enhancing vertical zonal wind shear, strengthening the TEJ, and increasing upper-level divergence and lower-level convection—favourable conditions for a strong ISM. On the contrary, the westerly phase of QBO (WQBO) exhibits opposite features, signifying weak monsoon conditions. Temperature and static stability anomalies further support these findings. The QBO effect extends to the monsoon intraseasonal variability as well. The active spells are more persistent and spatially extended during EQBO, while break spells are shorter and weaker. Contrarily, the breaks are of higher amplitude and long-lived during WQBO. The robustness of these relationships is confirmed by ENSO-neutral cases, highlighting the independent role of QBO in modulating the subseasonal to seasonal variability of ISM. These findings emphasize the potential of incorporating QBO signals into monsoon prediction frameworks, aiding in the differentiation of QBO and ENSO-driven influences.