The stratospheric quasi-biennial oscillation (QBO) and the tropospheric Madden–Julian oscillation (MJO) are strongly linked in boreal winter. In this Review, we synthesize observational and modelling evidence for this QBO–MJO connection and discuss its effects on MJO teleconnections and subseasonal-to-seasonal predictions. After 1980, observations indicate that, during winters when lower-stratospheric QBO winds are easterly, the MJO is ~40% stronger and persists roughly 10 days longer compared with when QBO winds are westerly. Global subseasonal forecast models, in turn, show a 1-week improvement (or 25% enhancement) in MJO prediction skill in QBO easterly versus QBO westerly phases. Despite the robustness of the observed QBO–MJO link and its global impacts via atmospheric teleconnections, the mechanisms that drive the connection are uncertain. Theories largely centre on QBO-related temperature stratification effects and subsequent impacts on deep convection, although other hypotheses propose that cloud radiative effects or QBO impacts on wave propagation might be important. Most numerical models, however, are unable to reproduce the observed QBO–MJO relationship, suggesting biases, deficiencies or omission of key physical processes in the models. While future work must strive to better understand all aspects of the QBO–MJO link, focus is needed on establishing a working mechanism and capturing the connection in models.

平流层准双年振荡（QBO）和对流层马登-朱利安振荡（MJO）在北方冬季密切相关。在这篇综述中，我们综合了这种 QBO-MJO 联系的观测和建模证据，并讨论了它对 MJO 遥相关和亚季节到季节预测的影响。1980 年之后，观测表明，在平流层下 QBO 风向东的冬季，与 QBO 风向西时相比，MJO 强约 40% 并且持续时间大约长 10 天。反过来，全球次季节预测模型显示 QBO 东风阶段与 QBO 西风阶段的 MJO 预测技能提高了 1 周（或提高了 25%）。尽管观察到的 QBO-MJO 链接的稳健性及其通过大气遥相关的全球影响，驱动连接的机制尚不确定。理论主要集中在 QBO 相关的温度分层效应和随后对深对流的影响，尽管其他假设提出云辐射效应或 QBO 对波传播的影响可能很重要。然而，大多数数值模型无法重现观察到的 QBO-MJO 关系，这表明模型中关键物理过程存在偏差、缺陷或遗漏。虽然未来的工作必须努力更好地理解 QBO-MJO 链接的所有方面，但需要重点关注建立工作机制和捕获模型中的联系。无法重现观察到的 QBO-MJO 关系，表明模型中关键物理过程存在偏差、缺陷或遗漏。虽然未来的工作必须努力更好地理解 QBO-MJO 链接的所有方面，但需要重点关注建立工作机制和捕获模型中的联系。无法重现观察到的 QBO-MJO 关系，表明模型中关键物理过程存在偏差、缺陷或遗漏。虽然未来的工作必须努力更好地理解 QBO-MJO 链接的所有方面，但需要重点关注建立工作机制和捕获模型中的联系。