Articles | Volume 25, issue 11
https://doi.org/10.5194/acp-25-5647-2025
https://doi.org/10.5194/acp-25-5647-2025
Research article
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06 Jun 2025
Research article | Highlight paper |  | 06 Jun 2025

Explaining the period fluctuation of the quasi-biennial oscillation

Young-Ha Kim

Data sets

Complete ERA5 from 1940: Fifth generation of ECMWF atmospheric reanalyses of the global climate H. Hersbach et al. https://doi.org/10.24381/cds.143582cf

ERA-Interim global atmospheric reanalysis D. Dee et al. https://doi.org/10.24381/cds.f2f5241d

MERRA-2 inst3_3d_asm_Np: 3d, 3-hourly, instantaneous, pressure-level, assimilation, assimilated meteorological fields, V5.12.4 GMAO https://doi.org/10.5067/QBZ6MG944HW0

The Japanese Reanalysis for Three Quarters of a Century JMA https://doi.org/10.20783/DIAS.645

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Executive editor
The cause of fluctuations of the stratospheric quasi-biennial oscillation (QBO) period has been debated since its discovery. Explanations for variations in the QBO period are of great interest given the relevance of the QBO as one of the major modes of atmospheric interannual variability that affects not only the tropics, but also on the surface weather and climate in the extra-tropics. This study analyses the latest versions of atmospheric reanalyses, which resolve a part of the gravity wave spectrum, to show that the period fluctuations can be explained by seasonal variations in the forcing by small-scale (gravity) waves in the equatorial region. In doing so, the study improves our understanding of one of the fundamental modes of stratospheric variability and suggests that improvements in our ability to capture multi-scale interactions in the models can improve the accuracy of seasonal forecasts and the reliability of future climate projections.
Short summary
The paper addresses a fundamental but unresolved question about the tropical stratospheric wind oscillation: why does the period of the oscillation fluctuate irregularly? We use global reanalysis data to provide evidence that the oscillation period is primarily modulated by seasonal variations in small-scale atmospheric wave activity. The findings have implications for seasonal and climate predictions.
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