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The quasi-biennial oscillation (QBO) was unexpectedly disrupted for only the second time in the historical record during the 2019/20 boreal winter. As the dominant mode of atmospheric variability in the tropical stratosphere, and a significant source of seasonal predictability globally, understanding the drivers behind this unusual behaviour is very important. Here, novel data from Aeolus, the first Doppler wind lidar in space, is used to observe the 2019/20 QBO disruption. Aeolus is the first satellite able to observe winds at high resolution on a global scale, and is therefore a uniquely capable platform for studying the evolution of the disruption and the broader circulation changes triggered by it. This study therefore contains the first direct wind observations of the QBO from space, and exploits measurements from a special Aeolus scanning mode, implemented to observe this disruption as it happened. Aeolus observes easterly winds of up to 20 ms-1 in the core of the disruption jet during July 2020. By co-locating with radiosonde measurements from Singapore and ERA5 reanalysis, like-for-like comparisons of the observed wind structures in the tropical stratosphere are produced, showing equatorial Kelvin wave activity and key parts of the Walker Circulation during the disruption period. The onset of the disruption easterly jet occurs 5 days earlier in Aeolus observations compared with the reanalysis. This analysis highlights how Aeolus and future Doppler wind lidar satellites can deepen our understanding of the QBO, its disruptions, and the tropical upper-troposphere lower-stratosphere region more generally. [ABSTRACT FROM AUTHOR]

Stratospheric variability is examined in a vertically extended version of the Met Office global climate model. Equatorial variability includes the simulation of an internally generated quasi-biennial oscillation (QBO) and semiannual oscillation (SAO). Polar variability includes an examination of the frequency of sudden stratospheric warmings (SSW) and annular mode variability. Results from two different horizontal resolutions are also compared. Changes in gravity wave filtering at the higher resolution result in a slightly longer QBO that extends deeper into the lower stratosphere. At the higher resolution there is also a reduction in the occurrence rate of sudden stratospheric warmings, in better agreement with observations. This is linked with reduced levels of resolved waves entering the high-latitude stratosphere. Covariability of the tropical and extratropical stratosphere is seen, linking the phase of the QBO with disturbed NH winters, although this linkage is sporadic, in agreement with observations. Finally, tropospheric persistence time scales and seasonal variability for the northern and southern annular modes are significantly improved at the higher resolution, consistent with findings from other studies. DOI: 10.1175/2010JAS3338.1

Introduction and background to the Stratosphere–troposphere Processes And their Role in Climate (SPARC) project, the QBOi, and the papers contained in this Special Section. [ABSTRACT FROM AUTHOR]

Causal Effect Networks (CEN) are a recently developed method of timeseries analysis that can be used to reconstruct causal relationships between various processes within the climate system. The multi-model SPARC-QBOi dataset consists of models with a high stratospheric resolution, an internally generated quasi-biennial oscillation (QBO), and greater stratospheric variability compared to previous datasets (e.g. CMIP5). We apply CEN to the SPARC-QBOi dataset to determine the most important factors affecting the Northern Hemisphere wintertime circulation, and the ability of the models to simulate tropical-extratropical teleconnections involving the QBO - on hemispheric (e.g. high latitude stratosphere) and regional scales (e.g. North-Atlantic/Europe). Processes with variability on weekly, monthly to seasonal timescales are analysed - such as the Polar Vortex, the North Atlantic Oscillation, Arctic sea ice, Siberian snow and sea level pressure, and Large-scale (Rossby) wave fluxes. We also investigate the ability of longer term processes - such as the QBO – to modulate the monthly to seasonal teleconnections. [ABSTRACT FROM AUTHOR]