The effect of the Quasi-Biennial Oscillation (QBO) on the Northern Hemisphere wintertime stratospheric polar vortex is evaluated in five operational subseasonal forecasting models. Of these five models, the three with the best stratospheric resolution all indicate a weakened vortex during the easterly phase of the QBO relative to its westerly phase, consistent with the Holton-Tan effect. The magnitude of this effect is well captured for initializations in late October and November in the model with the largest ensemble size. While the QBO appears to modulate the extratropical tropospheric circulation in some of the models as well, the importance of a polar stratospheric pathway, through the Holton-Tan effect, for the tropospheric anomalies is unclear. Overall, knowledge of the QBO can contribute to enhanced predictability, at least in a probabilistic sense, of the Northern Hemisphere winter climate on subseasonal timescales.
Bibliographical noteFunding Information:
C. I. G., C. S., and I. P. W. are supported by the Israel Science Foundation (grant 1558/14) and by a European Research Council starting grant under the European Unions Horizon 2020 research and innovation program (grant agreement 677756). D. D. is supported by the Swiss National Science Foundation through grant PP00P2170523. S.-W. Son’s work is partly supported by the Basic Science Research Program through the National Research Foundation (NRF) funded by the Ministry of Science and ICT (2017R1E1A1A01074889). We thank the three anonymous reviewers for their comments. This work is based on S2S data. S2S is a joint initiative of the World Weather Research Programme (WWRP) and the World Climate Research Programme (WCRP). The original S2S database is hosted at ECMWF as an extension of the TIGGE database and can be downloaded from the ECMWF server http://apps.ecmwf.int/datasets/ data/s2s/levtype=sfc/type=cf/. Correspondence and requests for data should be addressed to C. I. G. (email:email@example.com.
©2018. The Authors.
- Quasi-Biennial Oscillation
- annular modes
- month-ahead prediction
- polar vortex