Sudden stratospheric warmings can be better predicted by combining different forecast models

Researchers documented for the first time the ability of an ensemble of nine sub-seasonal forecast models to predict a sudden stratospheric warming and following multi-week period of cold weather across northern Eurasia.

The authors of recently published study showed that the stratospheric warming occurred in February 2018 was predicted by most models at least four days in advance and by some models even thirteen days in advance. The cold period after the stratospheric event was reasonably well predicted at lead times up to one month.

Sudden stratospheric warmings are extreme examples of anomalous atmospheric circulation in wintertime polar stratosphere, at altitudes above 15 kilometres. These events characterised by sudden rise of stratospheric temperatures by several tens of degrees and breaking up of stratospheric polar vortex are often followed by anomalous long-lasting weather patterns in Northern Hemisphere, in particular by cold air outbreaks across Europe and North America.

Although weather prediction beyond approximately two weeks remains a challenge for scientists, in certain situation, such as after stratospheric warming, the atmosphere can be more predictable.

"Although extended atmospheric predictability following sudden stratospheric warming is somewhat expected result it has never been demonstrated using an ensemble of forecast models, each of them having own strengths and weaknesses. Combining predictions from several models can in principle lead to even better forecast," explains researcher Alexey Karpechko from the Finnish Meteorological Institute.

More research is needed to understand factors limiting predictability of stratospheric warmings

The authors demonstrated that accurate prediction of an anticyclone over Ural Mountains was crucial factor limiting predictability of the stratospheric warming in February 2018. This anticyclone was an important ingredient in atmospheric propagation of planetary-scale waves that ultimately caused the stratospheric warming.

Improving predictability of this anticyclone would improve prediction of sudden stratospheric warmings; however, how exactly it can be improved remains an open question. According to the authors better forecasts of sudden stratospheric warming can improve our ability to forecasts weather up to one month ahead, which would bring certain benefits for society.

Research paper "Predicting Sudden Stratospheric Warming 2018 and Its Climate Impacts with a Multimodel Ensemble" was published in Geophysical Research Letters by a group of authors led by Dr. Alexey Karpechko from Finnish Meteorological Institute. The paper has been selected by journals editors to be featured as a Research Spotlight on AGU's EOS news web-site.

Further information:

Head of group Dr. Alexey Karpechko, Finnish Meteorological Institute, tel. +358 45 315 6020, Alexey.Karpechko@fmi.fi

Reference: Karpechko, A. Y., Charlton-Perez, A., Balmaseda, M., Tyrrell, N., & Vitart, F. (2018). Predicting sudden stratospheric warming 2018 and its climate impacts with a multimodel ensemble. Geophysical Research Letters,45,13,538–13,546. https://doi.org/10.1029/2018GL081091