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Climate dynamics

Tropics to stratosphere

J. Clim. http://doi.org/cbs8 (2017)

Sudden Stratospheric Warming (SSW) events — a rapid heating of the upper Artic atmosphere — occur roughly 6 times per decade and strongly influence the weather of the Northern Hemisphere. Recently it has been shown that they are impacted by the Madden–Julian Oscillation (MJO), a dominant mode of tropical intraseasonal variability that describes the eastward propagation of large-scale convection. With anthropogenic warming, it is anticipated that MJO activity will increase, but it is unknown to what extent this will affect SSWs. Wanying Kang and Eli Tziperman from Harvard University, USA, investigate the SSW response to a strengthening of the MJO using both idealised and realistic climate model simulations.

In both models, the authors find that the frequency of SSW events significantly increases in response to enhanced MJO activity, the change of which is dependent on the amplitude of the MJO strengthening. As a result, average Arctic stratosphere temperatures also increase. Two mechanisms are found to be responsible for these changes: direct poleward and upward propagation of transient MJO-forced waves, and enhanced stationary waves in response to this propogation. Such an MJO-driven increase in SSW events may consequently impact tropospheric jet stream location and extreme weather in the Northern Hemisphere.

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Simpkins, G. Tropics to stratosphere. Nature Clim Change 7, 624 (2017). https://doi.org/10.1038/nclimate3385

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