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Recent modeling studies have shown an important role for stratosphere-troposphere coupling in the large-scale atmospheric response to Arctic sea ice loss. Evidence is growing that the Quasi-biennial Oscillation (QBO) can contribute to or even mitigate teleconnections from surface forcing. Here, the influence of QBO phase on the atmospheric response to projected Arctic sea ice loss is examined using an atmospheric general circulation model with a well-resolved stratosphere and a QBO prescribed from observations. The role of the QBO is determined by compositing seasons with easterly phase (QBO-E) separately from seasons with westerly phase (QBO-W). In response to the sea ice forcing in early winter, the polar vortex during QBO-E weakens with strong stratosphere-troposphere wave-1 coupling and a negative Northern Annular Mode-type response. At the surface, this results in more severe Siberian cold spells. For QBO-W, the polar vortex strengthens in response to the sea ice forcing.

Plain Language Summary Rapid loss of Arctic sea ice area and thickness are key indicators of global climate change. Global climate models project further loss of Arctic sea ice through the end of the 21st century. How weather patterns and the jet stream will respond to this sudden loss of sea ice is still poorly understood. Here we use a series of climate model experiments to understand how the atmospheric response to sea ice loss is affected by alternating easterly and westerly winds in the tropical middle atmosphere, known as the Quasi-biennial Oscillation. We show that the Quasi-biennial Oscillation has an important role in understanding how weather patterns can respond to a decrease in sea ice.