N. Hall gratefully acknowledges many conversations with Prashant Sardeshmukh that helped form the initial impetus for this work. We thank Brian Hoskins and the team at Reading University for making the model available, and the three reviewers for comments that led to improvements in the manuscript. Thanks also to Hai Lin for providing the shading on Fig. 9. This work was funded by the Atmospheric Environment Service of Canada through the Canadian Institute for Climate Studies, and by the Fonds pour la Formation de Chercheurs et l’Aide à la Recherche through the Centre for Climate and Global Change Research.
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