We thank John Wilson (GFDL) for his help in providing the data from the GFDL SKYHI model. We also want to express our gratitude to Dinh Tran (McGill) for pointing out an error in an early version of this work, Peter Bartello (RPN), three anonymous reviewers for comments that led to improvements of the manuscript, and Bernard Dugas (RPN) for his technical assistance. Part of this work was done while one of us (MC) was visiting the Geophysical Fluid Dynamics Laboratory (NOAA/GFDL) in Princeton (New Jersey) during the summer of 1996 under a fellowship provided by Fonds pour la Formation de Chercheurs et Paide à la Recherche (FCAR). Martin Charron thanks Kevin Hamilton for his hospitality.
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