It is a pleasure to thank Z. Hao, K. Ide, P. Malanotte-Rizzoli, R. N. Miller, A. Or, D. Stammer, R. Todling, and C. Wunsch for helpful discussions and suggestions. SJ is greatly indebted to P. Malanotte-Rizzoli for letting him complete this project while at MIT. The two reviewers’ comments helped improve the presentation. This research was supported at UCLA by ONR Grant N00014-89-J-1845 (MG and SJ) and at MIT by a NOAA Postdoctoral Fellowship in Climate and Global Change (SJ), administered by UCAR. MG also benefitted from the support of the Condorcet Visiting Chair he held while on sabbatical at the Ecole Normale Supérieure, Paris.
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