This investigation began while the first author was a visiting scientist at KNMI and continued while the second author was a visiting scientist at NCAR. The study was further supported by Contract NA04OAR4310061 from the NOAA Climate Program Office program in Climate Variability and Predictability, and by the Office of Science (BER), U.S. Department of Energy, Cooperative Agreement DE-FC02-97ER62402. The figures were generated by A. Mai, and the text benefited from comments offered by three anonymous reviewers.
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