We greatly appreciate assistance from Drs. James Purser and Kingste Mo during the preparation of the manuscript. The GCM experiment was originally performed to evaluate seasonal forecasts at NCEP by Dr. Ming Ji. We appreciate his making the data available for this work. We would like to thank Dr. George Kiladis and Mr. John Janowiak, who provided us with the OLR data. Daily data for the NCEP–NCAR reanalysis were obtained from an archive maintained by Dr. Wayne Higgins. Dr. R. J. Purser provided compact high-order finite-difference programs for this work. This work is partially supported by the NOAA Office of Global Programs.
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