The daily mean NCEP–NCAR reanalyses were obtained from the National Oceanic and Atmospheric Administration Climate Diagnostics Center. We are very grateful to Mark Baldwin for making the NAM signature time series available and providing an update. We thank Dr. A. J. Miller of the Climate Prediction Center at NCEP and Dr. Paul A. Newman of the Atmospheric Chemistry and Dynamics Branch (Code 916) at NASA GSFC for producing the stratospheric analyses. We also thank the Goddard DAAC for distributing the data as part of NASA's Mission to Planet Earth program. We thank Ted Shepherd, Paul Kushner, Marvin Geller, David Rind, James Hansen, and an anonymous reviewer for helpful comments on the manuscript. JP's research is supported by the NASA Earth Science Program. NH is supported by National Oceanic and Atmospheric Administration Grant UCSIO-CU-02165401-SCF and a Stork-Doherty Lecturship at the Lamont-Doherty Earth Observatory.
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