We thank T.G. Huntington, Lisa Osterman, M.J. Pavich, H.W. Markewich, and Stacey Verardo (all of the
USGS) for helpful comments that improved the manuscript. We thank Phil D. Jones, C.F. Ropelewski, R.J. Allan, and the Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, U.K., for production of the SOI data set and the Distributed Active Archive Center at the Goddard Space Flight Center, Greenbelt, Md., for formatting and distributing the digital data set.