Rotated Global Modes of Non-ENSO Sea Surface Temperature Variability

Abstract

A varimax rotation was applied to the EOF modes of global SST derived by Enfield and Mestas-Nuñez. The SST anomaly record is more than a century long, with a global complex EOF representation of ENSO and a linear trend removed at every grid point. The rotated EOF modes capture localized centers of variability that contribute to the larger-scale spatial patterns of the unrotated modes. The first rotated EOF represents a multidecadal signal with larger response in the North Atlantic. The second rotated EOF represents an interdecadal fluctuation with larger response in the eastern North Pacific and out of phase fluctuations of smaller amplitude in the central North Pacific. The third rotated EOF captures interdecadal fluctuations in the eastern tropical Pacific with a dominant peak that coincides with the 1982/83 ENSO. The fourth rotated EOF has interdecadal to multidecadal nature with larger response in the central equatorial Pacific and quasi-symmetric out-of-phase response in the western North and South Pacific. The fifth mode represents multidecadal fluctuations with large response at about 40°N in the North Pacific. The sixth mode has interannual to interdecadal timescales with largest response confined to the South Atlantic. The authors? rotated modes are dominated by intra- rather than interocean fluctuations supporting the hypothesis that the non-ENSO variability is more regional than global in nature. Analyses of sea level pressure and surface wind stress show that in general the non-ENSO rotated EOFs are consistent with an ocean response to local atmospheric forcing. An exception is the eastern tropical Pacific mode, which is more consistent with an atmospheric response to changes in the ocean SST.