A Rotated EOF Analysis of Global Sea Surface Temperature Variability with Interannual and Interdecadal Scales

Spatiotemporal variability of preferred global-scale sea surface temperature anomaly patterns is documented, applying a varimax-rotated empirical orthogonal function (R-EOF) analysis to monthly mean SST anomalies. The present study focuses especially on the interdecadal variability of leading R-EOF modes. It is first found that temporal variability of R-EOF1 has a quasi periodicity of 2–5 years and coincides quite well with the occurrence of the ENSO event; hence this mode can be identified with the ENSO mode and distinguished from the other modes dominated by interdecadal variability. The authors find that R-EOF2 typically shows the dominance of interdecadal variability and signals of the ENSO phenomenon are removed. This mode is characterized by increasing Indian Ocean SST and decreasing central North Pacific SST around 40°–50°N in the recent ten or more years. A further indication is that both R-EOF3 and R-EOF4, which show the dominance of interdecadal variability, are fundamentally regarded as preferred localized modes confined only to the Atlantic Ocean. Therefore, we find the existence of two kinds of prevailing SST modes; one is a mode fluctuating between oceans, corresponding well to R-EOF2, and the other is an oscillatory mode isolated only in a specific ocean (e.g., R-EOF4). Analysis of implications for low-frequency modes in the atmosphere showed that the Pacific/North American (PNA) mode, which prevails in the Northern Hemisphere winter, is closely related to the large-scale SST variability with interdecadal time scale rather than the ENSO time scale. Additionally, in the Northern Hemisphere summer, the Subtropical Zonal (SZ) mode, which has a north-south dipole structure over the North Pacific, corresponds fairly well to R-EOF2. It is suggested that the increasing tropical ocean SST in the recent ten or more years, especially the Indian Ocean SST, is responsible for the increase of the zonal, summertime 500-hPa geopotential heights in the low-latitude regions of the North Pacific.