Modality of semiannual to multidecadal oscillations in global sea surface temperature variability

Repeating the history of study on El Niño‐Southern Oscillation (ENSO) in the 1980s, interdecadal oscillation (IDO) in climate variability is currently an area of active research and debate, following the recognition of its emerging significance in nature and science. In this work, a two‐dimensional propagating modal extraction technique is applied to a reconstructed global monthly sea surface temperature (SST) data set spanning 1854 through 2007, to examine the spatiotemporal structure of SST variability with an emphasis on the fine modal pattern of IDOs. In the time domain, it is revealed that a canonical modal spectrum of decadal‐to‐centennial SST variability constitutes four most distinct oscillations with periodicities at 9.0, 13.0, 21.2, and 62.2 years, which are naturally defined as primary modes and are, respectively, termed as the subdecadal mode, the quasidecadal mode, the interdecadal mode, and the multidecadal mode (modes S, Q, I, and M). They join the energetic annual mode (mode A) and two major ENSO modes at 3.7 and 5.8 years (modes B and C), as well as a dozen of secondary modes ranging from semiannual to multidecadal, in determining the key pattern of SST‐related climate variability. In the space domain, seven modally dynamic areas, analogous to the Niño regions for ENSO, are clearly identified and are named as IDO zones. Contrary to ENSO, dominant IDO zones are most visible in the extratropical oceans, especially in the North Atlantic/North Pacific sectors, while secondary signatures are observed in the tropical oceans. The array of (four) primary modes with respect to (seven) major zones yields a sophisticated yet canonical pattern of IDOs, leading to a basic conclusion that multimodality (for a given region) and multiregionality (for a given mode) are fundamental features of the IDO system.