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Earth rotation variations; polar motion; ENSO; ocean bottom pressure; climate models
Abstract:
The El Niño–Southern Oscillation (ENSO) exerts a strong control on interannual length-of-day variations, but its imprint on polar motion excitation remains to be identified. We explore the hypothesis that part of this imprint is embedded in oceanic angular momentum (OAM) changes, particularly that component driven by ocean bottom pressure <Pb> variations. Analysis of coupled climate model output suggests that the main ENSO signatures in <Pb> are intensified fluctuations in the Bellingshausen Basin and a large-scale see-saw between Pacific and Indian oceans. These patterns are also present in satellite gravimetry data and primarily excite polar motion along 90°E. Inferred OAM changes account for ~40%–50% of the variance in observed polar motion excitation during El Niño/La Niña cycles, upon removal of known geophysical fluid effects. However, given the co-occurrence of ENSO and other (oceanic) excitation signals, polar motion data may only provide limited insights into variability of this climate mode.
