Indian Ocean Dipole Changes During the Last Interglacial Modulated by the Mean Oceanic Climatology

• Published in: Geophysical research letters 2024-01, Vol.51 (1), p.n/a
• Main Authors: Liu, Shanshan, Yuan, Chaoxia, Behera, Swadhin, Luo, Jing‐Jia, Yamagata, Toshio
• Format: Article
• Language: English
• Subjects: Advection; Amplitude; Amplitudes; Anomalies; Anticyclones; atmosphere‐ocean interaction; Climate; climate change; Climate variability; Climatology; Coefficients; Cold water; Cooling; Correlation coefficient; Correlation coefficients; Dipoles; Easterlies; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Equator; Equatorial easterlies; Heat; Indian Ocean; Intercomparison; Interglacial periods; Last Interglacial; Monsoon precipitation; numerical modeling; Oceans; Paleoclimate; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Southern Oscillation; Subtropical anticyclones; Summer monsoon; Surface temperature; tropical variability; Variability; Water temperature
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL106153

Investigating the Indian Ocean Dipole (IOD) during the Last Interglacial (LIG) can advance knowledge of IOD behaviors in orbitally‐induced warmer‐than‐present scenarios. Based on multiple model outputs from the Paleoclimate Modeling Intercomparison Project Phase 4, the analysis suggests reduced frequencies of the IOD compared to the preindustrial period. Spatially, the whole growing and mature stages of the IOD feature suppressed variability over the west and westward expansions of eastern anomalies, while the eastern perturbation enhances only at the initial phase. The overall amplitude assessed by the dipole mode index shows only minor reductions. These changes are attributed to orbitally‐induced enhancement in mean‐state westward currents along the equator, which transport more anomalous cold water westward. In addition, the subdued El Niño–Southern Oscillation (ENSO) during the LIG is unlikely to cause a weakening of the IOD, in association with a less important role of ENSO in the formation of the IOD. Plain Language Summary The IOD is one of the leading modes of interannual climate variability in the tropical Indian Ocean, characterized by west–east contrasted sea surface temperature (SST) anomalies. The connection between changes in the IOD and mean states is an important issue to be addressed. This study examines IOD behaviors during an orbitally‐induced warm scenario, the LIG (∼127 ka BP), using the preindustrial period as the baseline. The results suggest significant reductions in IOD frequencies and structural changes, with westward extended eastern cooling and spatially uniform suppression in western warming throughout the growing and mature stages, accompanied by intensified eastern cooling at the initial phase. The overall amplitude of the IOD, as measured by the dipole mode index, exhibits only minor reductions. The main mechanism behind the change lies in enhanced equatorial easterlies over the Indian Ocean, which are triggered by orbitally‐induced amplifications in Pacific subtropical anticyclones and increases in northern Africa–South Asia summer monsoon precipitation. Subsequently, equatorial westward currents enhance, modulating the mean advection of SST anomalies during IOD events. Further composite analyses show that the concurrently subdued ENSO is unlikely to induce an IOD attenuation since the ENSO–IOD connections are diminished as indicated by decreased correlation coefficients. Key Points Spatial structural change and less freque