Variability of the Indian Ocean Dipole in coupled model paleoclimate simulations

Abstract

The Indian Ocean Dipole (IOD) mode of variability has been observed to influence atmospheric circulation and precipitation over the Indian Ocean basin and surrounding continental areas, interacting with the Asian monsoon and El Niño Southern Oscillation (ENSO). Paleo‐IOD reconstructions from fossil corals from the eastern tropical Indian Ocean suggest that IOD events may have varied in strength and timing under past climate conditions. The variability of the IOD and interactions with the Asian monsoon and ENSO are investigated here using a series of coupled model simulations of time slices during the last 55,000 years. The Fast Ocean Atmosphere Model (FOAM) is used to simulate pre‐industrial climate and paleoclimate time slices at 6,000, 11,000, 21,000, 35,000, and 55,000 years before present. The strength and timing of IOD events in the FOAM simulations is found to vary, with larger amplitude IOD variability being associated with a weaker Asian summer monsoon and stronger ENSO variability. FOAM simulates a reduced strength IOD in the mid‐Holocene and stronger IOD variability in the Last Glacial Maximum time slice. There is some evidence that the timing of IOD events varies in response to changes in insolation seasonality over the tropical Indian Ocean and resulting changes in the timing and amplitude of the Asian summer monsoon and ENSO.