Publication Date:
2015-04-30
Description:
In a transient accelerated simulation of a coupled climate model, we identified a zonal dipole-like pattern of sea surface temperature (SST) anomalies in the tropical Indian Ocean, which is forced by precessional insolation changes since 300 ka and named as the paleo-IOD. A positive paleo-IOD mean state at 23-kyr's precessional band exhibits warmer and wetter conditions over the western Indian Ocean and cooler and drier conditions over the eastern tropical Indian Ocean from August to October. The zonal thermal seesaw at the sea surface can extend downward to the subsurface ocean between 60 m and 80 m and accompanies stronger oceanic upwelling in the eastern tropical Indian Ocean. The associated boreal summer-autumn tropospheric circulation anomalies are characterized by anomalous ascent over the western Indian Ocean and anomalous descent over the southeastern tropical Indian Ocean, with anomalous easterlies at the surface along the equatorial Indian Ocean. This positive paleo-IOD largely originates from local air-sea interactions that are induced by the increased summer insolation, and is also contributed by the reduced boreal winter insolation through oceanic “heat memory effect”. Our simulated dipole mode index (DMI) of SST is qualitatively consistent with the paleoceanographic reconstructed DMI based on the UK37 proxy of SST at precessional band. This paleo-IOD provides a possible explanation for the in-phase precessional variation between boreal winter insolation and the UK37 proxy of SST in the eastern tropical Indian Ocean. This article is protected by copyright. All rights reserved.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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