Contrasting Indian Ocean SST variability with and without ENSO influence: A coupled atmosphere-ocean GCM study |
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Authors: | Jin-Yi Yu K M Lau |
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Institution: | (1) Department of Earth System Science, University of California at Irvine, Irvine, CA, USA;(2) NASA/Goddard Space Flight Center, Greenbelt, MD, USA |
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Abstract: | Summary In this study, we perform experiments with a coupled atmosphere-ocean general circulation model (CGCM) to examine ENSO’s influence
on the interannual sea-surface temperature (SST) variability of the tropical Indian Ocean. The control experiment includes
both the Indian and Pacific Oceans in the ocean model component of the CGCM (the Indo-Pacific Run). The anomaly experiment
excludes ENSO’s influence by including only the Indian Ocean while prescribing monthly-varying climatological SSTs for the
Pacific Ocean (the Indian-Ocean Run). In the Indo-Pacific Run, an oscillatory mode of the Indian Ocean SST variability is
identified by a multi-channel singular spectral analysis (MSSA). The oscillatory mode comprises two patterns that can be identified
with the Indian Ocean Zonal Mode (IOZM) and a basin-wide warming/cooling mode respectively. In the model, the IOZM peaks about
3–5 months after ENSO reaches its maximum intensity. The basin mode peaks 8 months after the IOZM. The timing and associated
SST patterns suggests that the IOZM is related to ENSO, and the basin-wide warming/cooling develops as a result of the decay
of the IOZM spreading SST anomalies from western Indian Ocean to the eastern Indian Ocean. In contrast, in the Indian-Ocean
Run, no oscillatory modes can be identified by the MSSA, even though the Indian Ocean SST variability is characterized by
east–west SST contrast patterns similar to the IOZM. In both control and anomaly runs, IOZM-like SST variability appears to
be associated with forcings from fluctuations of the Indian monsoon. Our modeling results suggest that the oscillatory feature
of the IOZM is primarily forced by ENSO. |
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