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IJMS Vol.37(1) [March 2008] >


Title: Interannual variability of the South Indian Ocean in observations and a coupled model
Authors: Huang, Bohua
Shukla, J.
Keywords: South Indian Ocean
Air-sea interaction
Interannual variability
Coupled ocean-atmosphere general circulation model]
Issue Date: Mar-2008
Publisher: CSIR
Abstract: The mean state, annual cycle, and interannual variability of the coupled ocean-atmosphere in the South Indian Ocean produced by a 300-year simulation of a coupled ocean-atmosphere general circulation model (CGCM) are compared with those from 51-year (1950-2000) observational datasets. The CGCM simulates realistically the mean annual cycles for both the sea surface temperature (SST) and lower atmospheric circulation, including the seasonal positions of the 10ºC and 20ºC SST isotherms, the zonal and meridional migration of the South Indian Ocean subtropical high, and the fluctuation of the southeast trade winds and mid-latitude westerly winds. Interannually, the dominant model anomalous SST pattern in austral summer and fall showed some similarities to the observed Indian Ocean subtropical dipole mode, featuring opposite SST anomalies between the northeastern ocean to the west of Australia and the southern ocean. The model pattern is different from the observed one in its overly zonal spatial structure. Both the model and observed anomalous events are generated in response to atmospheric perturbations over the subtropical and mid-latitude South Indian Ocean that disturb the subtropical high during austral spring and summer. The corresponding wind speed changes of the trade winds and westerly modulate the surface heat flux into the ocean and generate SST anomalies, which usually persist into austral fall and in turn modify the lower atmospheric circulation in the subtropical Indian Ocean, especially the areas near Madagascar in the fall season. In the observations, the initial extratropical atmospheric fluctuations are significantly correlated to the global tropical variations associated with El Niño/Southern Oscillation. They are more strongly linked to the southern annular mode in the model.
Page(s): 13-34
ISSN: 0379-5136
Source:IJMS Vol.37(1) [March 2008]

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