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Performances of 5 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating the chlorophyll concentration over the tropical Indian Ocean are evaluated. Results show that these models are able to capture the dominant spatial distribution of observed chlorophyll concentration and reproduce the maximum chlorophyll concentration over the western part of the Arabian Sea, around the tip of the Indian subcontinent, and in the southeast tropical Indian Ocean. The seasonal evolution of chlorophyll concentration over these regions is also reproduced with significant amplitude diversity among models. All of 5 models is able to simulate the interannual variability of chlorophyll concentration. The maximum interannual variation occurs at the same regions where the maximum climatological chlorophyll concentration is located. Further analysis also reveals that the Indian Ocean Dipole events have great impact on chlorophyll concentration in the tropical Indian Ocean. In the general successful simulation of chlorophyll concentration, most of the CMIP5 models present higher than normal chlorophyll concentration in the eastern equatorial Indian Ocean.

Interannual variations in the surface and subsurface tropical Indian Ocean were studied using HadISST and SODA datasets. Wind and heat flux datasets were used to discuss the mechanisms for these variations. Our results indicate that the surface and subsurface variations of the tropical Indian Ocean during Indian Ocean Dipole (IOD) events are significantly different. A prominent characteristic of the eastern pole is the SSTA rebound after a cooling process, which does not take place at the subsurface layer. In the western pole, the surface anomalies last longer than the subsurface anomalies. The subsurface anomalies are strongly correlated with ENSO, while the relationship between the surface anomalies and ENSO is much weaker. And the subsurface anomalies of the two poles are negatively correlated while they are positively correlated at the surface layer. The wind and surface heat flux analysis suggests that the thermocline depth variations are mainly determined by wind stress fields, while the heat flux effect is important on SST.