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Joaquim Ballabrera-Poy, Eric Hackert, Raghu Murtugudde, and Antonio J. Busalacchi

based on the knowledge of the geographical location of the most energetic signals within the IO, and a set of phenomenological features such as the intertropical front (ITF), cross-equatorial overturning cell, and the location of upwelling zones. One of the interesting features of the seasonally reversing monsoons is the thermocline ridging along ∼10°S, which has many interesting climatic and biogeochemical consequences ( Reverdin et al. 1986 ; Murtugudde et al. 1999 ; Xie et al. 2002 ). The air

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Debasis Sengupta, Retish Senan, B. N. Goswami, and Jérôme Vialard

100-m temperature is too cool by 2°–3°C, and the thermocline is more diffuse than that observed (not shown). These limitations might be due to the relatively coarse model vertical resolution (about 25 m) below 100-m depth, as well as deficiencies in the mixing parameterization. The equatorial Indian Ocean circulation is rather sensitive to the choice of wind product used to force the model, which is consistent with the findings of Anderson and Carrington (1993) . Westerly winds in the EqIO are

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Annalisa Cherchi, Silvio Gualdi, Swadhin Behera, Jing Jia Luo, Sebastien Masson, Toshio Yamagata, and Antonio Navarra

Niño–Southern Oscillation (ENSO) are negatively correlated. Moreover, evidence of a decadal variability affecting this relationship has been found, as its amplitude has decreased during recent decades ( Kumar et al. 1999 ). Lau and Nath (2000) provided a mechanism, also known as the atmospheric bridge, to explain the influence of the tropical Pacific Ocean on the monsoon by means of a suppression of convection over the western part of the Walker circulation in correspondence of a warm ENSO event

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J. C. Hermes, C. J. C. Reason, and J. R. E. Lutjeharms

found evidence that this flow through the channel contributes substantially to the seasonality of the Agulhas Current. The eddy-permitting, regional ocean AGAPE model has been shown to realistically reproduce the general circulation of the Agulhas Current system ( Biastoch 1998 ; Biastoch and Krauß 1999 ; Biastoch et al. 1999 ; Reason et al. 2003 ), and we have used this model to investigate the variability of the three source regions on monthly to interannual scales. Since the model is forced

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R. J. Murray, Nathaniel L. Bindoff, and C. J. C. Reason

. King , R. J. Sanders , S. A. Cunningham , and R. Marsh , 2005 : Decadal changes in the South Indian Ocean thermocline. J. Climate , 18 , 1575 – 1590 . Murray , R. J. , and C. J. C. Reason , 2001a : A curvilinear version of the Bryan-Cox-Semtner Ocean Model and its representation of the Arctic circulation. J. Comput. Phys. , 171 , 1 – 46 . Murray , R. J. , and C. J. C. Reason , 2001b : A curvilinear ocean model using a grid regionally compressed in the South Indian

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Lisan Yu, Xiangze Jin, and Robert A. Weller

the boreal summertime under the influence of prevailing southwesterly monsoon winds ( Schott and McCreary 2001 ), and the upwelling process cools the sea surface despite the fact that positive Q net goes into the region. The central southern basin between 5° and 12°S is the location of a thermocline ridge ( Wyrtki 1971 ) owing to the persistent Ekman suction ( McCreary et al. 1993 ), where the wind-induced thermocline variations impose a major control on the regional SST variability ( Donguy and

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J. Stuart Godfrey, Rui-Jin Hu, Andreas Schiller, and R. Fiedler

1. Introduction This paper and the following one ( Hu and Godfrey 2007 , hereafter Part II ) suggest that ocean general circulation models (OGCMs) are systematically underestimating the annual mean net heat flux (AMNHF) into the northern Indian Ocean, and explore possible reasons for this. The magnitude of interannual variation of any quantity is often roughly proportional to its mean. If the AMNHF into this region is underestimated, its interannual variability—and hence the amount of heat

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Jean Philippe Duvel and Jérôme Vialard

, an intraseasonal SST perturbation of more than 1.5 K over a large region in the Indian Ocean between 5° and 10°S was found in both in situ and TMI SST data. From this observation, Harrison and Vecchi (2001) concluded that the strong SST variations are mainly due to vertical and horizontal heat transport with the vertical exchange with the cold subsurface being more efficient during the winter season during which the thermocline is closer to the surface. However, DRV concluded based on a

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Clémentde Boyer Montégut, Jérôme Vialard, S. S. C. Shenoi, D. Shankar, Fabien Durand, Christian Ethé, and Gurvan Madec

et al. 2004 ; Durand et al. 2004 ), and the resulting penetrative solar radiation play a crucial role in these regions. The above studies were successful in describing the seasonal cycles, but the natural extension to interannual variability has not been made owing to the paucity of salinity data. It is this lacuna that numerical models can fill. Murtugudde and Busalacchi (1999 , hereinafter MB99 ) used an ocean general circulation model (OGCM) to show that the interannual variability of SST

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