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Bohua Huang and J. Shukla

gradient and the warming in the western Indian Ocean precondition the subsequent warming over the basin. Overall, ENSO seems to be an effective and persistent remote factor to stimulate the air–sea feedback in the Indian Ocean, both dynamically and thermodynamically. However, it is not yet clear how important the regional air–sea feedback and oceanic dynamics are in shaping the spatial and temporal evolution in response to this external forcing. On the other hand, even though there is a historical

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Gabriel A. Vecchi and Matthew J. Harrison

spun up for 10 years using the monthly mean climatological wind stress field of Harrison (1989) , with fluxes parameterized as in Vecchi and Harrison (2003 , 2005 ). For all experiments, sea surface salinity was restored to the annual mean Levitus (1982) climatology using a 50-day restoring time scale. Two model hindcast experiments were run starting from the end of this 10-yr spin up with climatology: one using the 1986–2003 wind forcing computed from the European Centre for Medium

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Tommy G. Jensen

1. Introduction In recent years there has been increased focus on the interannual variability of sea surface temperature (SST) in the Indian Ocean due to the discovery of the Indian Ocean dipole (IOD) ( Saji et al. 1999 ), alternately named the Indian Ocean “Zonal Mode” (IOZM) ( Webster et al. 1999 ; Clark et al. 2003 ). Whether the IOD is related to El Niño (e.g., Baquero-Bernal et al. 2002 ) or not ( Behera et al. 2003 ) is still controversial, but there is no doubt that forcing conditions

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

decelerate while the wind stress continues to be westerly; each jet is followed by a westward flow in the upper ocean lasting a month or longer. From the observed winds and currents at Gan, Knox (1976) deduced that the jets are accelerated by the zonal wind stress, but decelerated by the time-varying zonal pressure gradient (ZPG). He suggested that the westward pressure force required for momentum balance arises because the westerly wind stress temporarily raises sea level in the east relative to the

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

sectional changes that have taken place during the periods between the cruises of 1965, 1987, and 2002 in the context of simulations performed using an ocean general circulation model. We have attempted to reproduce the subsurface changes by modeling the ocean response to the application of gridded surface forcings from 1948 to the present and have investigated how these changes are related to variations in conditions at the surface. To limit the scope of this study somewhat, we have chosen not to

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

in the AS and in the Somali Current depends not only on variability in air–sea fluxes, but also on the wind forcing: in other words, oceanic processes play an important role in regulating SST. Vinayachandran (2004) used data from Argo floats to show that the length of the summer monsoon plays a key role in the summer cooling. None of the studies on interannual variability, however, are as comprehensive as those (cited above) on the seasonal cycle. Hence, in this paper, we use an OGCM to

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

with the same monthly fluxes and winds each year, any interannual variability that occurs must be due to internal ocean processes. For example, Jochum and Murtugudde (2005) showed that the instability processes that generate internal ocean variability within the south Indian Ocean are nonlinear and thus the SST will be different from year to year, even under climatological forcing. The model output allows us to explore the variability of the Agulhas retroflection and possible relationships with

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Bohua Huang and J. Shukla

coupling is thermodynamic in nature ( Behera and Yamagata 2001 ; Suzuki et al. 2004 ). In Part I of this study, we examined the influences of remote forcing on the tropical Indian Ocean using the regional coupling strategy (e.g., Huang 2004 ) in a global ocean–atmosphere general circulation model with active air–sea coupling only within the Indian Ocean. Through an ensemble of simulations with prescribed observational sea surface temperature (SST) anomalies for 1950–98 over the oceanic region

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Rui-Jin Hu and J. Stuart Godfrey

wind stress pattern used). The exception occurs when discussing the “minimum depth” concept ( section 4a below), which should only be valid for experiments with purely steady forcing and steady resulting flow. In this case experiment 1 is used. Figures 7a,b show the annual mean heat flux for year 6 for experiments 2 and 3. The area-integrated AMNHF north of latitude y (thick purple lines in Fig. 1 ) is considerably greater in magnitude in experiment 3 (more negative purple line) than

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H. Annamalai, H. Okajima, and M. Watanabe

1. Introduction For short-term global climate prediction, the sea surface temperature (SST) anomalies associated with the El Niño–Southern Oscillation (ENSO) phenomenon are recognized as the most dominant forcing factor (e.g., Wallace et al. 1998 ; Trenberth et al. 1998 ; Lau and Nath 2000 ; Su et al. 2001 ; Annamalai and Liu 2005 ). Of special interest here is the role of El Niño on the Pacific–North American (PNA) pattern defined by Wallace and Gutzler (1981) . From regression analysis

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