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Rui-Jin Hu and J. Stuart Godfrey

—was built to create a crude analog of the heat budget of the region. The Ekman transport passed out through the open top 50 m of the southern boundary and was replaced by colder inflow through a full-depth “Indonesian gap.” A zonal jet from this gap fed a north-flowing western boundary current, which fed upwelling at the northern boundary. Diapycnal mixing did occur in this model; it was confined to the strongly sheared currents around an eddy in the northwest corner of the rectangular model domain

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

western boundary currents ( SM ). The work of Sengupta et al. (2001) focuses mainly on the intraseasonal variability of off-equatorial zonal currents in the region south and east of Sri Lanka, not on equatorial currents. Han et al. (2001) and Han (2005) show that the 30–60-day variability of the zonal current is directly wind forced, and report a dominant 90-day peak in observed sea level in the eastern EqIO, as well as in the model upper-ocean current. The 90-day variability is attributed to a

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

was held fixed at 2000 m 2 s −1 , giving a constant Munk western boundary current width ( A M / β ) 1/3 of 46 km in all experiments—just resolvable with the model grid. There was no bottom friction. In a “rigid lid” model, the barotropic flow through open boundaries must be specified. Barotropic flow through the shallow gap in the southern boundary was set at each longitude to the instantaneous value of Ekman transport, that is, B ( t )/ ρβ . The streamfunction along the eastern boundary has

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Vinu K. Valsala and Motoyoshi Ikeda

-dimensional track of the ITF. A probability density function analysis over the Lagrangian trajectories of the particles initialized at the ITF entrance region by Song et al. (2004 , hereafter SGV ) has concluded that 67% ± 5% of the ITF turns to the northern Indian Ocean at the western boundary and is eventually transmitted to the south following the annual mean Ekman transport. It is well known that the Indian Ocean undergoes dramatic seasonal reversals [Somali Current ( Schott et al. 1990 ), Coastal

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

1. Introduction The Agulhas Current is the strongest western boundary current in the Southern Hemisphere and transports warm tropical water southward along the east coast of South Africa. There are thought to be three major sources in the south Indian Ocean for the Agulhas Current: recirculation in the southwest Indian Ocean, flow through the Mozambique Channel, and the East Madagascar Current. Based on all available hydrographic data up until the mid-1990s, Stramma and Lutjeharms (1997

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Tommy G. Jensen

masses ( Jensen 2003b ). It was concluded that a clockwise cross-equatorial gyre circulation exists on the average. The freshwater route in the Ekman layer follows the same pattern: A classical interior southward and southwestward flow closed by a northward western boundary current. The strong subsurface northward flow in the Somali Current, which has its origin in the southern Indian Ocean and the Indonesian Throughflow, provides a source for upwelling in the northern Indian Ocean. Since this water

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Tommy G. Jensen

circulation is intensified during El Niño, and in particular during IOD. Valsala and Ikeda are identifying the major pathways of water from the Indonesian Throughflow using particle trajectories, passive tracers, temperature, and salinity from an OGCM. They found three main routes: A clockwise circulation cell in the thermocline confined to the south of the equator, a near-surface branch entering the Arabian Sea via the Somali Current, and a cross-equatorial subsurface branch at depths between the two

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Gabriel A. Vecchi and Matthew J. Harrison

of Mariano et al. (1995) , though the Mariano et al. currents tend to be slightly stronger. The model represents the seasonal changes in the surface currents relatively well, including the reversal of the western boundary current, the equatorial current changes, and the mean currents in the southern Indian Ocean. There are regional differences between the model and observations (in particular, in the region of the Indonesian Throughflow, which is not represented in the model), but, on the whole

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Tomoki Tozuka, Jing-Jia Luo, Sebastien Masson, and Toshio Yamagata

annual mean. Also, the South Equatorial Current (SEC) and western boundary currents (East Madagascar Current, Mozambique Current, and Agulhas Current) transport a large amount of heat. In particular, the large heat transport in the lower layer (50–440 m) is associated with the western boundary currents and the SEC. The direction of the net meridional transport is northward in the lower layer so that it compensates the heat loss in the lower layer to the north of 15°S. The upwelling north of 15°S is

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

of Cane and Patton (1984) . The model state variables include the normalized height anomaly, zonal current, and Kelvin wave amplitude for each of the first two baroclinic modes. The model is set up for the tropical IO with a fairly idealized topography. The model domain spans from 30° to 20°S, 40° to 113°E with a resolution of ∼0.5° latitude and ∼1° longitude. Figure 2 shows the land mask for Africa, India, and Indonesia and the grid resolution for the model setup. The model is forced by the

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