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Suryachandra A. Rao, Sebastien Masson, Jing-Jia Luo, Swadhin K. Behera, and Toshio Yamagata

equatorial downwelling Kelvin waves and deepens the thermocline in the eastern Indian Ocean, and that it is the major contributor to the termination of IOD events. The role of incoming solar radiation in the termination of IOD events is also suggested by Rao and Yamagata (2004) . Owing to a lack of observations, however, they were unable to provide a detailed analysis of the processes involved in the termination of IOD events. In this study using 200-yr simulation results from a coupled general

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

: positive SST anomalies in the equatorial central and eastern regions of the Pacific Ocean favor enhanced deep convection there; this leads to an increase in the release of latent heating throughout the troposphere and in the divergent flow at upper levels; subsequently, the upper-level divergence forces planetary Rossby waves that project onto the PNA pattern ( Hoskins and Karoly 1981 ; Webster 1981 ; Simmons 1982 ; Branstator 1985 ). One limitation of this conceptual scenario is the requirement

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

February and March the pressure force in the upper 200 m is eastward, with a maximum at 100-m depth of about −2.0 × 10 −7 N kg −1 , comparable to that in the equatorial Atlantic or Pacific. The ZPG associated with equatorial Kelvin and Rossby waves generated/reflected at lateral boundaries determines ocean adjustment to uniform westerly wind stress. Since eastward jets are surface intensified, it has been argued that these waves must have a vertical structure resembling the second baroclinic mode

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Vinu K. Valsala and Motoyoshi Ikeda

Indian Ocean, is only a half of the total air–sea cooling. This implies that the surface ITF flows southward, gradually cools in the higher latitudes, and sinks to the subsurface. A more detailed seasonal variability in the deepening of ITF at this pocket will be shown later using the tracer analysis. It is worth mentioning that the thermocline variability of this region is influenced by the remote wave energy propagating from the western Pacific as coastal Kelvin waves and radiating Rossby waves

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Bohua Huang and J. Shukla

increased solar flux and reduced evaporative heat loss at the sea surface due to the reductions of both cloud cover and surface wind speeds during an El Niño event (e.g., Klein et al. 1999 ; Venzke et al. 2000 ). Xie et al. (2002) and Huang and Kinter (2002) also found that the surface warming in the southwestern Indian Ocean at the end of an El Niño year can be caused by an anomalous deepening of the thermocline associated with westward propagating Rossby waves. Before reaching this basinwide

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Hae-Kyung Lee Drbohlav, Silvio Gualdi, and Antonio Navarra

in summer enhances the evaporative cooling in this area. Assume initially there is a modest cold SSTA off Sumatra. Since the southeastern Indian Ocean is a region of intense convection, the cold SSTA implies the decrease of atmospheric convective heating or an atmospheric heat sink. According to Gill’s (1980) solution, the heat sink will induce a descending Rossby wave response to its west, resulting in an anomalous low-level anticyclonic flow. In the northern summer, the mean flow is

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

are seen in the eastern (western) equatorial Indian Ocean. Then, the negative decadal IOD event starts to emerge in year +6. We note that a negative decadal IOD event is almost a mirror image of the positive event described here, although the amplitude is somewhat weaker compared with that of the positive decadal IOD. It is hard to imagine, however, that tropical ocean dynamics permit such a slow propagation of ocean waves (cf. Gill 1982 ). We, therefore, suspect that the variations in the

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

Rayleigh friction with decay times of 30 and 11 months for the first and second baroclinic modes, respectively. Kelvin wave speeds correspond to 2.53 and 1.56 m s −1 , e -folding length scales L ≈ ( c / β ) 1/2 = 3.0° and 2.35°, and time scales ( T ≈ ( cβ ) −1/2 ) = 1.52 and 1.94 days, for the two baroclinic modes, respectively. Model wave speeds, length scales, and time scales are derived from density profile created using an average temperature and salinity profile from the World Ocean Atlas

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Bohua Huang and J. Shukla

Indian Basin. Another shortcoming of the model simulation is the weak oceanic waves in the Indian Ocean within the equatorial waveguide due to weak equatorial zonal winds, which generates the symmetric SST patterns with respect to the equator from boreal summer to early fall in the observations ( Huang and Kinter 2002 ; Rao and Behera 2005 ). The coupled model, however, captures the thermocline disturbances to the south of the equator more realistically. In the absence of ENSO in the CLIM simulation

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

the central and eastern Indian Ocean tend to prevent propagation of the annual-period Rossby wave from the eastern south Indian Ocean ( Matano et al. 1998 , 1999 ). Biastoch et al. (1999) suggested that an increase in flow through the Mozambique Channel derived from the Agulhas as Primitive Equations (AGAPE) model during austral winter was due to increased Ekman transport when the south Indian Ocean anticyclone is situated farther to the north. By tracing the model tropical surface water, they

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