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

that Rossby wave forcing has to be in mean westerly flow while the observed forcing during El Niño years is in mean easterlies; this and other related issues are addressed in subsequent studies and the details can be found in the review article by Trenberth et al. (1998) . Many atmospheric general circulation models (AGCMs) forced by ENSO-related SST anomalies have simulated the PNA pattern with moderate success ( Shukla and Wallace 1983 ; Blackmon et al. 1983 ; Geisler et al. 1985 ; Lau 1981

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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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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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Bohua Huang and J. Shukla

SST anomalies in the southwestern Indian Ocean as a regional atmospheric response, a feature also discernible in Fig. 11c to some degree. A new development in this season is that positive HC anomalies appear near the Sumatra coast and most of the equatorial ocean ( Fig. 11a ), which implies that at least part of the southwestern warm HC signals have penetrated into the equatorial waveguide and propagated eastward as the equatorial Kelvin wave to suppress the thermocline there. This propagation

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

National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis ( Kalnay et al. 1996 ) wind anomalies with respect to the 1993–2003 mean. The winds are linearly interpolated to the 5-day time step of the model. The model uses the linear shallow-water equations on the equatorial β plane subject to the long-wave approximation and finite differences in the horizontal directions to describe the evolution of each baroclinic mode. Linear damping is imposed by

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Vinu K. Valsala and Motoyoshi Ikeda

between the SMC and reflected Rossby waves from the eastern boundary ( Vinayachandran and Yamagata 1998 ). The vorticity east of Sri Lanka ( Vinayachandran and Yamagata 1998 ) was also well simulated. However, the recently found equatorial “Twin Gyre” by Rahul et al. (2004) is not well evolved, which is attributed to the coarse resolution of the model in simulating such a fine mesoscale feature. The model-produced ITF seasonal transport is shown in Fig. 2 . The model has two openings in the

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

of a strong “decadal IOD.” They claimed that it is not correlated with the decadal ENSO events and suggested that ocean dynamics are involved in the decadal IOD. However, their analysis was limited because of the coarse resolution of their coupled model and the sparseness of observational data. In the present article, we use outputs from a 200-yr integration of a coupled general circulation model (CGCM) with a horizontal high-resolution atmospheric component, and focus on the decadal climate

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Karumuri Ashok, Hisashi Nakamura, and Toshio Yamagata

. This may not necessarily be a statistical artifact, as Saji et al. (2005) showed through a wave activity flux diagnosis ( Takaya and Nakamura 2001 ) applied to observed 200-hPa streamfunction anomalies that the IOD teleconnection extends almost over the entire extratropical SH in the form of a stationary Rossby wave train propagating through the midlatitude westerly jet. They substantiated this diagnostic result by carrying out idealized experiments with a mechanistic atmospheric model. As seen

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Peter R. Oke and Andreas Schiller

the design of specific observing systems and the configuration of multisensor observing networks, provide an assessment of the potential for future observing systems and innovative uses of existing systems to achieve major improvements in forecast skill, test advanced data assimilation methods, and to assess the relative role of observations and forecasting methods in improving the utility of forecasts. For some time now atmospheric models have been used to aid the design of observing systems (e

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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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