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Jean Philippe Duvel and Jérôme Vialard

1. Introduction The intraseasonal variability (ISV) of deep convection is one of the most organized and reproducible large-scale perturbations in the Tropics, with maximum amplitude over the Indo-Pacific region. Over the Indian Ocean, this ISV has a strong seasonality. During the summer monsoon, the convective perturbation propagates northward from the equator to the Indian peninsula with maximum amplitude over the Bay of Bengal (see Lawrence and Webster 2002 ). These summer perturbations are

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Gary Meyers, Peter McIntosh, Lidia Pigot, and Mike Pook

Abstract

The Indian Ocean zonal dipole is a mode of variability in sea surface temperature that seriously affects the climate of many nations around the Indian Ocean rim, as well as the global climate system. It has been the subject of increasing research, and sometimes of scientific debate concerning its existence/nonexistence and dependence/independence on/from the El Niño–Southern Oscillation, since it was first clearly identified in Nature in 1999. Much of the debate occurred because people did not agree on what years are the El Niño or La Niña years, not to mention the newly defined years of the positive or negative dipole. A method that identifies when the positive or negative extrema of the El Niño–Southern Oscillation and Indian Ocean dipole occur is proposed, and this method is used to classify each year from 1876 to 1999. The method is statistical in nature, but has a strong basis on the oceanic physical mechanisms that control the variability of the near-equatorial Indo-Pacific basin. Early in the study it was found that some years could not be clearly classified due to strong decadal variation; these years also must be recognized, along with the reason for their ambiguity. The sensitivity of the classification of years is tested by calculating composite maps of the Indo-Pacific sea surface temperature anomaly and the probability of below median Australian rainfall for different categories of the El Niño–Indian Ocean relationship.

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

coefficient is 0.76. In particular, the surface heat flux plays an important role; the correlation between the principal component and the area-averaged surface heat flux north of 15°S amounts to 0.53, with the latter leading the former by 2 yr. Also, a composite analysis of the decadal net heat flux anomaly based on the principal component shows a positive (negative) anomaly in the Tropics for the positive (negative) principal component (figure not shown). Thus, we may conclude that the surface heat flux

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

simulate a realistic climatology and variability of the Indian Ocean region ( Gualdi et al. 2003a ; Fischer et al. 2005 ). The analysis of the basic state in the Tropics, as simulated by SINTEX, indicates that there is no trend in the SST ( Gualdi et al. 2003b ). Many of the systematic errors of SINTEX are still present in SINTEX-F ( Luo et al. 2005 ; Masson et al. 2005 ). In the Pacific Ocean the cold tongue regime extends too far westward, in association of strong trade winds simulated in the

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Karumuri Ashok, Hisashi Nakamura, and Toshio Yamagata

; Inatsu and Hoskins 2004 ). The core regions of the SH storm track and PFJ are anchored around the baroclinic zone throughout the year regardless of the intensity of the STJ ( Nakamura and Shimpo 2004 ). ENSO events can influence the SH storm-track activity by changing the strengths and positions of the STJ and/or the PFJ in response to anomalous convective activity in the Tropics ( Trenberth et al. 1998 ). The anomalous convection can influence the STJ via an anomalous divergent wind ( Sardeshmukh

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

response in an AGCM is forced by the precipitation anomalies throughout the Tropics, it is not surprising to note that the strength of the height response over the PNA sector in the TIP solutions appears more realistic. d. Potential predictability In AGCMs the response to the boundary forcing (signal) is embedded with the internal atmospheric variability (noise). From the ensemble solutions we estimate reproducibility, a measure for detecting the model’s robustness to the imposed boundary forcing (e

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

activity. Another possibility could be an active El Niño in the tropical Pacific. In general, when IOD events are active in the tropical Indian Ocean, we observe a single anomalous Walker cell within the Indian Ocean with a descending limb over Indonesia and an ascending limb over the western Indian Ocean ( Yamagata et al. 2004 ; Fig. 13a ). However, when IOD events co-occur with El Niño, we observe two anomalous Walker cells in the Tropics ( Yamagata et al. 2004 ; Fig. 13b ). An active Walker cell

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

. , 14 , 1853 – 1863 . Chen , D. , L. M. Rothstein , and A. J. Busalacchi , 1994 : A hybrid vertical mixing scheme and its application to tropical ocean models. J. Phys. Oceanogr. , 24 , 2156 – 2179 . Deser , C. , A. S. Phillips , and J. W. Hurrell , 2004 : Pacific interdecadal climate variability: Linkages between the Tropics and the North Pacific during boreal winter since 1900. J. Climate , 17 , 3109 – 3124 . Fukumori , I. , and P. Malanotte-Rizzoli , 1995 : An

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

. 6b ). The transport entering the system from the EMC has a greater heat content than that from the recirculation since it emanates from the Tropics and therefore contains warmer water. The zonally averaged wind stress curl over the south Indian Ocean from 20° to 45°S is plotted in Fig. 7 , along with the monthly mean volume flux of the recirculation. The wind stress curl has a maximum in July when the winds over the south Indian Ocean are strongest and the South Indian anticyclone has shifted

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Roxana C. Wajsowicz

scales: The initial value problem. Climate Dyn. , 19 , 671 – 692 . Gill , A. E. , 1980 : Some simple solutions for heat induced tropical circulations. Quart. J. Roy. Meteor. Soc. , 106 , 447 – 462 . Gill , A. E. , 1985 : Elements of coupled ocean–atmosphere models for the tropics. Coupled Ocean–Atmosphere Models , J. C. J. Nihoul, Ed., Elsevier Oceanography Series, Vol. 40, Elsevier, 303–327 . Griffies , S. M. , and K. Bryan , 1997 : Predictability of North Atlantic multidecadal

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