Interannual subsurface variability in the tropical Indian Ocean with a special emphasis on the Indian Ocean Dipole

Rao, Suryachandra A.; Behera, Swadhin K.; Masumoto, Yukio; Yamagata, Toshio

doi:10.1016/s0967-0645(01)00158-8

Cited by 325 publications

(276 citation statements)

References 43 publications

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“…After another 2 years (Figure 2c), we see anomalous equatorial westerlies with a reversed thermocline structure relative to Figure 2b. About eleven years after the beginning of the decadal IOD episode, the system returns back to the original positive IOD-like conditions; the whole process similar to that of the interannual IOD [Saji et al, 1999;Rao et al, 2002] except for the much longer timescale. This situation reminds us of such similarity between delayed oscillator theory for the interannual ENSO [Schopf and Suarez, 1988] and that for the decadal ENSO [Knutson and Manabe, 1998].…”

Section: Resultsmentioning

confidence: 92%

Decadal variability of the Indian Ocean dipole

Ashok

Chan

Motoi

et al. 2004

Geophysical Research Letters

145

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[1] Using the Simple Ocean Data Assimilation (SODA), NCEP/NCAR reanalysis and the GISST datasets from 1950 -1999, and an atmosphere-ocean coupled general circulation model, we explored the possible existence of decadal Indian Ocean Dipole (IOD) variability for the first time. We find that there are strong decadal IOD events, and that the time series of the decadal IOD and decadal ENSO indices are not well correlated. The simulated decadal signal of the IOD index is highly correlated with the 20°C isotherm depth anomaly, indicating that ocean dynamics is involved in the decadal IOD. It is also associated with the zonal wind anomaly. We suggest that the decadal IOD in the tropics is interpreted as decadal modulation of the interannual IOD events.

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Section: Resultsmentioning

confidence: 92%

Decadal variability of the Indian Ocean dipole

Ashok

Chan

Motoi

et al. 2004

Geophysical Research Letters

145

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“…Some authors like Chambers et al (1999); Allan et al (2001); Banquero et al (2002); Dommenget and Latif (2002); Hastenrath (2002); Shinoda et al (2004); Yu and Lau (2004) argue that IODZM events are triggered by ENSO and hence are not independent of ENSO. While on the other hand, others like Webster et al (1999) ;Iizuka et al (2000); Rao et al (2002); Yamagata et al (2002); Ashok et al (2003); Gualdi et al (2003); Lau and Nath (2004); Behera et al (2005) contradict these findings by presenting the independence of the IODZM mode from ENSO. At the same time, Behera and Yamagata (2003); Saji and Yamagata (2003); Ashok et al (2004a); Yamagata et al (2004) also further acknowledged that both phenomena interact with each other.…”

Section: Introductionmentioning

confidence: 94%

“…However, evidence on the physical existence of the IODZM has been amply demonstrated by showing that the IODZM is an internal coupled mode in the IO, which at times co-occurs with ENSO in the Pacific (Saji et al, 1999;Webster et al, 1999;Iizuka et al, 2000;Murtugudde et al, 2000;Rao et al, 2002;Vinayachandran et al, 2002;Yamagata et al, 2002 andAshok et al, 2003). noted that there is evidence on the active role played by the IO on some of the IODZM mode events, but concluded that it is its self-sustainability and impact on regional and global climate that is still a matter of debate.…”

Section: Introductionmentioning

confidence: 99%

The impact of the positive Indian Ocean dipole on Zimbabwe droughts

Manatsa

Chingombe

Matarira

2008

Intl Journal of Climatology

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A comparative study of the impact of the anomalous positive Indian Ocean SST gradient, referred to as the Indian Ocean Dipole/Zonal Mode (IODZM), and El Niño-Southern Oscillation (ENSO) on Zimbabwe seasonal rainfall variability for the period 1940-1999, is documented. Composite techniques together with simple and partial correlation analyses are employed to segregate the unique association related to IODZM/ENSO with respect to the Zimbabwe seasonal rainfall.The analysis reveals that the IODZM impact on the country's summer rainfall is overwhelming as compared to that of ENSO when the two are in competition. The IODZM influence remains high (significant above 99% confidence level), even after the influence of ENSO has been removed, while that of ENSO collapses to insignificance (even at 90% confidence level) when the IODZM contribution is eliminated. The relationship between ENSO and Zimbabwe seasonal rainfall seems to be sustained through El Niño occurring in the presence of positive IODZM events. However, when the co-occurring positive IODZM and El Niño events are removed from the analysis, it is apparently clear that ENSO has little to do with the country's rainfall variability. On the other hand, positive IODZM is mostly associated with the rainfall deficits, whether or not it co-occurs with El Niño. However, the co-occurrence of the two events does not necessarily suggest that El Niño influences droughts through the positive IODZM events. The El Niño event components during co-occurrence seem to be unrelated (at least linearly) to the droughts, while the positive IODZM events display a relatively strong relationship that is significant above the 95% confidence level. It thus becomes important to extend the study of this nature to cover the whole of southern Africa, so that the extent of the impact of the phenomena can be realized over the whole region.

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“…This easterly wind piles up warm water in the western Indian Ocean and enhances the SST gradient (Figures 10b, 10c, and 10d). The wind stress in the western Indian Ocean (Figure 10a) also produces a warm off-equatorial anomaly in the southern hemisphere (Figure 10b) by producing a downwelling Rossby wave because of the wind stress curl [Rao et al, 2002;Xie et al, 2002]. The warm anomaly propagates westward, and strengthens the warm SST along the western Figure 11.…”

Section: Indian Ocean Dipolementioning

confidence: 99%

Development of a four‐dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations

et al. 2008

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[1] A four-dimensional variational (4D-VAR) data assimilation system using a coupled ocean-atmosphere global model has been successfully developed with the aim of better defining the dynamical states of the global climate on seasonal to interannual scales. The application of this system to state estimations of climate processes during the 1996-1998 period shows, in particular, that the representations of structures associated with several key events in the tropical Pacific and Indian Ocean sector (such as the El Niño, the Indian Ocean dipole, and the Asian summer monsoon) are significantly improved. This fact suggests that our 4D-VAR coupled data assimilation (CDA) approach has the potential to correct the initial location of the model climate attractor on the basis of observational data. In addition, the coupling parameters that control the air-sea exchange fluxes of mass, momentum, and heat become well adjusted. Such an initialization using the 4D-VAR CDA approach allows us to make a roughly 1.5-year lead time prediction of the 1997-1998 El Niño event. These results demonstrate that our 4D-VAR CDA system has the ability to enhance forecast potential for seasonal to interannual phenomena.

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Interannual subsurface variability in the tropical Indian Ocean with a special emphasis on the Indian Ocean Dipole

Cited by 325 publications

References 43 publications

Decadal variability of the Indian Ocean dipole

Decadal variability of the Indian Ocean dipole

The impact of the positive Indian Ocean dipole on Zimbabwe droughts

Development of a four‐dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations

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