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Decadal IOD

PI: Tomoki Tozuka
Institution: University of Tokyo
Abstract:
The Indian Ocean Dipole (IOD) is an air-sea coupled phenomenon associated with a positive sea surface temperature anomaly (SSTA) to the west and a negative SSTA to the east (Saji et al. 1999; Webster et al. 1999). It has turned out that the IOD has a large impact on climate of both the surrounding and remote regions such as East Asia, Europe, and South America (Yamagata et al. 2004). Thus, understanding as well as simulating the IOD is crucial to global climate research.

Recently, Ashok et al. (2001) have shown that the Indian Summer Monsoon Rainfall (ISMR) is not correlated with the Southern Oscillation Index (SOI) in recent decades owing to the frequent occurrences of the IOD. Behera and Yamagata (2003) have revealed that the IOD even weakens the link between El Niño and the Southern Oscillation through influencing the pressure at Darwin. Since the seminal work by Nitta and Yamada (1989), the decadal variability in the tropical Pacific has been studied extensively in recent decades. However, the decadal phenomenon in the tropical Indian Ocean has received little attention, partly owing to lack of available observational data.

Among a few studies, Meehl et al. (1998) and Allan et al. (2003) discussed a link with the decadal ENSO-like variability in the Pacific. Also, Reason et al. (1996a) suggested the importance of decadal variability in the subtropical anticyclone in the southern Indian Ocean, while Reason et al. (1996b) showed that the decadal variability in the winds over the Pacific may introduce decadal variations in the southern Indian Ocean via the Indonesian Throughflow. More recently, Tozuka et al. (2006) have revealed, using SINTEX-F1 coupled GCM, that the decadal modulation of the interannual IOD events is associated with that of the southward Ekman heat transport across 15°S induced by changes in the Mascarene High (Reason et al. 1996). They have also shown that the heat transport by the Indonesian Throughflow associated with the ENSO (Meyers 1996) is a major factor that explains the decadal modulation.

Using the IPCC model outputs, we plan to investigate the decadal variation in the tropical Indian Ocean. In particular, we investigate how and why the occurrence of simulated Indian Ocean Dipole varies decadally using both atmospheric data (such as OLR, wind stress, and rainfall), and oceanic data (such as temperature and current fields).

Publications:
  • Yokoi, T., T. Tozuka, and T. Yamagata, 2009: Seasonal Variations of the Seychelles Dome Simulated in the CMIP3 Models. J. Phys. Oceanogr., 39, 449–457, doi:10.1175/2008JPO3914.1. Abstract. Edit.

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