Intrinsic precursors and timescale of the tropical Indian Ocean Dipole: insights from partially decoupled numerical experiment
The intrinsic precursors and timescale of the tropical Indian Ocean Dipole (IOD) are examined with the help of a partially coupled global experiment with decoupled SST over the tropical Pacific. The IOD does exist in the absence of sea surface temperature interannual variability in the tropical Pacific in our modeling framework, but has weaker amplitude and damped Bjerknes feedback. However, IOD variability is much more biennial in the absence than presence of El Niño Southern Oscillation, especially in the eastern equatorial Indian Ocean (IO). Such biennial rhythm results mainly from two mechanisms internal to the IO. The tropical ocean dynamics play a key role in the biennial anomalies during boreal winter with a sudden reversal of thermocline anomalies in the eastern equatorial IO forced by intraseasonal disturbances reminiscent of the Madden–Julian Oscillation (MJO). However, this preconditioning is not sufficient for triggering IOD events in the next boreal spring per se. The main trigger for pure IODs relates to tropical–extratropical interactions within the IO. Convection and diabating heating associated with negative IODs promote a Gill-type tropical response, excite mid-latitude wave-trains and subtropical blocking in the Southern Hemisphere that trigger positive subtropical IOD events during boreal winter. The latter promotes cold SST and anticyclonic circulation anomalies over the southeast IO that persist and migrate northeastward, triggering positive IOD events during the next boreal spring. Accounting for the complementary influence of tropical ocean dynamics coupled to MJO and tropical-extratropical ocean–atmosphere interactions may thus help improving IOD predictability.
KeywordsBiennial variability Coupled climate model Indian Ocean Dipole MJO Ocean dynamics Tropical–extratropical interactions
This work was funded by the Earth System Science Organization, Ministry of Earth Sciences, Government of India under Monsoon Mission (Project No. MM/SERP/CNRS/2013/INT-10/002 Contribution #MM/PASCAL/RP/07. This work was performed using HPC resources from GENCI-IDRIS (Grants 2015, 2016, 2017—016895). We thank the three anonymous reviewers for their constructive comments.
- Chan SC, SK Behera, T Yamagata (2008) Indian Ocean Dipole influence on South American rainfall. Geophys Res Lett 35:L14S12. doi: 10.1029/2008GL034204
- Guo F, Liu Q, Zheng XT, Sun S (2013) The role of barrier layer in Southeastern Arabian Sea during the development of positive Indian Ocean Dipole events. Ocean Coast Res 12:245–252Google Scholar
- Han W, Shinoda T, Fu LL, McCreary JP (2006) Impact of atmospheric intraseasonal oscillations on the Indian Ocean dipole during the 1990s. J Phys Oceanogr 111:679–690Google Scholar
- Luo JJ, C Yuan, W Sasaki, SK Behera, Y Masumoto, T Yamagata, JY Lee, S Masson (2016), Current status of intraseasonal-seasonal-to-interannual prediction of the Indo-Pacific climate. In: Behera SK, Yamagata T (eds) Indo-Pacific climate variability and predictability, chapter 3, pp 63–107, World Sci Publ Co. http://www.worldscientific.com/worldscibooks/10.1142/9664
- Madec G (2008) NEMO ocean engine. Note du Pôle de modélisation, Institut Pierre-Simon Laplace (IPSL), France. No 27. ISSN No 1288-1619Google Scholar
- Rao SA, Behera SK, Masumoto Y, Yamagata T (2002) Interannual subsurface variability in the Tropical Indian Ocean with a special emphasis on the Indian Ocean Dipole. Deep-Sea Res 49:1549–1572Google Scholar
- Roeckner E, G Baüml, L Bonaventura, R Brokopf, M Esch, M Giorgetta, S Hagemann et al (2003) The atmospheric general circulation model ECHAM5: Part 1: model description. Max-Planck-Institut für Meteorologie, MPI-Report 353, HamburgGoogle Scholar
- Saji NH, Goswami BN, Vinayachandran PN, Yamagata T (1999) A dipole mode in the tropical Indian Ocean. Nature 401:360–363Google Scholar
- Schott FA, SP Xie, JP McCreary Jr (2009) Indian Ocean circulation and climate variability Rev Geophys 47:RG1002. doi: 10.1029/2007RG000245
- Valcke S (2006) OASIS3 user guide (prism_2-5). PRISM support initiative report No 3, p 64Google Scholar
- Yamagata T, SK Behera, JJ Luo, S Masson, MR Jury, SA Rao (2004) Coupled ocean-atmosphere variability in the tropical Indian Ocean. In: Wang C, Xie SP, Carton JA (eds) Geophysical Monograph Series, vol 147, p 414Google Scholar