Climate change contributes to more frequent consecutive positive Indian Ocean Dipole events

Are the 2006-2008 three-consecutive positive Indian Ocean Dipole (pIOD) events linked to climate change? Using 20th century experiments submitted for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), we show that a 19-model average IOD index over the 1950-1999 period yields an upward trend. The associated circulation trends provide a favourable environment for pIOD development, leading to a 17% increase in pIOD frequency compared with the case in which trends are removed. The majority of the increase manifests as a frequency increase in the two- and three-consecutive events. The circulation trends are in turn consistent with wind changes associated with a weaker Walker circulation in the Pacific and an enhanced land-sea temperature contrast in the Indian Ocean (IO) sector. Our results suggest that although it is difficult to attribute the trigger of the recent consecutive pIODs, climate change is increasing the occurrences of such events. Citation: Cai, W., A. Sullivan, and T. Cowan (2009), Climate change contributes to more frequent consecutive positive Indian Ocean Dipole events, Geophys. Res. Lett., 36, L23704, doi:10.1029/2009GL040163.