A Comparison of the Relationship between the Southern Oscillation Index and Extended Tropical Precipitation in Coupled Global Climate Models.

The interannual variability of the Southern Oscillation Index (SOI), its relationship with precipitation, and how greenhouse gas-induced changes in climate may modify these relationships has been examined in 12 coupled atmosphere-ocean Global Climate Model (GCM) experiments. The model SOI series constructed for the different GCMs show opposing trends in both the future SOI mean state and future SOI interannual variability. EOF analyses of the dominant mode of precipitation reveals that most models display the main observed features of precipitation related to ENSO. Only modest changes in the modelled EOF1 coefficient fields between the periods 1900-1949 and 2050-2099 are found. The model EOF1 amplitude series in general correlate highly with the model SOI series for the 1900-1949 period. This reflects the strong negative relationship between the SOI and ENSO-like precipitation that is found in observational data. However, for the future 2050-2099 period this correlation decreases in a number of the simulations.