Modelling past changes in the El Nino/Southern Oscialltion

Paleoclimate modelling: There are a number of paleoclimate proxies from the tropical Pacific that show that the El Nino/Southern Oscillation (ENSO) has evolved over the late Holocene (10,000 years ago to the present). These data can be compared with model results that can help reveal the causes of these changes. The figure shows an example: The black line shows the number of warm ENSO events per 100 years from data published in Moy et al. (2002) from an Ecuadorian lake record. Warm ENSO events are defined as light colored strata in the sediment record, which Moy et al. argue reflect pluvial episodes during large (warm) El Nino events. The green lines show an ensemble of seven simulations with the Zebiak-Cane model with the solar forcing of the last 12,000 years imposed (Clement et al. 2001). The blue line is the ensemble mean. Warm ENSO events are defined in the model as years in which the DJF NINO3 anomaly exceeds 3 K. This event index corresponds to the middle of the rainy season in coastal South American during which large SST anomalies associated with ENSO events are capable of causing the ITCZ to move equatorward and bring large precipitation anomalies to the region. Contact: Amy Clement