Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years

Mark A. Cane [mcane@ldeo.columbia.edu], Lamont-Doherty Earth Observatory of Columbia University; Amy Clement, Rosensteil School of Marine and Atmospheric Sciences; and Michael E. Mann, University of Virginia, Charlottesville

We investigate the response of El Niño to natural external radiative forcing changes over the past 1000 years based on numerical experiments employing the Zebiak and Cane (1987) intermediate model of the tropical Pacific coupled ocean-atmosphere system. Previously published empirical results (Adams et al, 2003) demonstrating a statistically significant tendency towards El Niño conditions in response to past volcanic radiative forcing are reproduced in the model experiments. A combination of responses to past changes in volcanic and solar radiative forcing closely reproduces changes in the mean state and interannual variability in El Niño in past centuries recorded in fossil corals. We find that the eastern equatorial Pacific becomes cold (warm) when the mean global temperature becomes warm (cold). We present evidence for a connection between the state of the tropical Pacific and drought in the western US.