PHYSICAL MATHEMATICS SEMINAR

TOPIC:	SIMULATED CHANGES IN THE EL NIŅO SOUTHERN 	
	OSCILLATION (ENSO) FROM THE LAST ICE AGE TO TODAY


SPEAKER: 	ANDREW B.G. BUSH
		Department of Earth & Atmospheric Sciences
		University of Alberta, Canada

ABSTRACT:

The El Niņo Southern Oscillation (ENSO) is a dominant mode of temporal 
variability in the coupled atmosphere-ocean system. It induces global 
temperature and precipitation anomalies that affect global food production, 
disease spread, and wildfire activity. Although the coupled dynamics 
underlying ENSO are relatively well understood, there have been observed 
changes in ENSO frequency and amplitude over the Earth's recent past that 
remain unexplained yet are crucial to long-term predictions of ENSO in any 
global change scenario. 

A sequence of numerical simulations is performed with a coupled 
atmosphere-ocean general circulation model configured for various times in 
Earth's recent past in order to better understand the dynamic factors that 
control ENSO period and intensity.  

From the last Ice Age (approximately 21,000 years ago) to today, 
simulations suggest that ENSO events increased in amplitude and decreased 
in frequency. An additional simulation with doubled atmospheric carbon 
dioxide indicates that this trend continues in a warmer climate. A comparison 
to linear stability analyses of the coupled atmosphere-ocean system reveals 
that such changes in ENSO are entirely consistent with the simulated changes 
in strength of the climatological easterly trade winds over the tropical Pacific 
Ocean. We therefore discuss the dynamic and thermodynamic mechanisms 
that regulate trade wind speed and how these mechanisms were likely different 
in the Earth's past. Finally, we discuss the numerical results in the context of 
observational data and of the numerical methods that are used to solve the 
dynamic and thermodynamic equations.

TUESDAY, APRIL 13, 2004
2:30 pm
Building 2, Room 338

Refreshments will be served at 3:30 PM in Room 2-349


Massachusetts Institute of Technology, Department of Mathematics
Cambridge, MA  02139