Extended Abstract (852K)3.12
The dynamics of ENSO in a CGCM: Preliminary Results
Lynette Bettio, The University of Melbourne, Melbourne, Vic., Australia; and K. Walsh and S. Power
The term El Niņo is associated with large scale warming in the eastern tropical Pacific Ocean. These anomalous changes in sea surface temperature affect atmospheric circulation over a large part of the world. El Niņo-Southern Oscillation (ENSO) is the largest interannual climate signal and has been shown to be associated with various climate phenomena, for example, incidences of drought in northeastern Australia. An understanding of the dynamics of the ENSO phenomenon and improved representation of ENSO in climate models could lead to enhanced predictions, important for planning purposes.
This project uses data from a Coupled General Circulation Model (CGCM) from the Bureau of Meteorology Research Centre (BMRC). One of the main uses of such models is to better understand the complex role that ocean dynamics play in the initiation, maintenance and predictability of ENSO events. Model studies, combined with observational analyses, have led to the development of various physical paradigms that attempt to explain the cyclic nature of ENSO events. Two of the current leading paradigms for ENSO are the delayed action oscillator and the recharge-discharge oscillator. Both these paradigms theorize that interactions between the ocean and the atmosphere are at the heart of ENSO variability. The delayed oscillator paradigm involves a positive feedback between ocean temperatures and winds as well as the reflection of oceanic waves at the western boundary of the tropical Pacific Ocean. The recharge-discharge paradigm involves the recharge and discharge of equatorial heat content. Indices of ENSO in the BMRC CGCM are analyzed for their adherence to these theories. Initial results suggest that aspects of both these mechanisms are represented in the model. The analysis will be used to illustrate how increased understanding of the dynamics of an ENSO event in a coupled modeling system could lead to improved climate predictions of Australian rainfall.
Session 3, The Southern Hemisphere oceans and air-sea interactions I
Monday, 24 March 2003, 10:30 AM-3:00 PM
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