WAVE INTERACTIONS AND BAROCLINIC CHAOS - A PARADIGM FOR LONG TIMESCALE VARIABILITY IN PLANETARY-ATMOSPHERES

Baroclinic instability is the principal mode of non-axisymmetric flow in the large-scale atmospheric circulation at mid-latitudes, and is re sponsible for oganising the structure and behaviour of major weather s ystems. This instability can also be fruitfully studied in the laborat ory under controlled conditions. In this paper, we review recent work carried out by the authors and collaborators on various routes to chao tic behaviour in rotating, stratified flows. Results include the disco very of new multi-mode regimes in which small ensembles of baroclinic waves interact in a nonlinear mode competition with the thermally-driv en axisymmetric component of the Bow, generating chaotic oscillatory v ariability on very long timescales. We discuss various attempts to cap ture this type of behaviour in simple models, and consider the signifi cance of the phenomenon as a paradigm for understanding the nature of long timescale variability in the climates of the Earth and Mars. (C) 1998 Elsevier Science Ltd. All rights reserved.