CLIMATE VARIABILITY: EXTERNALLY DRIVEN CHAOS

Self-sustained models related with generating three dimensional dynamical systems results to multi equilibria, periodic, quasiperiodic and chaotic trajectories, with no external forcing mechanism. The simpler models just show the results without the direct connections with the natural events. In nature there are number of systems that can be governed by the external forces. These forces itself relates with many other parameters and some time they are internal and some time it may be external. So there must be corresponding modification in the model. The existence of the forces may not be at a time but they vary with time factors. In atmospheric model the Coriolis force is added. This addition makes geostrophic balance at mid latitudes closer to the real characteristics. Hadley circulation suggests at bigger scale atmospheric circulation gives high rise of air at equator (Burroughs, W. J. (2001)). The circulation is at basic states ‘zonally asymmetric'. Strong transient disturbance converts into storms which produces randomness that disturbs the zonal patterns. The atmospheric nature has considerable external factors in the daily and yearly periodicity. In a chaotic system a very small periodicity may give rise of massive and remarkable effects. The external forcing factor must have sufficiently larger amplitude that drives the model to overcome from the potential barrier that barrier between the two equilibria. If the amplitude of the periodic forcing external factors that the driving force then the system will cross the barrier between different attractors. Human activities also add to the climate as an external factor and are different in different time scale. The oceanic thermoheline circulation is because of temperature and also the salt content in the water, adding them to model of an ocean will range to the Tropics to higher latitudes. Mainly it is found that the surface water is denser than the bottommost and there is the formation of convection current which will contribute to the effect on temperature, and hence in climate variation