Coexisting chaotic climate attractors in a two-layer quasi-geostrophic model

An intriguing manifestation of the underlying nonlinear fluid dynamic character of the atmosphere is found in a simple quasi-geostrophic model of the troposphere. For identical forcing and dissipation, the model’s climate is found to depend sensitively upon the choice of initial conditions, tending either toward a state resembling the current Northern Hemisphere wintertime circulation, characterized by significant mobile synoptic-scale transient disturbance activity, or a circulation characterized primarily by weak quasi-stationary (non-propagating) transient activity. Both of these dynamical states evolve chaotically, suggesting the existence of multiple underlying strange attractors for the system. The climates of these states differ substantially, with the synoptic transient dominated state having a zonal mean meridional temperature gradient 25 % smaller than that of the quasi-stationary transient dominated state. This result raises the possibility that the atmosphere may possess the ability to jump into quite different globe-encompassing states of operation.