Coexisting Turbulent Climate Attractors in a Two-Layer Quasigeostrophic Model

Abstract

An intriguing manifestation of the underlying nonlinear fluid dynamic character of the atmosphere is found in an idealized quasigeostrophic 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 still possessing vigorous synoptic transient behavior but more characterized by lower-frequency transient activity. Both of these dynamical states are strongly turbulent, with well-developed inertial ranges in their energy cascades, and transient kinetic energy on the same order as the kinetic energy of the time mean flow. This suggests the existence of multiple underlying turbulent strange attractors for the system. The climates of these states differ substantially, with the turbulent attractor with reduced synoptic transients having a zonal mean meridional temperature gradient substantially larger than the other climate attractor. This result suggests that turbulent behavior is not equivalent to uniqueness in atmospheric-like dynamical systems.