Characterisation of Chaotic Regimes and Transitions in a Thermally-Driven, Rotating Stratified Fluid

Abstract

The transitions from regular, steady or periodic baroclinic waves to aperiodic, chaotic flow in a thermally-driven, rotating fluid annulus are discussed. Two distinct transitions are found, depending mainly on the value of the thermal Rossby number Θ. At moderate Θ a transition to chaos occurs via a doubly-periodic ‘amplitude vacillation’ which develops a very low frequency irregular modulation. The transition towards classical ‘geostrophic turbulence’ at low Θ occurs at a well-defined point in parameter space, apparently via an intermittent ‘structural vacillation’. Emphasis is placed on the characterisation of the transitions and chaotic states from phase portraits constructed using singular value decomposition methods.