A NUMERICAL STUDY OF WAVE-NUMBER SELECTION IN THE BAROCLINIC ANNULUS FLOW SYSTEM

An investigation is made of the wavenumber selection of baroclinic dis turbances in the rotating, differentially heated annulus flow system w ith a three-dimensional fully nonlinear high resolution model. Along t he constant thermal contrast of 10-degrees-C that traverses the nondim ensional parameter space defined by the laboratory experiments of Pfef fer et al. (1980b), a series of numerical experiments with a quiescent -start initial condition is conducted to explore the equilibrated flow regimes as a function of the rotation rate of the annulus. The wavenu mber selections in the regular wave regime are robust in the sense tha t the time required for the dominant wavenumber to emerge is short, an d the wavenumber selected tends to persist over a relatively wide regi on of parameter space. In contrast, the wavenumber selections in waven umber transition regions are characterized by one or more of the follo wing behaviors: two-stage equilibration, side-banded wave dispersion, and irregular wavenumber selection as a function of the external param eter (here, rotation rate). Wavenumber selection in the wavenumber tra nsition regions is highly sensitive to physical and numerical paramete rs and is only statistically predictable. In a set of incremental-star t experiments, it is shown that hysteresis effects prevail inside and near the wavenumber transition regions.