DNS of structural vacillation in the transition to geostrophic turbulence

Abstract

The onset of small-scale fluctuations around a steady convection pattern in a rotating baroclinic annulus filled with air is investigated using Direct Numerical Simulation. In previous laboratory experiments of baroclinic waves, such fluctuations have been associated with a flow regime termed Structural Vacillation which is regarded as the first step in the transition to fully-developed geostrophic turbulence. In the present work, we find the emergence of a new steady wave solution with complex radial structure, associated with a change in the balance of forces to a centrifugally-dominated regime, followed (at high rotation rate) by a further transition to a form of structural vacillation associated with regular m = 3 eddies driven by centrifugal buoyancy.