Towards an understanding of weak turbulence close to the convection threshold in large aspect ratio systems

We analyse the evolution of a turbulent transient observed in a numerical simulation in rectangular geometry at moderate Prandtl number on a simplified model of convection which includes the effects of drift flows. A particular process of drift flow convergence, compression of the rolls and dislocation nucleation is seen to play a repeated rôle. The non-relaxational behaviour observed seems to follow from a « dynamical frustration » due to a lack of compatibility between the drift flow and the overall curvature of the pattern, which could « explain » the occurrence of weak turbulence in extended geometry.