MEMORY-INDUCED LOW-FREQUENCY OSCILLATIONS IN CLOSED CONVECTION BOXES

The origin of the low frequency oscillation of the large-scale, recirc ulating how specific to the high Rayleigh number regime in closed conv ection cells is investigated. It is shown how the oscillations result from the delayed coupling of the boundary layer instabilities by the s low convective motion of the recirculation. The model developed explai ns (i) the form of the dependence of the oscillation frequency with th e Rayleigh number f similar to Ra-gamma, including the prefactor, the ''anomalous'' value of the exponent gamma approximate to 0.49, and (ii ) the opposition of phase of the oscillations between the tap and bott om boundary layers.