The recent paper by Patterson and Imberger [1], which analysed the transient phase of natural convection in low aspect ratio cavities, gave a criterion for the presence of an oscillatory approach to steady state in such flows. However, the experiments of Yewell et al. [3] displayed no evidence of this oscillatory approach, even though the criterion was apparently satisfied. In this paper, it is shown that since the flow regimes are described by a series of critical Rayleigh numbers, the ordering of which changes with changing aspect ratio, a criterion for the existence of transient internal waves, valid for all orderings, may be established. Further, the results of [1] are extended by means of flow descriptions valid for two additional orderings. Consequently, it is shown that the experiments addressed a transient flow regime in which internal wave activity would not be expected and that the experimental results are in support of the scaling analysis of [1].

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