In a recent article, Jiang et al. (2004) analyzed the northward propagations of the tropical convergence zone during the boreal summer monsoon and proposed a simple theory to explain the scale selection of the propagations. Here, we argue that this mechanism of scale selection relies on the choice of two parameters whose values are not justified in their paper. Furthermore, it appears that the effects of the variation of the Coriolis parameter with latitude Can nort be neglected