We present numerical calculations of the generation, growth and impingement of a thermal plume in a two-dimensional buoyancy induced flow. Numerical values are obtained for the aspect ratios H/W = 1/4, 3/8, 1/2, the Grashof numbers Gr = 10(4), 10(5), and the Prandtl number Pr = 170. Impingement heat transfer on the upper wall is evaluated at various times. Numerical results show that before a thermal plume impinges on the upper heated wall, the thermal conduction layer, which is the stable stratification, near the upper wall becomes thinner and the local heat transfer peaks. The local Nusselt number approaches the steady condition after the impingement of a thermal plume. Additionally, under certain conditions the stream function takes a symmetrical form of two ellipses. (C) 2003 Elsevier Science Ltd. All rights reserved.