Intense convective systems were simulated for the period 19-27 December 1992, over the TOGA COARE Intensive Flux Array (IFA), making use of a cloud resolving two-dimensional model (ARPS), in order to investigate where the boundary layer air mass was detrained from convective systems over tropical oceans. Inert Euler tracers originating in the surface boundary layer were used to evaluate the detrainment amounts from the convective systems. Two peak detrainment amounts of the tracer were found around the 200 hPa, and 600 hPa levels. The 200 hPa level corresponded to the top heights of the most intense clouds. Sensitivity tests demonstrated that the detrainment peaks at the 600 hPa level were controlled by horizontal vorticity developed at the same level. The horizontal vorticity was enhanced by both the stable layers around 500 hPa, which were often observed during the period of simulation, and the melting process from ice to water.