The main topic of this paper is the analysis of momentum and heat transfer mechanisms occurring inside a disturbed boundary layer. This analysis is carried out based on a phenomenological decomposition using von Karman's integral equations, in which appear terms that account for several contributions: the flat plate term, and the unsteady and external gradient terms. This method is applied to the interaction between a single transverse vortex and a boundary layer developing on a flat plate. Based on numerical simulations, we present a qualitative and quantitative study of the behavior of momentum and heat wall transfer described by the terms resulting from the phenomenological decomposition. Finally, the time-dependent behavior of the analogy factor is investigated. (C) 2003 Elsevier Science Ltd. All rights reserved.