The effect of a dielectric barrier discharge at an increased power level on the structure of a two-dimensional subsonic boundary layer is studied. It is shown that the formation of high-current stationary filaments in the discharge plasma (constriction) leads to the appearance of pairs of counter-rotating longitudinal vortices associated with each filament. The momentum transfer in these vortices causes the formation of longitudinal streaks in the boundary layer downstream of the actuator. With sufficient depth of velocity modulation in these structures, low velocity streaks become unstable with respect to high-frequency perturbations. Amplification and breakdown of the secondary disturbances finally leads to the transition of the boundary layer to a turbulent state. (C) 2017 Elsevier Ltd. Alt rights reserved.