Previous studies have shown that forcing a low Reynolds number, confined 2-D wake may lead to greatly enhanced molecular mixing. This study presents whole-field measurements of the velocity and vorticity fields in such a flow in order to examine its underlying flow structure and the features connected to mixing enhancement. The variation of the spanwise vorticity field versus forcing amplitude is presented. Results show that the downstream location where the magnitude of the mean velocity gradient dw/dz starts to increase coincides closely with the location where mixing has been noted to increase. The downstream evolution of the streamwise vorticity ωx shows that the high amplitude forcing cases corresponding to significant mixing enhancement are characterized by large values of ωx. For these cases, the regions of ωx move quickly away from the facility sidewalls towards the center-span of the test section. In contrast, these regions remain close to the sidewalls in the low amplitude forcing conditions which result in a modest mixing increase.