  We present an experimental study on the effect of a electromagneticaly
generated vortex flow on parametrically amplified waves at the surface of a
fluid. The underlying vortex flow, generated by a periodic Lorentz force,
creates spatio-temporal fluctuations that interact nonlinearly with the
standing surface waves. We characterize the bifurcation diagram and measure the
power spectrum density (PSD) of the local surface wave amplitude. We show that
the parametric instability threshold increases with increasing intensity of the
vortex flow.
