A possible mechanism for the creation of strange nonchaotic attractors
close to the boundary of mode-locked tongues in a family of maps of t
he torus is described. This mechanism is based on the numerical observ
ation that there are parameter values on the boundary of the mode-lock
ed tongues at which the saddlenode bifurcation of invariant curves is
not smooth, and assumptions about the nature of intermittency just out
side the mode-locked tongues. (C) 1998 Elsevier Science B.V.