The nonlinear coupling between inertial and Rossby waves is considered accounting for the action of the low‐frequency nonlinear force associated with the inertial waves. It is found that this interaction is governed by a pair of equations, which can be useful for studying the modulational instability of a constant amplitude inertial wave as well as the dynamics of nonlinearly coupled inertial and Rossby waves. ©1995 American Institute of Physics.