The results show that, when the wind shear of basic flow is not zero, there exists continuous spectrum of gravitational inertial wave and vortex wave.

This paper discusses the stability of internal inertial gravity wave in the heterogeneous stratified atmosphere when basic flow appears to be weak vertical shear by the WKB method.

The well-known phase speed formulas of surface inertial gravity wave and internal shear inertial gravity wave are the special cases of this frequency equation.