A formalism is developed for approximating tidal structures in a spherical, rotating, viscous atmosphere by equivalent gravity waves (EGW's) on an f plane. The frequency and zonal wave number of the EGW is chosen to match that of the simulated tidal mode. Then, for a given planar rotation rate f the meridional wave number of the EGW is determined by matching the vertial structure (equivalent depth) of the tidal mode in the absence of dissipation. Simulations are performed for the thermospheric extensions of the first two symmetric and antisymmetric semidiurnal tidal modes and compared to a full numerical treatment of the inseparable tidal equations in the thermosphere. Development of this technique forms the basis for investigation of a number of problems associatad with thermospheric tides which might overwise be precluded by computer limitations.