We have carried out numerical simulations of the thermospheric response to the morningside intense diffuse aurora, using a three-dimensional (3-D), nonhydrostatic, composition-dependent, regional-scale, high-resolution numerical model. A diffuse aurora is represented in the model by its equivalent 3-D features of ion drag and joule heating. The diffuse aurora propagates westward within the model grid, which is fixed in the terrestrial frame. Our numerical results show that the neutral atmospheric response to the diffuse aurora is much weaker in a 3-D simulation than in a two-dimensional (2-D) simulation. For example, the predicted zonal flow is weaker by a factor of roughly 2. The fidelity of the 3-D results is supported by a recent study (Brinkman et al., 1995) in which zonal winds predicted from a 2-D model were shown to be larger than observations by a factor of 2. Our numerical results also show that the inertial gravity waves that are generated in the 3-D flow control the energy dissipation and reduce the dynamical response in the source region. These waves propagate in both the north-south and east-west directions. However, the longitudinal propagation rate is relatively small compared to the latitudinal propagation rate. The simulated westward drift of the diffuse aurora creates a distinct displacement of the propagating disturbances, which further reduces the dynamical response in the source region. The study described here underscores the importance of 3-D high-resolution treatments of upper atmospheric physics to analyze and interpret dynamical, compositional, and electrodynamic observations in this region. ¿ American Geophysical Union 1995