THERMOSPHERIC RESPONSE TO MORNINGSIDE DIFFUSE AURORA - HIGH-RESOLUTION 3-DIMENSIONAL SIMULATIONS

We have carried out numerical simulations of the thermospheric respons e to the morningside intense diffuse aurora, using a three-dimensional (3-D), nonhydrostatic, composition-dependent, regional-scale, high-re solution numerical model. A diffuse aurora is represented in the model by its equivalent 3-D features of ion drag and joule heating. The dif fuse 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 sim ulation than in a two-dimensional (2-D) simulation. For example, the p redicted zonal flow is weaker by a factor of roughly 2. The fidelity o f the 3-D results is supported by a recent study (Brinkman et al., 199 5) in which zonal winds predicted from a 2-D model were shown to be la rger than observations by a factor of 2. Our numerical results also sh ow that the inertial gravity waves that are generated in the 3-D flow control the energy dissipation and reduce the dynamical response in th e source region. These waves propagate in both the north-south and eas t-west directions. However, the longitudinal propagation rate is relat ively small compared to the latitudinal propagation rate. The simulate d 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 th e importance of 3-D high-resolution treatments of upper atmospheric ph ysics to analyze and interpret dynamical, compositional, and electrody namic observations in this region.