It has widely been presumed that most horizontal divergence in Earth's thermospheric wind field results from pressure gradients established by localized heating. A simplified local-scale, three-dimensional, time-dependent, finite element model has been used to determine other possible sources of horizontal divergence over spatial scales of less than 200 km. In a limited study to test the hypothesis that inertial processes contribute to the generation of horizontal divergence, a non-divergent, time-varying ion convection pattern was used to deposit momentum. Divergent neutral winds resulted. Divergence was induced by both localized heating and time varying momentum deposition. Further, for the geometries considered, thermal expansion resulting from heating was the dominant driver of the horizontal gradient perpendicular to the background flow, whereas inertial processes dominated the horizontal gradient parallel to the background flow.