The Global Theoretical Ionospheric Model (GTIM) has been used to study a mechanism which generates F-region electron density enhancements known as boundary blobs. The model calculates the O+ density as a function of altitude, latitude, and local time. It includes the effects of production of ionization by solar extreme ultraviolet radiation and electron precipitation; loss through charge exchange with N2 and O2; and transport by diffusion, neutral winds, and ExB convection drifts. Using time-dependent convection patterns that previously were used to study polar cap patch formation, it was found that patches can be convected out of the polar cap and swept sunward by the dusk convection cell. The resulting structures have many of the features associated with boundary blobs: extended in local time and altitude, narrow in latitude, located in the return flow region of the aurora, and densities up to a factor of 8 over background. These results are the first quantitative, first principles verification and extension of the trajectory modeling of Robinson et al., (1985). ¿ American Geophysical Union 1996