The modeling of ionospheric plasma density irregularities (ΔN/N) is a necessary first step towards forecasting ionospheric scintillation effects. This modeling challenge is difficult not only because the linear-nonlinear saturation levels of instabilities are not completely understood but also because ΔN/N often evolves on time scales which are long compared to the characteristic time constants of the instability drivers. In this study, the linear 1-D gradient drift instability (GDI) is used in a high latitude simulation of ΔN/N evolution. For the first time snapshots (maps) of ΔN/N are presented demonstrating that it is possible to use a physical model simulation of the ionosphere coupled with a time dependent convection electric field to simulate meso-scale irregularities. It is found that to evaluate the density irregularity in any given location, it is not sufficient to know the instantaneous growth rate; it is necessary to follow the history of the plasma along the convection streamlines. ¿ 2000 American Geophysical Union