When meteor-generated plasma trails diffuse into the ionosphere they create large ambipolar electric fields mainly perpendicular to the Earth's geomagnetic field (B) and extending many kilometers from the trail along B. These fields will cause ionospheric plasma to collect into ridges extending from the trail along B, enhancing the density by as much as a factor of 2, and they will also remove up to 90% of the plasma on each side of the ridge. We predict that meteor-induced density perturbations may fill as much as 20% of the ionosphere between 95 and 120 km altitude. This paper presents simulations and theory to show how meteors produce plasma ridges and troughs. We estimate the extent of these as a function of altitude and meteor density. This process may explain observations of extensive nighttime E-region density structures made by rockets and radars.