Polar cap F region digital ionosonde height measurements occasionally show a type of height variation that we call a downward rippling variation because of its appearance. The variation typically extends over about 2 hours, and the overall height change is of the order of 100 km. We can simulate similar appearing height variations from vertical perturbations caused by gravity waves if the gravity waves have limited vertical wavelengths (a few hundred kilometers) and if there is high-speed convective flow. ¿ 1998 American Geophysical Union