Gravity wave activity in the lower ionosphere and in the F2 region - Similarities and differences

The gravity wave activity (T similar to 10 min-3 hours) is inferred from the continuous digital nighttime LF radio wave absorption measurements in the lower ionosphere and from ionosonde measurements (from rapid sequence measurements) in the F-region. All measurements have been performed at the Pruhonice Observatory (similar to 50 degrees N, 15 degrees E). During solar proton events we observe a simultaneous and similar change of the gravity wave activity at both ionospheric levels (an increase of activity at shorter periods), which very probably indicates the important role of high latitudinal ionospheric/thermospheric source of gravity waves. Also spread-F conditions are associated with simultaneous changes of gravity wave activity in both regions.