Observation of gravity waves in the high-latitude F-layer by using fixed frequency sounding

Abstract

Fixed frequency soundings at 4.2 MHz frequency were carried out at Sodankylä (67°22′N, 26°38′E) using aerials with a northward tilted antenna pattern. The second-order echo in virtual height versus time recording occasionally shows a peculiar sawtooth behaviour. Model calculations indicate that the phenomenon can be explained by medium-scale gravity waves in the F-layer. The period of the gravity wave can be reduced most accurately from the second-order trace, and it is possible to make a distinction between the poleward and the equatorward propagation of the disturbance. The measured periods vary from 15 to 65 min. In the daytime, when the measurement is possible, the propagation is invariably equatorwards. The phenomenon is only observable during the winter months. It does not seem to have any correlation with magnetic activity.