Finding gravity wave source positions using the Super Dual Auroral Radar Network

Through the groundscatter process the Super Dual Auroral Radar (Super-DARN) has become a powerful tool for studying F region gravity waves. However, the measurement of the gravity wave position is not direct and relies on an assumption relating ground scatter distance to reflection distance. In previous studies it has been assumed that the tilting of the ionospheric reflecting layer was negligible. Hence the gravity wave distance has been calculated as if the reflecting layer was strictly horizontal. Using virtual height data from an ionosonde and ray tracing; we show that this assumption leads to a systematic error of about 16% in the positioning of the ionospheric reflection point, with the error more than 30% on occasion. Using ray tracing, we obtained an improved relation between ionospheric reflection and ground scatter distances. With this improved distance calculation, we have found the direction and velocity for a number of gravity waves. These waves were found to be traveling equatorward, usually, with velocities between 50 and 280 m/s, in agreement with previous gravity wave observations and with the notion of filtering by the thermospheric wind; In some cases the source locations were determined by using gravity wave dispersion. These locations were found to be on the poleward side of the auroral oval during periods of weak, but observable, magnetic disturbance. Our ray-tracing studies found that the strongest features were due to gravity waves of 3-20 km amplitude.