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, t he measurement of the gravity wave position is not direct and relies on an assumption relating ground scatter distance to reflection distance. In prev ious studies it has been assumed that the tilting of the ionospheric reflec ting layer was negligible. Hence the gravity wave distance has been calcula ted as if the reflecting layer was strictly horizontal. Using virtual heigh t data from an ionosonde and ray tracing; we show that this assumption lead s 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 traci ng, we obtained an improved relation between ionospheric reflection and gro und scatter distances. With this improved distance calculation, we have fou nd the direction and velocity for a number of gravity waves. These waves we re found to be traveling equatorward, usually, with velocities between 50 a nd 280 m/s, in agreement with previous gravity wave observations and with t he 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 o f weak, but observable, magnetic disturbance. Our ray-tracing studies found that the strongest features were due to gravity waves of 3-20 km amplitude .