Evidence for thermospheric gravity waves in the southern polar cap from ground-based vertical velocity and photometric observations

Zenith-directed Fabry-Perot Spectrometer (FPS) and 3-Field Photometer (3FP) observations of the lambda 630 nm emission (similar to 240 km altitude) we re obtained at Davis station, Antarctica, during the austral winter of 1999 . Eleven nights of suitable data were searched for significant periodicitie s common to vertical winds from the FPS and photometric variations from the 3FP. Three wave-like events were found, each of around one or more hours i n duration, with periods around 15 minutes, vertical velocity amplitudes ne ar 60 ms(-1), horizontal phase velocities around 300 m s(-1), and horizonta l wavelengths from 240 to 400 km. These characteristics appear consistent w ith polar cap gravity waves seen by other workers, and we conclude this is a likely interpretation of our data. Assuming a source height near 125 km a ltitude, we determine the approximate source location by calculating back a long the wave trajectory using the gravity wave property relating angle of ascent and frequency. The wave sources appear to be in the vicinity of the poleward border of the auroral oval. at magnetic local times up to 5 hours before local magnetic midnight.