Rayleigh/Raman lidar observations of gravity wave activity from 15 to 70 km altitude over Syowa (69°S, 40°E), the Antarctic

The potential energy of gravity waves (GWs) per unit mass (E_p), at altitudes of 15-70 km, has been examined from temperature profiles obtained by a Rayleigh/Raman lidar at Syowa Station (69°S, 40°E) from May 2011 to October 2013, with the exception of the summer months. The GWs with ground-based wave periods longer than 2 h and vertical wavelengths between 1.8 and 16 km were extracted from the temperature profiles. E_p was larger in winter than in spring and fall, although in 2012, at altitudes below 30 km, E_p was larger in spring than in winter and fall. E_p increased with a mean scale height of 11.3 km. E_p profiles showed a local maximum at an altitude of 20 km and a minimum at 25 km in almost every month, which has not been reported by previous studies observed by radiosondes. The values of E_p in October of 2012 were smaller at 35-60 km and larger at 20-35 km than those in October of 2011 and 2013. This difference in the E_p profile is most probably caused by different seasonal variations of zonal winds. The larger and smaller E_p values seem to be observed both below and above the altitude at which the zonal wind speed reached 0 m s^-1. This result suggests that wind filtering of gravity waves with small phase speeds is significantly important in early spring.