Since January 2002, the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument has performed continuous measurements from near the tropopause into the thermosphere. For the time period 29 January 2002--31 January 2006, we spectrally analyzed time series of weekly zonal root mean square gravity wave (GW) amplitudes for systematic intra-annual, annual and inter-annual GW activity. GWs considered have horizontal wavelengths between 100 km and zonal wave number 6 and vertical wavelengths between 5--30 km. Height-latitude cross sections of spectral amplitudes and phases between 20--100 km and 550S--550N show several relevant oscillations. A strong semiannual variation is evident in the high-latitude upper stratosphere/mesosphere. Annual components reveal two isolated maxima at mid-latitudes in both hemispheres, associated with the winter polar vortices, and summertime maxima in the subtropics. Biennial amplitudes in the equatorial stratosphere coincide with the descending westerly shear phase and can be attributed to the quasi-biennial oscillation.