Abstract
Rocket wind soundings for several stations within 10° latitude of the equator are used to analyze details of the structure of the recently discovered semi-annual wind variation in the equatorial upper stratosphere. The cycle is characterized by winter and summer easterlies and equinoctial westerlies and in 1966 appeared to have maximum amplitude at 45–50 km. Its global extent is confirmed with the aid of rocket data from widely separated longitudes. The semi-annual variation is discussed in relation to the quasi-biennial oscillation, which has maximum amplitude in the lower stratosphere. A possible explanation of the origin of the semi-annual variation is mentioned and attention is called to semi-annual variations in other parameters in the upper atmosphere.
