Quasi-biennial oscillation

From Glossary of Meteorology

quasi-biennial oscillation

An oscillation in the zonal winds of the equatorial stratosphere having a period that fluctuates between about 24 and 30 months.

This oscillation is a manifestation of a downward propagation of winds with alternating sign. This phenomenon is sometimes referred to as the stratospheric quasi-biennial oscillation to distinguish it from other atmospheric features that also have spectral peaks near two years.