A note on the variation with height of the quasi-biennial oscillation

Abstract

Mean-monthly zonal winds obtained from rocketsondes are examined from the point of view of the quasi-biennial oscillation. These data indicate that, between heights of 60 and 25 km, the quasi-biennial west wind maximum propagates downward at a speed of about 2 km/month in tropical latitudes and about 5 km/month in temperate latitudes. Accordingly, the quasi-biennial zonal wind oscillations of temperate and tropical latitudes appear to be in phase at heights near 25 km and out of phase at heights near 60 km. The amplitude of the quasi-biennial zonal wind oscillation has a maximum at a height of 25 to 30 km in tropical latitudes and decreases to a quite small value at 60 km. In temperate latitudes, however, there is evidence for an increase in amplitude with height so that, above 55 km, the quasi-biennial zonal wind oscillation appears to be larger in temperate latitudes than in tropical latitudes. In both temperate and tropical latitudes the amplitude ratio of the quasi-biennial and annual zonal wind oscillation decreases with height, attaining a value of about 0.1 at 60 km. The more doubtful Umkehr-ozone data suggest that, between heights of 50 and 25 km, the quasi-biennial ozone maximum propagates downward at a speed of about 4 km/month in temperate latitudes. Contrary to the wind results, the amplitude ratio of the quasi-biennial and annual ozone oscillation is twice as great at 50 km as at 25 km. Over these same height intervals there is the implication that, in temperate latitudes, the quasi-biennial west wind maximum precedes the quasi-biennial ozone maximum by 4 to 5 months.