Mean meridional winds estimated from constant level balloon flights in Southern Hemisphere temperate latitudes

Abstract

Temporal and longitudinal variations in mean meridional wind are estimated from GHOST and EOLE constant level balloon flights at 100 and 200 mb in south temperate latitudes during the period 1966/72. At these latitudes there is evidence of about a 0.3 m s−1 poleward flow in winter-spring and equatorward flow in summer-autumn, with the oscillation at 100 mb preceding that at 200 mb by 1 to 2 months. This annual oscillation may reflect a direct circulation between summer and winter hemispheres. At 200 mb in south temperate latitudes there is also evidence for about a 0.1 m s−1 poleward flow during the west wind phase, and equatorward flow during the east wind phase, of the quasi-biennial zonal wind oscillation in the low tropical stratosphere. The significance of this relation has not yet been ascertained. The overall mean equatorward drift of 0.04 m s−1 points up the existence of the Ferrel Cell in the long-term average. A breakdown of the data by longitude shows that the annual variation in zonal-average meridional wind is due to large seasonal variations in meridional wind over the South Atlantic.