LONGITUDINAL VARIABILITY OF THE MESOPAUSE SAO

A longitudinal variation in the mesopause semi-annual oscillation (SAG ) is documented from wind observations made by the High Resolution Dop pler Imager satellite instrument. The asymmetry is dominated by a wave number 1 pattern with a variable phase. During the easterly phase of t he mesopause SAO (equinoxes), maximum tropical easterlies occur over e astern South America and the Atlantic Ocean in the longitude band 300 degrees-360 degrees. During the westerly phase (solstices), the wester ly winds descend more rapidly and are larger below similar to 80 km in this same (Atlantic) longitude band. To the best that can be determin ed with sparse data, the longitudinal asymmetries near the stratopause are weak and are in phase with those in the mesosphere.