The yearly wave in pressure and zonal geostrophic wind at sea level on the southern hemisphere and its interannual variability

The yearly wave (first harmonic) in the sea level mean pressure on the southern hemisphere is largest at 30° S over and near the three continents, where it also explains most of the mean annual variance. In middle and high latitudes, the half-yearly wave dominates so that even in the Antarctic the yearly wave is mostly secondary. In single years, the amplitude of the yearly wave south of 40° S may be large, but as the phase varies widely from one year to another, the mean wave becomes small.

The yearly wave in the mean zonal geostrophic wind at sea level is largest in the tropics and subtropics. Like the pressure wave, it is second to the half-yearly wave over most of middle and high southern latitudes. The phase of the yearly wave appears in four concentric belts as follows: maximum westerlies/minimum easterlies in summer in the tropics outside the eastern Pacific Ocean; maximum westerlies/minimum easterlies in winter in the subtropics; maximum westerlies in summer in the latitudes round 50° S (unlike the northern hemisphere); and maximum westerlies/minimum easterlies in winter over most of the area covered by sea ice. Just as the pressure wave, the yearly wave in the zonal wind has a large interannual variation.