The Signature of a Blocking Episode on the General Circulation in the Southern Hemisphere

Two major blocking events took place over the South Pacific Ocean east of New Zealand, 23 July-4 August and 19–27 August 1979. The configuration of the overall flow, including the split in the westerlies, the location of the blocking highs, and the wavenumber breakdown were very similar. The tendency for blocking highs to reform in the same location in close sequence is referred to as a blocking episode. The blocking events are analyzed in detail and the imprint they left on the general circulation statistics for the winter as a whole are presented. Since the blocking episode mostly prevented eddies from moving through the region, the variance of meridional velocity is small. Nevertheless, owing to the sequence of blocks the variance of geopotential height is a maximum. This signature on the general circulation is in marked contrast to that in storm track regions where the variance of geopotential height and meridional wind are both a maximum. A global-scale redistribution of mass was associated with the blocking episode.