Record Negative Antarctic Oscillation Developing

Strongest August High Latitude High Pressure Blocking pattern on Record for August in Southern Hemisphere?

Fig. 1: The 15-day AAO forecast using all models indicates a sharp negative phase which could produce the strongest –AAO on record for the month of August.

Discussion: Evolution of a super high latitude/high pressure blocking pattern is forecast to develop this weekend and next week in the southern hemisphere. The result is a negative Antarctic oscillation (-AAO) which goes “off the charts” to values near -6 according to some forecast models (Fig. 1). The all-time strongest –AAO for August occurred in 1981 (-2.118). The blocking high pressure is centered over Australia to well southwest of South America in the 6-10 day period (Fig. 2) and amplifies in that position in the 11-15 day period (Fig. 3). The most affected land masses in the southern hemisphere due to this climate regime is Argentina when another chilly outbreak occurs in the 11-15 day period preceded by heavy rains in northern Argentina while a vigorous storm track stays just south of Australia while the continent turns quite warm as mid-August approaches. Strong blocking patterns are produced by Rossby Waves transporting tropical heat pole ward at high altitude into the polar region or sunspot activity.

Fig. 2-3: The GFS ENS identifies a 4 long wave trough pattern caused by strong high latitude blocking in the 6-10 day period. The blocking high in the polar region remains in the 11-15 day period.