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Figure 5.5 (a) Simple
upper-tropospheric/lower-
stratospheric circulation
model over Antarctica.
(b) Representative wind
directions at four altitudes
over Antarctica. (After King, J.
and Turner, J. 1997 , with
permission Cambridge
University Press)
meridional temperature gradient reverses between 200 and 300 hPa, defining the
location of the seasonally weaker polar front jet stream (28m s 1 ) near 558 S.
The East Antarctic Plateau anchors the upper tropospheric and lower strato-
spheric circumpolar circulation, and strongly influences the standing and
transient waves in the circumpolar westerlies; an influence that extends well
into the mid-latitudes (see Section 4.6 ). King and Turner ( 1997 ) state that, in
comparison to the Arctic, the standing waves in the Southern Hemisphere are
more barotropic in structure, and transport less moisture and heat. Therefore the
transient waves and eddies become very important to the energy and moisture
transport process. Simmonds ( 1998 ) emphasizes that knowledge about how this
influence operates is incomplete and unclear, and a matter of some debate.
5.4 Surface pressure variations
Figure 5.6 , based on NCEP/NCAR reanalysis (see Section 4.3 ) over a 12-year
period by Simmonds ( 1998 ), establishes a clear pattern of low pressure (below
990 hPa except over the Antarctic Peninsula) around the continent edges, the
circumpolar trough (CPT). Figure 5.6 shows that there are three centers of lower
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