Geoscience Reference
In-Depth Information
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Figure 7.9
The mean sea-level pressure distribution (mb) in
January and July for the northern hemisphere, 1970 to 1999.
Source
: NCEP/NCAR Reanalysis Data from the NOAA-CIRES
Climate Diagnostics Center.
Figure 7.10
The mean sea-level pressure distribution (mb) in
January and July for the southern hemisphere, 1970 to 1999.
Isobars not plotted over the Antarctic ice sheet.
Source
: NCEP/NCAR Reanalysis Data from the NOAA-CIRES
Climate Diagnostics Center.
massif and the Himalayas. Over Antarctica, it is mean-
ingless to speak of sea-level pressure but, on average,
there is high pressure over the 3 to 4-km-high eastern
Antarctic plateau.
The mean circulation in the southern hemisphere is
much more zonal at both 700 mb and sea-level than in
the northern hemisphere, due to the limited area and
effect of landmasses. There is also little difference
between summer and winter circulation intensity (see
Figures 7.3, 7.4 and 7.10). It is important here to
differentiate between mean pressure patterns and the
highs and lows shown on synoptic weather maps. Thus,
in the southern hemisphere, the zonality of the mean
circulation conceals a high degree of day-to-day vari-
ability. The
synoptic map
is one that shows the principal
pressure systems over a very large area at a given time,
ignoring local circulations. The subpolar lows over
Iceland and the Aleutians (see Figure 7.9) shown on
