Geoscience Reference
In-Depth Information
lower latitudes occurred during the glacial period and supports the validity of the
circulation pattern reconstructed by Harmer.
Lamb's analysis of his winter chart shows an anticyclonic centre over Scan-
dinavia comprising an outlier of the high pressure system over the Arctic basin and
like Harmer's chart another large anticyclone is situated over Asia. An extensive
belt of low pressure over the Atlantic extends east across the Mediterranean to the
Caspian Sea.
Harmer's analysis of his summer chart shows a large blocking anticyclone over
the Norwegian Sea covering Scandinavia and much of Greenland, again with an
easterly flow over the British Isles. The track of the travelling depressions over the
Atlantic now divides into two branches off Iberia with one branch proceeding
northeast into central Europe and the other east over the Mediterranean and then
via the southern Black Sea into a large area of low pressure over Asia, again
probably related to the southward shift of the zonal circulation.
Harmer's charts clearly show that there was less change in the character of the
circulation from winter to summer than today, with persistent blocking anticyclonic
pressure patterns over Scandinavia effectively controlling the overall situation in
both seasons during the maximum glaciation.
Lamb's analysis of his summer chart shows an extensive anticyclone over the
Arctic basin with a ridge extending towards northern Scandinavia. A multi-centred
area of low pressure is situated over Asia with outlying centres over Europe and off
southwest Iberia. Another low pressure system occurs over the eastern North
Atlantic.
Lamb concluded that two of the main features of his reconstructed pressure
patterns were firstly, an intensification of the circulation, especially in summer,
both of the mid latitude westerlies and the Trade winds; and secondly, like
Harmer, a general displacement equatorwards of the zonal circulation. Further-
more, he added, it was likely that the winter circulation in higher latitudes over the
ice sheets was weaker than today and, following Harmer, that there was less
change in the character of the circulation from winter to summer than now.
Harmer stated that the great extension of Swiss glaciers during the Pleistocene
epoch indicated that considerable masses of moisture-laden air must have reached
the ice fields from maritime sources mostly from the west. Also travelling
depressions moving eastward from the Atlantic, as suggested in his summer chart,
may have occasionally affected southwestern parts of Europe. He continued that
the climate of the region north of the Swiss massif was colder at this period than
that to the south of it, the former having been more or less under the influence of
anticyclonic winds proceeding from the ice sheets of northern Europe. While ice
was steadily accumulating in the north, the sun's heat during summer on the
southern slopes of the ice-clad Alpine mountains together with the rains that may
have fallen there, produced violent floods which inundated the lowlands of
Piedmont and Lombardy from the foot of the Alps to the Adriatic leaving a thick
and continuous deposit of diluvial gravel and mud.
