Geoscience Reference
In-Depth Information
10
Weather and climate in middle and
high latitudes
Learning objectives
When you have read this chapter you will:
Be familiar with the major factors determining climate in many regions of middle and high latitudes, and
the subtropical margins,
Appreciate the role of major topographic barriers in determining regional climate,
Be aware of the contrasts between climatic conditions in the Arctic and Antarctic.
A EUROPE
In Chapters 7 and 8, the general structure of the atmos-
pheric circulation has been outlined and the behaviour
and origin of extratropical cyclones examined. The
direct contribution of pressure systems to the daily and
seasonal variability of weather in the westerly wind belt
is quite apparent to inhabitants of the temperate lands.
Nevertheless, there are equally prominent contrasts
of regional climate in mid-latitudes that reflect the
interaction of geographical and meteorological factors.
This chapter gives a selective synthesis of weather
and climate in several extratropical regions, drawing
mainly on the principles already presented. The climatic
conditions of the subtropical and polar margins of the
westerly wind belt, and the polar regions themselves,
are examined in the final sections of the chapter. As far
as possible, different themes are used to illustrate some
of the more significant aspects of the climate in each
area.
1 Pressure and wind conditions
The dominant features of the mean North Atlantic
pressure pattern are the Icelandic Low and the Azores
High. These are present at all seasons (see Figure 7.9),
although their location and relative intensity change
considerably. The upper flow in this sector undergoes
little seasonal change in pattern, but the westerlies
decrease in strength by over half from winter to summer.
The other major pressure system influencing European
climates is the Siberian winter anticyclone, the occur-
rence of which is intensified by the extensive winter
snow cover and the marked continentality of Eurasia.
Atlantic depressions frequently move towards the
Norwegian or Mediterranean seas in winter, but if they
travel due east they occlude and fill long before they can
penetrate into the heart of Siberia. Thus the Siberian
high pressure is quasi-permanent at this season, and
when it extends westward severe conditions affect much
of Europe. In summer, pressure is low over all of Asia
