Geoscience Reference
In-Depth Information
10
CHAPTER TEN
Weather and climate
in middle and high
latitudes
LEARNING OBJECTIVES
When you have read this chapter you will:
n
be familiar with the major factors determining climate in many regions of middle and high
latitudes, and the subtropical margins
n
appreciate the role of major topographic barriers in determining regional climate
n
be aware of the contrasts between climatic conditions in the Arctic and Antarctic
In Chapters 7 and 8, the general structure of the
atmospheric circulation has been outlined and
the behavior 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. Never-
theless, 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 sub-
tropical 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.
A
EUROPE
1
Pressure and wind conditions
The dominant features of the mean pressure
pattern over the North Atlantic 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 anti-
cyclone, the occurrence 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
