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Реферат Climate and Weather in Great Britain

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Текст реферата Climate and Weather in Great Britain

Climate and Weather in Great Britain
Weather is not the same as climate. The weather at a place is the
state of the atmosphere there at a given time or over a short period.
The weather of the British Isles is greatly variable.
The climate of a place or region, on the other hand, represents the
average weather conditions over a long period of time.
The climate of any place results from the interaction of a number of
determining factors, of which the most important are latitude,
distance from the sea, relief and the direction of the prevailing
winds.
The geographical position of the British Isles within latitudes 50 o
to 60 o N is a basic factor in determining the main characteristics of
the climate. Temperature, the most important climatic element, depends
not only on the angle at which the sun’ s rays strike the
earth’ s surface, but also on the duration of daylight. The
length of day at London ranges from 16 hours 35 minutes on June to 7
hours 50 minutes on 21 December. British latitudes form the temperate
nature of the British climate, for the sun is never directly overhead
as in the tropical areas.
Britain’ s climate is dominated by the influence of the sea. It
is much milder than that in any other country in the same latitudes.
This is due partly to the presence of the North Atlantic Drift, or the
Gulf Stream, and partly to the fact that northwest Europe lies in a
predominantly westerly windbelt. This means that marine influences
warm the land in winter and cool in summer. This moderating effect of
the sea is in fact, the cause of the relatively small seasonal
contrasts experienced in Britain.
The moderating effect of the ocean on air temperature is also
stronger in winter than in summer. When the surface water is cooler
than the air above it – as frequently happens during the summer
months – the air tends to lose its heat to the water. The lowest
layers of air are chilled and become denser by contradiction, and the
chilled air tends to remain at low levels. The surface water expands
because it is warmed, and remains on the surface of the ocean. Unless
the air is turbulent, little of it can be cooled, for little heat is
exchanged.
Opposite conditions apply in winter. The air in winter is likely to
be cooler than the surface water, so that the heat passes from water
to air. Air at low levels is warmed and expands and rises, carrying
oceanic heat with it, while the chilled surface water contracts and
sinks, to be replaced by unchilled water from below. This convectional
overturning both of water and of air leads to a vigorous exchange of
heat.
The prevailing winds in the British Isles are westerlies. They are
extremely moist, as a result of their long passage over warm waters of
the North Atlantic. On their arrival to Britain, the winds are forced
upwards, and as a result largescale condensation takes place, clouds
form and precipitation follows, especially over the mountainous areas.

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