Polar Front Dissects Britain Its Climate example essay topic

Countries that can be described as having a cool, temperate, western, maritime climate are countries such as our own Great Britain. The reason Britains climate fits this description is because it is situated between the tropical and polar latitudes which results in a lack of extremes of temperature, precipitation and wind. A typical temperature for a summer day in Britain is around 23^0 C and a typical temperature for a winter day in Britain is around 14^0 C, as you can see there is not much change. Britain has around 600 mm to 800 mm of rain a year depending on the area.

This rainfall is evenly dispersed throughout the year with little change between monthly rainfalls. Great Britain is an island and therefore it is under the constant influence of the ocean. This tends to be from the west coast due to the Gulf Stream and the North Atlantic Drift combined with the common South Westerly prevailing wind. Another area on a global scale that can be described as having a similar climate to that of Great Britain is the state of Washington in the United States of America. Great Britains latitude results in a lower intensity of heating from the suns rays than that you would find at the equator because the same number of rays are dispersed over a larger area due to the curvature of the earth, (see figure 1). However Britain receives more heating from the suns rays than a country of higher latitude, therefore it is some what of a medium between the two extremes.

Great Britains latitude also results in a seasonal climate. This is because the earth orbits the sun rotating about its axis of 23.5^0 to the vertical. This means that as the earth orbits the sun once a year there are going to be four distinct time periods in that orbit for a country on a latitude such as Britains. This is because for part of the year the angle of the axis will result in exposing Britain to more of the suns rays, for another part of the year it will result in shielding Britain more from the suns rays and the other two parts of the year are spent between these two stages. These parts of the year are also distinctly different however. These four seasons are called summer, winter, autumn, and spring.

The maritime influence on Great Britain results in a moderating effect preventing extremes from taking place. This is because in the summer the sea is colder than the land and therefore air passing over the ocean is cooled and then has the same affect on the land it passes over. The opposite of this is true in the winter when the ocean has a warming effect on the land. The other effect the ocean has on the climate of Britain and similar areas is that the air picks up moisture when it passes over it and then when it reaches the coast it is often forced to rise and condense resulting in relief rain, (see figure 2 below). Relief rain is very prominent in the west of Britain. As a result of this rain a rain shadow can also be created over a following area of land, again the east coast of Britain is a good example of this as that is where the lowest rainfalls are found.

As the air passing over Britain is often moist as a result of it passing over the ocean clouds are often formed which again contribute to moderating the temperature found in Britain. This is on more of a short-term basis however from day to night because the clouds can provide insulation at night decreasing the diurnal range, which is rarely greater than 10^0 C. Although Britains climate does not undergo extremes it is however very changeable on a daily or even hourly basis. The reason for this is that Britain and areas that experience a similar climate are situated within a belt, which is dominated by low pressure for all of the year. The reason for low pressure formation over Britain is that the polar and tropical air masses, which are transporting air from the zones of high pressure to the north and south respectively, have different characteristics. They meet but do not mix. The warm tropical air being less dense, is forced above the cold polar air along the polar front.

Circulations of low pressure develop at points where the air is rising most vigorously and where this coincides with waves in the polar front and active jet streams above. The typical frontal depression with its leading warm front and trailing cold front is created, (see figure 3 on following page). As the polar front dissects Britain its climate is constantly under the influence of depressions. A line of depressions can form over the Atlantic Ocean and are driven by the prevailing Ferre l Westerly winds over Great Britain. As the frontal depressions gain plenty of moisture from the ocean they bring with them precipitation.

This precipitation falls mainly at two points in the depression, the two fronts. The style of precipitation at the two points however is noticeably different. The precipitation associated with the primary warm front is a period of rain and drizzle lasting for several hours. The precipitation associated with the secondary cold front is quite different however being allot more vigorous and concentrated due to the more rapid uplift of warm air and therefore faster condensation that occurs.

Aswell as being heavier the precipitation along the cold front is sometimes accompanied by thunder and lightning. As frontal depressions move eastwards and develop, the faster moving cold front can catch up and join up with the warm front to create an occluded front along which the considerable uplift of air leads to pulses of heavy rain, (see figure 4 below).