Climate and Polar Maritime Air Essay.
To what extent is the climate of the British Isles a product of the air masses that affect it?
Climate is defined as the weather averaged over a 30 year period, with weather being determined by temperature, humidity, wind and precipitation. The climate in the British Isles is described as cool temperate western maritime climate, although there are regional differences in climate across the British Isles; with average temperatures ranging from -0.2 to 20.9 degrees Celsius. The climate of the British Isles is influenced by the movement of five major air masses.
However, it is also influenced by other factors, including its topography, ocean currents, latitude, and weather systems. Firstly, it can be argued that air masses play a large part in the overall climate of the British Isles. Air masses are large bodies of air with reasonably uniform temperature, pressure and humidity throughout. There are five main air masses that influence the climate: tropical maritime(TM), polar maritime (PM), tropical continental (TC), polar continental (PC) and arctic maritime (AM).
The direction of the air masses can be seen in the diagram below. Tropical Maritime brings warm moist air from the Atlantic Ocean.
This warm air hits areas of high relief in western England and Wales, causing the air to rise, which means clouds form. Areas of high relief in the west of England include Dartmoor and Exmoor. The air is very moist as it is from the ocean, so there is lots of precipitation. This wind is warm, which means that is has a warming affect in the winter, however in the Summer because the land has a lower specific heat capacity, it heats up more than the Atlantic ocean. Therefore it has a cooling affect in summer. Tropical Continental air masses bring hot and dry air in summer. This causes high temperatures with very little precipitation, and is the reason for heat waves in the British Isles. For example the heat wave in July 2013, where temperatures reached 33.5°C . Polar Maritime air masses bring cold moist winds as they originate from a north westerly direction, over the Atlantic Ocean.
This therefore causes very cold wet weather in the British Isles, especially in the westerly parts of the British Isles where there is high relief causing precipitation. Polar Maritime air is dominant over the winter season. Polar Continental air masses originate from high latitudes such as Siberia so therefore bring very cold conditions with them, however as they come from land not ocean, the air masses bring dry conditions. Arctic air masses originate over the Arctic Ocean where high pressure dominates.
The air masses bring extremely cold temperatures, however is only dominant in winter, and sometimes in spring. However this air mass is more likely to affect the climate in Scotland, and northern England, as it has come from a northernly direction. Overall this shows that air masses do play a significant role in the overall climate of the British Isles, however some air masses are more dominant than others in different seasons, and some air masses are dominant in different areas of the British Isles.
The climate of the British Isles is also greatly affected by weather systems such as depressions. Mid Latitude depressions are formed over the Atlantic Ocean on the Polar front. They move in an easterly direction across the British Isles. The depressions are low pressure systems that are formed when moist, warm ™ air meets drier, colder PM air. The warm, moist air is forced upwards, by the colder denser air. The Coriolis effect causes the air to rotate in an anticlockwise direction. The jet stream is also involved as it moves the depression from west to east. The climate associated with depressions is strong winds, clouds and precipitation. However the climate is dependent on which air mass is over the British Isles. Polar maritime air brings average temperatures for the season in winter, around 5°C-8°C in January, but cooler temperatures for the summer season, at around 16°C to 18°C in July. This air mass also brings lots of precipitation.
Tropical maritime air brings humid and mild weather in winter, with temperatures averaging at around 12°C-14°C in January. Tropical maritime can also bring thunderstorms , due to the humidity and low pressure. An example of when a depression has greatly affected the British Isles was the Great Storm in 1987. This fast moving depression caused wind speeds of up to 81mph. The British Isles experienced lots of rainfall, and there was even an increase in temperature by 6°C in places, where the warm front was situated. This shows how depressions can have great impacts on the climate of the British Isles, however this large depression is not common, so does not usually affect the climate. Overall, depressions have a great impact on the climate of the British Isles both in winter and summer, however it can be argued that air masses play an important role in the formation of depressions, so this also shows that air masses indirectly affect the climate.
The British Isles has a latitude between 50°N and 60°N. This has a great impact on the climate that it experiences, meaning that the latitude is another factor that will influence the climate of the British Isles. The latitude of an area will affect how much insolation it will receive. This is due to the angle of incidence, which can be see in the diagram below. A larger angle of incidence will mean that the insolation from the sun will only disperse over a small area, whereas a small angle of incidence means the same amount of insolation will be spread over a larger area. At a 30° angle, a one wile wide ray of insolation will be dispersed over a two mile radius, whereas an angle of incidence of 90° with the same ray of insolation will be dispersed over a one mile radius. Higher latitude have smaller angles of incidence, meaning that they will receive less insolation.
Therefore the latitude of the British Isles means that there will be temperate conditions. It is not likely that the British Isles will experience a very hot climate due to the fact that id does not receive enough insolation to heat up the surrounding air and ground. This can be seen if you compare the average yearly temperatures of the British Isles compared to Somalia, which is found at a lower latitude of 2.03°. The British Isles has an average temperatures ranging from 8.5-11°C. In contrast Somalia has temperatures around 24-31°C. This demonstrates how that latitude of an area can greatly impact the temperature, which means it affects the overall climate of the area. This shows that latitude is a factor other than air masses that will impact the climate of the British Isles.
Altitude is another factor that influences the climate of the British Isles. On average the air temperature falls by 0.65°C every 100m rise in altitude. This is due to the fall in pressure as the altitude increases, meaning molecules have less kinetic energy. For example Ben Nevis has a height f 1,344 metres, and has an average annual temperatures of -5°C, compared to the British Isles which has an average annual temperature of around 8.5-11°C. This shows that altitude has a direct impact on the temperature of the British Isles, so areas of high altitude in the west of the British Isles, such as Cambrian will have lower temperatures.
The altitude of the British Isles will also cause precipitation, as when moist air masses move across areas of high relief, the air masses are forced upwards, where the cool condense and form clouds. For example in Wales the Cambrian mountains receive over 100mm rainfall per month all year round. This is due to the tropical maritime and polar maritime winds bringing moist air. Overall this shows that altitude can have a large impact on the climate of the British Isles, however air masses are also involved in this, which demonstrates that air masses still play a significant role in the overall climate. Lastly, ocean currents are another factor that have a large impact on the climate of the British Isles. The most significant ocean current is the Gulf Stream, which . Gulf Streams are influenced
In conclusion, the climate of the British Isles is a product of air masses so a large extent. Although there are many other factors that also affect the climate, air masses are also involved in these factors, such as the formation of depressions, or the movement of ocean currents. Therefore air masses so also indirectly influence the climate of the British Isles, meaning that they play the most significant role in affecting the climate.