Describe and explain the characteristics of the British climate (40)

The purpose of this essay is to describe, with specific reference to highland and lowland regions, the British climate. also an explanation of how air masses, latitude, continentally, and ocean currents can interact to determine the British climate before reaching a conclusion as to the ultimate determining factor.

The climate or average weather conditions in Britain for a protracted period of time can be classified as ‘Temperature Maritime’. This is the climate typical of the west coasts at middle latitudes of most continents, and generally features warm summers and cool winters, with a relatively narrow annual temperature range. In 2014, the UK mean temperature for summer was 14.8°C and in the winter the mean temperature was 5.2°C. In the UK, the average rainfall in the lowlands is a lot lower than the average rainfall in the highlands. the overall total rainfall for 2014 was 1300mm, 113% of the 1981-2010 average.

Highland Britain, lies north of Tees-exe line, is usually colder, in both winter and summer than lowland Britain Manchester is located in highland Britain and is much colder than Brighton, which is located in lowland Britain. The mean maximum temperature in summer between 1981 and 2010 in the UK’s lowlands was 20°C, and the minimum mean temperature was 11°C. In the highlands however, the mean maximum temperature was 15°C and the mean minimum temperature was 8-9°C. in the summer, it was the coldest in the Scottish midlands with a temperature of 5°C. These 4 sets of data show that over a 29 year period, there has been a significant difference in the temperatures of highland and lowland Britain.

Precipitate, both rain and snow. is much greater in highland Britain than lowland Britain. Cardiff is known as Britain’s wettest city, with on average 115cm of rainfall a year. The driest areas occur along the coast such as Southend-On-Sea. It tends to be wetter in the west and in the highland areas (such as the Pennines and Grampians) than in the east due to relief rainfall, the prevailing winds that hit the UK and the passage of depressions systems. Relief rainfall is a dominant process, coupled with the fact that Britain’s prevailing wind direction is South Westerly.

Relief rainfall is a dominant method of precipitation formation in the UK and relates to the precipitation that is created as air masses are pushed up and over mountainous or highland areas. Warm air is carried to the West coast of Britain by our prevailing wind. This air encounters the highland on the coast of Ireland, then the Lake District and the Pennines and it is forced to rise above this barrier. As it continues to rise, the warm air cools with height (at a rate of 9.8°C per 100om). As the air cools water vapor condenses to form clouds and eventually it rains over Britain’s highland areas. Air descends in the East coast and warms slightly therefore there is less rainfall. The Pennines receive 2000+mm of rainfall per year, Newcastle 700mm and Blackpool receive 950mm.

One explanation for the difference in climate between the highlands and lowlands of Britain is The Tri-Cellular Model. With Britain being located on the edge of the Ferrel and Polar cells, it means that it is subject to warm air moving from the Tropics and cold air moving from the Artic. High rates of insolation create rising air at the equator. Rising moist air cools rapidly forming towering cumulonimbus clouds and at the surface winds are very low, creating doldrums, an area of low-pressure around the equator where the prevailing winds are calm. Cooler air moves away from the equator and begins to sink at 30°N. when the air sinks to the surface it moves back to the equator (trade winds) or polewards (westerlies). The convergence of warm tropical air and cold polar air at 60°N forces the warm air to rise, creating an area of depressions. Due to the tilt of the earth, the Inter-tropical convergence zone migrates north and south, causing seasonal shifts in weather patterns, which in turn could have serious impacts.

Air masses also effect the British climate and there are 5 main types which affect the British Isles. The Tropical continental air mass affects the South-east of the UK and it originates over North Africa and the Sahara (a warm source region). This type of air mass is more common during the summer months and our highest temperatures usually occur under the influence of this air mass. It brings hot, dry weather, especially in southern England in summer heat waves. The Tropical maritime air mass affects the South-east and is from the Atlantic Ocean, between the Azores and Bermuda. This is the predominant wind direction across the British Isles and the air is warm and moist in its lowest layers and, although unstable over its source region, during its passage over cooler waters becomes stable and the air becomes saturated. When a tropical maritime are mass reaches the British Isles it brings with it low cloud and drizzle. However, on high ground, the cloud may break up and in the summer months it may become sunny. This air stream is mild and can raise the air temperature several degrees above the average.

The polar continental air mass originates from Eastern Europe and is considered a winter air mass. The weather characteristic of this air mass depend on the length of the sea track during its passage from Europe to the British Isles; this air is very cold and dry and if it reaches southern Britain with a short sea track over the English Channel, the weather is characterized by clear skies and severe frosts. With a longer sea track over the North Sea, the air becomes unstable leading to added moisture, consequently leading to showers of rain or snow, especially near the east coast. The lowest temperatures occur in this air mass. Polar maritime air masses originate over northern Canada and Greenland and reaches Britain on a north-westerly air stream. They make up the sold sector air in the depressions that pass over the UK regularly and cause most of the UK’s precipitation. Latitude affects the temperature of the British Isles due to the more northern latitudes receiving less insolation than the southern latitudes. This is due to the angle of the sun relative to the axis tilt of the Earth. The equator and tropics receive more insolation because the sun is highest in the sky relative to the orientation of the earth’s surface. The further the distance from the equator, the lower the angle of the sun and the less insolation the surface receives. At a 30° angle, a one-mile-wide ray of insolation is dispersed over a two-mile radius. Compared to the equator when the sun is directly above it, insolation is dispersed over just a one-mile radius. A higher latitude causes a lower temperature which is one of the reasons it is colder in highland Britain than lowland Britain. The incoming solar radiation has further to travel through the atmosphere when at higher latitudes. Continentality it a measure of the difference between continental and marine climates characterized by the increased range of temperatures that occur over land compared with water. Inland areas away from the influence of the sea tend to be drier than the coast. In summer, the energy from the sun heats up the land more rapidly than the sea, causing higher summer temperatures inland. In winter, the land loses heat more rapidly, causing colder winters inland. Latitude is the angular distance of a place north or south of the earth’s equator. Temperatures are highest in low latitudes (tropics) and low in polar altitudes. The gradual decrease in temperature between the equator and poles is due to reduced insolation. The sun shines from a high angle in the sky in the tropics and because of the sun’s rays travelling directly through the earth’s atmosphere, less is lost by reflection. Because the sun shines from a high angle and the rays are almost vertical, there is a smaller area of the earth’s surface for each ray to heat up. Near to the poles the suns rays approach the earth’s surface at an oblique angle which means that each ray has a larger surface area to heat up. Albedo is the fraction of solar energy reflected from the Earth back into space. It is a measure of the earth’s surface. The lower the albedo, the more energy from the Sun is absorbed. Surfaces with a very high albedo rate reflect between 70-95% of incoming solar radiation ie snow and thick clouds. The lower the albedo, the less incoming solar radiation is reflected ie oceans, 7-9%. A lower albedo rate also means a higher absorbance rate therefore oceans absorb more solar radiation than snow. Specific heat capacity is the amount of energy needed to change the temperature of 1kg of the substance by 1°C. the Atlantic Ocean acts like a heat reservoir in the winter so as land surfaces cool down quickly, the Atlantic retains its heat, influencing a milder temperature, keeping the west coast a couple of degrees colder than the east. water has a higher SHC than sand and it takes the same amount of energy to heat water by 1°C than it does to heat sand by 5°C. water is deeper than sand therefore more energy is needed to heat it. Oceans have a high specific heat capacity therefore low maximum temperatures. Due to transparency, they are heated to a depth of 10m and movement will mix the water, transferring heat to greater depths. Altitude is the height of an object or point in relation to sea level or ground level. This also is an influencing factor on the British Isles climate. The influence of altitude can be clearly seen in northern England and Scotland however the higher ground is very recognizable in wales. On average, air temperature falls 0.65°C every 100m of altitude. This is due to insolation and how more incoming solar radiation is re-radiated back into the atmosphere at higher altitudes. There are multiple factors that all influence the characteristics of the British climate. Air masses, latitude, altitude, specific heat capacity, albedos and Continentality are the main 6 influences. Most factors play a part in affecting both precipitation and temperature however in my opinion, the most important factor are the different types of air masses. The 5 main types of air masses are the main cause to there being large differences between the climates in different areas of the British Isles. Clashing air masses can cause the most sever weather, when dry-cold continental air clashes with warm-humid maritime tropical air. Air masses are also behind the formation of fronts and depressions at certain times of year (areas of low atmospheric pressure, producing cloudy, rainy and windy weather). Without different air masses there would be fewer variations in climate in different parts of Britain. These latter weather systems are easier for weather forecasters to predict; the westerly low pressure airstreams not only bring more variable weather, but they tend to move at less predictable speeds, resulting in the correct sequence of weather events being predicted, but not necessarily at the times stated in the forecasts.