To what extent is the climate of the British Isles a product of the air masses that affect it? (40 marks)

The UK experiences a temperate, maritime climate which is subject to change on a day to day basis throughout the year, therefore making it extremely difficult to predict the weather for up to more than just a couple of days ahead. This variable climate is so apparent due to the geographical positioning of the UK in relation to the Earth in terms of the fact that it is situated just off the edge of continental Europe and yet is surrounded by sea. These locational characteristics mean that the UK is subject to weather determined by five major air masses travelling from all different directions over both the sea, and the land. Air masses are bodies of air which pick up the characteristics of the area that they have come from in terms of the temperature, moisture content and pressure.

The air masses which play the biggest role in determining the weather in the UK are the Polar and Tropical maritime air masses. These come to the UK from over the Atlantic Ocean and are thought to influence up to 80% of the weather that we receive. The first of these is the Tropical continental air mass which travels over the Atlantic Ocean from the south west of the UK. During the winter, when we are affected by this particular air mass, we can expect conditions to be relatively mild and often rainy. This is due to the fact that this maritime air mass travels to the UK over sea therefore gradually warming and picking up moisture on its way. Stratus clouds are often found therefore indicating reduced visibility and sometimes fog around coastal areas. Throughout the summer however, temperatures are warmer and winds are moderate. Despite the fact that the lower layers of the mass tend to be stable as a result of its passage over cooler waters, when it’s forced to rise over hills, thundery showers can occur due to the instability of the upper layers. As this air stream is relatively mild, its influence throughout the winter months can often cause temperatures to rise by up to several degrees above the average.

The polar maritime air mass is also extremely common over Britain. This also travels to Britain over the sea, however from the North West over the North Atlantic Ocean. This particular air mass brings relatively cool conditions all year round for the majority of Britain. As it crosses the Atlantic, the air gradually warms and picks up moisture therefore becoming unstable in its lower layers and causing heavy rainfall across the Highlands. Cumuloform clouds are often associated with this type of air mass, and in contrast to the tropical maritime, the visibility is mainly good. These two maritime air masses are particularly influential on the British Isles due to the fact that the leading fronts of these masses can meet over the Atlantic therefore causing the formation of depressions. Depressions are constantly passing over the UK throughout the year affecting factors such as temperature, cloud cover, and the occurrence of frontal rainfall, as well as the fact that in extreme circumstances, storm events such as the Great storm of 1987 can occur as a result of this.

The final maritime air mass is formed over the Arctic Ocean therefore bringing Britain lots of cold northerly air. This air mass brings extremely cold conditions during the winter and cold weather in the spring, however it rarely affects the UK throughout the summer. Alike to the other maritime masses, the moisture picked up across the ocean causes instability in the lower layers which, due to the cold conditions, often brings snow during the winter in the northern-most parts of Britain, as well as hail and heavy rainfall.

In terms of the other two air masses affecting the UK, these come to Britain from over the continents of Europe and Africa which are situated to the east and south east of Britain and bring over contrasting weather conditions. The first of these air masses is the Polar Continental which forms over Siberia and tends to affect the UK throughout the winter. Due to the fact that this mass will have adopted conditions from Siberia, it tends to bring sub-zero temperatures to British winters even in the south (often below 10 degrees Celsius at night). Despite the fact that continental air masses tend to bring stable conditions, the crossing of the North Sea taking place in order to get to the UK causes the lower layers to become slightly unstable therefore sometimes causing heavy snow in eastern Britain. If we are influenced by this air stream during the summer however, temperatures are much higher and conditions are often more stable.

The final air mass that determines the climatic conditions of the UK is the tropical continental mass formed over Northern Africa bringing that warmest conditions that Britain will experience throughout the year. We only experience the effects of this air mass during the summer which can often lead to extremely high temperatures and heatwave conditions. The average temperature that this brings is often over 30 degrees Celsius during the day and even up to 15 or 20 degrees throughout the night. The lower layers of this air mass tend to be stable which can lead to droughts such as in 1976 – the hottest UK summer on record – although the uppermost layers can become unstable with thunderstorms. Visibility is often poor with the influence of this air mass due to the air picking up pollutants such as sand particles being blown into the air from Saharan dust storms.

Despite the fact that these air masses are clearly extremely influential on the climatic conditions that we receive in the UK, there are also other factors that can determine this as well. For example, I believe that the UK’s climate had come about as a result of its latitude and location. In terms of latitude, Britain is of mid-latitude between 50 and 55 degrees North, this is a cause of the relatively ‘average’ conditions of the UK as temperatures never get particularly high as the sun is never high enough in the sky, however they are also never extremely low as even during the winter, we still get several hours of daylight. In relation to the atmospheric cells, Britain is located on the northern edge of a Ferrel Cell. This means that surface winds bring warm air from the south which rises causing an area of low pressure (depression) which brings the UK rain throughout the year. The final climatic influence that I believe there is in Britain is the fact that we are located relatively near to the Gulf Stream – or North Atlantic Drift. This is a powerful, warm current in the western North Atlantic Ocean which allows temperatures in the UK to be warmer than many places located at the same latitude. It is estimated that the British Isles would be on average 5 degrees colder without the influence of the Gulf Stream.

To conclude, I believe that the UK is a product of the air masses that affect it up to an extent in terms of the fact that without them, the weather would not be so variable, and the depressions which arguably have the most impact on determining our weather would not occur in the same way. Although I think that these have most vital influence on the UK, I cannot disregard the other factors that affect our climate such as the ocean currents and latitudinal location which help Britain to maintain the temperate maritime climate that it has obtained.