UK Weather

What causes the weather in the UK?

The two major atmospheric characteristics that are the reason for the majority of the weather in the UK are depressions and anticyclones.

A depression is an area of low pressure. Air rises leading to the formation of clouds and rain. UK weather is associated with the movement of depressions across the land. Depressions form over the Atlantic Ocean and pass from West to East across the UK driven by the prevailing winds. Depressions form at the boundary between cold polar air moving South and warm tropical air moving North and is known as the polar front. Once formed, the air begins to rotate, spiralling upwards in an anti-clockwise direction forming clouds and then rain.

Within a depression there are two further ‘fronts’, one cold and one warm. The warm front signifies the front of the warmer air (hence the name, genius!) and the cold front........you get the idea. As the depression builds it eventually dies out as the cold front catches up with the slower warm front. As depressions pass over the UK a sequence of weather is produced. At the front of the depression a steady rain falls. Behind this, small patches of rain begin to fall as the temperature rises slowly due to the warm air. The advancing cold front causes the temperature to drop and the rain ceases.

Unlike depressions, anticyclones are areas of high pressure cause by descending air. The chances of rain are slim as the descending air prevents air from rising and therefore forming clouds. Winds also travel clockwise, the opposite of depressions. Anticyclones can be separated further into two main types, winter and summer anticyclones. In winter, cloudless skies result in bright but cold conditions. As there is no cloud heat it lost rapidly into the atmosphere and this is what causes frost to appear on the ground in the early morning. If the air is particularly heavy with moisture from the surrounding seas then can condense into mist and fog. In the summer time the sun is much stronger due to Earths’ rotation on its axis and is easily able to burn away and resulting mist and fog. Summer anticyclones typically result in dry, sunny conditions (of which we see very little these days). The below diagram is a basic example of an anticyclone situated over the UK.

Rain, Rain, Go Away!

In the next ‘block’ of posts I’m going to discuss aspects of weather and climate, in particular focusing on the UK. The UK may be the obvious choice, however, it is important that students can relate to a particular topic as such they will all have experience of the British weather. I was swayed to discuss climate next as I have just returned from work and unfortunately endured a soaking on the way.

The climate of the UK is largely influenced by its physical position. The UK lies at the forefront of confrontation between descending polar air from the North and rising sub-tropical weather from the South. As a result we experience varied weather conditions throughout the year. The below image shows the major air flows which circulate Earth.

There are a number of other factors that the climate of the UK. These include:

• The North Atlantic Drift - a warm ocean current that provides the UK with relatively warm winters considering our latitude.
• Prevailing winds - typically flowing in from the south-west, these, along with the North Atlantic Drift result in a warm but wet climate.
• The relief of the UK - as air is forced upwards in upland areas the temperature decreases and clouds form causing subsequent rainfall and hence why the Lake District and the majority of Scotland typically have a large number of rainy days a year. The below diagram is a excellent illustration of how relief rainfall works.

As I have mentioned in my previous posts I believe that before beginning to teach a new topic it is important to have a knowledge of what the students already know. For climate in the UK a possible idea would be to provide a trace of the coastline and then suggest students to shade areas of the UK which they believe to be typically wet in blue, and the warm areas in red. Discussion on why they had chosen those areas would allow the teacher to get a good insight into current understanding.

As a final point I found the Met Office website to be an extremely valuable resource when researching this topic. It contains a huge amount of data available in an instant and even provides basic lesson plans, including presentations and slide shows, which introduce certain topics.

Just A Quick One

Just to a quick note to highlight the importance of media in geography today. I managed to catch a repeat of Top Gear over the last couple of days in which one of the presenters was faced with the challenge of collecting some freshly fallen molten rock in Iceland.

Firstly, although a very short piece it was an excellent visual example of a volcano at work, and being a modern show which the majority of people are aware of and watch, is easily accessible. It's great that how the simplest of things can produce useful resources.

Secondly, how on earth did they get permission to do that?!?

Desertification

Desertification is the degradation of formerly productive land through the expansions of the desert landscape. It is not a simple process and can involve multiple causes and occurs at different rates. Desertification is concerned with desert margins where the landscape changes gradually from a dry, arid climate to a more humid environment. This ‘transition zone’ typically has a fragile and delicately balanced ecosystem. Studies have led scientists to believe that the Sahel region in Africa moved close to 100km southwards between 1950 and 1975 leading to the landscape we see today.

Poor land management is the main factor that contributes to desertification. Increasing populations and larger livestock herds place greater pressure on the desert margins. Local ecosystems become disrupted and can increase the rates of erosion of the land. Nomadic tribes which traverse the landscapes are often trying to escape the desert but unintentionally are taking the desert with them. A greater population leads to a greater need to feed the people. Increased ploughing of the earth for crops further disturbs the landscape. Key words from these ideas are overgrazing, overcultivation, deforestation and sustainability. These are terms which as essential for students to both know and be able to apply to geographical concepts.

Desertification may not be able to be prevented completely but steps to mitigate the human effects can certainly be employed. Better land management is the obvious option. A greater understanding of how planting crops and sufficient irrigation can lead to the stabilisation of soils can ensure that conditions improve. As I suggested it is difficult to reverse losses that have already occurred in terms desert encroachment, however, the Sahel region has proven to buck the trend. An article produced through the BBC website identified regions of the Sahel that have begun retreat (note the article was published in 2002 and subsequently the situation may have changed further). The article highlights both natural and anthropogenic reasons for this.

A UN-sponsored study relating to desertification, known as the Millennium Ecosystem Assessment, was published in 2005 and is well worth a quick scan to get an overall perspective on desertification but also includes some deeper thought into the concept.

Throughout my time that I spent researching this topic the Sahel was clearly favoured as a case study and therefore with the amount of information available it would be a bit silly not to use it as such. It would be useful for student to develop their knowledge around a case study which can be used later in assessments and exams. Other areas can also be used. I came across the below during my research. Asking the question at the beginning of the lesson and then at the end would be a good method to discover whether student has understood the lesson being taught.

The boundary between Chaco Canyon National Monument and the Navajo reservation. On one side, long-term rest from livestock grazing. On the other, livestock grazing with relatively few animals for long periods. Can you tell which is which? Why do you think it looks this way?