The British climate is temperate - this means that it does not experience extremes of temperature or rainfall. The climate can be divided into four sections. In winter, the west is kept warm by the Gulf Stream whilst the east is cooled by air masses from continental Europe. In summer, temperatures are influenced much more by latitude.
These images show surface temperatures for January and July.
By the end of this lesson you should have been able to name and explain the three types of rainfall. You should also have drawn an annotated diagram to show why rain falls in each of the three cases.
We get rain because of rising air. As air rises, it cools. As cool air can't hold as much water vapour as warm air, the water vapour condenses and turns into water droplets. These fall to earth as precipitation.
In class, we used an animation to show why convectional, relief and frontal rainfall occur. You can see the animation here.
Convectional Rainfall
This is very common in areas where ground is heated by the hot sun, such as the Tropics. We do get some of this type of rainfall in Cambridge in the summer - in fact, its the reason why last year's school sports day was cancelled!
The sun heats up the ground, which heats the air above it. This then rises and cools, and the water vapour condenses into water droplets, forming clouds. The droplets falls as rain under the influence of gravity.
This video shows convectional rainfall in Costa Rica.
Relief Rainfall
With relief rainfall, it is the presence of hills or mountains that leads to the warm aid rising. Its particularly common on the west coast of the UK, since the prevailing winds come from the west and have to rise to pass over hills and mountains in areas such as the Lake District and Snowdonia.
The winds pick up moisture from the sea as they pass over it, and this makes the air moist. As the air rises to pass over the higher land, it cools and the water vapour condenses, forming clouds. The droplets then fall as rain, sleet, hail, or snow, depending on the atmospheric conditions.
On the leeward side of the mountain (the side not facing the wind), it is much drier. This area is said to be in the 'rainshadow'. There is little rain here as the air is descending and warming up.
This video clip shows relief rainfall on New Zealand's south island.
Frontal Rainfall
Frontal rainfall in the UK is associated with depressions. It happens when two air masses (a warm one and a cold one) meet. The warm air is pushed upwards over the cold air, and, as it rises, it cools down. The water vapour condenses to form clouds, which give rain.
This video shows frontal rainfall.
Test Yourself!
Download this PowerPoint, then move the objects into the correct place on each slide and custom animate to help you explain the rainfall processes.
Note for teachers: I'm not sure who wrote this activity - but I think it may be someone from Manchester. Please let me know if it's you so that I can add an acknowledgement.
You need to be able to both draw and interpret weather maps (synoptic charts) and climate graphs.
Synoptic Charts
Weather maps use standard symbols to show a variety of weather data. The information you need to read these charts can be found in the key. Here are the standard symbols used on weather charts:
Synoptic charts also show isobars. These are lines joining points of equal pressure. Remember: pressure is measured in millibars. The pressure readings are shown on the isobars as numbers.
You also need to know about isohyets (which join points of equal rainfall) and isotherms (joining points of equal pressure).
The Met Office pages about synoptic charts can be found here. They offer a very clear summary of the topic, with some activities to complete.
Climate graphs Climate graphs show temperature and rainfall for each month of the year in a given location.
Rainfall is shown as blue bars (a bar chart). Temperature is shown as a red line (a line graph).
When interpreting a climate graph, make sure you are reading from the correct axis as there are two different vertical scales, one on each side of the graph.
When plotting a climate graph, make sure that the temperature plot is placed in the middle of the month.
There is a superb living climate graph interactive activity here. Its in two parts - you have to finish the first one to gain access to the second. Thanks to Russel Tarr for making and sharing this activity.
- To be able to define the terms weather and climate. - To know the names of the key components of weather. - To know the names of the key weather instruments.
Weather is the short term state of the atmosphere over a small area. By contrast, climate is the 'average weather', usually taken over a period of 30 years, for a larger area. It considers long term trends.
You need to be able to define the following aspects of the weather, know how they are measured, and give the units of measurement:
- precipitation - temperature - air pressure - cloud cover - wind speed - wind direction - visibility
Precipitation means water falling from the sky in any form eg. rain, sleet, snow, hail. It is measured in millimetres using a rain gauge.
Temperature means how hot or cold it is. It is measured in degrees, using a thermometer.
Air pressure is how 'heavy' the air is. It is measured in millibars using a barometer.
Cloud cover is how much of the sky is hidden by clouds. You use your eyes to measure cloud cover. Cloud cover is expressedin oktas - one okta cover means that one eighth of the sky is obscured by clouds.
Wind speed is how fast the wind is blowing, and it is measured using an anemometer. As you will know from our fieldwork in the lesson, it can be given in a variety of units eg. miles per hour, kilometres per hour, metres per second, knots.
Wind direction is which direction the wind is coming from - it is measured using a weather vane and given as a compass direction eg. north, south, east, west.
Visibility means how far you can see. It is measured using a lightmeter, and usually given in metres.
Here's a 1 minute review of the Amazon topic. Could you produce a better summary? If so, let Dr Hutchinson have a copy of your work and we will post it here for other pupils to see.
Today's objectives were as follows:
