What factors affect Britain’s Climate?

1. Rainfall: relief, frontal (depressions), convectional

2. Temperature: latitude, distance from sea, winds, ocean currents, anticyclones, air masses.

How is rain How is rain formed?formed?

1 The sun is the driving force behind the process of convection which is the main process behind the creation of rain.

2 The sun heats up the sea and this in turn heats up the air. The sun cannot directly heat the air. When the water is heated, it turns to water vapour.

3 As the air in contact with the sea is warmed, it rises up into the atmosphere, taking the water vapour with it. As it does so, it cools as it gets further away from its heat source (the sea).

4 Eventually, the air and vapour cool to the point where the vapour condenses, making it visible as clouds.

5 Water droplets within the clouds collide and join together to form rain drops, which fall back down to the sea / ground.

Relief RainfallRelief Rainfall

1 Air is forced to rise and cools by 1°C per 100m.

2 As the water vapour in the air condenses, it forms clouds and rains.

3 The air starts to descend and begins to warm up again.

4 As air warms up, it can hold more water vapour - clouds disappear and rain stops. This side is known as a RAINSHADOW.

Relief rain is formed when air is forced to cool as it rises over relief (height) features in the landscape (hills or mountains).

Rain Rain shadow shadow

mapmapFort William

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1200160020002400

Dundee

LincolnBuxton

EastbourneAshburton

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12001600

400800

1200

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1200

400800

1200

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Grampian Mountains

Dartmoor

Pennines

Air massesAir masses may be cold or warm, humid or dry depending on where they originated and from which direction they have come. The British Isles are located at the meeting point of air from many parts of the world.

Which brings us:

a. Sunbathing weather

b. Gives us our worst weather

c. Is the best for skiers?

d. Brings our most common weather?

e. Least common in summer?

f. Might cause a winter thaw?

Warm Fronts

• Warm fronts occur when light, warm air meets cold air. The warm air rises gradually over the cold air as they meet. As the warm air rises it cools and condenses to form clouds. Rain falls along the front as long periods of drizzle or steady rain. The symbol on a weather map for a warm front is made up of red semi-circles along a line.

Cold Fronts• Cold fronts form when cold air

advances towards warm air. The cold air undercuts the warmer air in front of it, forcing the warm air to rise above it more vigorously than at a warm front. As the warm air rises much faster it may cool more rapidly and may form large cumulonimbus clouds.

• Heavy rainfall may result and the air temperature may become noticeably cooler as the cold front passes by. A cold front is symbolised on a weather map by blue triangles along a line.

Example

• Below is an example of a weather map showing a warm and a cold front for the British Isles.

Q. Describe what the weather will be like in East Anglia as the warm front and cold front pass overhead.

1. 9am

2. 11am (warm front overhead)

3. 3pm (cold front overhead)

Convectional Convectional rainfallrainfall

1 - The sun provides the heat source, heating up the ground quickly.

2 - The ground then heats up the air through convection and the air rises very quickly, carrying water vapour with it.

3 - As the air rises it cools very rapidly.

4 - Large clouds develop directly above the rising air .

5 - Heavy rain and thunderstorms occur. (afternoon - evening)

This form of rain is common in the east of England during the summer.

Key points of convection rainfall

• Sun shines on land and warms the air above it; • Warm air rises; • Warm air can pick up moisture from water

sources (seas, lakes etc.); • Warm air cools as it rises; • Water vapour condenses to form clouds; • Rainfall may occur.

Forecast