Pressure

Write the title ‘Pressure’ in your books.

Write the aims below:

1. To know the causes high and low pressure.2. To be able to explain the weather conditions

associated with high and low pressure.3. To understand the impact of pressure on people.

PressureThe air is constantly moving. Generally speaking, warm air masses rise and cool air masses sink. Draw the following 2 diagrams:

Rising air cools down and condensation occurs. This makes cloud and rain.

Falling air warms up and any moisture becomes absorbed. This leads to clear skies.

Pressure

Low pressure is the most difficult system to understand, so today we’ll start with the easy one. Write a new title ‘High Pressure Systems’ into your book.

High Pressure (Anticyclones)

High pressure occurs when cool air masses sink. Put the following statements in order:

• This leads to high surface pressure.• Weather conditions are cold and dry in the winter.• Any moisture within the air evaporates.• Weather conditions are hot and dry in the summer.• Temperature inversions also occur in the winter.• The air under pressure heats up.• Cool air sinks as it’s lighter than it’s surroundings.• This means that there are no clouds.• Winds are light and move in a clockwise direction.

High Pressure (Anticyclones)

ANSWERS:

• Cool air sinks as it’s lighter than it’s surroundings.• This leads to high surface pressure.• The air under pressure heats up.• Any moisture within the air evaporates.• This means that there are no clouds.• Weather conditions are hot and dry in the summer.• Weather conditions are cold and dry in the winter.• Temperature inversions also occur in the winter.• (Winds are light and move in a clockwise direction.)

You will now watch a video on anticyclones (I didn’t choose the music!!!) Whilst watching it, you need to note down:

High Pressure (Anticyclones)

Positive effects on people Negative effects on people

Sum

mer

Winter

Positive effects on people Negative effects on people

Summer

Winter

Low Pressure (Depressions)

1. Read page 46 of the text book.2. Draw the following diagram using the template provided:

Low Pressure (Depressions)

A cold front means that cold air is coming. At a cold front, cold air pushes under the warm air. This produces strong winds and heavy rain.

A warm front means that warm air is coming. At a warm front, warm air is rising over cold air. This usually produces clouds and rain.

Low Pressure (Depressions)Use the animation below to describe the weather you’d experience if a depression passed over you.

Pressure

Let’s review the aims:

1. To know the causes high and low pressure.2. To be able to explain the weather conditions

associated with high pressure (summer and winter).3. To understand the impact of pressure on people.

Exam Practice Plenary

d) Weather forecast for August Bank Holiday.

“A depression will move across the British Isles during the day. A belt of light continuous rain will move from the west across the country to be followed by drier milder conditions. By evening this will give way to colder north westerly winds with showers. Temperatures will be warm though low for the time of year.”

Explain how your knowledge of a depression accounts for this weather forecast.