Depressions

Question 1

What are depressions

Answer 1

Low pressure weather systems- areas of low atmospheric pressure, often below 1,000 mb

Question 2

How are depressions represented on a weather map

Answer 2

A system of closed isobars with pressures decreasing towards the centre

Question 3

Where do depressions move

Answer 3

Rapidly from west to east across the British isles

Question 4

What are the isobars of a depression like

Answer 4

Usually close together, producing a steep pressure gradient from the outer edges to the centre

Question 5

Winds in a depression

Answer 5

Often strong and blow inwards towards the centre of the low in an anti-clockwise direction

Question 6

When is the wind said to veer

Answer 6

In the Southern part of the British Isles, a change in wind direction occurs from south to southwest to west to northwest as the depression moves across from west to east

Question 7

When is the wind said to back

Answer 7

In the northern parts of the British isles the wind changed direction from southeast to east to northeast to east

Question 8

What are the two air masses involved in a depression affecting the British isles in the North Atlantic

Answer 8

• polar maritime air, which is dense, moist and cold

- tropical maritime air, which is light, moist and warm

Question 9

What happens as the two bodies of air that form the depression above the British Isles move towards each other

Answer 9

The warmer, less dense air from the south rises above the colder, dense air from the north- the rising air is removed by strong upper atmospheric winds (the jet stream) , but as it rises the Earth’s rotational spin causes it to twist
= a wave at ground level in the polar front, it increases in size to become a depression

Question 10

What two parts of the original front have developed after the two bodies of air have mixed and twisted

Answer 10

• the warm front at the leading edge of the depression where warm, less dense air rises over the colder air ahead
• the cold front at the rear of the depression where colder dense air pushes against the warmer air ahead

Question 11

What lies between the warm front and the cold front

Answer 11

The warm sector

Question 12

What is the warm sector

Answer 12

An area of warm and moist air

Question 13

What is an occlusion

Answer 13

As the depression moves eastwards, the cold front gradually overtakes the warm front to form an occlusion in which the colder air undercuts the warmer air so that it no longer touches the ground