2. Be able to describe the formation of a depression weather system. Objectives Be able to describe the air movement within a depression weather system. Be able to identify the features of a depression upon a satellite image. Be able to identify the features of a depression upon a synoptic weather chart.

3. Polar Front Cold artic or polar air Tropical air Somewhere over the Atlantic… Depressions form at the boundary between cold artic/polar air in the North and tropical air in the South.

4. Cold artic or polar air Tropical air The cold air is pushing south and the warm air is pushing north, this creates a bulge along the polar front.

5. Can you identify the bulge along the polar front signifying the start of a depression?

6. Cold artic or polar air Tropical air Due to the Coriolis Effect, caused by the rotation of the Earth, the air moves around an area of low pressure in an anti-clockwise direction.

7. Cold artic or polar air Tropical air We can now see three fronts within the depression. Cold Front Warm Front Occluded front

8. Identifying a depression on a synoptic chart. Can you identify? Areas of low pressure Isobars tightly packed Characteristic fronts, warm, cold and occluded

9. In order to be sustained, depressions need a source of warm moist air. This is provided by the warm conveyor. Warm conveyor This rises rapidly over the cold air in front of it. As it does, the moisture within it cools and condenses to form a characteristic area of clouds. The cloud edge is sharp along the cold front. Like humans, depressions are both born and mature over time…

10. Can you identify the warm conveyor on this satellite image?

12. A ‘cold conveyor’ bring cold air in along the warm front, which rapidly rises in the centre of the system. This forms a characteristic band of cloud and precipitation as air rises towards the centre of the depression. This is called the emerging cloud head. cold conveyor

13. This encourages the warm air along the warm conveyor to rise. Behind the cold front, cold air descends from the upper atmosphere and spreads out along the cold front.

14. Can you identify the emerging cloud head on this satellite image?

16. Over time the depression begins to decay, the cold air cuts off the supply of warm moist air- leaving the emerging head cloud along the cold conveyor.

17. Can you identify the cloud associated with the decaying depression on this satellite image?

19. Movement of depression Klaus… http://www.youtube.com/watch?v=K_9ciOB8Ot0

20. Depression or not?… Which of the following would you associate with a depression? StatementTrueFalse Depressions begin when two types of cold air meet. Depressions are associated with low pressure. The air moves in a clockwise direction within a depression. Depressions usually bring rainfall. In a depression we could expect to see isobars packed closely together. There is usually no wind in a depression.