Formation of a depression

Objectives Be able to describe the formation of a depression weather system. 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.

Somewhere over the Atlantic… Depressions form at the boundary between cold artic/polar air in the North and tropical air in the South. Cold artic or polar air Somewhere over the Atlantic… Polar Front Tropical air You may like to show this video https://www.youtube.com/embed/knxrOk8Jsok

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

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

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. Cold artic or polar air Tropical air

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

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

Like humans, depressions are both born and mature over time… In order to be sustained, depressions need a source of warm moist air. This is provided by the 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. Warm conveyor

Can you identify the warm conveyor on this satellite image?

A ‘cold conveyor’ bring cold air in along the warm front, which rapidly rises in the centre of the system. cold conveyor 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.

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. This encourages the warm air along the warm conveyor to rise.

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

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.

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

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

Which of the following would you associate with a depression? Depression or not?… Which of the following would you associate with a depression? Statement True False 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.