Depressions Flashcards
explain Stage 1 of a depression (warm front)
A warm front marks the front of an area of air that is warmer than the air ahead of it. When warm and cold air meet the warm air has to rise over the cold air. As it does so the air cools, condenses and forms low sheets of nimbostratus cloud. These clouds produce a long period of steady rainfall. Wind increases when the warm air rises because air pressure is dropping. This is because air from high pressure areas are rushing in to replace the escaping air. The movement of air from a high to a low pressure area creates winds. Those winds move SW
explain stage 2 of a depression (warm sector)
This is an area of milder air behind the warm front. Here the mild air is not in contact with any cold air. This means less air is rising, as less air is rising, less cloud is being produced. This causes the rain to become lighter or stop altogether. As less air is rising the winds drop. The wind direction changes to westerly
explain stage 3 of a depression (cold front)
This marks an area of air that is cooler than the air ahead of it. Cold air moves faster than warm air so the cold air in the cold front catches up with the milder air at the warm sector. As the cold front moves in the wind direction changes from westerly to north-westerly. This sudden change of wind direction causes gusty wind to form. The cold air pushes the warm air up very rapidly. This causes large cumulonimbus clouds to form that bring heavy rain. As the cold front moves away the rain becomes lighter and then turns to showers. The air is colder as winds are coming from the NW
explain occluded fronts in a depression
- Will sometimes form at the top of a depression where a cold front has moved in quickly
- The cold air in front of the warmer air creates a wedge which the warm air has to travel over
- Meanwhile cold air is cutting into the warm air in the warm sector
- This causes cumulonimbus clouds to form very quickly
- Occluded fronts bring short torrential rainfalls and strong winds
