Depressions
Low pressure systems or depressions bring the cloud, rain and wind that we usually associate with British weather. Low pressure systems develop when less air flows into an area than out of it. They are the opposite in nature to high pressure systems or anticyclones.
The Development of a Low Pressure System
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/af/frnts/home.rxml
This diagram shows the development of a low pressure system. The cold air is heavier than the warm air so that is why it seems to plough it's way through the warm air. When the warm air meets the cold air they do not mix due to differences in both density and temperature. The warm air is forced over the cold air, forming clouds.
When the two different air masses meet, a front is formed.
When the warm air approaches the cold air, the warm air is forced to rise over the cold air. This forms a warm front.
When the cold air approaches the warm air, the warm air is also forced to rise over the cold air. This forms a cold front.
Would you like to explore the tutorial on fronts?
Or would you like to carry on with the tutorial on depressions?
