Cyclonic rainfall is caused by cyclonic activity and occurs along fronts. It is formed when two air masses of different temperature, humidity and density meet such as the meeting of a tropical maritime air mass and a polar air mass. A zone called a front separates them. At the warm front, the lighter warm air rises gently over the heavier cold air which remains close to the ground. As the warm air rises, it expands and cools and condenses to form clouds (altostratus). The rain falls steadily for a few hours to several days. At the cold front, the cold air forces warm air up aggressively, causing it to rise quickly and condense, forming cumulonimbus clouds. The heavy rain that falls is of short duration. Such rain is usually associated with temperate depressions (temperate cyclones).
|