ZIMSEC O Level Geography Notes: Convectional Rainfall
- This is the main type of rainfall in the humid tropics such as the Amazon and Congo rain forests.
- Occurs when the ground surface is locally overheated because in the tropics the surfaces and the air above them gets very hot and powerful convection currents are set up in the air.
- First the adjacent air is heated by conduction,
- Then it expands and rises.
- During the ascent the air mass remains warmer than the surrounding environmental air thus becoming unstable.
- The air is cooled as it rises producing towering cumulonimbus clouds.
- The updraught (upward rising of the air) is maintained by energy released as latent heat is released at both condensation and freezing levels.
- Since the air is hot before it is forced to rise, it is able to absorb very large amounts of moisture and when it is forced to rise by the convectional currents torrential rainfall results.
- Due to the large amounts heat released by release of latent heat at condensation and freezing level very powerful thunderstorms that are associated with rain forests develop.
- Maximum heating of surfaces occurs during the afternoon and it is at this time that convectional rain tends to fall.
- Most rainfall that fall in West and Central Africa is convectional rainfall.
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