Convection in tropical latitudes

When the earth's surface is heated by the sun, the layer of air in contact with it becomes warmer, and is therefore less dense and more buoyant, so that it starts to rise. It expands and cools as it rises: if sufficiently moist, it will become saturated, and the water vapour it contains will start to condense, forming cumulus clouds.

The enormous amount of energy released by condensation causes the air to rise further. If it is very moist, it may generate towering cumulonimbus thunderstorm clouds growing to 17-20,000 metres in height. The released energy causes violent up- and down-draughts.

High evaporation rates over the tropical oceans lead to very moist air and large cumulonimbus clouds. In a tropical cyclone, convective cloud patterns become organised, and circulating gale-force winds develop.

(bottom left) This infrared satellite photograph taken in February 1992 shows the wet season in full swing with widespread thunderstorms over northern Australia, Papua New Guinea and Indonesia. The very cold tops of the cumulonimbus clouds, which reach 17-20,000 metres, stand out brightly.