Science Puzzle
Where Does a Hurricane Get Its Energy?
A hurricane can be hundreds of kilometres across, with winds over 250 km/h, and keep going for a week or more. Hurricanes only form over warm tropical seas, usually 26 °C or more, and they quickly weaken once they move over land or cold water.
Where does a hurricane get its enormous energy?
The Answer
From the warm sea. Evaporating water soaks up heat; when the water vapour later condenses into cloud and rain high in the storm, all that heat is released again, and it's this heat that drives the hurricane.
Turning liquid water into vapour takes a lot of energy. That's why you feel cold when you step out of a pool: the evaporating water is taking heat from your skin. Over a warm tropical sea, huge amounts of water evaporate, and the energy is carried up into the air inside the vapour, hidden.
In a hurricane, that damp air spirals inwards and rises. As it rises it cools, and the vapour condenses into towering clouds and torrential rain, giving out the hidden heat. That warms the air, which makes it rise even faster, which pulls in more damp air across the sea surface, which evaporates more water. The storm is an engine running on sea water. Scientists at the US weather agency estimate that the heat released this way in an average hurricane is about 200 times the electricity-generating capacity of the whole world.
Cut off the fuel and the engine stalls. Over land, or over cooler water, far less water evaporates, and the storm runs down within a day or two.
The principle: Latent heat. Evaporating water takes in heat and condensing vapour gives it out again, so warm ocean water carried up into clouds powers a hurricane like fuel.