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d ~ 90'048'000 km: day 35 of Earth's orbit

1000km (620 miles) wide and packing winds of 300km per hour (186mph), the recent cyclone Yasi was possibly the biggest and most powerful to hit the Australian coast in recorded history.

NASA Earth Observatory

It was the strongest storm globally since , which hit the Philippines in October 2010 and comparable to which raged across the Caribbean and Gulf of Mexico in 2008.

So what's the difference between cyclones, typhoons and hurricanes? Simply geography. They are all the same phenomenon, but given different names around the world. Cyclones in the southwest Pacific and Indian Ocean, typhoons in the northwest Pacific and hurricanes in the tropical Atlantic and eastern Pacific. To make things easier, I'll just refer to tropical cyclones from now on!

The habitat of these heat-fuelled beasts is confined to a zone between 5 and 30 degrees of latitude north and south of the equator. Any closer to the equator and our old friend the Coriolis force is too weak to induce any spin to the developing storm, while outside of the 30th parallel there just isn't enough heat to provide the necessary energy.

To make a tropical cyclone, you need very warm sea water with a temperature of at least 27C. This is why the storms occur seasonally, once summer sunshine has pushed sea temperatures beyond the threshold. They work like a huge heat engine, sucking up very warm, moist air from the sea surface which is then lifted and condenses into clouds. This releases even more heat which keeps the air buoyant and moving upwards before it finally cools and flows outwards at higher levels.

Cyclones play a very important role in transferring heat from the tropics to higher latitudes, acting as a natural safety valve. They also provide a large percentage of the annual rainfall in places such as the Philippines.

So despite the destructive power of cyclones, without their sustaining rain survival would be much more difficult in many parts of the world.

More on Tropical Cyclones:

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