The sun heats the tropical areas more than the polar regions. If there were no wind, then the tropics would keep getting hotter and hotter, and the poles would get colder and colder. The atmosphere's basic function is to redistribute heat from the equator to the poles, and tropical cyclones are one mechanism by which this occurs. However it is still quite remarkable that such a thing as a tropical cyclone should arise. It has been said that if we had not actually observed tropical cyclones then, despite all we know about the physics of the atmosphere, we would never have guessed at their existence.