自然科学 台风是怎么形成的？

    A bit of rain and wind in summer can be nice. But bad storms are quite different.
    Some of the worst storms are typhoons（台风）. Every year, about 80 typhoons hit different places around the world. The strongest ones are usually around the Pacific Ocean and the South China Sea. Most of them happen in July, August and September.
    Why? When lots of seawater gets hot in the summer sun, it evaporates（蒸发） into the air. This makes the air hotter, too. When the air gets warm enough, it starts to move higher up into the sky. Then, cooler air around it rushes in to fill the space that is left. Once the air gets warmer, it starts to move more quickly, making wind. The wind goes in circles, and it keeps moving higher in the sky. The warmer the air gets, the quicker the wind moves. And when the wind moves faster than 30 meters a second, a typhoon begins.
    A typhoon has two parts. One is called the “eye”. This is right in the middle of a typhoon and is calm. The eye of typhoon can be about 40 kilometers wide. In the eye, the wind does not move so fast, and there are not many clouds in the eye. The other part of a typhoon is the wall of clouds around the eye. This is where the strongest winds and hardest rains are.
    Typhoons are very dangerous. They blow away houses and cars. And they can also kill people! Typhoons’ hard rains are bad for farmers’ crops.