Copyright © 2007 Dorling Kindersley
A storm is a bout of severe weather, with strong winds roaring at more than 55 mph (88 km/h), lightning flashes, thunder, and heavy rain. HURRICANES and tornadoes are whirling storms that can wreck whole towns.
Inside black thunderclouds, ice crystals and water droplets are whirled about and clash together, producing tiny electric charges. Positive charges build up at the top of the cloud, negative charges at the base. The ground below the thundercloud is also positively charged. When the difference between the charges gets big enough, the charge is unleashed inside the cloud as sheet lightning, or to the ground as forked lightning.
When lightning surges through the air, it instantly heats the air to around 45,000ºF (25,000ºC). The heated air expands and sends a shock wave through the air, which we hear as a clap of thunder.
Also called a typhoon or cyclone, a hurricane is a powerful, revolving storm that strikes in the tropics. It can cause great damage when it sweeps inland.
Hurricanes form over tropical oceans in humid weather, usually in the summer and fall months. Warm air charged with moisture from the sea starts to spiral upward around a calm area called the eye. Cool air is then sucked into the center, taking the place of the warm air, and fueling the storm.