through the sky. Before she can open her parachute, she falls into a cloud. A thick, white fog surrounds her. She is quickly drenched by the millions of tiny water droplets she plummets through. She worries that she might be hit by hail or winds might toss her around. You may think that clouds are huge, fl oating
J
cotton balls. In fact, some clouds do look like that, but others don’t. In fact, some clouds are really odd looking.
Fascinated by Clouds High, wispy clouds that look like horsetails streak across the sky. Big, puff y, white clouds that look like grazing sheep driſt through the sky. Dark, powerful, storm clouds churn through the sky. T ey growl with thunder and fl ash with lightning bolts. You’ve probably seen all these kinds of
clouds. T ey’re pretty common in most places. But if you really look, you can fi nd some really odd clouds. For instance, I’ve seen clouds that shine a ghostly blue at night. I’ve watched some clouds curl like breaking waves, and others roll toward me very quickly. T e more clouds I observe, the more they
fascinate me. I want to learn how these cool clouds form and why they come in so many shapes and sizes. Here’s some of what I know. Clouds may look diff erent, but they all
basically form in the same way. It’s all in how Earth’s major systems—water, land, and air— interact. To see how this happens, let’s tour some of my favorite clouds.
4 The water falls from clouds as
precipitation.
umping from a plane, a skydiver falls
Drop by Drop, a Cloud Forms T e fi rst thing to know is that all clouds are made of a lot of water or ice crystals. As much as 200 tons of water can collect in a single puff y, white cloud. T at’s as heavy as 80 elephants! T e water in clouds is part of our planet’s
hydrosphere. T e hydrosphere contains all the water on Earth, no matter where it is or which state it is in. Energy from the sun warms the water. Some water gets warm enough to evaporate, or change into a gas called water vapor. T e vapor rises into the atmosphere, or the air that surrounds Earth. T e molecules that make up water vapor
expand as they rise. As the vapor expands, it cools. When conditions are just right, the vapor condenses, or turns back into microscopic droplets of liquid water. T e droplets cling to tiny specks of dust fl oating in the air. When hundreds of millions of these droplets collect in an area, they appear as a cloud.
3 The water droplets cling to dust in the atmosphere,
forming clouds.
18 NATIONAL GEOGRAPHIC EXTREME EXPLORER NATIONAL GEOGRAPHIC EXTREME EXPLORER
Fun Fact
At any moment, clouds cover 70 percent of Earth’s sky.
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