Clouds change from one minute to the next. Sometimes they look like billowy, white marshmallows. Other times they look like wispy, thin feathers.
It's nice that clouds are so interesting to watch, but they have a much more important job. They are the water transportation system of the world! They work very hard moving water around, from one place to another. Without clouds, all the water would eventually end up in the oceans, with none left for lakes, rivers or streams.
Clouds are made when water from Earth's surface evaporates into the sky. This means that as the sun warms the surface of the ocean or the land, water on the surface turns from a liquid to a gas and rises into the air. As the warm, moist air rises, it cools off. As it cools, the water gas turns again to droplets of liquid water.
When there are lots of droplets, we see them as clouds. When the droplets stick together, they make bigger droplets. Finally, they get too heavy to remain in the cloud and they fall out as rain. If it's very cold, they freeze into solid form, and fall as snow or hail. But no matter how much water they dump out, clouds do not give the Earth any more water than it had before.
Cloudsat is a new spacecraft that will be launched in 2003 to study the clouds. It will use radar to take 3-D pictures of clouds, and measure how much water and ice are in them at various heights. Cloudsat will work with other satellites that take different kinds of cloud measurements. Data collected by all these satellites will help scientists understand better how clouds work and how they affect climate all over the world.
To learn "cloudspeak" and do a cloud picture scramble, go to http://spaceplace.jpl.nasa.gov/cloudsat_puz.htm.
The Space Place is a Web site for children, offering educational activities and facts related to many of NASA's space missions. This article was provided by NASA's Jet Propulsion Laboratory, managed by Caltech in Pasadena.
