Nancy Jones, age 13, of Whittler, CA for her question:

How does air cool itself?

The air gets its heat from the ground and from the warm face of the sea. There are several ways in which it can lose its heat. Warm air expands and becomes thinner. As this happens it loses heat and becomes cooler. A mass of hot air near the ground may expand, pushing upwards. Once aloft it cools, for it has become thinner. The vapor it held may be forced to condense into misty droplets. The hot air near the ground has launched a cloud, high in the sky.

Warm air often loses heat as it runs up the slope of a high mountain. A cold surface, such as a polar ocean current, also tends to lower the temperature of the air above it. A vast mass of warm air may also lose heat when it tangles with a large mass of very chilly air.