Water in the Atmosphere Water in the Atmosphere Additional Resources Climate Precipitation Temperature T he atmosphere forms a protective layer around the Earth. Air can contains many gases including water vapor. The amount of water vapor in the air depends on the temperature.
Water vapor is lighter than the nitrogen and oxygen in the air, so rises in the atmosphere.
When it reaches a cooler temperature, the air can hold less water vapor, causing some to condense around particles of dust or spores in the air, forming floating droplets of water. Clouds move through the atmosphere in bands more or less parallel to the equator. Temperature differences within clouds cause air currents that move the water droplets around, sometimes carrying them into higher, cooler regions, where the rate of condensation increases, causing the droplets to grow larger. Droplets can rise and fall within a cloud until the air can no longer hold them up, and they fall. When those droplets grow large and heavy enough, they fall toward Earth as precipitation.