The atmosphere is a mixture of gases, suspended solids, and liquids that surrounds the planet. It is divided into four layers based on temperature.

The troposphere is the layer nearest the earth. It contains 75% of the gases of the atmosphere, as well as dust and water vapor. This layer is the zone where weather occurs.

Temperatures decrease with increasing height in the troposphere. Near the top of this layer, about 11 kilometers from earth, a boundary called the tropopause acts as a ceiling to the weather zone. The tropopause contains strong winds called the jet streams. Airplanes fly in this area and jet planes fly above this area. So pilots must understand how this part of the atmosphere creates weather.

Layers of the Atmosphere Diagram (PDF version)

Evaporation and Condensation Lesson Plan

Cloud Formation

Clouds are collections of tiny droplets of water suspended in the air. They are formed from the condensation on these tiny particles called condensation nuclei. Droplets may range from 0.002 to 0.1 millimeters in diameter. In clouds where large amounts of moisture are present, water droplets may join together. When these droplets reach about 2.0 to 6.5 millimeters in diameter, they may fall as rain. Rain is a form of precipitation. Snow, hail, and sleet are also forms of precipitation.

Cloud Formation Lesson Plan

Fog Formation

Condensation may occur near the ground. When this happens, fog forms. Fog is a cloud that forms near the ground. The ground cools quickly on a clear night. It cools the layer of air that lies above it. The air may be cooled to the dew point. If it is, the water vapor in the air condenses and forms fog.