Layers of the Atmosphere

Earth’s atmosphere can be divided into four layers based on temperature variations. The layer closest to the Earth is called the TROPOSPHERE. Above this layer is the STRATOSPHERE, followed by the MESOSPHERE, then the THERMOSPHERE. The upper boundaries between these layers are known as the TROPOPAUSE, the STRATOPAUSE, and the MESOPAUSE, respectively.

Temperature variations in the four layers are due to the way incoming radiant solar energy is absorbed as it moves downward through the atmosphere. The Earth’s surface is the primary absorber of this solar energy. Some of this energy is radiated back by the Earth and back into the atmosphere as heat, which warms the overlying troposphere that touches it in a process known as CONDUCTION. The temperature of the troposphere rapidly decreases with altitude until the tropopause, which is the boundary between the troposphere and the stratosphere.

The temperature then begins to increase with altitude in the stratosphere. This warming is caused by a special form of oxygen called OZONE (O₃), which absorbs ultraviolet radiation (UV) from the Sun which is converted to heat energy. The ozone in this layer protects us from most of the Sun’s UV radiation, which can cause sunburn, cancer, and even genetic mutations. Scientists are concerned that human activity is contributing to a decrease to ozone in the stratosphere. Nitric Oxide (NO₂), which is the exhaust of high-flying jets, and a class of chemicals called chlorofluorocarbons (CFC’s), which were used as refrigerants and in the making of plastics also contribute to this ozone decrease.

At the stratopause, the temperature stops decreasing with altitude. The overlying mesosphere does not absorb solar radiation, so the temperature decreases as altitude increases. At the mesopause, the temperature then begins to increase with altitude, and this trend continues in the thermosphere. Here, solar radiation first hits the Earth’s atmosphere and the air molecules there heat up. But because the atmosphere here is so thin, a normal thermometer cannot measure this temperature accurately, so special instruments are needed. At this point, the atmosphere gradually fades away until it is called space.

Most people assume that the temperature steadily decreases the higher you go in the atmosphere. This article below explains why the temperature appears to increase and decrease at different levels of the atmosphere.

The graphs in the image below are showing three things.

Graph 1 : Shows how the temperature changes as you go higher up in the atmosphere. Notice how the temperature does not decrease the higher you go up. Sometimes the temperature actually increases.

Graph 2 : Shows how the air pressure changes as you go higher up in the atmosphere. Notice how the air pressure is decreasing as you move up. What would cause this?

Graph 3 : Shows how the water vapor changes as you go higher up in the atmosphere. Most of the water vapor in the atmosphere is in the troposphere and it steadily and quickly decreases with altitude. How does this explain why all weather occurs in the troposphere?