The envelope of gas surrounding the Earth changes from the ground up. Five distinct layers have been identified using...
- thermal characteristics (temperature changes),
- chemical composition,
- movement, and
Each of the layers are bounded by "pauses" where the maximum changes in thermal characteristics, chemical composition, movement, and density occur.
- The troposphere begins at the Earth's surface and extends up to 4-12 miles (6-20 km) high. This is where we live. As the density of the gases in this layer decrease with height, the air becomes thinner. Therefore, the temperature in the troposphere also decreases with height. As you climb higher, the temperature drops from about 62°F (17°C) to -60°F (-51°C). Almost all weather occurs in this region.
The height of the troposphere varies from the equator to the poles. At the equator it is around 11-12 miles (18-20 km) high, at 50°N and 50°S, 5½ miles and at the poles just under four miles high. The transition boundary between the troposphere and the layer above is called the tropopause. Together the tropopause and the troposphere are known as the lower atmosphere.
- The Stratosphere extends from the tropopause up to 31 miles above the Earth's surface. This layer holds 19 percent of the atmosphere's gases but very little water vapor.
Temperature increases with height as radiation is increasingly absorbed by oxygen molecules leading to the formation of Ozone. The temperature rises from an average -76°F (-60°C) at tropopause to a maximum of about 5°F (-15°C) at the stratopause due to this absorption of ultraviolet radiation. This increase is temperature with height means no "convection" occurs since there is no vertical movement of the gases.
The transition boundary which separates the stratosphere from the mesosphere is called the stratopause. The regions of the stratosphere and the mesosphere, along with the stratopause and mesopause, are called the middle atmosphere by scientists.
- The mesosphere extends from the stratopause to about 53 miles (85 km) above the earth. The gases, including the oxygen molecules, continue to become thinner and thinner with height. As such, the effect of the warming by ultraviolet radiation also becomes less and less leading to a decrease in temperature with height. On average, temperature decreases from about 5°F (-15°C) to as low as -184°F (-120°C) at the mesopause.
However, the gases in the mesosphere are still thick enough to slow down meteorites hurtling into the atmosphere, where they burn up, leaving fiery trails in the night sky.
- The Thermosphere extends from the mesopause to 430 miles (690 km) above the earth. This layer is known as the upper atmosphere.
The gases of the thermosphere are increasingly thinner than in the mesosphere. As such, incoming high energy ultraviolet and x-ray radiation from the sun, absorbed by the molecules in this layer, causes a large temperature increase.
Because of this absorption, the temperature increases with height and can reach as high as 3,600°F (2,000°C) near the top of this layer; however, despite the high temperature, this layer of the atmosphere would still feel very cold to our skin because of the extremely thin air. The total amount of energy from the very few molecules in this layer is not enough to heat our skin.
Take it to the MAX! The Ionosphere
- The Exosphere is the outermost layer of the atmosphere. It extends from the thermopause - the transition boundary which separates the exosphere from the thermosphere below - to 6,200 miles (10,000 km) above the earth. In this layer, atoms and molecules escape into space and satellites orbit the earth.