Air's Properties as a Function of Altitude

The Troposphere

• The troposphere is the lowest level of the atmosphere, extending from the surface to around seven miles. Temperatures drop with altitude, ranging from an average of 59 degrees Fahrenheit to minus 71 degrees. This drop in temperature is due to adiabatic cooling, where surface heat cools as it rises. This also creates instability, which accounts for almost all the Earth's weather. Winds in the troposphere also increase with altitude, reaching a maximum at the jet stream that flows at its upper boundary. This layer also accounts for 10 percent of the atmosphere's ozone. Here, the ozone produces negative effects, such as smog and rising temperatures. The average atmospheric pressure at the surface is 1,013 millibars.

The Stratosphere

• The stratosphere represents the second level of the atmosphere, extending from around seven miles to 30 miles above the Earth's surface. A temperature inversion occurs in this layer, meaning temperatures rise with altitude. Temperatures rise from minus 71 to around 32 degrees Fahrenheit. This is caused by the absorption of solar heat by ozone. The stratosphere contains 90 percent of the planet's ozone. In this case, the ozone has the positive effect of absorbing harmful ultraviolet B and C radiation. Chlorine is the primary destroyer of this beneficial ozone, primarily coming from chlorofluorocarbons (CFCs) that eventually rise to this level of the atmosphere. The temperature inversion produces a very stable layer of air, preventing water vapor from rising into the stratosphere. The atmospheric pressure at its base is around 168 millibars.

The Mesosphere

• The mesosphere is the third layer of the atmosphere, extending from 31 miles to 53 miles above the surface. Scientists know the least about this layer because it lies above the reach of both aircraft and scientific balloons, and below the normal orbits of satellites. The temperature in the mesosphere drops with altitude, primarily due to carbon dioxide that reflects solar heat back into space. Temperatures drop from 32 to around minus 130 degrees Fahrenheit. At the start of the mesosphere, the atmospheric pressure is only around one millibar. It is here that noctilucent clouds form and special lightning, known as sprites, occurs.

The Thermosphere

• The thermosphere represents the outer layer of the atmosphere, extending from 56 miles to between 311 and 621 miles. There is another temperature inversion in this layer that is caused by solar radiation exciting atoms. However, the heat content is minimal because there are so few atoms. Unlike the other three layers, the main components are elemental. This is because the solar radiation breaks down the molecules into elements, primarily atomic oxygen, nitrogen and helium. Atmospheric pressure is less than 0.001 millibars. The Northern and Southern Lights occur in the thermosphere.