Did you know that you can see the layers of the atmosphere?
The layers of the atmosphere appear as different colors in this image from the International Space Station.
The atmosphere is layered, corresponding with how the atmosphere’s temperature changes with altitude. By understanding the way temperature changes with altitude, we can learn a lot about how the atmosphere works.
Papers held up by rising air currents above a radiator demonstrate the important principle that warm air rises.
Warm Air Rises
Why does warm air rise (Figure above)? Gas molecules are able to move freely, and if they are uncontained, as they are in the atmosphere, they can take up more or less space.
- When gas molecules are cool, they are sluggish and do not take up as much space. With the same number of molecules in less space, both air density and air pressure are higher.
- When gas molecules are warm, they move vigorously and take up more space. Air density and air pressure are lower.
Warmer, lighter air is more buoyant than the cooler air above it, so it rises. The cooler air then sinks down, because it is denser than the air beneath it. This is convection, which was described in the chapter Plate Tectonics.
The property that changes most strikingly with altitude is air temperature. Unlike the change in pressure and density, which decrease with altitude, changes in air temperature are not regular. A change in temperature with distance is called a temperature gradient.
The atmosphere is divided into layers based on how the temperature in that layer changes with altitude, the layer’s temperature gradient (Figure below). The temperature gradient of each layer is different. In some layers, temperature increases with altitude and in others it decreases. The temperature gradient in each layer is determined by the heat source of the layer (See opening image).
The four main layers of the atmosphere have different temperature gradients, creating the thermal structure of the atmosphere.
This video is very thorough in its discussion of the layers of the atmosphere. Remember that the chemical composition of each layer is nearly the same except for the ozone layer that is found in the stratosphere (8a): http://www.youtube.com/watch?v=S-YAKZoy1A0 (6:44).
- Warm air rises, cool air sinks. Warm air has lower density.
- Different layers of the atmosphere have different temperature gradients.
- Temperature gradient is the change in temperature with distance.
Use this resource to answer the questions that follow
https://www.youtube.com/watch?v=VJkbad6RWtU Start at 4:41 to 6:50 unless you would like to review previous concepts.
- What are atmospheric layers based on?
- If the average July temperature at sea level in city A is 100-degrees and no other factors come into play except altitude, what will be the average July temperature at city B if it is at 5,000 feet?
- What is the name of the outer boundary of the troposphere?
- What is the temperature structure of the stratosphere?
- What is the thickness of the stratosphere relative to the thickness of the troposphere?
- What is the temperature structure of the mesosphere?
- What are the major characteristics of the thermosphere?
- What causes convection in the atmosphere?
- Why do the different layers of the atmosphere have different temperature gradients?
- What is temperature gradient?