Properties of the Earth's Atmosphere:

The atmosphere is divided into four different zones: Troposphere, Stratosphere, Mesosphere, and Thermosphere. Each of these zones is separated by an interface, the tropopause, stratopause, and mesopause. The 4 graphs here make it possible to determine the temperature, pressure, and water vapor content at any altitude above the Earth in either miles or kilometers. Read questions carefully! Are you being asked about an altitude in miles or kilometers?

Be very careful about the altitude scales. Each division on the miles side of the scale is 5 miles (5, 10, 15, 20 etc) but each division on the kilometer side is 10 km (10, 20, 30, 40, etc). Be careful. Check your work!

 

Notice that as altitude increases through the Troposphere, the temperature decreases. This trend reverses through the Stratosphere which warms with increasing altitude and again reverses through the Mesospheres and Thermospheres.

You need to be able to find the temperature at any given altitude or the altitude at which a given temperature occurs. For example:

1) What is the temperature at an altitude of 45 miles (72km)?
Find 45 miles. Use a straight edge to draw a line to the temperature curve and drop straight down. The temperature is about -75C.

2) At what altitude is the temperature -75C?
Find -75C on the bottom axis and draw a straight line up to the temperature curve. Draw another line to the altitude (left) which is 45 miles (or 72km) above the Earth's surface.

 

 

Atmospheric pressure is given in units called 'atmospheres'. When you ate at sea level (0 altitude) there is one atmosphere pressing down on you so the pressure at sea level is 1 atm. Using the pressure chart on page 13 you can convert 1 atm to 1013.1 mb or 29.92 inches.

The higher you go the less atmosphere is pressing down from above so the pressure decreases. By the time you reach the Stratopause the pressure is very close to 0 but not quite. As long as there is any air above you there will be some slight pressure.

A typical question:
What is the atmospheric pressure at the tropopause (7 mi or 12 km)? Draw a straight line down from the tropopause and read the pressure. In this case, 0.25 atm. 

 

Almost all of the water vapor is found in the troposphere. As altitude increases, the concentration of water vapor decreases. This is why most weather, clouds, storms, etc is located in the troposphere and it is one reason why most commercial airliners fly at or near the Tropopause. By flying above most of the water vapor they avoid most of the weather. At an altitude of 12 - 13 miles or 21 - 22 km (blue line) there is no more detectable water vapor.

Some small amount of water vapor does reach the lower parts of the Stratosphere, usually as the tops of thunderstorms.

Typical questions:

Q: In which layer of the atmosphere is most of the water vapor found?
A: The Troposphere.

Q: What is the water vapor concentration at an altitude of 5mi (7 km)?
A: Find 5 miles and draw a straight line to the water vapor line. Drop straight down and read the value as accurately as possible: 10g/m3.

Be able to reverse the process: At what altitude is the water vapor content 10g/m3 ?

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