1. How does pressure change with altitude?
2. How does temperature change with altitude?
3. What are the different layers of the atmosphere, and how are they identified?
4. What is the composition of the atmosphere?
• What are the gases?
• Where did they come from?
  
• What is the abundance of the gases?
• I will not expect you to know exact numbers, especially for trace gases, but I do want you to know approximate values for the 4 most abundant gases.
• You should be able to rank the 4 most common gases in terms of abundance.
  
• You should know which gases ARE most abundant and which are trace gases.
  
• If they are trending up or down, I want you to know that.
  
• What is the importance of the gases?
• What are the pollutants, and why are they important?
• What is the Greenhouse Effect?
• What causes it?
• Why is it important?
5. What is the Radiation Balance?
• What are the numbers?
• What are the components?
• What types of solar radiation are important?
• What are greenhouse gases?
• Why is the Greenhouse Effect important?
  
• How does the Radiation Balance control our temperature?

Average Sea Level Atmospheric Pressure: 14.7 lbs/sq. in. or about 1000 milliBars (mB) [more precisely, 1013mB]
What does this mean?

1. On average, over every square inch of the earth's surface at sea level, there is a force of 14.7 pounds.
2. Where does that force come from?
1. Imagine a column of air, 1in x 1in (1 square inch), from sea level to the "top" of the atmosphere (we'll discuss "top" shortly).
2. How much would that weigh?
3. It would weigh 14.7 lbs.
4. The air pressure on the the earth comes from the mass of the atmosphere over every point, pulled by gravity; in other words, the weight of the atmosphere over every square inch of the earth's surface is what gives us air pressure.
5. Given that this is the case, how might you calculate the weight of the entire Earth's Atmosphere?
   
3. That pressure does not just go down, it presses on all surfaces.
1. Imagine a square on your belly, 10" x 10" (100 in²).
2. There would be a force of 14.7 lbs/in² x 100 in² = 1470 lbs (nearly 3/4 of a ton)
3. Why don't we go flying backwards then?  Because there's an equal and opposite force on your backside pushing in the other direction.
4. Why don't we get squished, then?  Two related answers:
• Liquids and solids that make up our bodies are incompressible.
• There is an equal and opposite outwards pressure in our bodies.
4. What happens to that pressure as we rise higher and higher?
1. As we rise, we get ABOVE some of the atmosphere, so the air above us is less heavy.
2. Therefore the pressure decreases as you rise (see figure below left).
   

Some things to note about this diagram:

1. 50% of all the atmosphere lies below about 5.5 km altitude
2. At an altitude of 11 km (roughly 35,000 ft, the altitude that WWII (non-pressurized) aircraft flew at from 1939-1945), the air pressure is <30% of sea level air pressure.  If you tried to breath at those altitudes, you'd quickly fall unconscious and die.  Many of our fathers, grandfathers, and (in some cases) great-grandfathers were fliers in WWII.  In order to stay conscious and alive, they HAD to breath oxygen continuously.  Our ancestors not only flew at those altitudes, but fought at those altitudes.  Today, we comfortably fly in pressurized jet airliners at that altitude without even thinking about it.
3. Note that in the graph on the right, of water pressure under the sea, decreases as you come up, for the same reason that air pressure decreases as you rise:  the weight of the overlying fluid decreases as you get above the fluid below.
• Water pressure decreases as you come up (or increases as you go down) by 1 atm (i.e 14.7 lbs/in²) about every 10 meters, in a straight line,
  
• because a 1 in² column of water 10 meters long weighs 14.7 lbs.
• Pressure is 1 atm at surface because of air pressure at sea level.
  
4. But there's a difference in how air pressure decreases as you go up.
   
5. Note that the higher you go in the atmosphere, the more slowly air pressure decreases for a given increase in elevation.
   
• From sea level to 2 km, air pressure decreases by about 200 mB.
• But if you rise 2 km from 8 to 10 km, air pressure decreases by less than 100 mB.
• To get a 200 mB decrease, you'd need to rise nearly to 14 km, a 3x greater increase in elevation than from sea level.
  
6. But as you rise in the ocean, the water pressure decreases by exactly the same amount for a given rise.
   
• Why?  Because air (a gas) is compressible and expandable. And as the pressure decreases, the air expands and its density decreases.
• Water (a liquid) is not compressible.  And it stays at the same volume no matter the pressure, so the density stays constant.
  
• So as you go higher and higher, you have to go over greater and greater thicknesses of air to lose the same amount of pressure.
7. The curve of air pressure to altitude never reaches zero pressure.
   
8. The net result of this is that there is NO TOP OF THE ATMOSPHERE. 
9. Instead, the atmosphere merges gradually with space.  There is no hard boundary.
10. Any boundary between "atmosphere" and "space" is arbitrary.
• NASA and the FAA set it at 100 km, about 62 miles high.
  

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Structure of Atmosphere: Based on how temperature changes.  Know the various layers.

• Thermosphere: Temperature increases as height increases.
• Mesopause (~80 km high)
• Mesosphere: Temperature decreases as height increases.
• Stratopause (~47km high)
• Stratosphere (Ozone Layer is here): Temperature increases as height increases.
• Tropopause (10 km high)
• Troposphere (Weather is here): Temperature decreases as height increases.

1. Troposphere: decreasing temperatures as elevation increases.
1. Another way of asking this is, WHY is the surface of the earth warm?
2. The answer, of course, is that it's heated by the Sun.
3. The Earth's atmosphere is largely transparent to radiation from the Sun.
4. That radiation comes down, hits the earth, is (partly) absorbed, and heats the ground.
5. This heats the atmosphere lying next to the ground (known as "sensible heating").
6. So as you move away from the surface, you're farther from the source of heating, and temperature decreases.
7. Also, as warm air rises, it expands and cools.  This decrease in temperature is known as the "adiabatic lapse rate" and is about 10^oC/km in the Troposphere.  This decrease in temperature occurs without any change in heat energy.
2. Stratosphere: increasing temperatures as elevation increases.
3. Mesosphere: decreasing temperatures as elevation increases.
4. We can combine the 2 observations above and note: Temperature reaches a maximum in the Stratopause.  Why?
1. The short answer is: The Ozone Layer
2. What does this mean?  Look at the figure below.
   
3. When ultraviolet (UV) light from the Sun hits an oxygen molecule (O₂), it breaks it into 2 extremely (and dangerously) reactive individual oxygen atoms.
4. These oxygen atoms immediately recombine with any available oxygen molecules, to produce a molecule with three oxygen atoms  That molecule (O₃) is known as "Ozone".
5. When UV light encounters an Ozone molecule, it is absorbed by Ozone.  We can say that Ozone is "opaque" to UV light.
6. Anything that absorbs energy (like UV light absorbed by Ozone) will warm up.  So the air warms up.
7. But note in the "Structure of the Atmosphere" diagram, that the altitude of maximum heating (the Stratopause) is significantly higher than the layer of maximum Ozone.  Why is that?
8. As UV comes DOWN through the atmosphere, it is, bit by bit, absorbed by Ozone.  So the amount of UV available for heating decreases, and by the time it reaches the maximum Ozone, there's only a little UV, so a small amount of heating.
9. As you go UP in the atmosphere, the amount of air decreases, so there's less and less oxygen available to be turned into Ozone, which means that there will be less absorption of UV and less heating.
10. The Stratopause, where there is a temperature maximum, is the location where there is enough Ozone to effectively absorb UV, and enough UV to cause maximum heating.
• Above that point, there's not enough Ozone to trap UV, so temperatures cool as you go up into the Mesosphere.
• Below that point, there's not enough UV to cause a lot of heating.  So temperatures cool as you go down into the Stratosphere.
5. Finally, note that as you go up from the Mesopause into the Thermosphere, temperatures again increase with increasing altitude.  Why?
1. Note the altitudes here - we transition into "space" as defined by NASA and the FAA.
2. While this is not a "perfect" vacuum, the pressures here are extremely low, and would be considered a pure vacuum nearly anywhere on Earth.
3. There are very few molecules and atoms of gas here, but they are exposed to the full force of the Sun's energy, so they are accelerated to very high speeds, which means very high temperatures.
4. That said, since the atoms and molecules are so widely dispersed, there is little energy out there, even if the temperatures are high.  It is similar to 4th of July sparklers, whose sparkles are very hot but so small that they are relatively harmless.
   

(For more information, click here!)

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Radiation Balance in Atmosphere (See your textbook as well):

Radiation: The Spectrum: 

Transparency of the Earth's Atmosphere.

• Charged particles (electrons mostly) vibrate,
• causing fluctuating electric and magnetic fields,
• which propagate outwards at the "speed of light".
• This is "electromagnetic radiation", AKA "light"
  
• The faster they vibrate, the higher the frequency and the more energetic the waves.
• Gamma rays (highest frequency (shortest wavelength))
• Then: Xrays,
• Ultraviolet
• Visible light:
• Violet
• Blue
• Green
• Yellow
• Orange
• Red
  
• Infrared (Most atoms on the surface of the earth vibrate fast enough for these to be given off)
  
• Microwaves
• Radio waves (lowest frequency, longest wavelength)
  

From the Sun:

• What kind is most abundant?
• This makes a lot of sense:
• Our eyes are adapted to use the most abundant light from the sun.
• If our sun gave off a lot of radio energy, we might expect to have little radar dishes instead of eyeballs.
  
• in contrast, UV (ultraviolet) light is shorter wavelength,
• and IR (infrared) is longer wavelength than visible light.
• And both are given off less by the sun than visible light.
  

Of 100% of incoming light:

• (from Science Direct)
  
• 30% is reflected (the albedo):
• 6% is scattered back to space
• 20% is reflected from clouds
• 4% is reflected from land and ocean
• Which has higher albedo, land or ocean?  Write down your answer, then click here to see if you can figure it out.
                                                              Or go to these links:  First   Second
  
• 70% is absorbed:
• 19% by clouds and atmosphere
• 16% absorbed by greenhouse gases and dust
• 3% absorbed by clouds
  
• 51% by land and ocean:
• 21% eventually released as infrared (IR) from surface (due to heating of surface)
• 7% released as "sensible heat" by conduction into atmosphere
• 23 released as "latent heat" by evaporation of water into atmosphere
• Of the 51% absorbed by land and ocean and 19% absorbed by clouds and atmosphere (70%):
• Only 6% IR makes it to space directly from the surface
• 38% is emitted out to space as IR from greenhouse gases in the atmosphere
• This means that IR is absorbed by greenhouse gasses in the atmosphere,
• which causes these gases to warm,
• in turn releasing IR in all directions,including back to the earth.
• The IR that is released BACK to the earth, warms it again, increasing global temperatures.
  
• 26% is emitted out to space as IR from clouds
  

(See your textbook for a more detailed explanation)

Air circulation - depends on changes in temperature:

• Heat air
• Temperature rises
• Molecules move faster
• Gas expands
• Density decreases
• Air rises

If you raise a parcel of air:

• expansion of air
• adiabatic cooling
• no change in heat
• adiabatic lapse rate (may be different from environmental lapse rate)

How do we lift Stable air?  We can do it when a wind blows over mountains; it falls right back down again!: