There is an Optional Assignment associated with this supplementary reading section.  It is due by Tue., Sep. 17.  You'll be able to earn extra credit points; see the assignment itself for more details.

Air temperature changes with altitude, troposphere & stratosphere

We have learned that both air pressure and air density decrease with increasing altitude.  What happens to air temperature?  Our personal experience is that it also decreases with increasing altitude.  It is colder at the top of Mt. Lemmon than it is here in the Tucson valley.

Temperature does decrease with height up to an altitude of about 10 km (about 30,000 ft.).  People were very surprised in the early 1900s when they used balloons to carry instruments above 10 km and found that temperature stopped decreasing (the information below is on page 31 in the ClassNotes).


The figure below is a graph of air temperature (green line) versus altitude and gives you a rough idea of how temperature changes with altitude.



Temperature drops between the ground and about 10 km altitude.  Temperature remains fairly constant between 10 and 20 km (an isothermal layer) then begins increasing with increasing altitude between 20 and 50 km.  The atmosphere can be split into layers depending on whether temperature is increasing or decreasing with increasing altitude.  The two lowest layers are shown in the figure above.  There are additional layers (the mesosphere and the thermosphere) above 50 km but we won't worry about them in this class.  You also don't need to worry about the specific temperature values on the x-axis of the graph.


The numbers below refer to the numbered points in the figure above.

1. We live in the troposphere.  The troposphere is found, on average, between 0 and about 10 km altitude, and is where temperature usually decreases with increasing altitude.  [the troposphere is usually a little higher in the tropics and lower at polar latitudes, the altitude also depends on time of year]

The troposphere can be stable or unstable (tropo means "to turn over" and refers to the fact that air can move up and down in the troposphere).  The troposphere contains most of the water vapor in the atmosphere (the water vapor comes from evaporation of ocean water and then gets mixed throughout the troposphere by the up and down air motions).  The troposphere is where most of the clouds and weather occurs. 

2a. The thunderstorm shown in the figure with its strong updrafts and downdrafts indicates unstable conditions.  When the thunderstorm reaches the top of the troposphere, it runs into the bottom of the stratosphere which is a very stable layer.  The air can't continue to rise into the stratosphere so the cloud flattens out and forms an anvil (anvil is the name given to the flat top of the thunderstorm).   The flat anvil top is something that you can go outside and see and often marks the top of the troposphere.


ISS016-E-027426

ISS015-E_27038

ISS007-E-13020

Here are several images of thunderstorms and anvil clouds taken from above, from the International Space Station (all 3 images courtesy of the Image Science and Analysis Laboratory, NASA Johnson Space Flight Center, www.eol.jsc.nasa.gov).  The space station is probably 200 or 300 km above the earth.

This photo of Mt. Everest was selected as the Picture of the Day on Wikipedia for Dec. 22, 2007.
Photo credit: Luca Galluzi www.galluzi.it 

2b.  The summit of Mt. Everest is a little over 29,000 ft. tall and is close to the average height of the top of the troposphere.

2c.   Cruising altitude in a passenger jet is usually between 30,000 and 40,000, near or just above the top of the troposphere, and at the bottom of the stratosphere.  The next time you're in an airplane try to look up at the sky above.  There's less air and less scattering of light.  As a result the sky is a darker purple color not blue.  If you get high enough the sky would eventually become black.

3.  Temperature remains constant between 10 and 20 km and then increases with increasing altitude between 20 and 50 km.  These two sections form the stratosphere.   Increasing temperature with increasing altitude is called an inversion.  This is what makes the stratosphere so stable.

4.   A kilometer is one thousand meters.  Since 1 meter is about 3 feet, 10 km is about 30,000 feet.  There are 5280 feet in a mile so this is about 6 miles (about is usually close enough in this class). 

5.    The ozone layer is found in the stratosphere.  Peak ozone concentrations occur near 25 km altitude.

Here's the same picture drawn again (for clarity) with some additional information.  We need to explain why when temperature decreases all the way up to the top of the troposphere, it can start increasing again in the stratosphere.


6.   Sunlight is a mixture of ultraviolet, visible (green in the figure above), and infrared light (colored red).  We can see the visible light.

6a. Much of the incoming sunlight passes through the atmosphere and arrives at the ground where it is absorbed.  This warms the ground.  The air in contact with the ground is warmer than air just above.  As you get further and further from the warm ground, the air is colder and colder.  This explains why air temperature decreases with increasing altitude in the troposphere.

5b. How do you explain increasing temperature with increasing altitude in the stratosphere? 

     Absorption of ultraviolet light by ozone warms the air in the stratosphere and explains why the air can warm (oxygen also absorbs UV light).  The air in the stratosphere is much less dense (thinner) than in the troposphere.  So even though there is not very much UV light in sunlight, it doesn't take as much energy to warm this thin air as it would to warm denser air closer to the ground.

    It's a little (maybe a lot) harder to explain why the temperature starts increasing around 20 km and continues to increase all the way to 50 km.  Most likely different amounts of different types of ultraviolet light are being absorbed throughout the stratosphere.  Ozone is not the only gas that can absorb UV light.  Oxygen is also a good absorber of UV light.

7.  That's a manned balloon; Auguste Piccard and Paul Kipfer are inside.  They were the first men to travel into the stratosphere and return alive (see pps 31 & 32 in the photocopied Class Notes).  It really was quite a daring trip at the time, and they very nearly didn't survive it.  More about the Piccard family below.

Some early studies of the atmosphere

Page 31 and page 32 in the ClassNotes list some of the significant events in the early study and exploration of the atmosphere.  A few of them are included below.



Once you realize that air has weight you can design an instrument to measure pressure.  The mercury barometer was invented in 1643.  Also once you understand that pressure depends on the weight of the air overhead it is a fairly easy step to figure out that pressure should decrease with increasing altitude.  This idea was verified in 1648 by carrying a barometer to the summit of a mountain.


The earliest balloon trips into the upper atmosphere were in unheated and unpressurized gondolas.  Climbers have made it to the summit of Mt. Everest without carrying supplementary oxygen but it is difficult and requires acclimation.  You can't acclimate to conditions above 25,000 ft and can't remain up there very long - it's referred to as the "death zone."  (Read "Into Thin Air" by Jon Krakauer if you'd like to get some idea of what it's like trying to climb Mt. Everest)

Balloon travel into the stratosphere

There was quite a competition in the 1920s and 30s to see who could travel the highest in a balloon (the Guinness Book of Records was in existence at that time).  Hawthorne Charles Grey was one of first of these adventurers.


Note the clothing that Capt. Grey had to wear to try to stay warm.  All of his trips were in an open, unpressurized gondola. 


Auguste Piccard was part of a two man team to first travel into the stratosphere and return alive.

 Source of the image below

I believe this is the gondola flown into the stratosphere by Auguste Piccard and Paul Kipfer is shown above (source).  The figure caption is in German so I am not sure that is the case.

Auguste Piccard is shown in the figure at left.  The sealed and pressurized gondola he took into the stratosphere is shown at right.  Note how one side is black and the other white.  By turning the gondola they could control the temperature inside (pointing the black side toward the sun would warm the gondola, turning the white side would allow the gondola to cool off).

You might have heard about Felix Baumgartner and the Red Bull Stratos balloon (or seen the GoPro commercial during the Super Bowl a few years ago).  On Oct. 14, 2012 he reached an altitude of nearly 128,000 feet (39 km or 24 miles) and then jumped.  He reached a speed of 843 MPH on the way down (Mach 1.25 or 1.25 times the speed of sound). 

Here's a short video (1:25) summary of the flight and jump.  Here's a longer version (9:31)filmed using cameras mounted on Baumgartner's space suit.  Baumgartner began to spin during the descent but was able get out of it.  He came very close to blacking out.

Jacques and Bertrand Piccard

The Piccards were/are really quite an adventurous family.  Jacques Piccard, Auguste's son, would later travel with Lt. Don Walsh of the US Navy to a depth of about 35,800 feet in the ocean in the Mariana Trench (Auguste participated in some of the test descents to 10,000 ft).  They did that in the Bathyscaph Trieste (shown below) on Jan. 23, 1960 (source of the image).



Here's a National Geographic video describing film director James Cameron's much more recent solo dive to the Challenger Deep in the Mariana Trench on Mar. 12, 2012 (2:16).  (note mention of the 16,000 psi pressure on the submersible at the bottom of the ocean, more than 1000 times higher than normal atmospheric pressure at sea level)



Bertrand Piccard, Jacques' son (Auguste's grandson) was part of the first two man team to circle the globe non-stop in the Breitling Orbiter 3 balloon (Mar. 20, 1999).  Brian Jones was the second team member (source of the left image above, source of the right image).   Here are a couple of online videos of the event: short summary (1:40) and a full documentary (54:06).

Bertrand Piccard is currently part of a project to fly a long-range, solar-powered aircraft (the Solar Impulse) around the world. 


A photograph of Solar Impulse 1 (source of the photo) A photograph of Solar Impulse 2 in a hanger in Oahu, Hawaii.  This photograph was originally posted on Flickr by Anthony Quintano.  (source of the photograph)




Here's a summary  from Wikipedia:
"On 9 March 2015, Piccard and Borschberg began to circumnavigate the globe with Solar Impulse 2, departing from Abu Dhabi in the United Arab Emirates. The aircraft was scheduled to return to Abu Dhabi in August 2015 after a multi-stage journey around the world. By June 2015, the plane had traversed Asia, and in July 2015, it completed the longest leg of its journey, from Japan to Hawaii. During that leg, the aircraft's batteries sustained thermal damage that took months to repair. Solar Impulse 2 resumed the circumnavigation in April 2016, when it flew to California. It continued across the US until it reached New York City in June 2016. Later that month, the aircraft crossed the Atlantic Ocean to Spain. It stopped in Egypt before returning to Abu Dhabi on 26 July 2016, more than 16 months after it had left, completing the approximately 42,000 kilometre (26,000 mile) first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power."