If today's quiz had been a "real" quiz, you would have had the
full class period to work on it. But today's quiz is just
for practice and we spend the first 10 minutes or so of class
covering some new material.
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.
That is true 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
p. 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 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 depends also 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 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.
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
Pages 31 and 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
You'll hear Captain Hawthorne Charles Grey mentioned
in a video that I will show next week.
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.
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).
We didn't have time today for a10 minute video segment
describing Piccard's first trip into the stratosphere
(Piccard and Paul Kipfer very nearly didn't make it back
down alive).
You might have heard
about Felix
Baumgartner and the Red Bull Stratos balloon (or seen
the GoPro commercial during a recent Super Bowl). 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. If you have time
you should really watch the longer
version (9:32). 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 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).
I'll try to show a short video of one of their test dives (to
10,000 ft.)
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)
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). I've
got a pretty good video summary of their trip. Here
are three 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)
Here's a
summary and a status update from Wikipedia:
"In
March 2015, Piccard and Borschberg began an attempt 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. By 1 June
2015, the plane had traversed Asia,
and on 3 July 2015, it completed the longest leg of its
journey, from Japan to Hawaii. During that leg,
however, the aircraft's batteries experienced thermal
damage that took months to repair. The Solar Impulse is
scheduled to resume the circumnavigation in April 2016,
after testing beginning in February."
