ATM S 211
Midterm Examination
April 25, 2005
Name _______KEY_______________________________
This examination consists of a total of 80 points. In each of the first two sections,
you have a choice of which questions to answer. Please note that you will not get
extra credit by answering more. You must answer both of the last two questions. If
you need more room, feel free to use the back side of the paper. If you do so,
however, indicate clearly which answer is being continued.
Briefly define any 6 of the following 8 terms, showing that you understand its meaning in the
context of this course. You may give examples, equations, and/or sketches if you think it is
helpful. [4 points each, maximum of 24]
1. Climate forcing
A change in energy balance imposed upon the planet for a sustained period of time.
(The difference between forcing and perturbation involves the length of time over which
the energy balance change is imposed, but to some extent this is contextual.)
2. Lapse rate
The rate at which temperature changes with height in the atmosphere
3. Greenhouse gas
An atmospheric gas that is capable of absorbing infrared radiation emitted by the earth
surface; this “traps” heat within the lower atmosphere, which then re-radiates it back to
the surface. This keeps the surface warmer than it would otherwise be.
4. Climate sensitivity
The response of the global annual-average surface temperature to a change in climate
forcing; defined by the equation ∆T = λ ∆F, where λ is the climate sensitivity
5. Dynamic equilibrium
When a property of a system remains constant as a result of a balance of mass or
energy fluxes that tend to operate in opposite directions; an example is the white daisy
world on the cool side of the temperature curve
6. Hydrogen bond
The attractive force between the negative end (O) and the positive end (H) of two
different water molecules; this bond is responsible for the high latent heat value of water
7. Isotope
An atom that differs in atomic weight for the most common atomic weight for the same
element; 14C is an isotope of 12C
8. Saturation vapor pressure
The maximum amount of water vapor (measured in units of pressure) in a parcel of air
before condensation (conversion to liquid water or ice) occurs; it is a function of
temperature only
Answer any 4 of the following 5 short questions. [8 points each; maximum of 32]
1. Draw a system diagram for the Ice-Albedo Feedback. Use the following 3 system
components: Surface Temperature, Ice-Snow Cover, and Planetary Albedo. Explain how it
works, starting with a small, initial decrease in temperature. Is this a positive or negative
feedback loop?
If temperature decreases, the ice cover increases; if ice cover
increases, albedo increases; if albedo increases, temperature
decreases. (Albedo increases because ice and snow are such
bright surfaces; brighter planet means less solar absorption,
so the temperature drops.
This loop has an even number of negative couplings (the
round-headed arrows), so it is a positive feedback loop.
2. What determines if a cloud has a warming or cooling influence on climate? In your answer,
be sure to explain how clouds interact with different types of radiation.
Clouds affect climate by (a) reflecting solar radiation and (b) contributing to the
greenhouse effect by absorbing infrared radiation from the surface, preventing its loss to
space, and then emitting infrared energy to space at a lower temperature. So the cloud
properties that determine its effect are: (1) thickness (better reflector) and (2)
temperature and/or height in the atmosphere. (Because atmospheric temperature
decreases with altitude, higher clouds are colder clouds and therefore more effectively
prevent loss of infrared radiation.) So, low clouds tend to cool the planet because they
reflect a lot of solar radiation; high clouds tend to warm the planet because they reflect
less solar radiation than low clouds (high clouds are thinner) and prevent the loss of
warm infrared radiation from the surface.
3. In Karl Popper’s view, some sources of knowledge have greater authority than others (for
example, our course textbook compared to a tabloid newspaper), but no source of knowledge
has ultimate authority. Explain what he means by this.
All knowledge is subject to being falsified (shown to be wrong). The key to scientific
progress is that we willingly and vigorously engage in a continuous process to discover
and eliminate “errors” in our current knowledge. Some sources of knowledge have
greater authority because they emerge from a more rigorous and careful evaluation and
elimination of errors. Our textbook is the result of such a process, because the material
in it is a summary of critiqued science and the textbook itself has been read and
reviewed by many professors and students. Tabloid newspapers go through no such
evaluation. Our textbook does not have ultimate authority, however, because aspects of
it may be shown to be false by future scientific investigations.
4. Answer the following:
a. What can the 14C/12C ratio tell us about ocean water?
b. Jamie builds a computer model for the ocean. In her model, the ratio of 14C to 12C in
the water at the bottom of the ocean is greater than the ratio of 14C to 12C in the ocean
mixed layer. Is that the same relationship that is observed in the real ocean?
c. Describe the process whereby the 14C/12C ratio in a parcel of water changes.
a) The 14C/12C ratio tells us the age of the deep ocean water.
b) In the real ocean, the 14C/12C ratio decreases with time in the deep
ocean, so the ratio in the deep ocean is less than the ratio in the
surface ocean. Jamie’s model is incorrect.
c) The 14C/12C ratio decreases with time because 14C radioactively
decays with a half-life of 5730 years. The ratio in surface water is the
same as in the atmosphere, where the 14C concentration is constantly
replenished by cosmic rays. In the deep ocean, however, there is no
way for the 14C concentration to be replenished, so the 14C/12C ratio
steadily decreases.
5. Distinguish “a change in weather” from “a change in climate”. Discuss the ease or difficulty
of knowing if you have observed a change. Mention at least three observable properties that
are involved in both “weather” and “climate”
Weather is the state of the atmosphere (temperature, cloud cover, wind speed,
precipitation, etc.) at any given moment. This state changes from one moment to the
next. Climate consists of the long-term statistical distribution of weather states over
some defined period (and region). Examples are annual average rainfall or temperature
in Seattle, annual average snowfall at Mt. Rainer. A change in weather can be observed
directly and easily (it is raining now, but was not raining last hour). Observing a change
in climate requires many years of data to detect.
Answer each of the following two questions. Each one is worth 12 points. [Total of 24]
1. Draw a sketch of the Hadley circulation.
• Indicate on your diagram the position of the circulation with respect to latitudes and the
position of high and low pressures associated with the circulation.
• What are the near-surface winds called? What is their direction? Explain why they have
this orientation.
• If the planet earth rotated more slowly than it does, what effect would this slower
rotation have on the Hadley circulation? (In other words, how would it change?)
H
H
The near-surface winds are called the trade winds. They are easterlies, meaning they
blow from east to west. Their direction is a result of the Coriolis effect. Because the earth
rotates about its axis from west to east, winds blowing towards the equator appear to
veer towards the right, or to the west.
If the earth rotated more slowly, the Coriolis effect would be lessened. Thus, the winds
blowing away from the equator would still veer to the right, but more slowly. This would
extend the Hadley circulation further towards the poles. The net effect would be to
expand the poleward extent of the Hadley circulation.
2. Draw a box diagram of the earth hydrologic cycle.
• Label the reservoirs and the sink and source connections clearly.
• List (separately from the box diagram) the reservoirs in descending order from the one
with the most to the least burden of water.
• Write down an equation for “residence time”. Given the following information, calculate
the residence time of water in the atmosphere.
Amount of water in the atmosphere
1.3 x1013 m3
Evaporation from land
62 x 1012 m3 /year
Evaporation from ocean
361 x 1012 m3 /year
Precipitation over land
99 x 1012 m3 /year
Precipitation over ocean
324 x 1012 m3 /year
[This is the figure from the text. Any
approximation of it that shows the three
reservoirs (land, atmosphere, oceans)
and the connections of evaporation,
precipitation and runoff is acceptable. The
actual numbers are not required.]
In order from most to least water are:
• Ocean
• Land
• Atmosphere
Residence time = Burden / Sink where burden is the amount in the reservoir and
the sink is the loss rate from the reservoir.
Using the figures provided:
Burden = 1.3 x1013 m3
Sink
= sum of precipitation rates = (99 + 324) x 1012 m3 /year
Residence time = RT = (1.3 x1013 m3 ) / ( 423 x 1012 m3 /year )
RT = (13 / 423) years = 0.031 years
RT = 11 days
This calculation indicates that an average molecule of water spends 11 days in
the atmosphere between evaporation from the ocean and precipitation back to
land or ocean.