Download Partial answers, references, and further questions are given be

ATMS 101 Midterm #1 Review Sheet with hints and answers. Partial answers (not
necessarily sufficient for full credit), references, and further questions are given below
in italics. EoM refers to the textbook Essentials of Meteorology.
1. What are the two most abundant permanent gases, and roughly what fraction of the
mass of the atmosphere does each make up?
Nitrogen, 78% ; Oxygen, 21%
2. Name three variable gases in the atmosphere, and discuss how each is significant.
EoM pp 2—7.
3. What keeps all the air molecules in the atmosphere from falling to the ground due to
the force of gravity?
Think in terms of hydrostatic balance; EoM page 160
4. Is a typical value of sea level pressure 1, 10, 100, or 1000 millibars?
1000 mb.
5. Is the fraction of the mass in the atmosphere that lies below 15 km (10 miles) roughly
10%, 50%, 90% or 99%?
At 15 km the pressure is about 100 mb; what is the relationship between pressure and
the mass of air above a level? See EoM pg 8.
6. What four layers show up in the vertical profile of temperature in the atmosphere?
The troposphere, stratosphere, mesosphere, and thermosphere.
7. What is the tropopause?
See Homework #1, Problem 3b.
8. Why does temperature increase with height in the stratosphere?
See #11 below; think about what the ozone layer does for us.
9. What is an inversion layer? Is it stably or unstably stratified?
An inversion is where the air warms with height. See #7 above; also consider that
there may be inversions below the tropopause as well. About stability: consider how
a dry parcel cools as it rises.
10. In what layer of the atmosphere does weather occur?
The troposphere.
11. Where is the ozone layer? Give a reason we should care about the ozone layer.
See EoM pp 10—11.
12. Is more of the mass of the atmosphere in the troposphere or in the stratosphere?
What is the pressure at the tropopause? Relate that to the answer to #5 above.
13. What are weather and climate? How do they differ?
See EoM pp 13—14.
14. What is kinetic energy? How is it related to air temperature?
See EoM pg 26.
15. What temperature scales do we use in meteorology?
Fahrenheit, Celsius (or Centigrade), and Kelvin (or Absolute). What is special about
the Kelvin scale compared to the other two?
16. What is heat capacity?
Heat capacity is the amount of heat needed to raise the temperature of a gram of a
substance by one degree Celsius. What has a higher heat capacity: water or land?
17. What is latent heat? Would it take more heat to bring a given amount of liquid water
from freezing to boiling, or to evaporate it? To bring it from freezing to boiling, or to
melt it from ice that is at 0 C?
See EoM pp 27—28 and the first two slides of Lecture 3. Keep in mind that it takes 1
calorie of heat to warm 1 gram of water 1 deg C.
18. In the Cascade Mountains, lakes may remain frozen until late summer. Explain the
roles of heat capacity and latent heat in explaining this.
Think about the heat capacity of water and where the heat to melt the ice must come
from.
19. What are the three heat transfer mechanisms? Give an examples of each of these.
See EoM pp 29—34, and Quiz #1 (both versions) Problem 2.
20. What kind of radiation does the sun emit? The earth?
What are the comparative temperatures of the sun and the earth, and how does that
impact the kind of radiation emitted? In addition, how do the sun and earth compare
in the total amount of radiation emitted (see EoM pg 34).
21. Does the presence of an atmosphere lower or raise the average surface temperature of
the earth?
The atmosphere includes water vapor, clouds, and carbon dioxide; what do they do
with the earth's emitted radiation?
22. Define albedo.
The amount of incoming radiation that gets reflected (as opposed to being absorbed)
back from a surface. For solar radiation, clouds and snow have very high albedos
while water and dirt have low albedos.
23. Why are visible satellite images only useful during daytime, but infrared satellite
images are just as good at night?
Where does the light for visible images come from, and where is it at night? See #20
above.
24. Explain how an infrared satellite image can distinguish between regions covered by
high cloud, low-lying cloud, and no cloud.
What temperatures are each of these? How does that change the amount of infrared
radiation emitted, and what does that have to do with the color on an infrared
image?
25. What does the "greenhouse effect" refer to?
See EoM pp 4—6 and 36—38.
26. Can you think of another planet beside Earth whose surface temperature is much more
strongly affected by the greenhouse effect?
See EoM pg 382. Additionally, what can we expect about the temperature on Mars,
which has a very thin atmosphere?
27. Do greenhouse gases warm the earth by absorbing sunlight?
Greenhouse gases are what are called “selective absorbers”. What does this term
mean?
28. What are the two most important greenhouse gases on Earth?
Water vapor and carbon dioxide, in that order. Clouds are not gases, although they
are very important in the greenhouse effect (see #30 below).
29. Why do we expect increasing concentrations of carbon dioxide should lead to "global
warming"?
See EoM pg 38; also keep #26 above.
30. Explain why clouds tend to keep the surface temperature warmer at night but cooler
during the day.
Clouds have a high albedo; what does that do to solar radiation? Clouds are also
very good absorbers of infrared radiation; what does that do to terrestrial radiation?
Note that clouds do not reflect infrared radiation!!
31. When is the earth closest and furthest from the sun? Is this the main cause of our
seasons? EoM pg 44. No, we must consider the angle of the sun and the hours of
daylight. See EoM pg 45.
32. The earth's surface absorbs more energy from sunlight during summer than winter.
We know that one reason is that days are longer than nights in summer. Give another
reason of comparable importance. See #31, think about how high in the sky the sun is.
33. About what fraction of sunlight hitting the top of the atmosphere is absorbed at the
surface, 10%, 50%, 90%, or 99%? 50%
34. Why do seasonal temperatures lag behind the astronomical seasons, especially over
the oceans? Astronomical season refers only to alignment of earth’s tilt and thus the
relative amount of heat absorbed. Our seasons are derived from surface
temperatures which change (on average) much more slowly than the heating rate.
Think about turning your oven up to 500 F for 30 seconds and then down to 375 F. It
will still warm even though the heating rate is lower.
35. Near the equator, more sunlight is absorbed over the year than the energy emitted as
longwave radiation. Where does this energy go? How is this related to weather?
Think about a drafty room with a leaky window (on a cold day) on one side and
heater on the opposite of the room. EoM pg 48.
36. At what time of day is the minimum temperature typically recorded? Name at least
two factors that contribute to low nighttime temperatures. EoM pg 57-8
37. On the slope of a valley, why does the wind typically blow downslope during the
night? Why might things be different during the day? Postponed, not on this midterm.
38. Explain how the three forms of heat transfer combine to affect air temperature on a
sunny day. The suns radiation heats the surface, a very thin layer next to the surface
is warmed by conduction, and the warm air is lifted by convection to form clouds.
EoM pg 56
39. Why is temperature typically not measured at ground level, but typically 1.5 meters
above the ground? See #38, pg 56, lowest several meters likely not representative of
temperatures a bit higher up and over a greater area.
40. How is heat transferred to and away from the surface of the moon? (The moon has no
atmosphere.) Convection and conduction require ______, so….
41. Which would have the greatest effect on the earth's greenhouse effect: Removing all
of the CO2 from the atmosphere or removing all of the water vapor? Water vapor, its
concentration is significantly greater than CO2. EoM pg 38
42. Explain why an increase in cloud cover would increase the greenhouse effect of the
atmosphere, yet not necessarily lead to a lower higher earth surface temperature.
Increased cloud cover would increase IR reemitted back to surface but would also
reduce surface heating by reflecting and scattering incoming sunlight. Eom pg 37
43. Consider two scenarios: (a) The tilt of the Earth decreased to 10°. (b) The tilt of the
Earth increased to 40°. How would each of these change the summer and winter
temperatures here at UW? (a) cooler summers, warmer winters, (b) opposite to (a)
both due to changes in length of day and angle of sunlight.
44. At what latitude would you expect to experience the smallest seasonal variation in
temperature? Why? Equator, smallest change in length of day and angle of sunlight.
45. Why does air expand and cool as it blows up a mountain? Pressure decreases, heat
energy does work to expand air, so heat energy (temperature) is lost to making the
volume bigger, and it must therefore cool.
46. What is the dry adiabatic lapse rate? The rate at which temperature decreases with
height.
47. Why does the atmosphere not convect everywhere, even though it is much warmer
near the surface than near the tropopause? If the warm surface air were to rise it
would cool to a temperature below that of the tropopause. See #45 EoM pg 31.
48. Why does the vertical pressure gradient not create a vertical wind? Hydrostatic
equilibrium or balance at every level. EoM pg 160.
49. Why does air pressure decrease with height? Pressure is weight of column above a
level. The higher up, the less air above. EoM pg 142.
50. Why does air density tend to decrease with height? Pressure decreases with height
so molecules are “squished” together less at higher altitudes which means density is
lower. EoM pg 144
51. Why do meteorologists like to look at contour maps of horizontal pressure variations?
On such maps what are 'isobars'? EoM pg 148-9.
52. What is "reduction to sea-level pressure" and why do we need to do it? EoM pg 147,
so we’re not comparing apples to oranges.
53. On a contour map of 500 mb geopotential height, why do the heights typically fall as
you move north? Explain what we can infer from this about the pressure gradient
force at this level. Colder air means greater density and a shorter column. Compare
City 1 and City 2 on EoM 143.
54. Why do higher 500 mb heights tend to be associated with higher temperatures
between the surface and 5 km elevation? Opposite of #53.
55. What three forces are most important in determining wind speed and direction? PGF,
Coriolis, friction. EoM 154-158
56. What is the pressure gradient force? Where does it exist on a contour map of sea-level
pressure? The difference in pressure on opposing sides of an air parcel, EoM pg 151.
57. What is the Coriolis force? What factors affect the Coriolis force? An apparent force
due to the Earth’s rotation similar to being on a merry-go-round. It’s affected by the
latitude and speed of an object. EoM pg 151.
58. Why is the earth's surface further from its center in low latitudes than in high
latitudes? The Earth’s rotation causes a greater “centrifugal” force closer to the
equator and creates a bulge..
59. Why do winds tend to blow along the isobars except near the surface, even though the
pressure gradient force is directed down the isobars? What is the name of the force
balance involved? It is in balance with the coriolis force, but near surface there is
also friction. See #55, EoM pg154-8
60. In what layer of the atmosphere is friction important in affecting the wind? Does
friction cause air to spiral out of or into regions of low sea-level pressure? Friction
layer, into Lows, EoM 159.