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Salt Lake Community College – Meteorology 1010
Mid-term Exam
J. Allred, Adjunct
Student Name: ____________________
1. Across the entire Earth, what weather condition is likely to be the greatest killer of people these days?
a. Tornado
b. Flood
c. Hurricane
d. Atmospheric heat
e. Atmospheric cold
Page 7 talks about atmospheric hazards. That information, combined with class discussion regarding climate
change and global warming theory, established that heat is probably emerging as the greatest ‘killer’ of people
in terms of natural hazards. This is particularly true because most severe weather relies on embodied heat, or
stored energy, as the motivator for weather activity.
2. Condensation (fog or clouds) forms any time moist air cools to the point where vapor pressure reaches
maximum and saturation occurs. Condensation occurs when air temperature cools to dew point
temperature.
True _X__
False ___
See pages 102-109, and 130, 136. Air pressure is lower with altitude. Less dense air cannot absorb or hold heat as
well as more compressed air at lower elevation or altitude. Also, as air rises it encounters lower pressure, and
thereby expands, resulting in cooling by dispersion or dilution. When air temperature reaches dew point
temperature we can say that the air “bucket” is now full, and vapor condensing back into visible water, releasing
the heat that was latent, or hidden in vapor.
3. X-rays and gamma rays from outer space exhibit small wave lengths and small amplitudes but deliver a
combined total of more actual electromagnetic power or energy than do sunlight and all other portions of
the microwave spectrum combined.
True ___
False _X__
See page 46. X-rays and gamma rays are not only small in wave length and amplitude but deliver much less energy
than do the visible light, infrared and ultraviolet radiation bands. In fact, visible light by itself provides more
than 40 percent of the total solar energy reaching the earth.
4. Descending air will tend to become warmer by compressing and concentrating on the way down.
True _X__
False ___
Air that is moving downward will be compressed as there is increasing weight of air above. Air that is compressed
occupies a smaller space. As such, the energy in that parcel of descending air will be compressed, or
concentrated, thus registering greater measured heat or temperature.
5. The quickest way to convert water vapor to liquid water is by:
a. Raising its temperature
b. Lowering its temperature
c. Compressing it
d. Taking the parcel to a higher elevation
e. Taking the parcel to a lower elevation
Air that is cooler is relatively less able to hold heat. Taking a parcel of air to a higher elevation may eventually
achieve the same result, but only after that air decompresses and then registers lower temperature due to energy
dispersing over a larger volume of air. See Question #6 below.
6. Which of the following parcels of air is most directly able to convert vapor to fog (liquid water)?
a. Descending air
b. Rising air
c. Cooling air
d. Warming air
e. Air moving in a clockwise, or anti-cyclonic direction
Like Question #5 above, the most direct way to release latent heat from vapor is to cool the air to the point where its
capacity to hold vapor is reached or exceeded. Further cooling will cause vapor to convert back to liquid,
releasing additional heat that was hidden with the invisible vapor. In a sense, if you cool humid air down
enough it will partially re-warm itself by converting vapor to liquid and release some of the additional heat that
was latent, or hidden with the humidity. See pages 102, 112, 130.
7. An air mass can become unstable and then move, or can be forced to move and thereby become unstable.
Air becomes unstable when it releases some of its latent heat (vapor as humidity) and re-warms itself,
promoting a pattern of more rising, cooling, condensing and re-warming.
True _X__
False ___
Any time air moves it may encounter different conditions along the way. Wind blowing over a mountain is
necessarily going to experience lower air pressure and lower temperature. If temperature drops to dew point
temperature, then saturation occurs and liquid water emerges from invisible vapor.
See pages 118-120.
8. Chlorofluorocarbons destroy atmospheric zone (O3). Atmospheric ozone helps keep the surface of the
earth warmer.
True ___
False _X__
The first statement in Question #8 is true. However, atmospheric ozone traps or collects a substantial amount of
solar energy in the ‘ozone layer.’ That energy does not reach the surface of the earth.
CFCs bond chemically with ozone, resulting in new compounds that prevent re-formation of ozone. Even one CFC
molecule can break and bind over and over with hundreds of ozone molecules. As atmospheric ozone is
depleted by CFCs, ultraviolet radiation is more easily able to pass through the atmosphere and reach the earth’s
surface. See pages 22 and 396-96. High-energy Uv rays convert to sensible heat after being absorbed by
substances, such as water and soil at the earth’s surface.
So, in the absence of atmospheric ozone, high-energy Uv rays are more easily able to reach the surface of the earth
and convert to heat.
9. What condition is most likely to reduce short-term risk of skin cancer?
a. Increasing ground-level ozone
b. A world-class (gigantic) volcanic eruption of aerosols and water vapor
c. Vast emissions of carbon compounds containing fluorine and chlorine (CFC, etc.)
d. None of the above
e. All of the above
Large volcanic eruptions may put enough dust, water vapor and other aerosols into the atmosphere to significantly
screen out in-coming solar energy. The result can be a temporary reduction in overall Earth atmospheric and/or
surface temperature. In addition, the blockage of harmful solar radiation, such as ultraviolet, can reduce overall
risk of skin cancer.
See page 21.
10. When a cloud in the sky is forming, heat is being absorbed. That heat becomes latent or ‘hidden’ and
thus helps cool the surrounding air.
True ___
False _X__
When clouds form, invisible water vapor is being converted back into liquid water that is visible as cloud or
fog. Latent heat is released when the vapor is released back into liquid. Evaporation would be the opposite –
absorbing energy to evaporate water, a cooling process. See Question #7 above and pages 57, 70, 101-106..
11. The term “conduction” refers to the way energy moves by direct contact between substances.
True_X__
False___
See pages 44 and 69. Convection is movement of energy in substances that are moving, carrying their heat with
them. Conduction is movement by direct contact.
12. Located at 20 degrees north latitude, Salt Lake City receives most of its weather from the East.
True ___
False _X__
Salt Lake City is located at about 40 degrees north latitude. Most weather patterns arrive from the west (westerlies),
following the general route of the jet streams that are also moving west to east.
13. Rain is more likely to occur before moist air begins to descend along the back side (lee side) of a
mountain.
True _X__
False ___
Air that is rising will cool down by decompression. After passing the top of the mountain, air may tend to descend
and re-warm itself by compression, or concentration of heat into a smaller volume. Air that is warming by
descent and decompression will tend to warm up, and will be almost impossible to become saturated or
precipitate. See Question #7 above, and pages 113 and 122.
14. At 40 degrees north latitude a city near the east coast of a continent will likely have a milder climate than
a city on the west coast of that continent.
True ___
False _X__
In the northern mid-latitudes (that includes most of the United States) winds prevail mostly from the west. As such,
weather patterns in the interior of continents tend to be carried toward the east. So, mild weather in Portland,
Oregon gradually becomes more severe as air moves eastward. The result is that Portland, Maine, on the east
coast of the United States has weather that is more like Chicago (severe) because winds reaching Maine carry
Chicago weather toward the east coast. See pages 197, 204-206.
15. For the earth to avoid overheating, which of the following processes is most important:
a. Conduction
b. Convection
c. Advection
d. Radiation
e. None of the above
Radiation is the only means by which solar energy reaches the earth, and the only means by which energy leaves the
earth. Other means of heat or energy transfer include conduction and convection between objects. Reflection is
just radiation going back in the same radiation state by which it arrived. See pages 46-54.
16. In a place with very wet air and a surface temperature of 100° F there should be frost at a location 9,000
feet directly above.
True ___
False _X__
From 100 degrees F, a total of 68 degrees of temperature must be lost for air to freeze (32 degrees F). Saturated air
tends to cool at an average rate of close to three degrees per thousand feet per higher altitude. So, 58/3 = about
23,000 feet of altitude difference between ideally saturated air at 100 degrees and air that begins to freeze at 32
degrees F. See pages 27 and 117-118. For Met 1010 we generalize by using extremes of humidity to create
extremes of lapse rates, with totally dry air cooling by about five degrees F per thousand feet and ideally wet air
cooling more slowly, at about three degrees per thousand feet.
17. The daily weather news will report simple absolute humidity rather than more complex percent vapor
saturation.
True ___
False _X__
The daily weather report will always report relative humidity, because the relative relationship between actual vapor
and capacity for vapor tells the story of whether the weather will be fair or stormy. See pages 91-111.
18. Which of the following options is/are represented by this generalized chemical relationship?
[HC + H2O + CO2 + electromagnetic energy  HC + O2]
a. Green plant growth
b. Conversion of sunshine into a form of fuel
c. A cooler planet than otherwise
d. Reduction in atmospheric carbon dioxide
e. All of the above
When a tree grows, it uses solar energy to store additional hydrocarbon in the form of new plant material. So,
solar energy creates more hydrocarbon. Trees are a fuel that can be burned. Thus, solar energy is absorbed in
the creation of more plant mass. That mass of hydrocarbon can be burned (oxidized), releasing the solar
energy as heat of combustion. The growth of green plants not only absorbs carbon dioxide that would
otherwise absorb more heat, but converts solar energy to fuel. Thus, the growth of green plants has a net
cooling effect when is considered. See pages 17-19.
19. All precipitation events fall into four categories: “frontal” weather is the most likely to be dangerous.
True _X__
False ___
Orographic (mountain), convection, convergent and frontal (or wedge) are the four primary types of ‘storminess’
that result in precipitation. Frontal/wedge storms include the most violent weather conditions because they
involve a collision between cooler/drier air and warmer, more humid air. The contrast between them combines
with coriolis acceleration to produce very high winds, often with lightning, hail and heavy precipitation. See
textbook index for a variety of references to frontal/wedge weather.
20. Severe daytime surface heating can cause air to rise, but it won’t become unstable unless there is
substantial moisture available.
True _X__
False ___
See page 192. On a normal day, surface temperatures rise due the availability of absorbing surfaces, especially dry
land. Brief, shallow “thermals” can develop as warming air becomes more buoyant and rises. However, that
rising will shut itself off as cooler temperatures are encountered aloft. This is normal daily instability that
causes valley—mountain breezes and ocean—land breezes.
However, if humidity is available, then cooling to condensation can result in latent heat being released, allowing air
to continue rising, a more significant unstable condition. This condition can accelerate if enough humidity is
available, resulting in potential severe weather that can include high wind, lightning hail and heavy precipitation
as the cycle “feeds” on itself. See Conditional Instability, on pages 118-120.
21. The occurrence of virga should make nearby air a little bit cooler than otherwise.
True _X__
False ___
Virga is rainfall that evaporates back into humidity before reaching the ground. The evaporation process is a
cooling event (like a swamp cooler), wherein heat and water are converted to invisible vapor and latent heat.
So, as rainfall evaporates, the surrounding air should become cooler. See page 145.
22. The general lapse rate of air temperature typically implies stable, fair weather because air naturally loses
thermal pressure and buoyancy with altitude.
True _X__
False ___
Air is typically cooler aloft. Air that rises to higher elevation should cool down eventually as well. See pages 27
and 117. Mild daily unstable air can occur but no stormy weather.
23. In contrast to Question #22 above, adiabatic cooling or warming can mean instability and potential
cloudiness and precipitation because of latent heat held in humidity.
True _X__
False ___
As air reaches dew point temperature, heat is released as vapor converts back to visible water. The release of
hidden heat allows that air to continue rising (warmer air rises when surrounded by cooler/drier air). Air that
can keep warming itself by condensation is considered genuinely unstable, compared to surrounding air that is
moving only a little each day with solar heating and cooling. See pages 112-116.
24. The presence of mountains can cause stable air to become unstable. So, a slow rise of air over a mountain
could convert to a convective storm after being ‘triggered’ to rise, decompress, cool, condense and rewarm.
True _X__
False ___
Ordinarily, moving air that encounters a mountain will rise in order to clear the obstacle. Such air will typically
descend back down the other side; however, if that air contains significant latent heat as humidity, then the
process of decompressing might release enough latent heat to re-warm itself enough to continue rising on its
own, regardless of the mountain. See pages 113-122. A mild orographic rainfall might include substantial
cloudiness and wind. In contrast, if orographic conditions set in motion a convective condition, then a more
substantial storm could result as moist air re-warms itself for further condensation and further release of heat
and moisture. That condition could continue until the air dries and cools enough to be no more buoyant than
surrounding air. The storm shuts itself off by cooling and drying enough to match surrounding air.
25. Super-saturated air (greater than 100 percent humidity) is most likely to occur in:
a. very clean air
b. very dirty air
c. very dry air
d. Stable (no wind) air.
e. Any air below freezing
It is much easier for humid air to condense back into liquid if there are objects on which to cling, such as bathroom
mirrors, automobile windshields and dust or ice particles. In super-clean air, condensation may not occur until
air temperature is far below the normal dew point. That is why “cloud-seeding” injects the air with trillions of
particles that can attract moisture, allowing condensation to more easily occur.
26. A “swamp cooler” is relatively efficient at cooling a building because hot, dry air can easily absorb or
“hide” water by converting that water to a more energetic state called vapor. In contrast, “central air”
conditioning is effective for people who are willing to spend a lot of energy (and money) to “squeeze” heat
out of air by mechanical compression and then cool it by expansion.
True _X__
False ___
Based on class discussion, very little energy is required to blow air across wet surfaces. The result is economical
cooling by evaporation. In contrast, “compression/expansion” cooling requires a large amount of energy to
‘squeeze’ the heat out of air by compression, and then decompressing the air, resulting in any desired amount of
cooling.
27. In the northern hemisphere, the Coriolis force will make airborne objects appear to deflect to the right.
So, mid-latitude storms tend to be more mild than storms at the equator.
True ___
False _X__
Mid-latitude storms tend to be more prone to violent winds because of the coriolis force that causes acceleration.
See pages 169-177.
28. By itself, the pressure gradient force moves objects directly across isobars. The Coriolis force tends to
turn objects away from the gradient force. So, the difference between them determines wind direction.
True _X__
False ___
See pages 173 and 204. Wind that would ordinarily flow “downhill” (from high to low pressure) is turned
rightward by the Coriolis force. The mix between gradient flow and coriolis deflection determines the net
effect, or blended direction of wind.
29. Which of the following is not true of the Earth’s spin:
a. causes wind to deflect away from the pressure gradient
b. helps create world-wide jet streams and other westerly flows in the northern hemisphere
c. helps cause complex wind patterns when encountering randomly shaped land masses
d. causes the Sun to appear to rise each day in the East, and set in the West
e. helps prevent storminess by spreading solar energy more evenly around the Earth’s surface.
The earth’s spin ensures that solar energy is cast on one side of the earth at a time. The resulting imbalance means
that only one part of the earth is heating while the other part is cooling. The resulting differential in heat results
in differential air pressure, which causes wind.
30. The “urban heat island” effect can pull cooler air from the countryside but can also concentrate air
pollution over big cities.
True _X__
False ___
As big cities heat up each day, the result is a rising ‘thermal’ of low pressure. Cooler, higher-pressure air from
outside the city will rush in to fill that low-pressure region. The result can be concentration of air pollution over
large urban areas, as well as excessive daytime heat. See pages 76 and 84.
31. The term “monsoon” refers to a strong seasonal reversal of wind direction. The Utah/Arizona monsoon
often brings moisture up from the South.
True _X__
False ___
Monsoon refers to wind. However, wind can bring moisture, or not. Prevailing high pressure zones in the
American Southwest rotate clockwise, sometimes ‘pulling’ moisture from the ocean northward, resulting in
precipitation. In India, the undulation of the ITCZ causes winds to either bring moisture from the ocean or blow
off-shore, preventing ocean moisture from bringing rain. See page 201.
32. During summer, intense heating of surfaces in continental interiors produces strong high pressure zones.
True ___
False _X__
High pressure is associated more with descending air. Intense heating of surfaces during the summer can produce
limited, local ‘thermals or low-pressure air that is more buoyant due to being heated from the surface. These
minor low-pressure systems die out at night. The general or regional high-pressure of descending air tends to
prevail.
Consider the far ends of world-wide Hadley cells: they may move a bit north and south with the ecliptic of the
sun, but regional high-pressure zones tend to persist in spite of day-time surface heating and occasional stormy
weather.
33. Utah is a dry-weather state because we are located:
a. far from a major source of water
b. near the edge of a world-class Hadley cell that provides high-pressure, sinking air that tends to warm as it
compresses
c. in a region where abundant sunshine can evaporate water
d. in a region where prevailing winds can carry that moisture away from us
e. All of the above are true of Utah
Deserts and dry country tend to prevail in regions located roughly 30 degrees north and south of the equator. The
general high-pressure and descending air masses tend to warm by compression as the descend, resulting in drier,
more ‘thirsty’ air. Utah is part of that general pattern and is located far enough from an ocean to not benefit from
that moisture.
Like question #32 above, day-time surface heating can cause ‘thermals’ of rising air, but the overall prevailing
pattern tends to be relatively high-pressure air that is overall more likely to descend than rise.
34. Dry air cools off more slowly than wet air.
True ___
False _X__
See Question #16 above.
35. Of the other five main characteristics of atmosphere, which one of the following is most directly the cause
of wind?
a. Temperature
b. Cloudiness
c. Precipitation
d. Air pressure
e. Humidity
Temperature causes air pressure differences, but air pressure differences lead directly to wind.
36. A few weeks ago the days and nights in Utah were about equal length, 12 hours each.
True _X__
False ___
See pages 37-41.
37. Utah does not have frontal (wedge) or convective storms like those in “tornado alley” or the tropics
because our region is too dry and mountains block air movement.
True ___
False _X__
Utah can experience any of the four types of precipitation weather. It is true that Utah’s generally dry air does not
host substantial convective storms, such as at the equator. It is also true that mountains tend to block some air
flows that might spawn frontal storms; however, severe weather, including tornadoes do occur every year in Utah,
whenever masses of cool, dry air encounter occasionally humid/warm air moving through the state.
38. Tropical regions do not experience tornadoes and hurricanes because there is little or no Coriolis effect,
and because they have little or no cool/dry air masses against which buoyant wet/warm air can “push off”
and accelerate more rapidly.
True _X__
False ___
See pages 169-178 and 412.
39. In the United States, there is often “Wind before the warm” and “Warm before the storm” because cold
fronts push cooler and drier air underneath warmer, wetter air. As vapor condenses, heat is released
causing unstable conditions, with a greater chance of precipitation, lighting, thunder and hail.
True _X__
False ___
We will talk about this question more thoroughly in class.
40. A “dry line” storm is usually mild, because it lacks moisture and latent heat that are needed to keep the
air mass rising vigorously. Without rapid lifting, tornadic winds and heavy precipitation do not develop.
True ___
False _X__
Pages 245-247 and 278-281. Dry-line storms are well-known for producing ‘squall lines’ of vigorous
thunderstorms that can stretch for hundreds of miles.
The key factor is that cooler-drier air prevails along the dry-line, with wetter-warmer air on the other side of the
invisible boundary. Cooler-drier air helps warmer-wetter air to rise more quickly. The faster warm-wet air
rises the faster it will re-invigorate itself with further cooling, condensing and re-warming. The greater the
difference between cool-dry and warm-wet, the more violent a storm may become.
Dry-line storms produce a substantial fraction of the world’s tornadoes.
41. Humid air:
a. will tend to rise because it is less dense than dry air
b. is more likely to rise because it contains light-weight water vapor that is “hiding”as latent heat
c. is more likely to be stable due to heaviness
d. answers ‘b’ and ‘c’ above are correct
e. answers ‘a’ and ‘b’ above are correct
Humid air is less dense because water vapor is chemically lighter weight than other constituents of the
atmosphere: nitrogen, oxygen, etc. Warm air is less dense and thereby more buoyant than cooler, more dense air
in which molecules are moving less energetically. See pages 44-45, 53-57, 91-92.
42. A relatively dry high-pressure system exhibits either stable air or clockwise descending air.
True _X__
False ___
See page 169.
43. Jet streams move from east to west, the same as the rotation of the Earth. The result is fast-moving,
high-altitude air that brings storminess to the northern hemisphere.
True ___
False _X__
Jet streams move from west to east. In the northern hemisphere, most weather changes arrive from the west, as
winds and moisture are pulled along by the jet stream. See pages 197-205.
44. On a normal or standard day, which of the following sets of numbers is most likely to show on an air
pressure map of conditions at an altitude of 17,000 feet above sea level?
a. 200mb to 300mb
b. 700mb to 750mb (507 to 550 is a reasonable answer)
c. 980mb to 990mb
d. 13.9 lbs/square inch to 14.7 lbs/square inch
e. 29.92 to 30.02 inches of mercury
This question contains no adequate answer. In general, air pressure at 18,000 feet should be about half of what is
found at sea level. With sea level at about 1,000mb or 15 pounds per square inch, air at 17,000 feet should
be only a little more than half of that, or about 520mb (about 7.5 pounds).
45. A cumulo-nimbus cloud is most associated with which condition?
a. Rising air pressure
b. Compressing air, squeezing vapor into liquid
c. Relatively high air pressure and rising air
d. Rising air currents and falling pressure, and then falling air currents
e. Rising air pressure and descending rain
Storminess is associated with rising air, and rising air always involves relatively low air pressure. As a storm
arrives, air pressure tends to drop. As a storm passes by or fades away, there may be downdrafts, because
“what goes up must come down” somewhere else.
46. In a wind pressure map of a tornado, isobars will appear unusually close together, showing a strong
pressure gradient.
True _X__
False ___
An “isoline” is a line drawn to collect all points of equal value. Closely spaced isolines indicate rapid change.
Near a tornado, wind is accelerating rapidly, so concentric lines of falling air pressure that are very close
together indicate rapidly rising air toward a center point or center cell. See pages 168-170.
47. Tornadoes are more likely to occur when an entire region consists of uniformly warm, wet air with no
compensating cold, dry air to prevent cyclonic or tornadic winds.
True ___
False _X__
Tornadoes are more likely to occur when a mass of cool/dry air collides with a mass of warm/wet air. The contrast
between air masses helps more buoyant air to rise more quickly. That process, combined with the mid-latitude
coriolis force, causes acceleration of wind to extreme speeds. See page 174.
48. As a storm develops at an ocean beach (sea level), which of the following numbers is most likely to show
on a barograph or barometer?
a. 200mb and falling
b. 200mb and rising
c. 990mb and falling
d. 1,000mb and rising
e. None of the above is a reasonable reading
At sea level, normal air pressure is typically just a little more than 1,000mb. Storms are associated with falling air
pressure. Answer ‘c’ is the only likely correct condition.
A severe ocean storm could show air pressure as low as 900mb. See pages 117, 166, 307.
49. A tornado, a hurricane and a “dust devil” all have in common:
a. Rising air and counter-clockwise wind
b. Rising air and clockwise wind
c. Descending air and counter-clockwise wind
d. Descending air and tornadic, or cyclonic wind
e. None of the above is a good description
Tornadic, or cyclonic wind, moves counter-clockwise and is associated with rising air, gusty wind and storminess.
See pages 174, 192, 249 and 291.
50. Take a moment to visualize a typical storm front moving into Utah. Which sequence is most applicable?
a. Wind from the southwest, followed by wind from the northwest as the storm passes by
b. Stratus clouds, followed by cirrus clouds and brief, sharp precipitation
c. Cumulo-nimbus clouds, followed by cirrus clouds that bring slow, steady precipitation
d. Winds from the east, followed by alto-stratus clouds from the east
e. Winds from the north, followed by alto clouds that thicken into heavy cirrus clouds
Jet stream flow moves from west to east. Storms arriving in Salt Lake valley tend to prevail from the southwest,
because of cyclonic, counter-clockwise flow. As a cyclonic condition (low-pressure system) moves on to the
northeast (most common), the back side of the counter-clockwise flow can show winds appearing to arrive from
the northwest. See page references for Question #49 above.
Extra credit essay option: Describe characteristics of a dry-line storm. Use words and/or drawings with labels.
Squall line storms are long lines of thunderstorms that move generally from southwest to northeast, following the
general flow of jet streams. The key to such vigorous storms is the presence of air masses that are cooler and
drier (prevailing or arriving mostly from the north and west) that encounter moist/warm air arriving mostly from
the southeast. This collision, combined with the coriolis effect, results in strong winds and rapidly rising air.
See pages 245-46.
See also Question #40 above.