Salt Lake Community College
Meteorology 1010
Quiz #3, Fall, 2013
A. J. Allred, Adjunct Instructor
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Student Name ___________________________
1. In a classic mid-latitude cyclone, cold air chases warm air around the outside of a low-pressure
center.
True _X___ False ____
Atmospheric pressure is higher in Los Angeles than in Salt Lake City. Lower air pressure allows relatively
more room for evaporated water (as vapor) to escape into the atmosphere. Total atmospheric pressure is
composed of everything that is dissolved in it.
We have previously noted that the primary basis for how much the atmosphere can hold vapor (vapor pressures)
is mainly a function of air temperature: the hotter the air, the greater its capacity to hold water vapor (the size of
the “bucket.” Other factors do matter, to a lesser degree: how much condensation nuclei is available to allow
vapor to convert back to liquid, and how much space there is in total air pressure to allow an increase in vapor
pressure. See page 165.
2. A low pressure system is a kind of paradox: it takes lower pressure to ‘draw’ wind in from higher
pressure areas. As air converges in low-pressure zones, it rises to the top where it tends to “pile up”,
resulting in high pressure at the top of the air column.
True __X__ False ____
The troposphere is thicker at the Equator than at the poles, because the low pressure end of Hadley cells draws
in air and sends it upward where it can then diverge (higher pressure) and move toward the downward part of
the ‘conveyor belt’ above deserts. Converging air masses carry some of their pressure with them as they rise
toward the top of the air column. The result is higher pressure at the same altitude over the equator that at the
same altitude over the poles. See pages 170 and 180.
.
3. A tornado is a low-pressure micro-scale event in which air is drawn upward by moist, warm air that
is lighter and more buoyant than surrounding air. A “dust devil” is also a low-pressure micro-scale
event, but its only source of energy is the hot ground surface that starting things lifting. So, a dust
devil runs out of heat energy as it rises away from its source of heating.
True __X__ False ____
The best explanation of the answer is in the question itself. See page 193. A tornado provides low pressure aloft
so that surface air is drawn upward. That condition is known as a “pressure low.” In contrast, a dust devil
exhibits rising air from super heating at the surface, a “thermal low”. Coriolis force causes both of these parcels
of rising air to turn cyclonically as they rise, sometimes causing acceleration and further lifting.
Dust devils run out of energy as they leave their sources of heating at the surface, while a genuine tornado can
keep lifting as long as there is moist air above that can condense out more heat as it condenses out vapor into
visible water. As long as that latent heat is available, the rising air parcel will be warmer and more buoyant
than cooler, drier adjacent air.
4. Related to question 3 above, a valley breeze and an on-shore breeze both originate from the fact that
daily heating and cooling is more dramatic over water than over land surfaces.
True ____
False __X__
The opposite is true: lower elevation surfaces and dry land surfaces heat more quickly each day than do their
opposites. See page 195.
5. In a classic mid-latitude cyclonic storm, a faster-moving colder air mass catches up to a slowermoving warmer air mass and pushes or wedges underneath. The warmer, wetter air is provoked to
adiabatic instability as it re-heats itself by being compelled to rise, decompress, cool down and then
condense out its moisture into clouds and precipitation.
True __X__ False ___
In the mid-latitudes, counter-clockwise air flow rotates around a low pressure center that is moving roughly
eastward. Air masses of differing temperature and/or humidity rotate around the low pressure center or pivot
point. These differing air masses are typically provoked to collide by having been induced toward each other
by meridional undulations of the jet stream. As these masses meet, they initially slide past each other before
wedging and eventually mixing. The air that is more humid (lighter weight) and warmer (lighter weight) lifts
above the colder (heavier) and drier (heavier) air, provoking adiabatic instability and storminess. The jet stream
overhead further helps create these cyclones by helping siphon high pressure air out and away from the tops of
low-pressure systems that are they key factor in mid-latitude storms.
In a classic cyclone, there is precipitation along both the cold wave and along the warmer wave up ahead, as
each intrudes on air ahead that differs in temperature and/or humidity.
See all of Chapter 9.
6. Northern hemisphere jet streams are similar to the ITCZ: they both undulate like a stream of water
around the globe, and their centerlines both tend to migrate generally southward during the summer
and northward during the winter.
True ____
False __X__
Everything above is true except that the jet streams and the ITCZ follow the apparent migration of the sun:
northward in summer and southward in winter.
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7. The mid-latitude jet stream affects U.S. weather by helping to mix colder northern air with warmer
air masses to the south, provoking low-pressure storm systems that slowly migrate from east to west.
True ____
False _X__
Everything above is true except that low-pressure storm systems in the northern hemisphere almost always
migrate toward the east as part of the world-wide ‘westerlies.’ See pages 205-208 and elsewhere.
8. Jet streams help promote stormy weather as they pass nearby, by helping remove high-pressure
diverging air at the top of low pressure systems.
True _X___
False ___
Remember, low pressure convergence at the surface turns into high pressure divergence higher up. As the jet
stream passes overhead, air flow heading east helps ‘pull’ diverging air away from the air, leaving yet more
‘room’ for rising air to keep rising to take its place. See Question #5 for more explanation.
9. An “El Nino” condition means that the normal west-bound flow of air and ocean water caused by the
trade winds either stops or even reverses direction. The result is that some places around the world
that are normally dry tend to experience much more precipitation than usual. Other places may
experience drought. An “El Nino” condition in Utah tends to mean more rain and snow than usual.
True _X___
False ___
All true. Ordinarily, trade winds ‘push’ ocean water from South America toward Australia. The result is cold
ocean water welling up along the South American coast. Cold water and west-bound wind produces a dry
climate there as well. Meanwhile, west-bound ocean water ‘piles up’ at the western side of the Pacific Ocean,
resulting in typical storminess and abundant precipitation in that region.
An El Nino tends to erase or reverse these conditions for a season, resulting in drought in the far western Pacific
and too much precipitation in some places like Utah, that are normally more dry. See pages 211-219.
10. The famous and hazardous “Nor’easter” storms of the U.S. east coast exhibit high winds from the
northeast, because the storm track is off-shore and the land-side portion of winds appear to be
coming from the northeast.
True _X__
False ___
Looking down on a cyclonic storm in the northern hemisphere, winds on the left side will be moving toward the
south and west, so their apparent source is from the north and east. Because “Nor’easter” storms pick up ocean
energy by traveling off-shore along the U.S. east coast, the western edges of these storms will pass over land.
People on land or near the shore will observe prevailing storm winds coming from the northeast.
Last year’s “Super Storm Sandy” was one of those ‘perfect storms’ in which huge amounts of energy from a
dying hurricane collide with a “Nor’Easter storm. The colder air from the Nor’easter provokes the release of all
possible remaining warmth and humidity from the hurricane, enhancing the effect of both storms.
See pages 234 and 258.
.
11. Which of the following air pressure changes in Miami, Florida indicates a sunny day turning into a
severe storm?
a. A pressure rise of 50 mb
b. A drop of 100 mb in air pressure
c. Any change in air pressure of at least 14.7 pounds per square inch (equal to 1013 mb)
d. A drop in pressure of 507 mb
e. None of the above is reflective of a severe storm moving into Miami.
Compared to normally rapid change in air pressure across small vertical distance, small horizontal changes in
air pressure mean substantial change in the weather. On the high side, it is unusual to see ground surface air
pressure rise more than 20mb above the “standard” day pressure of 1013 mb (about 14.7 pounds per square
inch). Since air pressure never goes very far above ‘normal’ or standard pressure, any significant drop below
normal portends an outlook or forecast for windy, cloudy or stormy weather conditions.
On the severe down side, a 50mb drop in air pressure will almost always mean that a significant storm is
forthcoming. A 100mb drop from a ‘normal’ day could portend a hurricane. A drop of 150mb would be
record-setting.
12. A northern hemisphere weather “front” can include:
a. a slower-moving warm front, where warm air over-rides cold air
b. a fast-moving cold front, where cold air pushes underneath warm air
c. a stationary front, where neither air mass moves very much
d. an occluded front, where warm air finally settles over cooler air below
e. All of the above can occur. In every case, the warmer, wetter air mass rises and settles.
In mid-latitude cyclones, southerly masses of warmer and/or more humid air tend to be mixed, or pulled toward
more northerly masses of cooler and/or drier air. As a low-pressure center develops, geostrophic winds flow
along isolines that are concentric to the center. Such winds blow counterclockwise as they rise. Rising air in a
low-pressure system results from warmer, more humid air encountering drier and/or cooler air. The result tends
to be windy, cloudy conditions and precipitation. .
A cold front generally moves faster, causing a sharply vertical front as cooler or drier air wedges under warmer
air. A warm front is the opposite: a more widely spread, gentler rise of warm or wet air across a broad area.
Thus, a cold front will tend to exhibit more sharply vigorous conditions while warm fronts will be less severe
and more broadly spread.
A stationary front is a similar collision, except that the collision zone is not moving much along the ground. An
occluded front represents the end of the “conflict” wherein warm air is established above cooler air.
A “dry line” storm is more about differences in humidity rather than temperature. Such storms can be quite
vigorous because the real energy in any storm is not the direct heat it contains but the latent heat it contains in
humidity (moisture). So, a stormy collision between hot and cold dry air would be more like a dust devil that
stops rising when it runs out of very limited heat. In comparison, a collision between humid and dry air, with
no difference in air temperature, can be quite violent because the wetter air holds a great reserve of heat in the
form of evaporated moisture (humidity). As that heat comes out of latency (hiding) it can rise vigorously,
provoking high surface winds, hail, lightning and heavy precipitation.
So, collisions between air masses that differ in heat and humidity are enhanced the most when those differences
are more about humidity than about heat - - more about “credit card” than “cash.”
.
13. A northern hemisphere weather “front” always includes an organized, or concentric center of:
a. high pressure, with colliding air masses that differ greatly in temperature
b. low pressure, with colliding air masses of very different temperature and/or humidity
c. high pressure, with air masses that first run past each other and then turn cyclonically
d. low pressure, with air masses that first run past each other and then converge cyclonically
e. options ‘b’ and ‘d’ are best
For sure, answers ‘a’ and ‘c’ are wrong - - frontal storms are not focused on a high-pressure center. Moreover,
everything in answers ‘b’ and ‘d’ is correct.
14. A mid-latitude frontal storm (a cyclone) will have dissipated when warm air is fully stationed above
colder air, and there is no longer any adiabatic rising and associated surface winds. Soon afterward,
natural instability slowly returns again as air aloft turns colder and sinks while surface air warms
and begins to rise.
True _X__
False ___
An occluded front is similar to a weather “inversion” because warm air ends up aloft while cool air is lodged
below - - neither has reason to move, so the storm is over. In fact, weather inversions are characterized by
stable air and dullness.
Of course, normal atmospheric processes soon take over, as ground surfaces heat up each day, provoking
relatively low pressure and rising air. Aloft in the atmosphere, less heating occurs and air cooler, with a
tendency to sink. Thus, instability begins to return soon after a storm of instability has ended.
15.
During a vigorous mid-latitude cyclone, sometimes called a frontal or wedge storm,
buoyant dry air will float over heavy, wet air, causing high wind and barometric pressure changes of
about 300mb at any given location.
True ____
False _X___
Dry air is actually heavier than wet air, so dry air will push underneath wet air, causing wet air to rise,
decompress, cool down, reach saturation (cloud forms) and then precipitate.
16. Which of the following statements is false?
a. Large bodies of water help make climate more mild (one of Mr. Allred’s Rules)
b. Utah has enough moisture, but not enough heat to provoke frequent major storms.
c. Evaporation of water hides heat that can come back as clouds that can kill thousands of
people.
d. Water helps climate more mild, and makes weather less predictable and sometimes
dangerous.
e. All natural hazards derive their energy from some form of radioactivity.
Utah has enough heat, but seldom has enough humidity, to provoke really severe weather. Severe mid-latitude
storms require vast quantities of latent heat, hidden in humidity to provide enough energy to create really severe
tornadic wind.
17. Based on class discussion about relative humidity, which of the following fractions represents the
most likely situation for a tornado?
a. 4/10
b. 3/6
c. 4/11
d. 8/8
e. 1/1
Answers (d) and (e) both represent what we call vapor saturation, dew point or “full bucket”. Clouds form and
precipitation may begin to fall. The difference between “8/8” and “1/1” is this: a warm day with lots of
humidity (80°F and roughly 100% humidity) contains enough sensible and latent heat to produce a genuine
storm. In contrast, a cold day that is very humid (10°F and roughly 100% percent humidity) contains far less
energy for storminess. In fact, a temperature increase of 10°F doubles the capacity of the air to hold vapor, so
an 80°F day at vapor saturation holds vastly more energy than does a cold, vapor-saturated day.
18. With warming conditions around much of the world, the likelihood of people being injured by
heat waves and drought is increasing. High air temperatures may bring more evaporative cooling,
but even more over-drying by over-heating. We may get more world precipitation, but even more
drought and heat distress.
True _X___
False ___
At places like the equator, where abundant water is found, solar energy evaporates water that results in
atmospheric cooling. More heat just results in more evaporative cooling and cloud cover that provides “sun
screen”.
However, for much of the world, as atmospheric temperature rises, the air can hold more water, which may lead
to a little bit more rain but a lot more evaporation. So, more heat just leads to more drying. If the Earth
continues to warm, drought is more likely.
19. Violent winds in tornadic storms are associated with:
a. Large amounts of latent heat
b. Relatively high humidity
c. Local differences between cooler/drier air and warmer/wetter air
d. Relatively low atmospheric pressure and rising air
e. All of the above
Humidity is latent heat ‘hidden’ in evaporated water. Humid air is lighter weight and more buoyant than drier
air, so it rises easily when it is also warmer than cooler air nearby. Such buoyancy provokes yet further rising,
rotation and acceleration of wind speed.
20. Doppler radar can detect a tornadic condition in thunderstorms by measuring the difference in
time required for radio signals to bounce back from parts of the atmosphere that are moving in
opposite directions.
True _X__
False ___
Doppler radar bounces radio waves off liquid water in the air, such as rain drops. If rain or snow is falling in
tornadic winds, then Doppler radar can detect how that water is pushed in opposite directions on opposite sides
of the storm. Where there is great divergence in wind speed, a tornado or severe cyclonic condition can be
suspected. Alarm bells may ring.
The key to “Doppler effect” is the time difference between objects moving toward the radar receiver and objects
moving away from the receiver. A radar signal will take increasingly more time to reach an object moving
further away than an object getting closer, so the signal pitch or frequency will be slower or longer than for
objects that are getting closer.
21. A heat index chart showing a temperature of more than 100 degrees will also provide an estimate
of how much comfort or relief can be provided by adding a large amount of water vapor
(humidity) to the air.
True ___
False _X__
High humidity makes hot air feel worse because the humidity represents water that is as warm as the air
temperature, like sitting in a hot tub all day. Worse, the human body cannot evaporate perspiration to provide
cooling, because the air is already close to saturation with humidity, and cannot absorb very much additional
humidity by evaporation.
So, a heat index chart does not indicate that adding humidity or water will provide any relief at all.
22. The number of people killed in France by a recent heat wave was more than 100 times more than
all people killed by tornadoes in the United States last year?
True _X__
False ___
This topic is considered more fully in a later chapter. However, we do take time to integrate topics that are
related. Excessive heat may be emerging as the most lethal natural hazard, particularly as heat is also the key
factor in many severe weather conditions. More heat may result in more frequent and more severe storm
weather events.
23. During a tornado or hurricane, isolines for rainfall and air pressure tend to be:
a. Very close together, indicating rapid change in wind or rain
b. Very far apart, indicating rapid change in wind or rain
c. Close together for rain, and far apart for wind
d. Close together for wind, and far apart for rain
e. None of the above is a good description of a severe tornadic storm
Isolines connect points of equal value. When conditions are changing rapidly, measured values are changing
rapidly as well. When isolines are close together on a map or chart, they indicate that a phenomenon is
radically different from what is relatively nearby.
In a tornado, isolines for wind and rain will be far apart at locations far from the storm. That is why wind may
not be strong when viewing a tornado from a distance. People who get very close to a tornado or dust devil will
notice that wind suddenly begins to increase rapidly.
This acceleration in rate of change can be graphically illustrated by showing how isolines get closer together
with less distance to a tornadic center.
24. For people, adding water makes cold air feel worse and makes hot air feel worse. In between,
humidity does not have much effect.
True _X__
False ___
High humidity makes everything feel worse for people: humid air cannot support evaporative cooling
because the air is already near saturation capacity. In cold weather, water will readily absorb heat from any
source, so people can become hypothermic (chilled) quickly in cold, wet weather, especially if the wind is
blowing.
Wind chill charts do not include humidity because really cold air is typically very dry. However, if a person
should fall in water and then confront cold-air wind chill, hypothermia and cold can follow quickly.
In mild air temperature, high humidity has relatively little effect. People don’t need to cool down by
perspiration, and they don’t lose a great deal of body heat to air that is not very cold. Windy conditions
don’t add or substract from comfort very much, because fresh air is neither hot, nor cold.
25. The visible light portion of the electromagnetic spectrum is probably the single most important
supply of energy for a hurricane.
True _X__
False ___
Visible light provides about 43% of all energy that is supplied to the earth by the sun. Other parts of the
spectrum add further energy for weather phenomena, but none so much as does visible light.