Download Salt Lake Community College Geography 1000 – Physical Geography AJ

Salt Lake Community College
Geography 1000 – Physical Geography
AJ Allred, Summer, 2015
Quiz #5
Explanations
1. When a rain storm moves into Salt Lake Valley, which of the following usually occurs?
a. Winds bring more humid air that tends to rise
b. Winds tend to move counter-clockwise as a weather front moves through
c. Low air pressure takes over from high air pressure
d. Surface heating can add to rising air that is already lifting because of high water content
e. All of the above are true
Winds are air that moves from higher to lower pressure. In doing so, they often bring moisture. As a
storm pushes through air will tend to lift or rise because it contains heat and humidity. Gusty winds
often result as air rises and falls. On a hot day, humid air will lift faster than on a dry day.
2. Adiabatic cooling is caused by:
a. rising air that decompresses as it encounters lower air pressure found at high altitude
b. rising air that compresses as it cools at higher altitude
c. air that loses energy by convection
d. air that is being compressed
e. air that sinks toward the surface on a cold day
Rising air will decompress as it reaches higher altitude where air pressure is lower. The heat energy
in rising air will de-concentrate or disperse as that parcel of air expands by decompression, so the
temperature of that air will also drop. Energy has not been lost, just dispersed. That same air will
become warmer once again if it descends and compresses, which essentially concentrates the
energy so temperature rises.
3. In the northern hemisphere, air that is moving from high to low pressure will tend to be
turned to the right by Coriolis force. Rising air in a low-pressure cell tends to turn in a
counter-clockwise direction when observed from above.
True ___
False ___
As we demonstrated in class using a dry erase marking on a moving globe, the eastward turning of
Earth causes objects in flight to curve to the right, in the northern hemisphere, and to the left in the
southern hemisphere. Rising air tends to be moving inward toward a low-pressure cell or ridge, and
its rightward Coriolis turn gets off-set by other incoming air. The result is important: In a lowpressure system in the northern hemisphere, air tends to turn counter-clockwise.
4. Because there is no “lid” on the Earth’s atmosphere, heated air tends to result in high air
pressure.
True ___
False ___
If the Earth were like a covered pot on the stove, then the “Ideal Gas Law” would ensure that adding
heat would cause air pressure to rise because molecules will be moving more energetically, pushing
against each other.
But there is no lid on the atmosphere, so heated air molecules push apart from each other without
restraint, which actually lowers air pressure: air molecules that are vibrating vigorously create space
between them, so less mass means less weight and less air pressure.
5. The “westerlies” are winds from the west that are created along the high-latitude side of highpressure cells in the sub-tropics. At the side closer to the Equator, sub-tropical high-pressure
zones tend to produce easterly winds that are called “trade winds”.
True ___
False ___
In the northern hemisphere, Hadley cells create relatively high pressure at about 30 degrees north
latitude. This region is called the “sub-tropical high” (STH). Because high-pressure zones produce
winds that tend to turn clockwise, the north side of the sub-tropical high (STH) zone is moving from
west to east, the “westerlies”. STH winds are still moving clockwise, which means they are now
flowing from east to west, the “easterlies” or “trade winds”.
6. Vertical differences in atmospheric pressure are extremely important. Even a change of
10-20mb in air pressure between the surface and an altitude of 10 miles will cause a severe
storm to develop. By comparison, a horizontal pressure change of 40-60mb from one day
to the next means little or no change in weather.
True ___
False ___
Air pressure changes rapidly with increasing altitude, as much as 500 mb between sea level and three
miles aloft. That is normal and does not mean much. In contrast, even a pressure change of 20 mb from
one surface location to another will produce significant wind as high flows to low. In fact, a pressure
change of 50 mb almost always results in a substantial storm. A hurricane can result from a pressure
change of less than 100 mb at any given sea level location. So, vertical pressure change is strong and
means very little; horizontal pressure means a lot, sometimes life or death.
7. Adding atmospheric water vapor through evaporation makes air heavier and less likely to
cause stormy weather. High humidity makes everything feel heavy, thick and slow to move.
Adding heat to humid air makes things even more stable and/or even stale, and may lead to
air inversions that collect air pollution.
True ___
False ___
Adding water vapor makes air lighter or less dense. Humid air contains a lot of energy and will rise
easily, provoking stormy weather. Humid air promotes instability. So does hot air. In contrast, cold
and/or dry air tends to be stable, rather than breezy or stormy, so air pollution may accumulate.
Air inversions result when air does not lift each day, such as by on-shore breeze, or valley breeze.
8. A hot day will always cause high air pressure. At night, air cools and becomes less dense, so it
sinks to the surface, increasing the likelihood of stormy weather developing.
True ___
False ___
Look at answers to questions above for evidence that nothing in Question 8 is true, except for the fact
that hot air does tend to rise.
9. A recent storm in the Salt Lake area included these features:
a. Prevailing high pressure moved eastward out of our area, while a low-pressure condition
moved in from the West
b. Relatively humid, warm air resulted in low-pressure, rising air
c. As the storm developed, gusty winds resulted from down-drafts of higher pressure air that
displaced lower-pressure rising air nearby.
d. Clouds were thicker and lower than usual because of large amounts of water vapor and
liquid water in the air.
e. All of the above are true
All of the above are true of most storms that pass through the Salt Lake area.
10. A monsoon occurs when prevailing winds shift for a season. In places like India, a shift from
winds going off-shore to winds coming on-shore tends to bring a rainy season as the ITCZ
delivers low-pressure conditions and humid air from the ocean.
True ___
False ___
Prevailing warm and wet (humid) air near the Equator provides for daily strong lifting and low-pressure
as higher pressure air can move in to take the place of rising air. So, that belt around the Earth is called
“Inter-tropical Convergence Zone” (ITCZ). Frequent clouds and rain prevail near the ITCZ. During
northern hemisphere summer, the ITCZ moves northward along with the Sun’s most vertical and intense
rays. When the ITCZ is over a place like India, winds blow on-shore for a season, resulting in a rainy
season.
The opposite occurs in northern hemisphere winter, when the ITCZ is mostly south of the Equator.
Winds push off-shore from India resulting in cooler, drier weather or even drought for a season.
11. Which of the following is not true of Coriolis force?
a. Coriolis is weak or non-existent near the Equator
b. Tornadoes and hurricanes do not occur at the Equator
c. Coriolis force is positively related to latitude
d. In the southern hemisphere, high-pressure air tends to rotate counter-clockwise
e. In the northern hemisphere, high-pressure air tends to rotate counter-clockwise
All of the options in Question 11 are true except ‘e’. High-pressure air is turned to the right in the
northern hemisphere, resulting in clockwise flow. Coriolis induces opposite patterns in the southern
hemisphere.
12. Which of the following factors helps create the world-famous “Tornado Alley” in the United
States?
a. Trade winds that bring cool, dry air into conflict with humid westerly flow.
b. Hot, dry air from Africa that conflicts with cool, moist air arriving from Portland, Oregon and
San Francisco.
c. Easterly flow of humid, warm air that rises more quickly when it collides with cooler, drier
air arriving from the west.
d. Coriolis force originating at the Equator that causes tornadoes to spin northward toward the
USA.
e. None of the above helps explain” Tornado Alley”
Trade winds at about 20 degrees north latitude tend to bring warm, humid air from the Atlantic and Gulf
of Mexico westward to the United States. Hot, dry air does originate over the Sahara Desert in Africa,
but as that air moves toward the United States it picks humidity from ocean water and arrives in Florida
full of energy in heat and humidity. Air from Portland dries-out as it moves from west to east, and
becomes much heavier than warm, humid air that it meets in “Tornado Alley”.
Coriolis is almost non-existent near the Equator and grows stronger with increasing latitude toward the
poles. Tornadoes and hurricanes do not occur anywhere near the Equator.
13. Portland, Oregon tends to be milder than Portland, Maine because _____________.
a. westerly winds push toward Oregon from the east coast, bringing continental heat that
protects Oregon from freezing.
b. westerly winds from the Pacific Ocean are cool enough to produce mild summers but
contain enough heat in water to keep coastal regions fairly warm during winter.
c. Gulf Stream air masses bring heated air directly to coastal Maine, producing hot summers.
d. hot winds from Africa make coastal Maine very warm during summer. Trade winds cease
during winter, so Maine often freezes.
e. All of the above explain why Oregon is milder than Maine.
Westerly winds move from the west to the east, so air from the interior of the United States and Canada
does not help Oregon stay warm. Answer ‘b’ is accurate.
Hot winds from Africa do not reach Maine. Trade winds blow year-round. Maine weather tends to be
more severe than coastal Oregon because weather becomes much more severe (hot and cold, not warm
and cool) as it crosses the continent from west to east. So, coastal Maine has weather more like
Minnesota, which is pretty severe.
14. Weather inversions in Salt Lake valley occur because ________.
a. lack of winter sunshine results in ground surfaces staying cold all day instead of warming
and lifting each morning as “valley breezes”
b. summer heat and air pollution create a haze layer that blocks surface air from rising
c. daily mountain breezes bring a dose of warm air to the valley floor, preventing winds that
would tend to clean the air
d. low air pressure prevails during dry, cold winters, preventing winds that would tend to blow
away air pollution
e. inversions cause winter air pollution. Eliminating thousands of cars would prevent
inversions and the pollution they cause
Answer ‘a’ is valid. For the other options consider that summer heat causes air to rise, with or without
haze. Inversions are a winter problem in Salt Lake valley. Mountain breezes come down to the valley,
and thereby do not bring heat. Instead, heat rises in a morning bring. Mountain breezes bring cold air
to the valley floor at night. Dry, cold weather in winter does not produce low pressure, but high
pressure because air tends to be heavy or dense due to pressure and/or dryness. Inversions do not
create air pollution, people do. Eliminating cars would eliminate reduce air pollution but inversions
would continue to occur in winter due to lack of solar heating of ground surfaces.
15. Hadley cells are giant-scale wind flow between low-pressure, warm and humid air near the
Equator, and drier, heavier air that develops at higher latitudes. On a local scale, a daily highpressure cell will cause wind to flow toward a low-pressure area where air is rising because it
is warmer and/or more humid than surrounding air.
True ___
False ___
The dominance of ocean water and sunshine along the Equator ensures that vast evaporation occurs.
So, air temperatures are not excessive because “water takes the heat for us”. Masses of lightweight,
humid air rise daily in the tropics, helping create Hadley cells that deliver dry, sinking air at about 30
degrees north and south of the Equator. On a micro scale, the same pattern occurs as rising air and
falling air replace each with daily heating and cooling. High pressure always flows to low pressure, and
low pressure exists because air is rising, leaving space for higher-pressure air to take its place.