EXAM 2

Question 1

Air pressure is not greatest near the top of the thermosphere

Answer 1

Air pressure is greatest at the surface of the earth (i.e., at the bottom of the troposphere). This is because air pressure is created by the weight of overlying air molecules being pulled downward by gravity. Therefore, there is more pressure at the bottom of a column of air than at the top. (By way of analogy, the guy at the bottom of a pile of football players has more weight on him than the guy on top!)

Question 2

The only cause of variation in air pressure is a change in air temperature

Answer 2

False - temperature is a major control of air pressure but the deflection of air into or out of a region as a result of the Coriolis force can also act to alter air pressure. In addition, a change in the water vapor content of the air also affects its density.

Question 3

Pressure changes in a non linear fashion with increasing height above the surface

Answer 3

True - it decreases in a nonlinear fashion; i.e., in a curvilinear fashion. This means that if you were to make a graph showing the change in pressure with altitude, the graph would be curved. Because of this relationship, about half the mass of the atmosphere lies below 3.5 miles–even though the atmosphere is about 63 miles thick. If the relationship were linear, the air pressure would be about one half of the surface pressure at an altitude of about 31 miles. The nonlinear relationship occurs because air is compressible, and so more air is squeezed into the lower atmosphere by the force of gravity. Examine the chart in your text to see how the pressure changes with altitude.

Question 4

As air pressure increases the height of a column of mercury in a barometer increases

Answer 4

. True - as pressure increases, more force is exerted on the tub of mercury, thereby causing the column to rise. An increase in air pressure is usually associated with a decrease in temperature, i.e., with cold air. Thus cold air is associated with high pressure (sinking air), while warm air is associated with low pressure (rising air) - remember this, it is very important!

Question 5

When air is heated the speed of air molecules

Answer 5

• Increases - temperature is molecular motion. The greater the temperature, the greater the speed of molecules.

Question 6

When air is heated the spacing of air molecules

Answer 6

Increases - the increased speed of the molecules causes them to collide with greater force, which in turn causes them to spread further apart.

Question 7

When air is heated, air density

Answer 7

Decreases - given that density = mass/volume, a decrease in the amount of mass (air molecules) in a given volume of air causes the density to decrease.

Question 8

When air is heated, it begins to

Answer 8

• Rise - because it has a lower density than the surrounding air, it begins to rise. This is why hot air balloons fly

Question 9

When air is heated, air pressure at the surface

Answer 9

Decreases - because the air density is lower, the air exerts less pressure on the surface.

Question 10

If the amount of water vapor in the air increases the air pressure decreases

Answer 10

This is because water molecules weigh less than nitrogen and carbon dioxide molecules, and because water molecules displace these other molecules, rather than fill the space between them, wet air is actually lighter than dry air (at the same temperature). As discussed in class, think of an elevator that originally contained ten heavy people, but when the doors open, five of the heavy people get off and are replaced by 5 lighter people. The weight of the loaded elevator is now less than it was originally. Because wet air is lighter than dry air, this means that, when wet air encounters dry air at the same temperature, the wet air will rise–and this facilitates the development of clouds and storms. This is why this concept is important.

Question 11

In the lower troposphere wind direction is controlled by the interaction of the pressure gradient force, the coriolis force, and also by friction

Answer 11

TRUE winds would flow approximate right angles (perpendicular) to the pressure gradient near the surface but they are deflected to some extent by the Coriolis force. As a result, the wind crosses the isobars at an angle. The amount of Coriolis deflection is diminished near the surface because friction reduces wind speed. Note that in the upper troposphere, the lack of friction enables the Coriolis force to become a more important control over wind direction. Consequently, in the upper troposphere, air flow is approximately parallel to the isobars due to deflection by the Coriolis force.

Question 12

The closer the spacing of the isobars

Answer 12

the faster the wind blows if isobars are closely spaced, this means that the pressure is changing rapidly from one area to the next. This is called a “steep” pressure gradient and results in faster winds.

Question 13

The earth rotates more rapidly at the poles than the equator

Answer 13

False - rotation is fastest at the equator because the equator has the greatest circumference of any other latitude and must therefore rotate through the greatest distance in a 24-hour period. At the hypothetical point that marks the exact North Pole, the earth, technically speaking, does not rotate at all!

Question 14

The Coriolis force causes winds to be deflected to the right of their direction in the northern hemisphere

Answer 14

True - it deflects air to the right of its direction of motion in the northern hemisphere. This can be remembered by visualizing a missile launched in a southerly direction from the North Pole toward the equator. While the missile is in flight, the equator, which rotates faster than the pole, rotates out from under the missile. Given that the direction of the earth’s rotation is from west to east, this means that the missile appears to be deflected to the right of its direction of motion. (Use a globe to illustrate this if you have trouble visualizing it.)
When air flows north from the equator, the same principle applies because the air moving north from the equator has a greater eastward velocity due to the greater rotational speed of the earth near the equator. Thus, as the air moves north of the equator, it moves into areas rotating at a slower speed and consequently appears to be deflected to the right of its direction of motion.
In the southern hemisphere, the air is deflected to the left of its direction of motion. Note that on a planet that rotates in the opposite direction, the Coriolis force would be reversed and all the winds (Trades, Westerlies, and Polar Easterlies) would change direction accordingly. For example, the Polar Easterlies would become Polar Westerlies.

Question 15

The faster the wind the greater amount of deflection caused by the coriolis force

Answer 15

True - the faster the wind speed, the greater the Coriolis deflection. This is why air flows parallel to the isobars high above the surface where there is no friction, and why it flows across the isobars near the surface where there is friction.

Question 16

Wind speed is controlled primarily by

Answer 16

wind speed is controlled primarily by the pressure gradient and secondarily by friction. Friction acts to slow the wind. Because friction is greater near the surface than aloft, the wind blows faster aloft - even though the pressure gradient may be the same at the surface and aloft

Question 17

Airflow in a surface high pressure system is downward, outward, and clockwise in the northern hemisphere

Answer 17

True - the air sinks because it is more dense, and then flows outward as it nears the surface. The Coriolis force deflects it to the right of its direction of motion in the northern hemisphere–which produces a clockwise flow.

Question 18

A cubic meter of air at a temp of 70 has the same heat content as a cubic meter of ocean water that also has a temp of 70

Answer 18

False - Although they have the same temperature–which means their molecules have the same average kinetic energy, their heat content differs. Heat refers to the total kinetic energy of a substance and, because water is more dense than air (i.e., it has more molecules per volume), it has a higher heat content. This is the basis for the Principal of Continentality.

Question 19

THe ITCZ is characterized by Rising air

Answer 19

True - the ITCZ (Inter-tropical Convergence Zone) represents a convergence of air flowing into a low pressure region. It is a low pressure region because the air is warmed by the tropical sun and therefore rises. As it rises, air flows into the area to replace the air that has risen. Remember, air flows into a low pressure region and then rises.

Question 20

THe subtropical highs are located at about 30 degrees north and south latitude and are characterized by sinking air

Answer 20

True - some of the air that rose in the ITCZ (near the equator) and in the Subpolar Lows (about 60° latitude) is transported to about 30° latitude where it becomes cool enough to sink, thereby creating a high pressure system. It is important to realize, however, that as it sinks, it is compressed and heated. Therefore, by the time it reaches the surface, it is warm and dry. Nonetheless, the area remains a high pressure area because of the sinking of cold air from aloft.

Question 21

THe subpolar low in associated with rising air

Answer 21

True – as with the Equatorial Low (and all low pressure systems) the Subpolar Low is characterized by rising air. The warm air from the midlatitudes rises up and over the cold air to the north. The uplift of this warm, moist air produces frequent cloud cover and storms – such as characterize Great Britain, which is located in the Subpolar Low.

Question 22

THe NE trades are the most persistent and steady winds in the northern hemisphere

Answer 22

True - their steadiness was the reason they were used by trading ships and why they are called the “trade winds”.

Question 23

THe westerlies blow fromeast to west

Answer 23

False - winds are named based on the direction they blow from–not to. Winds that blow from the east to the west are easterlies–not Westerlies.

Question 24

Kansas city mo is at 39 degrees n latitude and is therefore located in the westerlies

Answer 24

True - winds that sink in the subtropical high pressure belts at 30° north latitude, and that flow northward, are deflected to the right of their direction of motion. Thus, they blow from the southwest to the northeast and are called the Westerlies.

Question 25

Places located at about 60 deg latitude are located in the polar high pressure belt

Answer 25

False - they are in the Subpolar Lows (55° to 70° N). This is a region in which frequent, severe storms occur because of the uplift of warm, moist air.

Question 26

At the surface winds blow out of the ITCZ toward the subtropical highs

Answer 26

False - as discussed earlier, winds flow into the ITCZ at the surface because it is a surface low pressure system. However, at high altitude, the air diverges out of the ITCZ and flows toward the Subtropical Highs where it then sinks.

Question 27

In the Doldrums winds are strong and persistent

Answer 27

False - the winds are calm because much of the air motion is vertical (upwards), rather than horizontal. In addition, the convergence of air from opposite sides of the Equator tends to cancel the horizontal motion of the air–much as cars come to a stop when they collide.

Question 28

AT night winds tend to blow from the land to the sea, i.e. land breezes occur

Answer 28

True - because land has a lower heat capacity than water, it cools more rapidly at night. Because it is cooler, the air above it is cooler than the air above the water and therefore sinks. This causes it to flow from the land (high pressure zone) to the ocean (low pressure zone). During the day, the wind direction reverses because the land heats more rapidly, thereby creating a low pressure zone over the land.

Question 29

During winter, intense high pressure systems develop over Asia

Answer 29

True -during winter the interior of Asia cools off much more than the oceans (due to the Principle of Continentality, i.e., low heat capacity of the land) and this creates a strong high pressure system. In the summer, a low pressure system develops over Asia due to the low specific heat of the land.

Question 30

The term monsoon refers exclusively to a rainy period

Answer 30

False - the term “monsoon” refers to a seasonally-reversing wind. The summer monsoon in SE Asia does bring moist, ocean water into the continent which causes heavy rains. However, during the winter, the wind blows from the continent to the ocean and is therefore dry.

Question 31

Chinook winds are warm dry winds that form on the lee side of the mountains during winter

Answer 31

True - Chinook winds are regional winds that blow over mountain ranges. As they rise up one side of the mountain, they lose moisture, and as they sink on the other side, they are heated by compression. Consequently, Chinook winds are warm and dry.

Question 32

THe jet stream forms along the boundary between cold, polar air to the North and warmer midlatitude air to the south

Answer 32

True – This boundary is called the Polar Front and it is located along in the Subpolar Low. The extreme temperature contrast creates a strong pressure gradient that causes the wind to flow rapidly, as does the conservation of angular momentum which affects the air as it moves northward, thereby flowing in a smaller path around the earth (i.e., smaller radius of curvature).

Question 33

According to the equation for the Conservation of Angular momentum , air flowing above the equator should flow slower than air flowing into the Subpolar low

Answer 33

True - According to the equation, angular momentum remains constant when air flows in a circular path. Therefore, as the radius of curvature decreases at higher latitudes (i.e., as r becomes smaller), the velocity (v) must increase–even if the pressure gradient is the same! This question relates to the Jet Stream. This wind flows fast not only because the pressure gradient is steep in the vicinity of the Subpolar Low, but also because of the conservation of angular momentum. Both factors act to increase the velocity of the winds in this area.

Question 34

THe Mistral is an example of a katabatic wind

Answer 34

True - The Mistral, Santa Anna, and Bora are all examples of katabatic winds. These are winds that flow from higher elevations to lower elevations through mountain passes for the simple reason that cold air flows downhill because it is heavy.

Question 35

IF wind velocity doubles, the amount of force generated

Answer 35

quadruples