Lindsey Bristow

Chapter 5 Review Questions

1. How does Daltons Law apply to the atmosphere?

According to Daltons Law, the total pressure exerted by a mixture of gasses equals the sum of the

pressures produced by each constituent gas. Each gas species in the mixture acts independently of

all the other molecules. These gases compose the atmosphere.

2. Provide a defintition of air pressure that applies to the earth’s surface and any altitude within

the atmosphere.

Air pressure- the cumulative force exerted on any surface by the molecules composing air; usually

expressed as the weight of a column of air per unit surface area.

3. Compare the advantages and disadvantages of a mercury barometer versus an aneroid

barometer.

A mercury barometer is more accurate than an aneroid barometer; however an aneroid barometer

is more portable.

4. Explain how air pressure tendency can be a useful indicator of future weather.

It is a useful indicator because rising air pressure usually means continued fair weather or a clearing

of weather. Falling air pressure usually means a stormy weather system will be approaching.

5. Air is a compressible mixture of gasses. How does this property of air affect the rate at which air

pressure decreases with increasing altitude.

The spacing of molecules in gasses is most closely spaced at the earth’s surface, the spacing

between molecules increases with increasing altitude.

6. How does a change in temperature affect air density? How does a change in humidity affect air

density?

When air is heated, air density usually decreases because the greater activity of the heated

molecules increases the spacing between neighboring molecules. When air is cooled, the density

increases. Increasing humidity affects air density in the same way as rising air temperature. The

greater concentration of water vapor, the less dense the air.

7. Why does a cold, dry air mass exert a greater surface air pressure than an equally cold but more

humid air mass?

It exerts a greater surface air pressure because cold air increases the density of the air mass. The

dryer the particular air mass is, the denser it will be.

8. Why are air pressure readings adjusted to what they would be if the weather station were

actually located at sea level?

Air pressure is adjusted to what they would be if they were at sea level because that will give the

most accurate reading for pressure. It is the mean for low and high altitudes.

9. Distinguish between Charles law and Boyle’s law.

Charles’ law- With constant pressure, the absolute temperature of an ideal gas is inversely

proportional to the density of the gas. As a sample of gas is heated, the gas expands and its density

decreases.

Boyle’s law- When the temperature is held at a constant, the pressure and density of an ideal gas

are directly proportional. As the pressure on an idea gas increases, its volume decreases and its

density increases.

10. Why is the dry adiabatic lapse rate greater than the moist adiabatic lapse rate?

Critical Thinking

1. Is there some altitude which clearly marks the top of the atmosphere? Explain.

There is no specific altitude that marks the top of the atmosphere because it gradually merges with

interplanetary space.

On television weather casts, air pressure is often reported in units of length rather than units of

pressure, why?

Air pressure is often reported in inches because inches is easier to comprehend for viewers who are

unfamiliar with terms such as millibars.

2. On a particularly warm and humid evening, a sports caster comments that baseballs hit to the

outfield will ‘not carry far in this heavy air’. How valid is this observation?

Being a warm and humid night, the air masses will most likely be less dense and exert a lower

amount of pressure. However, this is not a valid observation because denser air will slow down

objects moving through it more because the object has to push aside heavier molecules.

3. If water is used in place of mercury in a glass tube barometer, what is the required height of the

tube?

In order to use water in the place of mercury, you would need to use 13x more water than mercury.

This is because mercury is 13x denser than water, therefore the tube would be 13x taller as well.

4. At Minneapolis, MN, the air pressure typically drops more rapidly with altitude on a cold day in

January than a warm day in July. Explain.

Because Minneapolis is in a low altitude area, the cold air is denser than the warm air. Therefore,

on a warm day, it would take longer for the air to warm because there are more molecules to heat

up.

5. The tropopause is higher over the tropics than over the middle latitudes. Explain why.

The tropopause is higher over the tropics because it is a very humid place with less dense air,

therefore, it affects the placement of the tropopause.

6. A jet aircraft is cruising at a 600mb level, that is, at the altitude where the air pressure is 600 mb.

What fraction of the atmospheres mass is below the air craft?

7. An unsaturated air parcel has an initial temperature of 15c. If the parcel is lifted 1500m and

remains unsaturated, what is its new temperature?

The temperature would have rose 29.7c.

8. What is an adiabatic process? Do adiabatic processes occur in the atmosphere? If so, provide an

example.

The adiabatic process is where no heat is exchanged between an air parcel and its surroundings.

Adiabatic cooling occurs in the earth's atmosphere when an air mass is forced from a low

elevation to a higher elevation.

9. Why do temperature changes accompany the vertical (up and down) motions of air parcels?

Temperature changes in motions of air parcels are directly related to the amount of saturation in the

parcel.