Meteorology ch5 critical and review questions

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

A cold dry air mass has a greater density than a more humid air mass. This would mean that the humid air mass has lower air pressure. This is because the molecular weight of water is less than the molecular weight of dry air.

At Minneapolis, MN, the air pressure typically drops more rapidly with altitude on a cold day in January than on a warm day in July. Explain the difference.

Air pressure drops more rapidly with elevation in cold, dense air than in warmer, less dense air.

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

An adiabatic process is a thermodynamic process in which no heat is exchanged between a mass and the environment. This is approximated in the atmosphere because rapid vertical movements of large bodies of air reduce the flow of energy to or from the ascending or descending body of air. Examples of adiabatic processes occurring in the atmosphere are expansional cooling and compressional warming of air.

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

An aneroid barometer is more portable but less accurate than a mercury barometer.

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

As a general rule, the weather becomes (or remains) fair as the air pressure at Earth's surface rises and the weather turns stormy as the air pressure falls. Pressure tendency is an indication of an approaching low pressure (stormy weather) system or an approaching high pressure (fair weather) system.

A jet aircraft is cruising at the 600-mb level, that is, at the altitude where the air pressure is 600 mb. What fraction of the atmosphere's mass is below the altitude of the aircraft?

Assume that the air pressure at sea level is 1000 mb. Then, 1000 mb - 600 mb = 400 mb. 400/1000 = 0.4. About four-tenths (or 40%) of the atmosphere's mass is situated below the 600-mb level.

On a particularly warm and humid evening, a sportscaster comments that baseballs hit to the outfield "will not carry far in this heavy air." How valid is the sportscaster's observation?

Baseballs hit to the outfield actually should travel farther through a hot, humid atmosphere. Air becomes less dense with increasing temperature and increasing humidity, thereby offering less resistance to a batted ball.

An unsaturated air parcel has an initial temperature of 15 °C. If the parcel is lifted 1500 m and remains unsaturated, what is its new temperature?

Because the air parcel remains unsaturated, use the dry adiabatic lapse rate (9.8 C° per 1000 m). The temperature at 1500 m would be 0.3 °C.

Distinguish between Charles' law and Boyle's law.

Charles' law defines the relationship between density and temperature in an ideal gas with constant pressure. Boyle's law defines the relationship between pressure and density when temperature is held constant. Together these two laws make the ideal gas law.

1. How does Dalton's law apply to the atmosphere?

Dalton's law of partial pressures states that the total pressure exerted by a mixture of gases equals the sum of the pressures produced by each constituent gas. Each gas species in the mixture exerts a pressure as though it was the only gas present. For example, the pressure exerted by water vapor (vapor pressure) can be considered as though it was the only gas present.

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

No one altitude can be defined as the top of the atmosphere because the atmospheric density decreases as height increases until the air density gradually asssumes the same density of outer space.

Why are air pressure readings adjusted to what they would be if the weather station were actually located at sea level?

Pressure readings are adjusted to sea level in order to observe changes in air pressure on a horizontal plane. It helps scientists identify air masses and weather changes and helps aid in weather forecasting.

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

Rising dry air is cooled by expansion while rising saturated air is simultaneously cooled by expansion and warmed by the release of latent heat accompanying the phase change of water vapor to liquid or ice in the rising air.

On televised weathercasts, air pressure is often reported in units of length (inches) rather than units of pressure (millibars). Explain why.

Surface weather observations have long been reported in British units in the U.S., and the general public has been resistant to change to metric units. Also, weathercasters typically use inches of mercury rather than millibars because "at home" barometers typically display in inches.

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

The air is warmer over the tropics than over the middle latitudes. Colder air is denser than warmer air, causing the height of the tropopause to be higher over the tropics.

Provide a definition of air pressure that applies to Earth's surface and any altitude within the atmosphere.

The air pressure at a given location on Earth's surface can be thought of as the weight per unit area of the column of air above that location. The pressure at any point within the atmosphere is equal to the weight per unit area of the atmosphere above that point.

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

The atmosphere compresses descending air, causing the air to warm. At the same time, when air rises, it expands and cools.

If water is used in place of mercury in a glass-tube barometer, what is the required height of the tube? The density of mercury (Hg) is 13.6 g/cm3 and the density of water is 1.0 g/cm3.

The glass tube for a mercury barometer is about 1 m in length. If water is used instead of mercury, the glass tube would have to be about 13.6 m in length because the density of mercury is 13.6 times the density of water. The column of water must be tall enough (close to 34 ft.) to exert the same pressure at its base as does the mercury column.

Air is a compressible mixture of gases. How does this property of air affect the rate at which air pressure decreases with increasing altitude?

The weight of the overlying air determines the air pressure. The lower the location in the atmosphere, the greater the air pressure, and the greater the air is compressed and the greater the air density. Conversely, as altitude increases, the amount of the air above decreases, compressional forces decrease, and air thins as the air pressure declines.

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. When the concentration of water vapor (humidity) increases, air density usually decreases as well.