Chapter 4

At what air temperature is the reading on the Celsius scale the same as that on the Fahrenheit scale?

-40

In northern climates in winter, how does the depth of the snow cover influence the depth to which the ground freezes?

A layer of snow includes open spaces that are occupied by air. Air (especially motionless air) is a relatively poor conductor of heat so that a deep snow cover insulates the soil from heat loss to the relatively cold air overlying the snow. As the snow depth increases, it becomes more difficult for the ground to freeze at a great depth.

Air, especially still air, is a poor conductor of heat. Provide some examples of how this property of air is used to conserve energy for space heating and cooling.

Air is used to insulate heat as in thick fiberglass blankets that are used as attic insulation in homes. Air is trapped between the fiberglass elements. Also double glassed storm windows make use of air's very low heat conductivity; air is trapped between panes of glass. The air space between panes is so thin that convective circulation of air is inhibited.

How and why would the temperature of an Arctic air mass change as the air mass moves from snow-covered ground to bare ground?

Air mass properties depend on the surface over which they form. An Arctic air mass that forms over snow-covered ground would be relatively cold but would become warmer as it moves over bare ground.

How would you expect the Bowen ratio of agricultural land to change as a drought becomes worse? Explain your response.

As a drought persists, soils dry out and plants become dormant so that more of the heat available at Earth's surface is used for sensible heating than for latent heating. Consequently, the Bowen ratio increases in value.

Compare the advantages and disadvantages of the Celsius versus Fahrenheit temperature scales for weather observation and forecasting.

Celsius is a convenient scale to use because it has a 100-degree interval between boiling and freezing points. It also corresponds to a one-degree increment on the Kelvin scale. The benefit of the Fahrenheit scale is that each degree represents a smaller interval making it more precise.

Explain how thunderstorms transfer heat from Earth's surface to the middle and upper troposphere

During a thunderstorm, sensible heating combines with latent heat to channel heat from Earth's surface into the troposphere. Convection currents surge to great altitudes to form cumulonimbus clouds.

A traffic sign along an Ohio highway warns motorists that a bridge freezes before the road surface. Why does the bridge surface freeze first?

Heat is conducted and convected to cooler air from both the top surface and underside of the bridge. The roadway leading to and away from the bridge loses heat to cooler air only from its upper surface. The underside of the roadway receives heat conducted from the ground that partially counters heat loss from the surface to the atmosphere. Hence, the bridge surface cools at a faster rate than does the road surface so that all other factors being equal the bridge surface temperature would drop to freezing sooner.

Explain how heat transfer follows the second law of thermodynamics.

Heat transfer follows the second law of thermodynamics by flowing from where the temperature is higher to where it is lower.

During which phase changes of water is latent heat released to the environment?

Latent heat is released during freezing, condensation, and deposition.

On a global annual average basis, what is the most important process in cooling Earth's surface?

Latent heat transfer during cloud formation is the most important cooling process on a global annual average. It is more important than radiational cooling and sensible heat transfer.

Distinguish between sensible heating and latent heating of the atmosphere. Which is more important on a global annual average basis?

Latent heating refers to the transport of heat energy through phase changes of water. Heat is absorbed from the environment when ice melts, liquid water evaporates, or snow sublimates (vaporizes). Heat is released to the environment when water freezes, water vapor condenses, or water vapor deposits as ice. Sensible heating includes both conduction and convection. On a global average annual basis, latent heating is more important than sensible heating.

Provide some examples of how Earth's surface properties influence air temperature in the lower troposphere.

Properties on Earth' surface that influence air temperature are snow cover and moisture. Snow has a relatively high albedo and reduces the amount of solar radiation that is absorbed. Dry soil has less moisture for vaporization and more of the available heat is channeled into raising the air temperature through convection and conduction.

What is meant by the response time of a thermometer? What type of thermometer has the fastest response time?

Response time refers to the instrument's capability of resolving changes in temperature. Electrical resistance thermometers have a rapid response time while bimetallic thermometers are the slowest.

Describe the relationship between the kinetic energy of the atoms or molecules composing a substance and temperature of that substance.

Temperature is directly proportional to kinetic energy therefore as the kinetic energy increases of a substance, so does the temperature.

The Kelvin scale has no negative values. Explain why.

The Kelvin scale is the best representation of kinetic energy and when a substance has a temperature of 0K it is at "absolute zero" and has no kinetic energy. A substance can not have negative kinetic energy.

Describe the mechanisms involved in poleward heat transport within the Earth-atmosphere system.

The three mechanism involved with poleward heat transport are air mass exchange, storm systems, and ocean currents.