Chapter 3 - Temperature

Question 1

Daily Mean Temperature

Answer 1

Temperature determined by averaging the 24 hourly readings or by adding the maximum and minimum temperatures for a 24-hour period and dividing by 2.

Question 2

Daily Temperature Range

Answer 2

The difference in a day’s maximum and minimum temperatures.

Question 3

Monthly Mean Temperature

Answer 3

Calculated by adding together the daily means for each day of the month and dividing by the number of days in the month.

Question 4

Annual Mean Temperature

Answer 4

An average of the 12 monthly means.

Question 5

Annual Temperature Range

Answer 5

Computed by finding the difference between the warmest and codes mean temperatures.

Question 6

Isotherm

Answer 6

A line that connects points on a map that have the same temperature (iso = equal, therm = temperature).

Question 7

Temperature Gradient

Answer 7

The amount of temperature change per unit of distance.

Closely spaced isotherms indicate a rapid rate of temperature change, whereas more widely spaced lines indicate a more gradual rate of change.

Question 8

Controls of Temperature

Answer 8

Factors that cause temperatures to vary from place to place and from time to time.

Question 9

What are the controls of temperature?

Answer 9

1. Variations in sun angle and length of daylight which depend on latitude - differences in the receipt of solar radiation.
2. Differential heating of land and water.
3. Ocean currents.
4. Altitude.
5. Geographic position.
6. Cloud cover and albedo.

Question 10

How can you tell latitude is not the only temperature control?

Answer 10

If it were, all places along the same parallel would have the same temperature but this is not the case.

Question 11

Why are there different air temperatures over different Earth surfaces? Which varies the most?

Answer 11

Different Earth surfaces reflect and absorb varying amounts of incoming solar energy, which in turn cause variations in the temperature of the air above. The greatest contrast being between land and water.

Land heats more rapidly and to higher temperatures than water, and it cools more rapidly and to lower temperatures than water. Variations in air temperatures, therefore, are much greater over land and water.

Question 12

Why do land and water heat and cool differently?

Answer 12

1. Water is highly mobile. As water is heated, convection distributes the heat through a considerably larger mass. Daily temperature changes occur to depths of 20 feet or more below the surface, and yearly, oceans and deep lakes experience temperature variations through a layer between 650 and 2000 feet thick. In contrast, heat does not penetrate deeply into soil or rock; it remains near the surface. No mixing can occur on land because it is not fluid. Instead, heat must be transferred by the slow process of conduction. Consequently, daily temperature changes are small below a depth of 4 inches, although some change can occur to a depth of perhaps 3 feet. Annual temperature variations usually reach depths of 50 feet or less. Thus, as a result of the mobility of water and the lack of mobility in the solid Earth, a relatively thick layer of water is heated to moderate temperatures during the summer. On land only a thin layer is heated but to much higher temperatures. During winter the shallow layer of rock and soil that was heated cools rapidly. Water bodies, in contrast, cool slowly as they draw on the reserve of heat stored within. As the water surface cools, vertical motions are established. The chilled surface water, which is dense, sinks and is replace by warmer water from below, which is less dense. Consequently, a larger mass of water must cool before the temperature at the surface will drop appreciably.
2. Because land surfaces are opaque, heat is absorbed only at the surface. Water, being more transparent, allows some solar radiation to penetrate to a depth of several meters.
3. The specific heat is more than three times greater for water than for land. Thus, water requires considerably more heat to raise its temperature the same amount as an equal volume of land.
4. Evaporation (a cooling process) from water bodies is greater than from land surfaces. Energy is required to evaporate water. When energy is used for evaporation, it is not available for heating.

Question 13

Specific Heat

Answer 13

The amount of heat needed to raise the temperature of 1 gram os a substance 1*C.

Question 14

Gulf Stream

Answer 14

An important surface ocean current in the Atlantic Ocean that flows Northward along the coast of the United States.

Question 15

What force drives ocean currents?

Answer 15

Surface currents are set in motion by the wind. At the water surface, where the atmosphere and ocean meet, energy is passed from moving air to the water through friction. As a consequence, the drag exerted by winds blowing steadily across the ocean causes the surface layer of water to move. Thus, major horizontal movements of surface waters are closely related to the circulation of the atmosphere, which in turn is driven by the unequal heating of Earth by the Sun.

Question 16

Are pollard-moving ocean currents warm or cold?

Answer 16

Poleward-moving ocean currents are warm, and equator ward-moving currents are cold.

Warm currents make temperatures higher than expected and cold currents make temperatures cooler than expected.

Question 17

How does altitude influence average temperatures?

Answer 17

The higher the altitude, the lower the average temperature.

Question 18

Where is daily temperature range usually greater: at the base or the top of a mountain? Explain.

Answer 18

The top of a mountain. The fact that high-altitude places are warmer than the value calculated using the normal lapse rate results from the adsorption and reradiating of solar energy by the ground surface.

Not only do temperatures drop with an increase in altitude but atmospheric pressure and density also diminish. Because of the reduced density at high altitudes, the overlying atmosphere absorbs and reflects a smaller portion of the incoming solar radiation. Consequently, with an increase in altitude, the intensity of solar radiation increases, resulting in relatively rapid an intense daytime heating. Conversely, rapid nighttime cooling is also the rule in high mountain locations. Therefore, stations located high in the mountains generally have a greater daily temperature range than do stations at lower elevations.

Question 19

How does geographic position affect temperature?

Answer 19

A coastal location where prevailing winds blow from the ocean onto the shore (a windward coast) experiences the full moderating influence of the ocean - cool summers and mild winters - compared to an inland station at the same latitude. A coastal location where prevailing winds blow from the land toward the ocean (a leeward coast) will have a more continental temperature regime because the winds do not carry the ocean’s influence onshore.

Question 20

How does cloud cover and albedo control temperature?

Answer 20

Cloud cover is important because many clouds have a high albedo and therefore reflect a significant proportion of sunlight that strikes them back to space. By reducing the amount of incoming solar radiation, daytime temperatures will be lower than if the clouds were absent. The albedo of clouds depends on the thickness of cloud cover and can vary from 25 to 80%

At night, clouds have the opposite effect as during daylight. They absorb outgoing Earth radiation and emit a portion of it toward the surface. Consequently, nighttime temperatures do not drop as low as they would on a clear night.

The effect of cloud cover is to reduce the daily temperature range by lowering the daytime maximum and raising the nighttime minimum.

Question 21

Heat Wave

Answer 21

A prolonged period of abnormally hot and usually humid weather that typically lasts from a few days to several weeks.

Question 22

Lag of the Maximum

Answer 22

The time of the highest daily temperature does not generally conincide with the time of maximum radiation. This delay is called the lag of the maximum.

Question 23

What causes the lag of the maximum?

Answer 23

1. Solar radiation received exceeds the rate of Earth radiation lost.
2. Air is a poor absorber of most solar radiation; it is heated primarily by energy reradiated by Earth’s surface. The rate at which Earth supplies heat to the atmosphere through radiation, conduction, and other means, however, is not in balance with the rate at which the atmosphere radiates away heat. Generally, for a few hours after the period of maximum solar radiation, more heat is supplied to the atmosphere by Earth’s surface than is emitted by the atmosphere to space. As a result, most locations experience an increase in air temperature during the afternoon.

Question 24

Urban Heat Island

Answer 24

The fact that temperatures within cities are generally higher than in rural areas.

Question 25

Liquid In-Glass Thermometer

Answer 25

A device for measuring temperature that consists of a tube with a liquid-filled bulb at one end. The expansion or contraction of the fluid indicates temperature.

Question 26

Maximum Thermometer

Answer 26

A thermometer that measures the maximum temperature for a given period of time, usually 24 hours. A constriction in the base of the glass tube allows mercury to rise but prevents it from returning to the bulb until the thermometer is shaken or whirled.

Question 27

Minimum Thermometer

Answer 27

A thermometer that measures the minimum temperature for a given period of time, usually 24 hours. By checking the small dumbbell-shaoed index, the minimum temperature can be read.

Question 28

Thermograph

Answer 28

An instrument that continuously records temperature.

Question 29

Bimetal Strip

Answer 29

A thermometer consisting of two thin strips of metal welded together, which have widely different coefficients of thermal expansion. When temperature changes, the two metals expand or contract unequally and cause changes in the curvature of the element. Commonly used in thermographs.

Question 30

Thermistor

Answer 30

An electric thermometer consisting of a conductor whose resistance to the flow of current is temperature dependent; commonly used in radiosondes.

Question 31

Instrument Shelter

Answer 31

A white box that has louvered sides to permit the free movement of air through it, while shielding the instruments from direct sunshine, heat from the ground, and precipitation.

Question 32

Ice Point

Answer 32

The melting point of ice.

0C, 32F, 273 K

Question 33

Steam Point

Answer 33

The boiling point of water.

100C, 212F, 373K

Pure water at standard sea-level pressure; boiling decreases with altitude.

Question 34

What is the Celsius-Fahrenheit relationship?

Answer 34

• F = (1.8 x *C) + 32

* C = (*F - 32)/1.8

Question 35

Absolute Zero

Answer 35

The temperature at which all molecule motion is presumed to cease.

Question 36

What is the relationship between the Kelvin and Celsius scales?

Answer 36

*C = K - 273

K = *C + 273

Question 37

Heating Degree-Day

Answer 37

Each degree of temperature of daily mean below 65*F is counted as one heating degree-day. The amount of heat required to maintain a certain temperature in a building is proportional to the heating degree-days total.

Question 38

Cooling Degree-Day

Answer 38

Each degree of temperature of the daily mean above 65*F. The amount of energy required to maintain a certain temperature in a building is proportional to the cooling degree-days total.

Question 39

Growing Degree-Days

Answer 39

A practical application of temperature data for determining the approximate date when crops will be ready for harvest.

Question 40

Apparent Temperature

Answer 40

The temperature that a person perceives.

Question 41

Why are hot, muggy days so uncomfortable?

Answer 41

Humans, like other mammals, are warm-blooded creatures who maintain a constant body temperature, regardless of the temperature of the environment. One of the ways the body prevents overheating is by perspiring. However, this process does little to cool the body unless the perspiration can evaporate. It is the cooling created by the evaporation of perspiration that reduces body temperature. Because high humidities retard evaporation, people are more uncomfortable on a hot and humid day than on a hot and dry day.

Question 42

Heat Index

Answer 42

A measure of apparent temperature with consideration of humidity.

Question 43

Why do strong winds make apparent temperature in winter feel lower than the thermometer reading?

Answer 43

A stiff breeze penetrates clothing and reduces its capacity to retain body heat while causing exposed parts of the body to chill rapidly. Not only is cooling by evaporation heightened in this situation but the wind is also acting to carry heat away from the body by constantly replacing warmer air next to the body with colder air.

Question 44

List severa reasons heat stress and wind chill do not affect everyone the same.

Answer 44

Age, physical condition, state of health, and level of activity.