Chapter 3 Questions

Look at Fig. 3.14, p. 66 (temperature map for January) and explain why the isotherms dip southward (equa-torward) over the Northern Hemisphere continents.

Because land has a much smaller specific heat than water, and because circulation cannot bring heat to a cooling land surface as it can in water, both annual and daily temperature variations are considerable greater over land than over water. In particular winter temperatures are lower over land than over water at a comparable latitude, especially over large land bodies such as continents. This lower winter temperature over continents, versus oceans at the same latitude, is the physical explanation for the southward dipping of isotherms over northern continents during the northern winter.

List four measures farmers use to protect their crops against the cold. Explain the physical principle behind each method.

1. Orchard Heaters - They circulate the air by setting up convection currents 2. Wind Machines - They mix cooler surface air with warmer air above 3. Coat with Ice - Sprinklers emit a fine spray of water which freezes to the vegetation. The release of latent heat when the water changes to ice keeps the ice at ≈ 32˚F, protecting the vegetation beneath the ice.

During the winter, frost can form on the ground when the minimum thermometer indicates a temperature above freezing. Explain.

During the winter, frost can form on the ground when the thermometer indicates temperature above freezing because air temperature readings are typically taken several feet above the ground, whereas the temperature right at the ground may be several degrees colder, possibly below freezing.

What weather conditions are best suited for the formation of a cold night and a strong radiation inversion?

during the winter months when, skies are clear, winds are calm, air is dry, and snow is on the ground.

Why are the lower branches of trees most suscepti-ble to damage from low temperatures?

the lowest temperatures on a clear, still night occur near the surface

Draw a vertical profile of air temperature from the ground to an elevation of 3 m (10 ft.) on - A clear, windless afternoon - An early morning just before sunrise. - Explain why the temperature curves are different.

- As the sun rises higher in the sky, the air in contact with the ground becomes even warmer, and, on a windless day, a substantial temperature difference usually exists just above the ground. - As the sun rises in the morning, sunlight warms the ground, and the ground warms the air in contact with it by conduction. However, air is such a poor heat conductor that this process only takes place within a few centimeters of the ground. -This explains why joggers on a clear, windless, hot summer afternoon may experience air temperatures of over 50°C (122°F) at their feet and only 35°C (95°F) at their waists.

Explain why the daily range of temperature is nor-mally greater in: - drier regions than in humid regions - on clear days than on cloudy days.

- Dry regions have clearer skies and less water vapor in the atmosphere versus a humid region, therefore, incoming solar radiation is greater during the day in dry regions because the sun's energy is not reflected by clouds (higher temps) and radiational cooling is greater during the overnight hours in a dry regions because less water vapor is available to re-radiate outgoing infrared radiation back to the surface (lower temps). - Clear days maximize daytime incoming solar radiation and nighttime radiational cooling (maximum daily temp range) while cloud cover will decrease daytime incoming solar radiation and hamper radiational cooling (minimal daily temp range).

- Assume the wind is blowing at 30 mi/hr and the air temperature is 5°F. Determine the wind-chill equivalent temperature using Table 3.2, p. 71. - Under the conditions listed in above, explain why an ordinary thermometer would measure a temperature of 5°F, and not a much lower temperature.

- If the 30 mph and the air temperature was 5 degrees F, the temperature with wind chill would be -19 degrees F. - Thermometers are designed to measure air temperature. Wind chill is based on the sensible temperature and the actual temperature we feel depends on the type of clothing we wear, sunlight striking the body, and exposed skin.

- Assume the wind is blowing at 30 mi/hr and the air temperature is 5 deg F. Determine the wind chill equivalent temperature in Table 3.2, p. 71. - Under the conditions listed above, explain why an ordinary thermometer would measure a temperature of 5 deg F.

- If the wind speed is 30 mi/hr, and the air temperature is 5 deg F, the wind chill equivalent temperature is -19 deg F. -An ordinary thermometer would still just read 5 deg F, because it will measure only the actual air temperature. Unlike our skin, the surface of a thermometer is unaffected by the chilling effect of the wind.

Describe each of the controls of temperature. Time of Year Latitude Land vs Water Distribution Ocean Currents Elevation

-Time of Year - location of the earth (season) -Latitude - amount of incoming solar radiation -Land vs Water distribution - more water (Southern) will have smaller seasonal temperature variations - Ocean Currents - warm vs cold currents will affect coastal temperatures - Elevation - higher elevations are colder due to decreasing temperatures with height but they also experience smaller temperature variations.

During a cold, calm, sunny day, why do we usually feel warmer than a thermometer indicates?

-because of sensible temperature: human's body perception of temp; changes w/ varying atmospheric conditions -reason for changes related to how we exchange heat energy w/ our environment

On a calm, sunny day, why is the air next to the ground normally much warmer than the air several feet above the ground?

On a calm, sunny day the air next to the ground is normally much warmer than the air several feet above because the air close to the ground is directly warmed by conduction of heat from the ground. When there is no wind, mixing of this heat upward through the air is slow.

Two cities have the same mean annual temperature. Explain why this fact does not mean that their temperatures throughout the year are similar.

For example, San Francisco, California, and Richmond, Virginia, are situated at nearly the same latitude (38°N). Both have similar hours of daylight during the year; both have a mean annual temperature near 15°C (59°F). Here, the similarities end. The temperature differences between the two cities are apparent to anyone who has traveled to San Francisco during the summer with a suitcase full of clothes suitable for summer weather in Richmond. Notice that the coldest month for both cities is January. Even though January in Richmond averages only 8°C (14°F) colder than January in San Francisco, people in Richmond awaken to an average January minimum temperature of -3°C (27°F), which is the lowest temperature ever recorded in San Francisco.

What is a heating degree-day? A cooling degree-day? How are these units calculated?

Heating and cooling degree days are calculated by subtracting the daily mean temperature from 65 degrees F. If the calculated value is negative, the result is referred to as "cooling degree-days", indicative of air conditioning requirements. If the calculated value is positive, the result is "heating degree-days", indicating building heating requirements.

What atmospheric conditions can bring on hypothermia?

Hypothermia will be enhanced by cold temperatures, wind, and moisture (water conducts heat away from your skin more efficiently than air does).

Why are the largest annual ranges of temperature normally observed over continents away from large bodies of water?

Inland continental areas exhibit larger annual temperature ranges than areas near bodies of water because they are not subject to the moderating influence of water's high heat capacity. In coastal regions, the high heat capacity of the adjacent water body helps keep the atmosphere at a more uniform temperature.

Explain how radiational cooling at night produces a radiation temperature inversion.

Radiational cooling produces a temperature inversion because the air near the surface is cooled from below as the earth's surface loses heat via radiation. This results in cooler temperatures near the surface, with warmer air aloft, or a lapse rate in which temperature increases with height (i.e., an inversion)

Why do the first freeze in autumn and the last freeze in spring occur in bottomlands?

The first and last freezes usually occur in bottomlands because the coldest air in any region typically drains to low-lying valleys or depressions. Thus subfreezing temperatures will occur first and last longest in such cold air pooling locations.

Explain how incoming energy and outgoing energy regulate the daily variation in air temperature

The incoming energy from the sun makes it hot. The outgoing energy is from the loss of energy from the sun. Thus it cools

Explain why the warmest time of day is usually in the afternoon, even though the Sun's rays are most direct at noon.

The warmest time of day is in the afternoon even though the sun's rays are most direct at noon because air temperatures near the earth's surface will continue to warm as long as incoming solar radiation reaching the earth's surface exceeds outgoing longwave earth radiation. Once the outgoing radiation exceeds the incoming, the surface will begin to cool down (late afternoon).

Explain why thermal belts are found along hillsides at night.

Thermal belts are found along hillsides at night because of the following process: (1) radiational cooling of the ground results in a cold air layer near the ground, which drains downhill into the valley; (2) the cold air pools in the valley, while the converging downhill air flow from the slopes on either side of the valley results in rising motion above the center of the valley, where the air aloft is relatively warm; (3) 3-dimensional circulation cells bring this warmer air aloft from over the valley back toward the mountain slope about half way down, producing the "thermal belt".