The following statements summarize and describe many of the key terms and concepts presented
in the chapter.
- Weather is the state of the atmosphere at a particular place for a short period of time. Climate, on the other hand, is a generalization of the weather conditions of a place over a long period of time.
- The most important elements, those quantities or properties that are measured regularly, of weather and climate are
(1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4) type and amount of precipitation, (5) air pressure, and (6) the speed and direction of the wind.
- If water vapor, dust, and other variable components of the atmosphere were removed, clean, dry air would be composed almost entirely of nitrogen (N), about 78% of the atmosphere by volume, and oxygen (O2) about 21%. Carbon dioxide (CO2), although present only in minute amounts (0.036%), is important because it has the ability to absorb heat radiated by Earth and thus helps keep the atmosphere warm. Among the variable components of air, water vapor is very important because it is the source of all clouds and precipitation and, like carbon dioxide, it is also a heat absorber.
- Ozone (O3) the triatomic form of oxygen, is concentrated in the 10- to 50-kilometer altitude range of the atmosphere, and is important to life because of its ability to absorb potentially harmful ultraviolet radiation from the Sun.
- Because the atmosphere gradually thins with increasing altitude, it has no sharp upper boundary but simply blends into outer space. Based on temperature, the atmosphere is divided vertically into four layers. The troposphere is the lowermost layer. In the troposphere, temperature usually decreases with increasing altitude. This environmental lapse rate is variable, but averages about 6.5°C per kilometer (3.5°F per 1000 feet). Essentially all important weather phenomena occur in the troposphere. Above the troposphere is the stratosphere, which exhibits warming because of absorption of ultraviolet radiation by ozone. In the mesosphere, temperatures again decrease. Upward from the mesosphere is the thermosphere, a layer with only a tiny fraction of the atmosphere's mass and no well-defined upper limit.
- The two principal motions of Earth are (1) rotation, the spinning of Earth about its axis, which produces the daily cycle of daylight and darkness; and (2) revolution, the movement of Earth in its orbit around the Sun.
- Several factors act together to cause the seasons. Earth’s axis is inclined 23 1/2° from the perpendicular to the plane of its orbit around the Sun and remains pointed in the same direction (toward the North Star) as Earth's journeys around the Sun. As a consequence, Earth's orientation to the Sun continually changes. The yearly fluctuations in the angle of the Sun and length of daylight brought about by Earth’s changing orientation to the Sun cause the seasons.
- The three mechanisms of heat transfer are (1) conduction, the transfer of heat through matter by molecular activity; (2) convection, the transfer of heat by the movement of a mass or substance from one place to another; and (3) radiation, the transfer of heat by electromagnetic waves.
- Electromagnetic radiation is energy emitted in the form of rays, called electromagnetic waves. All radiation is capable of transmitting energy through the vacuum of space. An important difference among electromagnetic waves is their wavelengths, which range from very long radio waves to very short gamma rays. Visible light is the only portion of the electromagnetic spectrum we can see. Some of the basic laws that govern radiation as it heats the atmosphere are (1) all objects emit radiant energy; (2) hotter objects radiate more total energy than do colder objects; (3) the hotter the radiating body, the shorter the wavelengths of maximum radiation; and (4) objects that are good absorbers of radiation are good emitters as well.
- The general drop in temperature with increasing altitude in the troposphere supports the fact that the atmosphere is heated from the ground up. Approximately 50 percent of the solar energy that strikes the top of the atmosphere is ultimately absorbed at Earth's surface. Earth emits the absorbed radiation in the form of long-wave radiation. The atmospheric absorption of this long-wave terrestrial radiation, primarily by water vapor and carbon dioxide, is responsible for heating the atmosphere.
- The factors that cause temperature to vary from place to place, also called the controls of temperature, are (1) differences in the receipt of solar radiation—the greatest single cause; (2) the unequal heating and cooling of land and water, in which land heats more rapidly and to higher temperatures than water and cools more rapidly and to lower temperatures than water; (3) altitude; (4) geographic position; (5) cloud cover and albedo; and (6) ocean currents.
- Temperature distribution is shown on a map by using isotherms, which are lines that connect equal temperatures. Differences between January and July temperatures around the world can be explained in terms of the basic controls of temperature.
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