This preview shows page 171 - 174 out of 950 pages.
Once the terrestrial infrared radiation is emitted as longwave radiation from the ground, much of it is absorbed by greenhouse gases in the atmosphere, such as carbon dioxide, methane and water vapor . It is this process that is responsible for the majority of atmospheric heating. The atmosphere is therefore heated indirectly, primarily from the ground up, by the absorption of terrestrial longwave radiation by greenhouse gases, rather from the top down by incoming solar shortwave radiation (Figure 2 .38)This process of indirect heating of the atmosphere is known as the greenhouse effectFigure 2.38. Once solar shortwave radiation is absorbed, it is then re-radiated from the surface at longer wavelengths, primarily as far-infrared radiation. Much of this longer terrestrial infrared radiation is then absorbed by greenhouse gases in the atmosphere. This process of indirect heating of the atmosphere is known as the greenhouse effect(Source/Credit: Dennis I. Netoff).Air Temperature
eWeather & Climate 1632The atmosphere acts like the glass of a greenhouse . Shortwave radiation from the Sun passes through the glass and is absorbed by objects inside the greenhouse (Figure 2 .39)Those objects emit far-infrared radiation which is blocked by the glass . The greenhouse temperature can rise far above the temperature of the outside air . The glass also prevents convectional heat loss .The process is similar to the overheating of the inside of an automobile on a summer day .Figure 2.39. The warming of a greenhouse is somewhat analogous to the heating of the atmosphere. The greenhouse glass, like the atmosphere, permits passage of incoming short-wave radiation. Objects inside the greenhouse act the same as the Earth’s surface, absorbing most of the incoming short-wave radiation and re-radiating it at longer wavelengths. The longer wavelengths are then trapped by the window glass, much in the same way as greenhouse gases prevent the escape of terrestrial radiation (Source/Credit: OZ Climate Sense).Air Temperature
eWeather & Climate 1642Clouds also affect atmospheric heating and cooling in many ways . Day-night temperature variations can be either enhanced or subdued by cloud cover . During the daytime, low, thick clouds reflect some of the incoming shortwave radiation, thereby keeping surface temperatures somewhat cooler than might be expected . However at night, those same clouds absorb some of the outgoing longwave radiation, keeping temperatures warmer . Cloudy days and nights tend to have less of a day-night temperature fluctuation than clear days and nights (Figures 2 .40a and 2 .40b)Figure 2.40a. (left) During the daytime, more of the incoming short-wave solar radiation reaches the ground under clear skies (Ozona), compared to overcast skies (Huntsville), so Ozona’s daytime temperature may be higher than Huntsville’s even though there is the same amount of solar radiation at the top of the atmosphere.