Solar and Terrestrial Radiation

The monochromatic emissive power of a blackbody Fs(l)(Wm 2m l) is related to temperature and wavelength by 

FIGURE 4.2 Solar spectral irradiance (Wm 2 pm-1) at the top of the Earth s atmosphere compared to that of a blackbody at 5777 K (dashed line) (Iqbal 1983). There is a reduction in total intensity of solar radiation from the Sun s surface to the top of the Earth s atmosphere, given by the ratio of the solar constant, 1370 Wm-2, to the integrated intensity of the Sun [see (4.4)]. That ratio is about 1/47,000. (Reprinted by permission of Academic Press.) 

Thus hot bodies not only radiate more energy than cold ones, they do so at shorter wavelengths. The wavelengths for the maxima of solar and terrestrial radiation are 480 nm and 10,000 nm, respectively. The Sun, with an effective surface temperature of 6000 K, radiates about 2 x 105 more energy per square meter than the Earth does at 300 K. 

2) is integrated over all wavelengths, the total emissive power Fb (W m-2) of a blackbody is found to be 

The Earth s climate is controlled by the amount of solar radiation intercepted by the planet and the fraction of that energy that is absorbed. The flux density of solar energy, integrated 

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There are a number of ARCSS data projects that provide CDs. They include the LAII Flux Study Alaska North Slope (data sampler CD) OAII Northeast Water (NEW) Polynya project CD Arctic solar and terrestrial radiation CD, etc. 

In addition to the effects on climate and soils, mentioned above, study of deep-sea sediments and ice cores indicate that, during glacial periods, dust deposition rates were 2-20 times the current values (Thompson and Mosley-Thompson, 1981 Hammer ef fll., 1985 Petit efal., 1990 Rea, 1994 Steffenson, 1997 Reader et al., 1999), possibly because of the effect airborne minerals had on global climate by their interactions with solar and terrestrial radiation (Andreae, 1995, 1996 Duce, 1995 Li et al., 1996 Sokolik and Toon, 1996 Tegen and Lads, 1996 Mahowald et al., 1999). Possible relations between glacial periods and dust have been the subject of intense speculation. 

The atmosphere can be considered to be a mixture of gases and particles exposed to the electromagnectic energy of the sun. An understanding of the dynamical and photochemical processes that occur in this environment requires evaluation of atmospheric radiative transfer. For example, the rate of reaction between two constituents often depends on the local temperature (see Chapter 2), which is affected by absorption, scattering, and emission of solar and terrestrial radiation. Further, solar radiation of particular energies can dissociate and ionize atmospheric molecules, producing reactive ions and radicals which, in turn, participate in many important chemical processes. 

Figure 4-2. Spectral distribution of solar and terrestrial radiation. Atmospheric absorption at different wavelengths. After Iribane and Cho (1980).

Before examining in detail the specific effects of solar and terrestrial radiation on the middle atmosphere, we present a few definitions relative to radiative transfer in the atmosphere. 

In the near infrared, the absorption of solar radiation is due chiefly to vibrational and rotational transitions of several atmospheric molecules. The most important absorber is water vapor with several absorbing bands between 0.8 and 3.2 gm. Carbon dioxide also exhibits absorption bands such as the 2.0 gm band, the 2.7 /.tin band (which overlaps with the 2.7 /nn band of water vapor) and the 4.3 /.tin band, located in a spectral region where both solar and terrestrial radiation is weak. Since these bands consist of many narrow lines, the transmission function corresponding to a given spectral interval cannot be described in terms of the Beer-Lambert law and empirical formulas must be used in practical applications. 

K. L. Coulson, Solar and Terrestrial Radiation , Academic Press, New York, 1975. 

Thermodynamic models that determine the equilibrium temperature distribution for an atmospheric column and the underlying surface, subject to prescribed solar radiation at the top of the atmosphere and prescribed atmospheric composition and surface albedo. Submodels for the transfer of solar and terrestrial radiation, the heat exchange between the earth s surface and atmosphere, the vertical redistribution of heat within the atmosphere, the atmospheric water vapor content and clouds are included in these one-dimensional models. Abbreviated as RCM. radiatively active gases... 

Between 0.3 and 0.7 pm (visible range) and 8-12 pm, with the exception of ozone bands, there is virtually no absorption in the atmosphere - therefore these ranges are called atmospheric windows, solar and terrestrial radiation can penetrate the atmosphere unopposed. Between 1 and 8 pm H2O (2.5-3.5 pm and 4.5-7.S pm) and CO2 (2.2-3.5 pm and 4-4.5 pm as well as 15-20 pm) absorb terrestrial radiation partially, and at > 15 pm nearly completely. 

Soot is emitted by incomplete combustion of fossil fuel and biomass. It is also caUed black carbon since it strongly absorbs the solar and terrestrial radiation in aU of ultraviolet, visible and infrared regions, and attention is paid as one of the radiatively active species from the cUmate change point of view. As reactions oti... 

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